Alkyd resins are any of a large group of thermoplastic resins that are essentially polyesters made by heating polyhydric alcohol with polybasic acids or their anhydride and used chiefly in making protective coatings and good weathering properties. These resins are useful as film forming agents in paint, varnished and enamels & as thermosetting plastics that can be moulded into solid objects. Hence, alkyd resins are one of the important ingredients in the synthetic paint industry. Alkyd resins are the synthetic resins which have a dominant position among the synthetic resins with respect of production volume & the frequency of the use in paint & varnish materials. Despite the growing popularity of acrylic, polyurethane and epoxy resins, alkyd resins remain highly favoured among paint producers for its variability of compositions & better value for money. Originally, alkyd resins were merely the reaction products of phthalic anhydride and glycerine. But these products were too brittle to make satisfactory coatings. The use of oils or unsaturated fatty acids in combination with the brittle alkyds resulted in the air-drying coatings which revolutionized the chemical coating industry. The oil or fatty acid portion of the alkyd is one of the factors which determine the paint formulator's choice of resin to be used. In general, the lower the phthalic content of an alkyd, the higher the amount of oil used. Alkyd resins products are suitable for wide range of products with application in decorative, maintenance and contractor paints where excellent gloss and good durability are required. Experts believe that the total consumption of paint & varnish materials will rise to a great extent in the coming years. Both cost wise & performance wise, alkyds have proven themselves over a wide swath of demands, from agriculture/construction equipment to general industrial metal and even architectural finishes.
Some of the fundamentals of the book are the basic chemistry of unsaturated polyesters, factors affecting alkyd production, monitoring the alkyd reactions, alkyd calculations, alkyd formulations based on theory, practical alkyd formulations, assessment of the performance of single and multicoat red iron oxide alkyd paint systems, styrenated alkyd resins based on maleopimaric acid, mechanical properties of alkyds resin varnish films and the effect of different weathering conditions on them, modification of alkyds, copolymerization of alkyd silicons for coatings, styrene copolymers in alkyd resins, etc.
This book contains alkyd formulation, modification of alkyds, styrene copolymers in alkyd resins, copolymerization of alkyd silicon, polyblends of polystyrene glycol and alkyd in surface coatings, alkyd calculations, and alkyd nomograms. This book will find very helpful to all its readers, entrepreneurs, scientists, technical institution, existing industries, paint technologist etc.
Importance of Alkyds
since alkyd resins were first introduced some thirty-five years ago,
enjoyed a consistent annual growth, with current production now running
over one-half billion pounds. Today alkyds outrank all other synthetic
resins in importance, accounting for approximately half of all resins
the paint industry, which approaches a size of two billion dollars
the United States.
alkyd reaction is concerned to be the most versatile resin-forming
known. No other resin lends itself to greater internal variation or to
useful modification by physical or chemical blending with other
Polymers commonly used to modify alkyd resins are listed in Table 1.
purpose of this book is to elucidate the theories and calculations
to this outstanding resin.
Nature of an Alkyd
resins, or alkyds, are tough resinous products formed by reacting
organic acids with polyhydric alcohols. Broadly speaking, this type of
esterification reaction produces compounds of the general class of
The key feature that distinguishes alkyds from other polyesters is the
of monoacid (commonly fatty acid) as a major part of its composition.
alkyd structures are shown in Fig. 1.
any polyacid or polyol should lend itself to the manufacture of alkyds.
However, from the standpoints of processing, paint performance, and
only a relatively few raw materials (see listing in Table 2) have found
commercial acceptance for trade sales and industrial applications.
alkyd is classed as a polymer (a huge molecule) formed by chemical
from many smaller molecules. The process whereby small unattached
joined together by chemical reaction to form a tight network of
molecules is called polymerization. Since the alkyd reaction usually
simple by-proudct molecule (commonly water) during the molecular
process can be thought of as a compacting or condensing action. For
reason, the preparation of an alkyd is referred to as a condensation
and the end alkyd product as a condensation polymer.
effect a chemical junction between two molecules, it is necessary that
mutually chemically reactive. Tabulated in Fig. 1 are typical chemical
reactions that can take place between two molecular species to effect a
or chemical linkage between them. The reaction between a carboxyl group
and an hydroxyl group (—OH) is termed esterification. This reaction is
there is only one reactive
site on each molecular species, that is, if they are both
monofunctional, it is
apparent that polymerisation cannot occur, for even at 100 per cent
no more than double molecules can ever be formed. Let A and B be
on two monofunctional molecular species:
fact, if either species of molecule has but one reaction site (the
have two or more sites), true polymerization again fails to occur, for
that can be expected is a saturation of the polyfunctional molecule
attachments of the monofunctional molecule and this is the maximum size
built-up molecule that can ever form under these conditions.
is true that the resulting polyfunctional molecule may be quite large,
can never progress to the stage of infinite interconnections which is
hallmark of a true polymeric structures.
if neither of the two reacting molecular species is mono-functional
be di–, tri–, tetra–, or of still higher polyfunctionalities), then
networks of tied-together molecules become possible, giving polymers of
dimensions. This concept of functionality underlies the design of alkyd
polymers suitable for paint vehicles.
the very outset, it must be pointed out that the alkyd chemist is
faced with a dilemma in formulating alkyd resins. For an alkyd to be
outstanding in performance, it must be processed to as high a molecular
as possible. At the same time, the molecular weight must not be allowed
become excessive, or the alkyd vehicle will get out of control during
processing (convert to an intractable gel) or exhibit an instability on
storage. Hence the alkyd formulator must at all times avoid the design
either unduly small or unduly large polymers. This is quite a trick. In
general, an alkyd is formulated to a point just short of gelation at
cent reaction. This criterion for proper alkyd design is used
Versus Branch Molecules
linear molecule is defined here as a difunctional molecule (two
sites). A branch molecule is defined as a tri-, tetra-, or higher
molecule (three, four, or more reactive sites).
molecules react to form molecular chains of infinite extent; ring
also occur. Branch molecules also react to form molecular chains but,
addition, branching connections are formed which tie the chains
give a three-dimensional polymeric network (Fig. 2). This is referred
of the linear type, with no branching (no cross-linking), are normally
thermoplastic, which means that they are fusible and can be forced to
new shape under heat and pressure—they are moldable. Polymers of the
cross-linked type are normally thermosetting, which means that they are
infusible and cannot be forced to take a new shape under heat and
are not remoldable. The rigidity and resistance to heat distortion that
characterize a cross-linked polymeric structure can be understood by
visualizing the many points of tie-in or cross-linking which restrict
movement of branched molecular chains, giving them a reinforced
However, the development of excessive cross-linking at the expense of
extension leads to brittleness.
calculations are greatly facilitated and better understood by using a
form for setting up and recording the data. For example, alkyd raw
can be listed in a left-hand column, with headings for proportions and
constants of these materials in a row across the top.
solving a given problem, the initial or given data are first entered in
table at appropriate points. Then as computed values are obtained, they
filled in. This manner of recording the calculations is
information is posted in a systematic fashion, and a visual reference
always available for checking. This recording technique is amply
examples throughout the text.
The Basic Chemistry of
polyesters are the product of a condensation reaction between
acids and alcohols one of which (generally the acid) contributes
unsaturation. This polymer is dissolved in styrene or other monomeric
containing vinyl unsaturation. With heat and/or free radical
polyester and reactive diluent crosslink into a solid, non-melting
photos show a simplified model of the basic materials required to form
this picture in mind, the methods of varying the polyester to tailor it
specific application requirements are readily apparent. The principal
variations effected by constituent changes are the frequency of cross
sites (crosslink density), the degree of steric protection afforded to
vulnerable functional groups and the rotational freedom within the
effects on properties
are produced by polyester molecular size — a joint function of the
ingredients and processing variations — and by coreactant selection and
this brief overview of polyesters indicates that several routes are
available to achieve a particular property. A goal of this brochure is
suggest useful paths of investigation to resin formulators seeking cost
effective resins to meet specific and use requirements. While the
emphasis will be on the role of ingredients in polyesters based on
acid, many of the trends observed in our laboratory can be extrapolated
other types of unsaturated polyesters.
brief description of processing included here is intended only as a
the discussion of processing’s influence on properties. A more complete
of Amoco’s recommendations for unsaturated isopolyester processing is
in other publications.
1. Molecular Weight Increase
Occurs As End Groups Disappear During Esterification
for processing good quality unsaturated polyesters includes: a heated
with agitator, temperature measurement devices, reactant addition and
ports; an overhead system with efficient fractionating and total
and apparatus for safely diluting the polyester with monomer.
quality unsaturated polyesters are processed by a two stage reaction in
aromatic and saturated acids are reacted with all the glycol until at
functional group of all diacid has reacted. The resin mixture is then
maleic anhydride added and processing continued to final properties as
determined by test methods, such as acid number or viscosity, that
the slower reacting acids with a substantial glycol excess produces low
molecular weight, hydroxyl terminated oligomers that react in the
to more evenly distribute unsaturated functionality throughout the
esterification reaction is accelerated by efficiently removing the
reaction (hence the need for an efficient partial condenser), higher
atmospheric pressure and/or certain catalysts.
polyester chain grows as acid and hydroxyl groups combine and release
Unreacted acid and hydroxyl groups left in the reaction mixture can be
monitored by conventional wet chemical techniques to indicate the
course of the
reaction. Figure 1 illustrates the growth of polymer size and increase
viscosity as the available end groups are consumed. Because virtually
isopolyesters are formulated with a hydroxyl excess, acid number is
used to quickly indicate the remaining level of reactive material.
residual carboxyl functionality contributes to viscosity drift and
to chemical attack in end use applications. Therefore, the preferred
controlling polyester molecular weight is to adjust initial hydroxyl
rather than prematurely end the esterification reaction.
variety of tests are available for determining the identity and
polyester resins as solutions and as cured solids. The concern of the
formulator is to use evaluation techniques that are useful for
resin uniformity, can be quality control tests during manufacture, can
performance in actual use conditions and are in-expensive and
perform. Resin users need tests showing handling and quality
of the wet or uncured resin and knowledge of the resin formulation and
ingredients can tell the molecular weight, level of unsaturation,
thickening rate and cure response. Conventional tests of uncured resin
their implication for the resin formulator and user are shown in Table
focus of this brochure is on
unsaturated resins themselves; however, in most applications the resins
combined with fibrous reinforcement or fillers. The user of the final
is most concerned with the properties of the composite which are
both the resin and the reinforcement.
properties are dominated by reinforcement and the contribution of the
resin is masked. Figure 2 illustrates the correlation of cured resin
composite tensile elongation for most of the resins studied in Amoco’s
Technical Service Laboratory. Up to about 2.5 percent the tensile
the composite is influenced by that of the resin. Thereafter it is
by that of the reinforcement.
composite properties, such as flexural strength (stress perpendicular
orientation of most of the reinforcement), are largely determined by
Corrosion resistance is among the properties that relate to the
between reinforcement and resin and that is best determined by testing
2. Reinforcement Masks Resin
Tensile Elongation Properties
most clearly focus on resin contribution to laminate performance and
scatter of test results inevitable with composite testing, most
discussed in ths brochure are based on testing of clear or unreinforced
castings of resins. Laminate testing is used only for corrosion
flexural fatgque evaluations that are functions of resin/reinforcement
in one property usually causes a change in some other property. The
most desired by the end user are frequently inferred from several
example, toughness, a most desirable property, is classically
considered as the
area under the tensile stress/strain curve. Figure 3 depicts a
charting of destructive tensile stress of a clear resin casting using
Instron Tester. The area of the roughly triangular figure formed under
curve is proportional to the toughness of the tested resin. This
obviously be affected by changes in either ultimate tensile elongation
ultimate tensile strength. If each component of a multivariate
as toughness changes slightly in the same direction, the cumulative
much greater than each individual change. For instance, a 30 percent increase in both
and tensile strength is a 70 percent increase in toughness.
3. Tensile Stress/Strain
Area Defines Toughness
a difference in destructive stress testing of laminates can reflect a
substantial difference in non-destructive, cylic stress. Table 2 shows
reinforcement partially masking the flexural strength advantage
inherent in an
isophthalic resin. When the laminate is subjected to flexural fatigue
testing (see Figure 22 for more detail of test and resins), the resin
difference is again apparent.
which underlies many physical properties of resins, is usually closely
correlated with tensile elongation. Figures 4 through 6 show the
between tensile elongation and flexural strength, tensile strength,
(flexural and tensile modulus) and heat distortion temperature for
studied in Amoco’s laboratories. The graphs indicate relatively
relationships between some properties heat distortion resistance and
elongation are not compatible combinations of properties in the same
resin. On the other hand, toughness can be increased in resins with low
by increasing tensile elongation, while in very flexible resins
be improved by reducing elongation.
3 Summarizes the physical tests and instrumental analyses that indicate
characteristics and usefulness for various applications.
in applications not normally referred to as corrosion resistant, the
reinforced polyester to resist conditions that would cause rusting or
other materials is a valued attribute. The vulnerability of a fiber
laminate may be attack of the resin, the glass fibers or the interface
them. Despite normal fabrication of corrosion resistant laminates with
essentially fiber-free surface, liquids can permeate polyesters to some
and contact the glass-resin interface. Consequently, Amoco’s preference
corrosion testing of complete laminates with edges protected from
of Amoco’s testing has been conducted on laminates constructed and
corrosive media by the procedures outlined in ASTM C581. Analysis of
properties and hardness at one, three, six and twelve months can be
log-log graphs to project ten year performance. An example of such
is shown in Figure 7. If the best straight line through the one year
indicates 50 percent or more retention of properties at ten years, the
is considered acceptable for commercial service in that media.
this test method are that its acceleration is through two-sided
heat which can distort results. The test evaluates the resistance of
laminate and is reliable. In Amoco’s tests property retentions have
reproducible to within 5 percent for flexural modulus and 10 percent
hardness and flexural strength.
of Unsaturation in
essential ingredient for an unsaturated polyester is the carbon-carbon
bond or olefinic unsaturation that will subsequently crosslink with the
reactive diluent. In virtually all commercial resins unsaturation is
by maleic anhydride or fumaric acid. As shown by the molecular models,
very similar in the esterified form, and their differences are minor
with the effect of their use level in the polyester (Illustration 4).
ratio of maleic or fumaric unsaturation to the total ingredients of the
polyester is the primary determinant of reactive double bond frequency
polymer. This frequency in turn determines the amount of crosslinking
occur with a reactive diluent, such as styrene, and thus, strongly
cured resin properties.
unsaturated polyester could be made with only the unsaturated acid or
and a glycol or oxide. As saturated acid replaces unsaturated, the
double bonds in the polymer will decrease causing an increase in
reflected by tensile elongation (Figure 8). The same trend is
still true, for resins made with quite different glycols. Figure 9
increased tensile elongation associated with higher aromatic acid
resins made with diethylene glycol.
distortion temperatures, as expected, decrease as crosslink density is
However, strengths, as noted in the previous section, vary with change
according to the resin flexibility. Thus the rigid, propylene glycol
strengthened (Figure 11) by increasing aromatic acid content, while the
flexible DEG resin exhibits lower strength as it is made more flexible
12) by increasing aromatic acid content.
polyester double bonds react via a catalyzed free-radical process with
double bonds in styrene or other coreactant. The reaction of each
releases a discrete amount of heat energy. The total amount of heat
during crosslinking is indicated by the SPI Gel Test. Propagation time
measure of the in-mold cure time) and peak exotherm as determined by
Gel Test correlate well with the amount of unsaturation in the
all other factors are constant. Figures 13 and 14 illustrate these
trends for a
series of resins made with propylene glycol and crosslinked with 45
styrene. Generally, higher polyester unsaturation levels will result in
cure and higher exotherm temperatures.
Effects of Crosslink
resistance is positively associated with flexibility. Thus, decreasing
unsaturation will increase impact resistance, reducing molded part
during fabrication and shipping.
with higher unsaturation levels can tolerate more inert filler because
crosslink density remains sufficiently high to provide good strength as
resin portion of compound volume is reduced.
higher heat distortion temperatures of more highly unsaturated resins
service at higher temperatures.
theoretically a great variety of unsaturated difunctional acids and
could be used to provide the required double bonds in the polyester,
all commercial unsaturated polyesters incorporate maleic anhydride (cis
configuration) or fumaric acid (trans configuration).
anhydride is usually less expensive than fumaric acid. It can be
and handled as a liquid. The anhydride form reacts faster than the acid
less mole of esterification water is released during processing.
acid readily isomerizes to form the more stable fumaric acid. During
esterification the maleate structure can rearrange into the fumarate
configuration. The rate of isomerization is apparently dependent on the
glycol. Table 6 shows isomerization rates reported in the literature.
implication of these rates is that fumaric acid has no advantage over
anhydride unless 100 percent of the trans configuration is required for
advantages of total trans configuration as reported in the literature
typical of a more linear and crystalline polymer: greater hardness;
moduli or stiffness; lower elongation; higher heat distortion
gel and propagation times; higher exotherms. The trend of these
to make the polymer more rigid.
Phthalic Isomer Differences
basic aromatic di-acid can form three sterically distinct isomers:
orthophthalic acid, isophthalic acid and terephthalic acid. These
the same chemical formula, but differ in the location of the acid
groups on the
aromatic ring. Orthophthalic acid, the only one of the three isomers
forming an anhydride, is normally used in that form.
phthalic isomer has particular advantages and liabilities. For most
applications the balance of cost and performance will generally provide
clear-cut choice for one of the isomers.
a great extent the application performance and property difference
the physical and chemical differences of the isomers. Amoco’s
indicate that IPA offers substantially better properties than
formulations made with phthalic anhydride. The properties of
are generally better than orthophthalic resins. The only property
consistently offered by TA is greater heat distortion resistance.
resin manufacturer’s cost analysis includes raw material costs,
costs and ancillary costs associated with special handling of any
an analysis is an overly simple view of the real cost and value to the
Customer oriented cost analysis must include not only resin purchase
fabrication costs, but life-cycle cost factors such as maintenance,
before replacement and performance in multiple environments. The
producing high quality resins can offer the savings of longer service
more varied conditions.
combination of better physical properties and superior corrosion
reported for isophthalic polyesters in this section can be exploited in
Handling and Processing
ortho isomer is normally used as the anhydride which reacts faster
and releases one, rather than two, moles of esterification water.
anhydride can be melted, providing some convenience for plants equipped
hot liquids to storage and process units.
acid is the slowest reacting of the three phthalic acids. Catalysts or
are required to esterify TA within a reasonable time period.
acid reacts more readily than TA, but its initial rate is slower than
anhydride. Isopolyesterification can be catalyzed to provide reaction
approximating those of anhydride esterification. A summary of typical
processing time with and without catalysts and pressure is shown in
K1 reported in Table 7 for orthophthalic acid is not indicative of the
reaction rate of the anhydride. Note, however, the significantly lower
ortho versus iso. The practical implication of this low K2 is a much
reaction rate for the second acid group of orthophthalic based
it is much more difficult to obtain high polyester molecular weight
phthalic anhydride than with the iso or tere conformations. Efforts to
orthopolyesters to high molecular weight increase the risk of gelation
aggravate the sublimation rate of phthalic anhydride. These efforts
the inherent advantages of ortho resins — fast reaction times and light
sublimation tendency of phthalic anhydride requires caution during
and can indirectly influence cured properties. Sublimed phthalic
fumes are flammable and can cause fractionator and condenser plugging.
Condensed phthalic anhydride and low molecular weight phthalic esters
back into the resin kettle during final stages of processing and after
reaction is complete. These low molecular weight materials have
water solubility, act as plasticizers of the cured resin and reduce
terephthalic acid require catalysis for efficient processing, the
of residual catalyst in cured resin must be evaluated in end use
Amoco’s experience indicates that certain catalysts may be detrimental
corrosion resistance properties and unacceptable for food contact
TA resins cooked with catalysts generally have dark color and poor
Gel characteristics can also be affected.
formulations made with the different phthalic isomers will have
different liquid properties resulting from the different target end
Resins based on isophthalic or terephthalic acid will normally be
higher molecular weights and will show higher viscosities and lower end
counts (acid numbers and hydroxyl numbers) than equivalent phthalic
To obtain proper solution viscosity for particular end uses, such as
application, somewhat more styrene dilution or relatively more glycol
required with IPA than with phthalic anhydride. Stopping the
isopolyesterification reaction at a lower molecular weight (higher acid
is generally not recommended as many of the cured resin advantages will
polyesters made with primary glycols such as neopentyl have poor
styrene compared with ortho and isopolyesters. Blends of glycols and
branched or cyclic glycols have been suggested to improve TA resin
Factors Affecting Alkyd
to briefly the more important factors that affect the preparation of an
a minimum of discussion will be devoted to the chemistry involved in
polymerization and the processing conditions controlling the alkyd
alkyd raw material may be supplied in one or more grades of purity.
glycerol is supplied in several concentrations as listed in Table 1.
glycerol refers to the pure chemical
amounts of foreign material may affect the alkyd reaction. For example,
synthetic glycerol under certain conditions may act different than
from natural sources.
alkyd raw material may be introduced as such or combined with some
material. Thus fatty acids may be added directly the alkyd reactor, or
be added, combined with glycerol, as an oil molecule (whole oil or
advantages and disadvantages of using fatty acids as opposed to
(whole oils in formulating alkyds are summarized in Table 2. A review
table suggests that when pricing takes precedence over performance,
will be selected for the alkyd raw material, especially for long oil
intended for trade sales items. However, where performance is all
fatty acids are referred, for they afford the alkyd chemist a much
latitude in alkyd design with a significantly higher probability of
requirements of a tough specification. Fatty acids are most frequently
the manufacture of short to medium oil length alkyds intended for
calculating a theoretical alkyd formulation, all ingredients are broken
into their uncombined form before any computation of a formulation is
could be theoretically argued that any given alkyd composition should
reach the same end equilibrium structure regardless of the order in
reactants are charged. From a practical and point, however, the order
addition is vitally important. In the formulation systems to be
optimum alkyd compositions one are computed. The question of how the
polymers are rest united chemically to achieve this optimum composition
matter of preparation technique. Chemists versed in alkyd technology
recognize the importance of the sequence of addition of alkyd
use it as a powerful tool in building up desirable structures.
example, in the preparation of alkyds from glyceride oils, the first
the reaction almost always consists of forming a monoglyceride
alcoholysis of the glyceride oil with added polyol. This is a necessary
step, for (a) alcoholysis converts the insoluble polyol and glyceride
into a single homogeneous monoglyceride phase and (b) the monoglyceride
provides a solvent for the phthalic anhydride added for the next step,
esterification of the monoglyceride with diacid to complete the alkyd
In the preparation of alkyds from fatty acids, order of addition can
important. For example, it is generally conceded that improved physical
properties are obtained when the polymer structure is predominantly
of high molecular weight. To achieve this, one proposed method
step by step esterification of the fatty acid. In this procedure, the
cooked with only a proportion of the total fatty acid present (from 40
per cent). By withholding a part of this chain-terminating ingredient a
structure is encouraged during the first part of the reaction. Later,
remaining fatty acid is added to complete the preparation. Alkyds
this so-called high polymer technique are said to be more viscous and
lighter color than those cooked by the conventional method, which calls
addition of all the fatty acid at the very beginning of the cook.
films of the high polymer alkyd are said to exhibit a faster dry,
flexibility, better adhesion, and enhanced resistance to detergents and
alkaline solutions. However, results reported from a recent
specifically set up to study this high polymer theory only partially
the original claims. Thus, some of the experimental results were
although the general trend supported the contention that this technique
upgrades an oil such as tall oil, with greatest improvement in a long
significant differences are also observed for alkyds that are identical
chemical composition standpoint but that differ in properties and
depending on whether they are made by the alcoholysis or the fatty acid
plausible explanation for this difference is afforded by considering
differential rates of reaction between —OH and —COOH groups, depending
specific location on the parent molecule. Table 3 lists the relative
reactivity for several —OH/—COOH pairs, listed in descending order of
the fatty acid preparation method, where there is a free-for-all
among the —COOH groups (all added at the beginning). the fatty acid
groups lag behind in joining primary —OH groups and hence must settle
connections with secondary —OH groups. In the monoglyceride method,
competition is rigged, the fatty acid —COOH groups are deliberately
with the primary groups of glycerol before any phthalic anhydride is
the diacid —COOH groups are placed at a competitive disadvantage and
to settle for a reaction with leftover —OH groups. Reasonable chemical
structures for these alkyd compositions as formed by the two cooking
are graphically shown in Fig. 1.
inspection of the two reaction rates at the bottom of Table-3 (for
that are responsible for cleaning up residual acidity) shows that a
in acid number should be attained more rapidly at the end of the
the fatty acid procedure.
agitation is necessary (a) to provide an intimate mixing of any
ingredients (say soya oil and glycerol during alcoholysis) and (b) to
accelerate the alcoholysis, polymerization, and allied reactions. The
rate of a
chemical reaction is promoted by agitation of the reacting molecules,
failure to provide adequate agitation leads to abnormally long cooks
inferior alkyd resins.
is furnished by both mechanical elements (propellers, paddles,
turbines) and by
sparging devices (bubbling of an inert gas through the reaction
Sparging is also highly effective in removing liberated reaction
as water (removal of water is necessary to permit the condensation
proceed) and contaminants such as air (the oxygen encourages color
diameter of the rotating mechanical element furnishing the mixing
generally about one-third the diameter of the alkyd kettle and should
located well down in the reactor. The revolutions per minute (rpm) of
rotating element is generally adjusted to an optimum peripheral speed
either nitrogen or carbon dioxide (which yield substantially equivalent
results), sparging effectiveness is dependent on the rate of blow and
fineness with which the gas is dispersed as it courses upward through
alcoholysis, a blow rate between 0.01 and 0.02 ft3/min/gal is
Sparging is continued throughout the reaction, including the upheat and
esterification, a rate of 0.01 to 0.04 ft3/min/gal is satisfactory with
faster blow rate applying to the beginning and the slower to the end.
dispersion is conventionally
accomplished by introducing the gas into the reaction mix through many
holes (facing downward to ensure drainage) drilled in a perforated
assembly which is spread out over the bottom of the alkyd kettle.
mechanical agitation and sparging are mandatory for the preparation of
choice of a reaction temperature or temperatures is usually a
namely, a temperature that is sufficiently high to permit the reaction
carried out within a reasonable time period, yet not so elevated as to
destructive decomposition, discoloration, and/or an excessive loss of
material through the stack.
example, a normal esterifying temperature for preparing a soya alkyd
soya oil, glycerol, phthalic anhydride) is 450 F (232 C). Increasing
esterification temperature by 40 F to 490 F halves the processing time,
loss of volatile material then becomes excessive. Decreasing the
temperature by 40 F to 410 F doubles the processing time, which makes
uneconomical from an over-all cost standpoint.
temperature of the reaction at different stages may also be influenced
possibly controlled by such factors as the melt point or volatility of
the alkyd raw material ingredients. Table 4 which compares reaction
for phthalic anhydride and iso-phthalic acid is a case in point.
Versus Solvent Cook
alcoholysis (to form a monoglyceride) is invariably carried out with no
present, alkyd esterification may be carried out either in the absence
solvent (fusion cook) or with solvent present (solvent cook).
amount of solvent used in the solvent cook must of necessity be held to
relative small percentage of the total charge by volume (5 to 10 per
Preferably it should be selected to have a boiling point in a range
which is 75
to 100 F less than the temperature at which the alky is to be refluxed.
higher percentages of solvent prevents the attainment of an
temperature. Moreover, owing to its slow evaporation rate (only a high
solvent is applicable to a solvent cook), a high percentage of the
solvent in the
final alkyd extends the alkyd dry time to an intolerable degree.
solvent cook is claimed (a) to facilitate the removal of water and
contaminants owing to the continuous sparging action of the solvent,
condensed and continuously returned to the alkyd kettle; (b) to give
temperature and viscosity control, as the presence of the solvent
more mobile mixture; (c) to establish conditions for a more uniform
is freer from skinning and overpolymerized gels; and (d) to yield a
kettle after the batch is completed caromatic solvent dissolves any
anhydride deposited in the condenser and returns it to the reaction
Despite these advantages, the fusion cook is a popular processing
method and is
preferred to the solvent cook when working with isophathalic acid. The
cook also requires less initial outlay of equipment, as no water
necessary, and is less expensive to operate, as no heat input is
refluxing of solvent.
Selection for Alkyd
oil alkyds are generally reduced to shelf-storage or application
with aliphatic solvents, whereas short oil alkyds require aromatic
with or without some admixture of alcohol or other polar sovent, as the
properties for typical long and short alkyds reduced with appropriate
are given in Table 5.
choice of catalyst is vital for facilitating the progress of the alkyd
conversion of a glyceride oil and a polyol to a monoglyceride (say soya
glycerol to form a soya monoglyceride) can be satisfactorily
without a catalyst by carrying out the alcoholysis reaction at a
high temperature (550 F). How ever, it is more expedient to carry out
reaction at lower temperatures (450 – 480 F) by resorting to a suitable
catalyst which greatly accelerates the rate of conversion (by 10 – 20
and markedly cuts down on volatile losses. As little catalyst as
should be used, for it also promotes color development and detracts
water and alkali resistance of the end alkyd product.
Ca(OH)2, and litharge, PbO, are common alcoholysis catalysts which are
effective at levels of 0.05 to 0.10 per cent based on the oil weight.
catalysts are rather ineffective and sodium catalysts, although
impart undesirable properties to the alkyd composition, such as
color development and slower dry Lithium ricinoleate, recently
finding favor owing to its excellent catalytic activity, relative
phthalic anhydride poisoning, and clarity of product formed; calcium
litharge cause precipitation as metallic phthalates.
Alkyds Formulations Based
chapter is devoted exclusively to the design of alkyds from theoretical
considerations. Of the four theoretical systems discussed, one in
has been amplified in Chapter 6 to give a highly practical formulating
for routinely designing and checking alkyd formulations.
four formulating systems to
be discussed in detail are predicated on:
Fav, an average over-all
functionality for the alkyd composition
p, the probability of a branch–to–branch
connection between reacting molecules at gelation
AN, the acid number of the
alkyd composition at its gel point
Mav, the average molecular
weight of the alkyd at gelation.
the sake of brevity, they will be referred to hereafter as the Fav, p,
Mav formulation systems, respectively.
make the discussion completely general, two molecular species
designated A and B will serve as co-reactants. For practical
they will be identified with actual molecules as required. It is
that A can react with B to form a chemical link. Since most alkyd work
with bonding through esterification, A can be thought of as an acid or
group (—COOH) and B as a basic or hydroxyl group (—OH). However, it
understood that A and B groups are not necessarily limited to this
the use of a subscript, it is possible to designate the functionality
molecule to which an A or B group is connected. Thus, A2 will indicate
this group is part of a difunctional A molecule (a molecule with two
sites). Or B4 will indicate that this B group is part of a
molecule (a molecule with four reactive B sites). The use of subscripts
provides a useful notation for tagging the A and B groups during the
calculation work, identifying their source.
much for likeness and a common ground for all four systems. It is the
derivation of the third basic equation (a much more complex affair)
radically different for each system and which serves to differentiate
k functional groups react for every molecule that disappears (through
with another molecule). Normally k is 2, but with highly functional
more than two functional groups can react per lost molecule to give
multiconnected mutual molecules.
P per cent of reaction, (m0 – mP) molecules have been lost. Hence the
corresponding number of functional groups that have been reacted is
extent of the reaction (extent of the condensation polymerization) P
be expressed in terms of m0, mP, and Fav by Eq. 6. Note that the
in this expression equals the total number of functional groups
available for the condensation reaction.
these expressions are beautifully simple statements of the conditions
formation when the reactants are present in stoichiometric proportions.
example, if both A and B molecules are difunctional and if they are
stoichior etric proportions, the reaction proceeds to completion (P =
2/2 = 1 =
100 per cent), at which stage there are present a number of tremendous
molecules which are inter-twined to form a gel-like composition.
if either the A or B group is present in excess (which is usually the
downward adjustment in functionality must be made for this group
to its excess.
Illustrating the Formulation of Alkyds Based on the Fav System
following problems serve to
illustrate the technique of assessing and formulating alkyd
on the use of an average functionality.
short OL dehydrated castor oil (DCO) alkyd given in Table 1 has been
as an experimental alkyd composition. Check the feasibility of its
101 per cent value indicates that the reaction can be carried to
with safety (1 per cent margin to spare). However, actual preparation
particular alkyd by the solvent method resulted in gelation at an acid
12. This premature gelation can undoubtedly be attributed to
the DCO FA (a side reaction taking place along with the main alkyd
which effectively contributes to the over-all polymerization.
next problem illustrates how information obtained from an initial alkyd
that gels prematurely can be employed to adjust the formulation of a
the data developed in Problem 1, formulate an adjusted alkyd
will avoid the onset of premature gelation.
acid number of the alkyd composition as charged to the alkyd kettle in
1 was 372. This value is calculated as shown in Table 3 from the total
equivalents and the charged weight.
extent of the reaction which was actually reached in Problem 1 was then
is comparable to the predicted value of 101 per cent. The discrepancy
predicted and experimental values calls for an adjustment of k in Eq. 8
it conform to the experimental findings of the initial cook. This is
accomplished by substituting the experimental value of P = 96.7 in the
equation; Fav remains unchanged at its value of 1.98. From Eq. 8,
calculations will now be based on this experimental k value of 1.91.
This is comparable
to the alue of 2 initially assumed for k.
prepare a nongelling variant of the DCO alkyd of Problem 6.1, let the
content be arbitrarily increased from 2.25 to 2.38 moles. This
greater excess of —OH groups (lowers the average effective
functionality of the
alkyd system) and permits the reaction to proceed further before onset
—OH excess here is 7.14/(1.00 + 4.36) = 1.33, which lowers the
glycerol functionality by the reciprocal of 1.33, or the factor 0.750
1.00/1.33). The effective over-all functionality of the alkyd
is then 1.93.
predicted extent of the reaction before gelation, using the
determined value of 1.91 for k, is 0.993, or 99.3 per cent.
percentage appears borderline, as a P of 100 per cent is an optimum
However, this alkyd was successfully prepared at 450 F and brought to
value of 8 (corresponding to a P of 97.7 per cent) without gelation.
had a Z2 – Z3 viscosity when reduced to 50 per cent solids content in
Note that the value of 97.7 per cent lies on the safe side of the
value of 99.3 per cent for incipient gelation.
Method for Computing
a P Value
proceeding with further illustrative problems, it is instructive to
short-cut method for arriving at a P value.
explain this method, let eD denote the sum of the equivalents for that
which is not present in excess (is deficient in amount for a
reaction) at the beginning of the condensation polymerization.
example, an alkyd is conventionally prepared by the reaction of —OH and
groups, with the —OH groups present in excess. According to the above
definition, eD denotes the sum of the acid equivalents in the reaction
since this is the group that is deficient in amount for a
the Problem 2, in order to compensate for an excess of one group in
an effective Fav, an excess factor was first calculated and the
this was used in turn to adjust the functionality of the excess
it can be shown that the net effect of this procedure is merely to make
effective number of equivalents of the group in excess equal to the
of equivalents of the deficient group.
can be checked by referring back to Problems 1 and 2 where adjustments
made in the functionality of the glycerol to take care of its excess.
both problems, the number of effective glycerol equivalents and the
equivalents are both equal to 5.36. Note that the effective glycerol
equivalents still remain equal to 5.36 in Problem 2 even though the
content was increased.
this 1 : 1 relationship
between effective equivalents of the group in excess (say —OH) and
equivalents of the deficient group (say —COOH) is established as valid,
becomes apparent that 2eD can be used as a replacement for e0 in
effective Fav for the system.
a P value can be calculated, the soya oil must be broken down into its
glycerol components. This is done in Table 7; the charged composition
tabulated to the left and the breakdown composition to the right.
these values of m0 = 0.561 and eD = 0.552, the percentage of reaction P
incipient gelation can be calculated from Eq. 12.
and Application of
a Unique Alkyd Constant for Routinely Assessing, Adjusting, and
Table 47, it was noted that of the four theoretical formulation systems
considered, the one based on an average alkyd functionality was of most
universal applicability. This particular system will now be developed
different and somewhat unique fashion, leading to the concept of an
constant K. The derivation, as before will be based on Carother’s
theorem with the adaptation applying to the specific case of alkyds.
the use of this alkyd constant, it is possible to routinely assess the
feasibility of preparing an untested alkyd, adjust an improperly
alkyd to a corrected composition, or formulate an alkyd from scratch.
derivation initially follows the line of reasoning developed under the
formulating system of the previous chapter leading to Eq. 1.
this point, a different approach is taken in containing the derivation.
Equation 1 as written above covers the case in which the alkyd
present in stoichiometric proportions. But what about the case in which
the reacting groups is present in excess? Thus alkyds are invariably
with excess hydroxyl groups. How does this affect the foregoing
problem can be resolved by considering the total of those equivalents
actually reacted when the condensation reaction is 100 per cent
is, when all the acid groups have been related. This total must of
equal twice the number of acid equivalents initially present in the
composition (one hydroxyl group is reacted for each acid group reacted).
far as effective use of functional groups is concerned, only those that
reacted count. The hydroxyl groups present in excess remain unused and
effect reduce the effective functionality of the molecule to which they
Hence for the case in which hydroxyl groups are present in excess, the
effective number of equivalents for the alkyd composition is 2eA (where
equals the total number of acid equivalents initially present in the
mixture) and not the actual number, e0.
are more rigorous ways of deriving this basic equation, but this is the
simplest and most straightforward.
an alkyd to be outstanding in performance, it must be processed to as
molecular weight as possible. At the same time, the molecular weight
be allowed to become excessive, or the alkyd vehicle will drift out of
during processing (will gel) or the alkyd will exhibit instability on
aging and prematurely convert to a gel in the paint can. Hence the
avoid unduly small or unduly large alkyd polymers.
general, an alkyd is formulated to reach a point just short of
gelation at 100 per cent of reaction. This is equivalent to saying that
gelation (incipient), P should equal 1.00. The importance of Eq. 2 in
design and assessment of alkyds now becomes manifest, for it provides
extremely simple criterion for formulating an alkyd to meet the
incipient gelation at P = 1.00, namely, that m0/eA also equals 1.00.
is now postulated that the ratio of total moles to total acid
any properly formulated alkyd is equal to unity. This is a theoretical
constant. As will be shown, this alkyd constant of 1.00 will be
increased in practical formulations to ensure a measure of safety
processing and storage.
Validity of the
Alkyd Constant K
would not be unnatural if the simplicity of the expression for the
constant should engender some doubt concerning its ability to hold for
a narrow range of alkyd compositions. Actually, the reverse is true and
rather remarkable that the alkyd constant should find such universal
example, the mean value for K for 24 alkyds randomly abstracted from
literature sources was found to be 1.022 + 0.023. The average deviation
0.023 for this empirically derived K value attests to its constancy,
fails by a small fractional amount to coincide with the proposed alkyd
of 1.00. This slight discrepancy in value can be reconciled by the
argument: The constant 1.00 is a theoretically derived value for the
m0/eA. It pertains to the conditions of full completion of the
reaction at incipient gelation. However, for any practical alkyd cook,
formulating this close to gelation is dangerous. Accordingly,
dictates that a margin of safety be provided. This accounts for the
between the theoretical constant of 1.00 and the experimentally
average value of 1.022. The 0.022 discrepancy is a safety factor.
immediately suggests that it might be more expedient to peg the alkyd
at a practical value of 1.02 rather than the theoretical 1.00 value,
provides no built-in safety factor. However, although this is a good
recommendation, it is felt that the base value of 1.00 should be
retained as a
foundation figure from which working alkyd constants can be built in
example, an inspection of the data for the 24 alkyds revealed that
based on phthalic anhydride tended to have low K values, whereas those
isophthalic acid tended to have high K values. By grouping the alkyds
type and calculating the mean alkyd constant for each group it was
that better constancy among the K values was obtained (average
smaller), and (b) that with isophthalic acid, a somewhat larger
safety factor must be provided.
the following approach is suggested for establishing an alkyd constant
practical alkyd resins. Unity will be retained as a base theoretical
the alkyd constant. From this theoretical value of 1.00, practical or
alkyd constants will be derived that will contain built-in safety
corresponding to the type of alkyd being processed.
adjustments of the theoretical alkyd constant of 1.00 to obtain
target K values for formulating experimental alkyd cooks are given in
of the Alkyd Constant for
Assessing the Feasibility of Preparing a Given Untested Alkyd
working alkyd constant K provides the alkyd chemist with a powerful
assessing the feasibility of preparing a given untested formulation. By
comparing the computed K (= m0/eA) for the proposed formulation against
working constant for that type of alkyd, the alkyd chemist is in a
gauge whether the preparation of the alkyd resin is feasible.
the computed K value is less than the working alkyd constant, then
short of 100 per cent reaction must be anticipated; if greater, then
unacceptable polymer formation (with concomitant unsatisfactory vehicle
performance) must be expected. About 0.05 units deviation from the
value is probably the maximum that can be tolerated without
certain gelation on the one hand or jeopardizing ultimate alkyd
the other hand.
illustrate, assume that an untested phthalic anhydride alkyd
submitted for preparation approval. The working constant for this type
is K = 1.01. A first step would consist in determining whether the
falls in the range 1.01 ± 0.05. A value close to 1.01 would indicate a
alkyd preparation with satisfactory ultimate performance assured. If
value for the alkyd fell in the extremes of this range, some question
feasibility of its preparation would be in order. However, if the m0/eA
fell outside the 1.01 ± 0.05 range, it is almost certain that its
is foredoomed to failure or that its ultimate performance properties
unsatisfactory. The problem that follows illustrates the details of
and using an m0/eA value for alkyd assessment.
medium OL alkyd is submitted for preparation approval. It consists of
soya oil, 200 parts PA, and 100 parts glycerol (weight basis). Is this
the actual K value (m0/eA) for the given alkyd and compare it with the
alkyd constant (optimum target K value) of 1.01 that applies to PA
of the actual alkyd constant of 1.02 with the optimum target constant
reveals the complete feasibility of proceeding with the preparation of
of the Alkyd Constant for
Adjusting an Improperly Formulated Alkyd Composition
alkyd constant can be used to adjust improperly formulated alkyd
by setting up successive paper modifications and checking them against
appropriate alkyd constant until a reasonable m0/eA value has been
With a little experience, it is entirely possible to correct an
formulated alkyd by a single formulation adjustment. The key to any
is course, judicious alteration of the relative proportions of the
until their m0/eA ratio equals the alkyd constant that applies to them.
next problem illustrates the details of how such an adjustment is
IPA alkyd is submitted for preparation which has the following weight
soya FA 40%, IPA 38%, benzoic acid 2%, glycerol 20%. Is this a feasible
preparation? If not, correct the formulation as necessary to carry out
the alkyd m0/eA ratio as it now stands.
comparison of this computed K value of 0.975 with the working alkyd
1.05 for an IPA alkyd reveals the certain gelation danger that can be
during the final stages processing. Adjustment to a safer and more
formulation is necessary.
way of accomplishing this is to increase the percentage of
benzoic acid at the expense of difunctional IPA. This lowers the
functionality of the system and permits a more complete reaction before
onset of incipient gelation. Based more or less on experience, the
content is accordingly raised to 8 per cent and the IPA content is
32 per cent. This gives the alkyd resin in Table 5.
comparison of this computed K value of 1.04 for the adjusted
the working alkyd constant for IPA alkyds of 1.05 indicates the
proceeding with the preparation of the corrected composition.
of the Alkyd Constant for
Formulating Alkyd Compositions From Scratch
obvious approach for setting up an alkyd formulation from scratch would
start with an educated guess for the required composition and then, by
successive approximations, arrive at an acceptable K for the final
However, it is possible to achieve the same result in a more orderly
The systematic approach will be illustrated by considering a common
which the alkyd is formulated from monoacid, diacid, and a polyol of
Assessment of the
Performance of Single and Multicoat Red Iron Oxide-Alkyd
prime requirements of exterior protective coating are resistance to the
in weather conditions, ability to withstand the attack of environmental
pollutens and protection of the substrate from corrosion. The growing
industrial development potentials demand paint systems which
protect steel structures and other installations from pollutants in the
surrounding environment. For this purpose the substrates are given a
coats of protective coatings comprising primer, intercoat and top coat.
However, in practice, instances have been observed where paint systems
score well in the initial testing fail prematurely, thus making the
of the installations more expensive. It is, therefore, essential to
performance of individual paints with respect to the location and the
performance of the paint system in combination (primer + intercoat +
critically examined test data on the performance of paint coatings
outdoor and laboratory conditions and suggested that for good
the test data strict methods and precise measurement of the individual
properties should be adopted. Kilcullen2 studied the relative
various factors related to the environment and to conditions of
procedures in assessing the performance of paint coatings on steel
and recommended that adequate thickness of coating of the paint systems
essential for good protection. Cooling and Wilkinson3 are of the view
weathering test data can be used confidently to predict the performance
coatings provided that the natural effects are taken into account in
accelerated weathering devices. Ellinger4 made an attempt to correlate
date on the performance of coatings obtained from various accelerated
weathering devices and from the natural weathering. He also quoted the
others on these aspects of the students.
workers5” have studied various properties of coatings and tried to
their findings in terms of quantitative assessment of the performance
coatings. In the present study an attempt has been made to study the
the properties of paints having different contents of synthetic red
pigment in linseed oil— penta — phthalate alkyd medium. The paints
contain 55% PVC of iron oxide are used as primers and the ones
30 and 35% PVC’s of the pigment are applied as to coats on the primer
effect of a number of coats on the properties of paints as well as the
in their properties when exposed outdoors are studied and the findings
Two resins11 (i) 66% linseed oil penta phthalic alkyd and (ii) 52%
oil-glycerol-phthalic alkyd were used as binders. Synthetic red iron
pigment (density 5.12g/cc) and white spirit + xylene mixture (1:1 v/v)
used for preparing paints in these alkyds. The details about the paint
formulations are given in Table 1.
of paints: In order to have particles of uniform size the pigments was
through 300 mesh. The calculated amount of the binder, pigment and
a particular mill base was mixed in the pot and left overnight. The
was ground in a steel Cowlishaw high speed planetary ball mill to a
7-8 Hegmann — gauge. After grinding and filtering the solvent content
adjusted to 21.0 ± 0.5% on weight of the paint. The paints were stored
tight sample bottles at 26 ± 1°C. 0.5% lead napthenate and 0.05% cobalt
napthenate on the weight of the binder content were added to the paints
hours before application. The following tests were conducted on the
either on a metal substrate or as free paint films:
Resistance to scratch in kg
Tensile strength of free film
coatings in kg/cm2.
Adhesion strength of coatings
Permeation of water vapour
through free films in g/m2/h/mil.
Resistance to corrosion in
Salt Spray Test.
on Tin Foil:
coatings applied on tin foil were used for conducting tests in which
were required. Coatings of a particular paint were applied on tin foil
mechanically driven applicator with Bird Blades (Gardner Laboratories
USA). They were left in the application room for 48 hours to air dry
handling them for any type of test. In the case of multicoat
time gap of 24 hours was allowed for between two coats. The
amalgamation of the
tin substrate was carried out to separate it from the coating for
testing. The free films of coatings thus prepared were used for
tensile strength and water vapour permeability tests.
on the Metal
surface preparation of mild steel panels (150 x 100 x 2mm) and the
them was carried out according to standard procedures prescribed for
to corrosion tests.12 The tin plated mild steel test panels (150 × 50 ×
were prepared for the scratch hardness test by a similar procedure. For
measurement of adhesion strength of coatings, mild steel discs (dia 30
thickness 2 mm) which had been abraded, degreased and dried before
in desiccators were used. The paint coating was applied on these discs
ICI spin coater.13
coatings (single coat, two and three coat systems) on tin foil backed
glass plate were tied to the support with mastic tapes. The painted
test panels were given a protective coating on their back and edges.
steel discs prepared for adhesion test were coated on their back with a
strippable coating. The prepared test specimens were exposed to outdoor
weathering facing South at 45° angle on racks four feet above the floor
terrace of the laboratory building14.
48 hours air dried coatings on tin foil were left for 24 hours in a
bath to amalgamate the tin substrate. The underside of the free film
allowed to dry for another 24 hours. Thus the films were air dried for
120 hours before any one of the tests was conducted on the free films.
obtained from the tests conducted on coatings air dried for one week
referred to as the initial readings, i.e., zero period of outdoor
the table and figures.
Hardness of Coatings:
this study the hardness of paint coatings air dried initially and of
weathered outdoor for various periods of time is determined by using an
automatic scratch hardness tester (Research Equipment Ltd., U.K.). The
reported in Table 2 and plotted in Figures 1a and 1b indicate a gradual
increase in scratch hardness of coatings with a PVC of up to 50-55%.
hardness of coatings having pigment content beyond 55% PVC decreases,
the decrease is not significant. The reason for the over pigmented
having good hardness is that when a wet coating is applied onto a
prepared metallic test panel the surface forces attract the active
present in the binder. Consequently, the pigmented binder develops
the coating — substrate interface.
plots of scratch hardness data of coatings weathered outdoors
gradual increase in hardness at up to 50 days of exposure and then a
during the following prolonged period of weathering (Figures 1a and
general, paints formulated with linseed oil — penta — alkyd show
scratch hardness in comparison to those formulated with linseed
oil-glycerol-alkyd. This is because penta-erthiritol-alkyd develops
cross linking in the course of its preparation as well as having good
interaction with pigment and solvent. This is due to the greater
of its polyol. Penta-erthiritol-alkyd also attains greater strength
auto-oxidation of the coating in comparison to coatings based on
oil-glycerol-alkyd. However, in the course of prolonged weathering the
based on linseed oil-glycerol-alkyd retain their hardness properties
longer period when compared to linseed oil-penta-alkyd based coatings.
information obtained from this test is quantitative and can be used in
assessing the performance of coatings in actual service.
Strength of Free Films
strength is one of the important properties of maintenance coatings. It
the reinforcing effect of the pigment in the binder and also the
strength of the coating. The tensile strength of free films of coatings
or weathered outdoor was determined using an Instron tensile tester
Ltd. UK). The results are reported in Table 3 and plotted in Figures
2a. 2b and
2c. The data of tests conducted on initially air dried free film of
that their tensile strength values increase with pigment content in the
formulation. For example the tensile strength of the free film of paint
containing 25% PVC of pigment in linseed oil-penta-alkyd is 71 kg/cm2
of the paint having 50% PVC is 117 kg/cm2. However, at higher PVCs the
tensile strength indicates that the amount of binder is not sufficient
the pigment compact. Hence a pigment content around 50% PVC may be
to be critical pigment volume concentration (CPVC). Paint formulations
linseed oil-glycerol-alkyd also show a similar trend, however their
attain the maximum tensile strength at about 55% PVC.
tensile strength of weathered coatings reaches maximum value after 40
days of exposure. For example, in Figure 2a paint number P1 attains the
strength of 153 kg/cm2 after 50 days of exposure whereas the initial
strength of its air dried coating was 71 kg/cm2. Among the linseed
oil-penta-alkyd paints the one which contains 45% PVC retains good
strength (134.66 kg/cm2), even after 180 days of outdoor weathering.
and P7, being pigmented, have low tensile strength in comparison to
figure 2b, the tensile data plots for paints in linseed
that, among these paints the free film of paint number pv (50% PVC)
maximum tensile strength and retains it even after 120 days of
observed in earlier cases, the tensile strength of the free film of
pigmented paint P11 (60% PVC) is relatively low.
changes in the properties of multicoat systems, i.e. primer + one top
primer + two top coats, were studied with the objective to assess their
performance in service. The tensile strength data reported in Table 3
plotted in Figures 2a, 2b and 2c show that the tensile strength
multicoat system is less than the average of the strengths of single
coat and single top coat. Even in the course of weathering the
not build up as much tensile strength as it is found in the case of
coats. The reason for this observation is that the curing of the top
the thin single coat by auto-oxidation is fast and it is also catalysed
metal ions at the metal-coating interface. Consequently, the single
attains good strength within a short period of time whereas top coat
onto the primer does not come in contact with the metal substrate and
does not get catalysed by the metal ions. Due to this fact the
systems do not attain as much strength as the single coat does in a
period of time. The coatings of single and multicoats exposed for
weathering also exhibit this feature in their properties.
Mechanical Properties of
Alkyd Resin Varnish Films and the Effect of
Different Weathering Conditions on them
durability of a surface coating depends on the physical characteristics
films, i.e., flexibility, tensile and bursting strengths, impact
resistance to the permeation of water vapour, ions and gases, and its
to the substrate. Generally, coatings fail in service by cracking and
due to the mechanical breakdown of their films, indicating that, at the
failure, the magnitude of the stresses present in the film exceeds that
cohesive forces. These stresses are set up as a result of the
dimensional changes in the film and in its substrate, and changes in
chemical structure of the film as a result of weathering. The stresses
in the film and the substrate are communicated to and resolved in the
the interface. The stress concentration and chemical changes lead
the breakdown of the film.
stresses induced (or developed) on ageing are opposed to the forces
coating to the surface of the substrate. In the process of drying,
varnishes are converted from the liquid to the solid state by
cross-linking. Since, under such conditions the paint film dries from
outside, rigidity will first develop at the exposed surface. To avoid
concentration in the film, which will bring about cracking and flaking,
reasonably high order of mechanical properties is required. Thus, the
determination of the mechanical properties of surface coatings under
weathering conditions is important in order to find out whether they
close examination of methods available for measuring mechanical
paint and varnish coatings, such as rocker hardness, impact, bend and
tests, shows some limitations particularly with regard to their time
and reproducibility. Since these tests are normally carried out on
on metal surfaces, the values obtained may be affected by the nature of
adhesion to the substrate. An alternative approach based on
on supported films could thus be advantageous.
considerable amount of work has been done on the stress-strain
paint and varnish films, and it has been found that tensile strength
measurements are in many ways a fare more reliable guide to film
the other methods. Film strength is related to the degree of
the film-forming material. Cross-linking imparts rigidiy, which shows
increased tensile strength and lower elongation. The stress-strain
be used not merely to define the ultimate tensile strength and
the material, but also to define its toughness, flexibility and
Toughness is best measured by the total work required to break the
indicated by the area under the load elongation curve. In agreement
definition of flexibility as extensibility or the ability to undergo
deformation, the ultimate elongation can be considered as a measure of
flexibility. The yield point on the load elongation curve is suggested
measure of hardness. The importance of physical specifications for
materials has been emphasized in connection with the relationship
physical properties and the general durability of a coating. The
of the physical properties of the coatings vary with the composition of
film-forming materials. The durability depends more on the rate of
physical properties than on their initial values. Periodical
these properties during the course of ageing will show the extent of
taking place in the film up to its ultimate failure. Such data will
classification of the film-forming materials with regard to mechanical
physical properties of varnish films on metal substrates have been
several workers at definite ageing intervals. The flexibility of the
was determined by bending a metal panel coated with the material under
around a mandrel. It was found that exposure to continuous carbon are
absence of water, had little visible effect on the films, hence the
exposure required to crack the varnish film on bending over a
oxidation of oil in the course of ageing generally increases the
strength and decreases the flexibility of the film.
function of the oil component of a varnish is to give the film the
extensibility to withstand the tensions caused by expansion,
bending, etc., which would otherwise make it crack. In the present
study a number
of alkyd resin varnishes of the following compositions were selected
determining the mechanical properties:
work outlined here was undertaken to determine the relationship between
composition of alkyd resin varnishes and their mechanical properties
tensile strength, elongation, modulus of rigidity and bursting
studies also included the periodical determination of some of the above
properties during the course of ageing by exposing the free films of
Natural weathering, and (ii) Carbon
alkyd resin varnishes were prepared as described in Appendix I.
free films of these varnishes were prepared by an amalgamation
thickness of the dry varnish film can be controlled by variation in the
percentage of thinner in the varnish and by using strips of known
while applying the varnish film over the tin foil with the help of a
applicator. For proper comparison of data obtained by the measurement
film properties, the thickness of the dried film was controlled at 60 ±
measured by dial gauge.
Strength and Per Cent
electrically operated Gardner tensile strength and elongation apparatus
used for determining the tensile strength and percentage elongation of
varnish films. Films were cut into test pieces of 12 × 1 cm and
fastened to the
upper and lower clamps of the apparatus so that the length of the film
between two clamps was 10 cm. The percentage elongation was noted for
reading of the load indicated by the scale and the observations were
until the film failed. At least six determinations were made for each
varnish films under test. The load values, calculated in terms of kg
plotted against percentage elongation (Figs. 2) and the area under each
estimated for the determination of the toughness of the film. The load
elongation curves of varnishes No. 2, 5, 6 and 12 which have high
strength are plotted separately in Fig. 3. The tensile strength,
toughness data are given in Table 1.
modulus of rigidity was also measured using the film as a torsion
results are reported in Table 1. These data were not useful in
change of film properties and so are not further discussed.
apparatus described in an earlier communication19 was used for
bursting strength of the varnish film.
Steadily increasing air pressure was applied to a known
area of the
film. The pressure was indicated by a mercury manometer and the
which the film burst gave the bursting strength expressed in terms of
height of mercury in mm.
order to study the effect of ageing on mechanical properties of alkyd
varnishes, their free films, supported on glass plates by pasting at
with cellulose adhesive tape, were exposed to natural weathering on
45° facing south.
mechanical properties of the varnish films were measured after 15, 30,
and 90 days’ exposure. On completion of each exposure period, the films
removed from the exposure rack and kept in a room maintained at 25 ±
2°C for 48
hours and their tensile strength and percentage elongation were
data are graphically represented in Figs. 7.
to Carbon Arc Lamp
study the effect of UV radiation on the mechanical properties of the
alkyd resin varnishes under accelerated conditions, their free films
to a carbon arc lamp in the Marr Fastness-to-light apparatus. The
determinations of tensile strength and percentage elongation of the
made after exposure periods of 30, 60, 100, 150, 200 and 300 hours and
graphically represented in Figs. 8 to 11. All determinations were
at 25 ± 2° C.
strength and elongation
load elongation curves for the first six films are of similar form and
almost linear up to a certain value of stress (Fig. 1). This
indicates that under low values of stress the extension of these
directly proportional to the load. The curves for the second set of
slight variations in their form. These curves show that the extension
varnishes is proportional to the applied load in a lower range of
the observations of stress-elongation for the two groups of varnishes
it may be
concluded that there is a certain analogy between the behaviour of a
film and a strip of metal when subjected to tensile stress. The degree
recovery of varnish film depends mainly on the nature and extent of
cross-linking in the surface coating material. The films differ from
that they are much affected by the duration of the stress or the number
the stress is applied, and hence the ratio between stress and
fluctuates considerably with such factors and also changes with the age
film and the type of exposure to which it is subjected.
et al. have summarized the mechanical properties of paints and
follows: (1) low elongation and low tensile strength mean hard brittle
liable to early failure, (2) low elongation and high tensile strength
hard, tough films that are resistant to abrasion, (3) high elongation
tensile strength result in flexible, soft and plastic films, (4) when
elongation and tensile strengths are high the film is flexible and
the film will have the best mechanical resistance.
the case of linseed oil-phthalic anhydride-glycerol alkyds, both
strength and elongation increase considerably when the oil length is
from 66 per cent to 55 per cent. But in the case of pentaerythritol
tensile strength increases from 23.1 kg cm–2 to 105.4 kg cm–2 and the
elongation decreases slightly on reducing the oil length. The alkyds
DCO do not show the same changes in their mechanical properties when
length is reduced from 66 per cent to 55 per cent.
determinations of tensile strength and percentage elongation show that
lengths of the alkyds affect their general properties. The long oil
alkyd films are initially soft and flexible and have low toughness and
due to the high percentage of oil. The medium oil length alkyds appear
a just sufficient amount of oil to impart a desirable flexibility,
and hardness, as is evident from the high initial values of their
load elongation curves for the second set of six alkyds are plotted in
Varnish no. 11 is very similar to varnish no. 1, except for the method
processing, varnish no. 11 being made by the fatty acid-oil process21
varnish no. 1 by the alcoholysis process. Thus they may be expected to
similar mechanical properties. Varnishes no. 7 to 10 are modifications
varnish no. 1 and varnish no. 12 is the modification of varnish no. 2
no. 10, in which the cardanol-hexamine condensate was cooked in, was
be very much inferior to varnish no. 9 where the modifications was by
mixture. Varnish no. 10 was found to be inferior to varnish no. 1 also.
no. 8 showed appreciable improvements in its properties as it attained
tensile strength and percentage elongation presumably due to the
modification. The modified varnishes no. 7 and 9 in general showed
in their mechanical properties (Table 1). The modification of varnish
no. 2 by
partial replacement of phthalic anhydride with styrenated rosin
12) was found not to have any appreciable effect on its mechanical
varnish films having high tensile strength and elongation were found to
high toughness as indicated by the area under the load-elongation
Amongst the varnishes studied, no. 6 was found to have the highest
tensile strength, elongation and toughness measurements, the bursting
of varnish films can also be taken as one of the measures for the
of the performance of coating. The initial values of bursting strength
reported in Table 1. It has been found that increase of oil length of
results in a decrease of bursting strength. Modification of the alkyd
incorporation of maleic-anhydride (varnish no. 7), styrene (varnish no.
cardanol-hexamine condensate as a physical mixture (varnish no. 9), and
styrenated rosin (varnish no. 12) led to an increase in bursting
pentaerythritol alkyds were found to have the greatest bursting
Exposure to Carbon Arc Lamp
information has been obtained from the data on the changes of the
properties of alkyd resin varnish films subjected to natural weathering
conditions and exposed to the carbon arc lamp.
tensile strengths of varnishes no. 1 and 2 increase during natural
ageing up to
an exposure period of 20 days; afterwards there was a decrease in these
These observations show that, after attaining maximum mechanical
film becomes brittle in the course of natural weathering and starts
deteriorating. The tensile strength and the percentage elongation of 66
cent linseed oil glycerine alkyd (varnish no. 1) films increase with
Generally, in the course of ageing, the tensile strength of a coating
and elongation decreases, but here both increase, showing that during
the toughness of the coating increases.
is an improvement in the tensile strength of the 55 per cent linseed
oil-glycerol alkyd film on ageing, but the percentage elongation
decreases. The films of this alkyd remained tought than those of the
length alkyds throughout the exposure period. The results of a whole,
suggest a deterioration of propertiesas
on exposure. It would see m preferable to use a long oil
alkyd as a
medium for outdoor exposure as its mechanical properties improve on
pentaerythritol linseed oil alkyds have been found to possess better
properties than linseed-glycerol alkyds.
various mechanical properties, the medium oil length DCO alkyd (varnish
remained very similar to the 66 per cent linseed oil-glycerol alkyd
no. 1), but it did not show as much improvement during ageing. The 66
DCO alkyd (varnish no. 3) was much inferior to both of the above
Thus it may be concluded that, as far as mechanical properties are
there is no particular advantage in the use of DCO in place of linseed
medium and long oil length alkyds.
varnishes no. 7 to 9, which were obtained by modification of varnish
showed some improvement in the initial values of their mechanical
It was found (Fig. 6) that all the varnishes improved in tensile
weathering up to a certain period of time, after which the films became
and failed. Among the varnishes studied, varnish no. 7 showed the best
performance and did not fail even after 90 days exposure. Varnish
similarly to varnish no. 1. Varnishes no. 8 and 10 attained the maximum
strength after 30 days ageing and failed immediately thereafter.
Varnish no. 9,
however, which also attained maximum tensile strength after 30 days,
fail immediately, but slowly deteriorated and failed only after 70
Varnish no. 2 behaved similarly to varnish no. 9, the corresponding
maximum tensile strength and failure being 70 and 90 days respectively.
other hand, varnish no. 12, which was a modification of varnish no. 2,
similarly to varnishes no. 8 and 10, failing immediately after
maximum tensile strength at 30 days.
regard to the change in the values of elongation of the varnishes on
uniformity is found. Varnishes no. 1, 3, 4, 7 and 11 showed increase in
elongation up to 30 days, after which the elongation value decreased,
elongation values of the other varnishes decreased continuously during
weather data obtained from the meteorological department for the
period under study are given in Appendix-II.
free films were exposed in the fastness-to-light chamber around the
lamp with a temperature in the vicinity of the varnish films of about
Varnish no. 1 attained maximum tensile strength of 90.0 kg cm–2 in 300
exposure and varnish no. 2 attained a constant value of 146.6 kg cm–2
hours with a tendency to slight decrease on further exposure, whereas
varnishes attained maximum tensile strength of 40.70 and 92.5 kg cm–2
respectively in 70 days under natural weathering. These observations
the maximum tensile strength attained by the varnish films in natural
weathering was comparatively less than that attained when exposed to
lamp. Both long and medium oil length DCO alkyds showed a constant
their tensile strength, varnishes no.5 and 6 showed better improvement
tensile strengths, both in this test and under natural weathering
Varnishes no. 1 to 6 followed a similar pattern with regard to their
elongation in both the tests (Figs. 5 and 9).
Modification of Alkyds
resinous polymer lends itself to more useful modification by other
physically and chemically, than the alkyd type. To these blends, the
contributes the vitally important properties of flexibility, toughness,
adhesion, and durability.
based on physical mixtures of alkyds with other resins provide the
foundation for the major portion of modern industrial coatings. The
of alkyds with urea/formaldehyde and melamine/formaldehyde resins is
appliance and automotive finishes. The upgrading of nitrocellulose
alkyd modification has enabled this oldest synthetic polymer to remain
competitive with the newer coatings. Physical admixture of alkyds with
chlorinated products (chlorinated paraffins, chlorinated rubbers)
heavy-duty coatings for concrete floors, swimming pools, and corrosive
all these paint systems are primarily physical mixtures, computations
normally relatively simple and straightforward. Resin formulation is
matter of evaluating the mixed resin systems in which the percentage of
content is systematically varied within conventional limits to
optimum balance between the alkyd and the modifying resin to meet any
this reason, only the
chemical modification of alkyds will be considered, since chemical
calls for somewhat involved computations.
the modification is physical or chemical, the properties and
performance of the
blended system will be a reflection of the resins that make it up.
alkyd will be styrene-like in proportion to the amount of styrene it
or it will take on the properties of a silicone resin in proportion to
amount of silicone intermediate introduced.
alkyds can be prepared by two main routes–a prestyrenation technique
one of the raw materials is styrenated prior to the main alkyd
reaction; or a
poststyrenation technique wherein the alkyd is reacted with styrene
main reaction has been completed.
these two preparation routes, the poststyrenation procedure is
preferred, as it gives better processing control and superior
properties of the product. This in no way disparages the utility of
oils, as such, as useful vehicles in their own right.
even partially polymerized styrene is incompatible with drying oils and
the key objective in styrenation is to chemically tie in at least a
the styrene to the alkyd polymer before the styrene monomer has had a
polymerize with itself to form an incompatible styrene homopolymer.
if the alkyd polymer prior to styrenation borders on a supermolecular
(shown by a very low acid number), it is almost certain that gelation
instability will result, for the styrenation process will inevitably
the polymer size to an uncontrollable dimension (to a gel). These two
must be kept constantly in mind in formulating styrenated alkyds.
of Conjugated Acids in
Formulating Styrenated Alkyds
tung, and oiticica oils are rich in conjugated fatty acids; hence these
oils are the ones commonly used in formulating styrenated alkyds.
anhydride is hardly permissible in this type of formulation, for this
unsaturated diacid would preempt the bulk of the reactive conjugated
during the alkyd reaction, leaving insufficient residual conjugated
unsaturation behind for adequate poststyrenation.
formulating this type of alkyd, there is frequently a tendency to be
overgenerous in supplying conjugated double bonds to the reaction
oversupply is not necessary and in fact dilution with soya oil down to
a 3 soya
oil to 1 DCO weight mixture has been proposed for routinely preparing
alkyds suitable for poststyrenation. A working alkyd constant of 1.04
suggested here rather than 1.01, to allow for the viscosity boost
the styrene addition. Table 1 gives an alkyd composition suitable for
processing this alkyd, the reaction must be terminated short of an acid
of about 15 to avoid excessive viscosity on subsequent poststyrenation.
higher percentage of conjugated acids is required in the base alkyd, a
correspondingly higher margin of safety must be formulated. This can be
conveniently done by raising the alkyd constant to a higher value. The
alkyd submitted in Table 2 is suitable for experimental
high working alkyd constant of 1.09 compensates for the high degree of
conjugation. Again the alkyd reaction should be terminated shy of an
number of 15 to allow proper poststyrenation.
of a Diacid with a
Reactive Double Bond
than MA) in formulating
the several diacids with reactive double bonds that have been evaluated
formulation of poststyrenated alkyds, only a few appear to be suitable.
these, the maleic adduct of cyclopentadiene has received the most
Unfortunately, of the two suppliers of this material, one has withdrawn
product from the market (Carbic Anhydride), whereas the other is
offering its product (Nadic Anhydride) at over $1.00 per pound, a price
uneconomical in most alkyd formulations. Further consideration of this
does not appear justified.
of Maleic Anhydride in
the section on conjugated acids, the fact was stressed that for
poststyrenation, maleic anhydride should be avoided. Conversely, when
anhydride is made the basis for formulating an alkyd for
must be used exclusively with nonconjugated acids (2 per cent
probably the maximum that can be tolerated in this system).
role of maleic anhydride is quite different during the alkyd and
reactions. During the alkyd condensation reaction (esterification),
anhydride functions mainly as a diacid, whereas during the styrenation
it functions strictly as a source of unsaturation.
percentage of maleic anhydride in the alkyd formulation is quite
low a percentage fails to provide sufficient double bonds for a tie-in
styrene monomer, leading to a cloudy, or worse, and incompatible
high a percentage furnishes an overabundance of double bond sites,
an overpolymerized or highly cross-linked gel. A formulating guide has
proposed to avoid these dangerous extremes. It is postulated that
for the poststyrenation are optimum (for a phthalate alkyd) when the
polymer has a maleic functionality of. This is equivalent to saying
that when 1
out of 3 polymer molecules in the alkyd provides a maleic-contributed
bond for poststyrenation, a clear homogeneous styrenated alkyd can be
which will exhibit a satisfactory and stable viscosity.
maleic functionality of an alkyd is computed and expressed as follows:
an alkyd prepared from monoacid (nonconjugated), maleic anhydride,
(phthalic anhydride), and polyol.
replacement of PA by MA to permit poststyrenation depends to a major
the acid number to which the alkyd is cooked. Let acid numbers of 10
and 20 be
selected as target values for the computation work. Substitute
values in Eq. 3.
Modification with Rosin
rosin is generally abietic acid, it is treated simply as another acid
for the alkyd reaction. In moderate proportions, rosin renders alkyds
soluble in aliphatic solvents, inhibits the onset of gelation (permits
of a lower alkyd constant), improves adhesion, enhances gloss, reduces
tendency towards wrinkling, and increase the resistance of alkyds to
soap and alkali solutions. However, rosin detracts from color,
toughness, and over-all durability; hence it must be used judiciously.
modification of alkyds with phenolic resins is based largely on
experience. This is partly because the exact structure of most phenolic
is not known with any degree of certainty, and partly because the
reaction of a phenolic resin with an alkyd is not fully understood.
an unsure starting point and an indeterminate chemical reaction, the
formulation of phenolic modified alkyds does not presently lend itself
precise theoretical treatment.
novalac-type phenol/formaldehyde resins and practically all
phenolics are physically compatible with alkyds. Unfortunately their
with the alkyd generally results in an intolerable reduction in
Resoles prepared from unmodified phenols thermoset too rapidly to
chemical reaction with alkyds. However, modified phenols, in which one
of the reactive positions in the aromatic ring are blocked by alkyl
p-tert-butylphenol) give phenolic resins that react readily with alkyds
do with varnish oils) to give satisfactory modified alkyds.
the modification is held to a low percentage, 5 per cent being most
20 per cent being extreme. Presumably the modified phenolic resin
the unsaturation of the fatty acids present in the alkyd composition,
reactions also probably take place and contribute to the ultimate
modification noted, substantial improvement in resistance to water,
solutions (alkaline or acid), and hydrocarbons can be effected with no
appreciable reduction in durability.
with any modification in which molecular size is enlarged by
viscosity increase must be anticipated and allowance made to maintain a
have enjoyed wide acceptance, especially for heat-resistant coatings,
since their first appearance in the journal literature in 1947. As a
the technology of a silicon-alkyd preparation for high-temperature
(400–550 F) is now fairly well established. In general, the formulation
superior silicone alkyd calls for a compromise composition. Basically,
silicone contributes thermal stability, gloss and gloss retention,
and solvent and chemical resistance, whereas the alkyd contributes
impact resistance, and freedom from crazing.
silicone content somewhat in
excess of 50 per cent is generally accepted as achieving optimum
properties for high-temperature service. The choice of alkyd
well as the selection of the silicone intermediate for the
reaction markedly affect the end performance properties.
(20 per cent methoxy content) having a molecular weight of 470 and an E
provides good alkyd compatibility and superior flexibility, adhesion,
impact resistance, but the product suffers from reduced thermal
functional concepts that have been previously applied with considerable
to the design of alkyd compositions appear to apply one casually to
intermediates. Presumably silicone polymerization takes a somewhat
course, with ring formation and intramolecular condensation competing
chain and the intermolecular cross-linking type of condensation
associated with an alkyd reaction.
considering silicone copolymerization, it is expedient to develop some
generalized equations relating the variables of a self-condensation
Consider the case of a single reactant that self-polymerizes to form a
m0F0 equals the initial number of equivalents present in the reaction
self-polymerization take place in which a given fraction f of the
groups is consumed (reacts). Assume that one mole of reactant
merger with another molecule) for each two equivalents that react. This
that the condensation proceeds by linear chain formation and by
cross linking (excludes ring formation and intramolecular
is, of course, an idealized type of condensation, which applies
to alkyd heteropolymers but, as will be shown, not so well to
this assumption still provides a criterion for estimating the deviation
silicone polymerization from an academic ideal.
effect of adding formaldehyde to an alkyd composition (in the form of
or formalin) has been found to result in the formation of cyclic or
formals, which leads to a reduction in the functionality of a polyol,
than in a cross-linking reaction between two different polyols, which
is therefore postulated, for purposes of alkyd formulation, that for
formaldehyde molecule (CH2O) present in an alkyd composition, two –OH
will be tied together on a single polyolmolecule. This formal formation
strong enough to resist deformalization at alkyd processing
Copolymerization of Alkyd
Silicons for Coatings
coatings are comparatively new, being first mentioned in the literature
1947. Patterson reviewed the properties of alkyd-silicones and reported
they are intermediate between alkyd-melamine and pure silicone enamels
and alkali resistance, adhesion, hardness and toughness. He also
varnishes made by chemical cocondensation of alkyds and silicones are
superior to those made from cold-blend mixtures of the two.
the only details of the synthesis of alkyd-silicone varnishes which
the literature until early in 1952 were those disclosed by Bowman in
British patent. They heated oil-modified alkyd resins with
organosilanols in a
solvent reflux process. The several patents issued since the early part
prepare alkyd-silicone varnishes either by the reaction of an alkyd
having excess hydroxyl groups with an organoalkoxysilane or by reacting
silane with glycerol and then reacting this intermediate with an acidic
compound or an acidic ester. The one exception found was in the patent
Millar who used a process similar to that of Bowman and Evans.
varnishes were prepared in ordinary round-bottomed, three-necked flasks
with an electric mantle. The reactions were run at 200°C, under a
dioxide atmosphere, and with agitation.
standard method for making the varnishes was to weight the desired
of dibasic acid, fatty acid and glycerol into the flask and heat at the
rate to 200°C. Samples of the alkyd reactants were withdrawn at 1/2
intervals to determine the acid number. When the acid number dropped
approximately 300 at the beginning of the reaction to less than 10, the
organoalkoxysilane was added. The two-phase mixture was then checked
clarity at 5-minute intervals. A clear homogeneous cold pill was
obtained after 15 minutes. The reactions was continued at 200°C, until
was imminent. This was determined by the cessation of cavitation around
stirrer. At this point the reaction was stopped by reducing the resin
flash naphtha to approximately 50% solids. After cooling, the solids
the varnish was adjusted to 50%.
simple enamel formulation of varnish and rutile titanium dioxide in the
of 1:1 on a solids basis was used. Enamels were satisfactorily prepared
ball mills and roller mills. The majority of enamels was made on a
three-roll mill because of the versatility and speed of the mill. High
naphtha was added to the enamel to obtain a viscosity of 30 seconds as
with a No. 4 Ford cup at 80° F. The finished enamel was then
centrifuged in a cup
centrifuge at 2500 r.p.m. to remove any oversize pigment particles.
finished enamels were sprayed on S.A.E. 1010, 20-gage cold-rolled steel
and plate glass panels. The steel panels were degreased and treated
Prep, a commercial phosphate solution for preparing steel surfaces for
enameling. The glass plates were washed with acetone.
enamels were sprayed onto the panels to obtain a dry film thickness of
0.1 mils as measured with a magnetic film thickness gage. Commercial
thickness range from 1 to more than 2 mils according to the desired
hiding. This thickness was chosen for this work in order to get optimum
retention and excellent hiding (see Figure 3). The films were cured for
hour at 400°F., and this bake was considered the initial point in the
enamels were tested for effect of film thickness on enamel properties
gloss and color retention, craze life, toluene resistance, alkali
impact resistance, flexibility surface hardness, adhesion and general
discussing experimental results, the formulation nomenclature used
kept in mind. It was assumed that the resins were composed of glyceryl
and alkyd resin. The composition of the resins was then defined in
terms of the
silicone content (the percentage by weight of glyceryl organosiloxane
totally reacted resin) and the oil length of the alkyd (the percentage
weight of fatty acid triglyceride in the alkyd portion. This method
more useful for correlating the results than did an equivalency basis.
additional benefit was that it is an adaptation of alkyd terminology
therefore familiar to the coatings industry.
formulation gives 87.5 grams of glycerol phthalate, 87.5 grams of
trilaurate, and 175 grams of glycerol phenyl polysiloxane.
grams of water and 42.5 grams of ethanol should be split out by
These calculations are based on phenylethoxypolysiloxane having an
weight of 204. This equivalent weight was based on the ethoxy content
silicone—in this case an ethoxy to silicon ratio of 0.80. It was
all the ethoxy groups were available for reaction with glycerol. Other
were formulated by determining the desired amounts of the reacted
phthalate, glycerol trilaurate, and glycerol phenylpolysiloxane and
the required amounts of reactants from the chemical equations of the
attempts were made to prepare varnishes according to the method of
consists of heating by a solvent process, an oil-modified alkyd resin
acid number of approximately 40 with organosilanols. Clear varnishes
obtained using as the silicone intermediates phenyl, amyl-, nonyl-, and
ethyl-trichlorosilanes hydrolyzed to the silanols. However, enamels
these varnishes had poor gloss and only fair color retention. It is
that little copolymerization was obtained because of the great tendency
silanols to condense to silicones and their small tendency to react
were also used as the silicone intermediate. These compounds had more
tendency to react with excess alcohol in the alkyd portion but were not
satisfactory because they were relatively volatile and it was difficult
remove the water and ethanol of condensation without losing some of the
silicone. The resulting products were not too satisfactory.
these reasons organoethoxypolysiloxanes were used in most of the work
this investigation. These were formed by partially hydrolyzing and
organotriethoxysilanes to form low molecular weight silicone polymers
containing residual ethoxy groups capable of reacting with the hydroxyl
of alkyd resins.
These compounds are
nonvolatile, require less excess glycerol based on organic acid content
when reacted with alkyd resins connect them to stable silicone nuclei.
the silicone intermediates used had ethoxy-to-silicon ratios of 0.8.
of Order of Addition
varnishes were obtained either by cooking all the alkyd and silicone
ingredients together throughout the reaction or by forming the alkyd
first and then reacting this with the silicone. Distinct differences in
properties resulted from the two methods of cooking.
one case, the phthalic anhydride, lauric acid,
glycerol were loaded the reaction flask at room temperature and heated
under agitation and an inert atmosphere. This temperature was
gelation was imminent. The reaction was then stopped by adding high
naphtha to the resin. The varnish had a color of 2, a viscosity of A
Holt) and an acid number of 75.
the second case, the phthalic anhydride, lauric acid and glycerol were
in the reaction flask at room temperature, heated to 200°C under
an inert atmosphere and held at this temperature until the acid number
decreased to 11. At this time the phenylethoxypolysiloxane was added,
was regained, and the batch was held at this temperature until gelation
appeared to be imminent. The resin was then thinned with high Flash
This resin had a color of 6, a viscosity of Cl and an acid number of 7.
varnishes were numbered 62 and 6, respectively. The total cooking time
62 was 30 minutes, and the alkyd reaction of No. 6 was 135 minutes with
reaction continuing for 15 minutes after addition of
Enamels were prepared from these varnishes and tested. The results are
difference in alkali resistance is to be expected from the acid numbers
varnishes. The large difference in gloss is typical of enamels prepared
varnishes cooked by the two procedures. Enamels prepared from varnishes
according to the technique used for varnish No. 62 always chalked very
The tendency was much less pronounced when the alkyd resin was formed
then reacted with the organoalkoxypolysiloxane. Apparently the varnish
the surface layer of pigment particles decomposes, leaving a chalklike
dust on the surface of the enamel. One explanation for the increased
decomposition of varnishes having high acid numbers is that the
ester can easily revert to the alcohol and phthalic anhydride under the
influence of heat, while the fully esterified phthalate does not
as easily. Another factor contributing to the poor gloss retention is
varnish No. 62 is probably not copolymerized to the extent that varnish
is copolymerized. The water of esterification can hydrolyze the ethoxy
of the siloxane to silanols which tend to condense to the silicone
As will be shown later, mixtures of alkyds and silicones tend to be
gloss to copolymers.
effect of temperature was investigated by cooking varnishes at 190°,
230°C. Resins cooked at 190°C. tended to be darker than those cooked at
other temperatures because of the long reaction time—200 minutes at
compared to 118 and 36 minutes at 200°C and 230°C., respectively. The
reaction is so fast at 230°C. that it is difficult to control.
reactions were run at 200°C. As a result of recent work, it is believed
the best technique is to cook the alkyd at approximately 200°C. and
temperature to approximately 165°C. for the silicone reaction. It is
to control the reaction’s end point by viscosity measurements with this
statement that copolymerization occurred in the varnish reactions is
the following evidence.
the organoalkoxysilane is first added to the alkyd resin in the
vessel, the mixture is incompatible and samples of the mixture are
two phase. As the reaction proceeds, the reaction mass becomes
clearer until finally cold-pill samples are completely clear and
Either solubility is increasing as reaction proceeds in a highly
reaction mass or the resin is becoming homogeneous because of
The latter is much more probable.
line of evidence is based on Flory’s theory of gelation. This theory
that gelation occurs when a rigid lattice work formed by primary
extends throughout the reaction mass, immobilizing the mass and causing
increase in viscosity. If an alkyd resin contains sufficient monobasic
excess glycerol to form only linear polymers, gelation will not occur.
organoalkoxysiloxane is added to this mass and gelation occurs, either
silicone itself or a copolymer of the alkyd and the silicone is
gelation. If a copolymer is formed, it is reasonable to expect that the
highly the alkyd resin is reacted before addition of the silicone, the
gelation will occur if copolymerization is taking place. Table 2 gives
reaction time for three different varnishes. The more highly reacted
resin was before addition of the silicone, the shorter the time for
This strongly suggests that copolymerization was occurring.
third line of evidence is a study of the possible reactions.
Phenylethoxysiloxane was heated by itself and with dioctyl phthalate
evolution of ethanol or evidence of further polymerization of the
Therefore it is itself stable and stable in the presence of esters.
when heated with glycerol, ethanol rapidly split out and gelation
Figure 1 shows the condensate collected versus cooking time for an
alkyd-silicone resin. The alkyd portion of the resin was cooked for 108
at 200°C. At this point, the acid number of the resin was 10 and the
removal of water was zero. It is probable that the alkyd resin mass
essentially of alkyd esters and unreacted glycerol hydroxyl groups.
Phenylethoxy, siloxane was added to this system which decreased the
to 160°C. As the temperature began to rise, ethanol split out of the
mass at an increasing rate. The only explanation for this evolution of
is that it was split out by the reaction of phenylethoxysiloxane and
unreacted hydroxyl groups in the alkyd resin. Therefore,
method for determining the heat stability of a resin is to measure its
weight loss when heated at a certain temperature. The weight losses of
resins prepared in this work are shown in Table 3. The value reported
average of three determinations made by spraying the resin solutions on
standard panels at 1-mil dry film thickness and measuring the weight %
versus time baked at 450° F.
weight loss depends primarily on the silicone content of the varnishes.
best illustrated by comparing the weight loss of varnishes 810, 14, 15,
the Dow Corning silicone mixture of 40% DC802 and 60% DC804. These
contain 0, 25, 35, 50, and 100% silicone, respectively. Other factors
determine the weight loss are the polyol (ethylene glycol varnishes
more weight than equivalent glycerol ones) and whether the
alkyd-silicone is a
mixture or copolymer. Varnishes 13 and 20 compared to varnish 1
statement. Apparently varnishes containing phenyl and dimethyl
ethoxypolysiloxane are not as stable as those containing
phenylethoxypolysiloxane as shown in varnishes 16 and 1 in the table.
products of resins heated to 475° F. were collected. The principal
collected was phthalic anhydride. The other product was a yellow oily
This was unsaturated and did not contain carbonyl groups. Further
unsuccessful. A small amount of water and ethanol was also collected.
physical properties of the varnishes are given in Table 3. The
in cooking the varnishes gives low viscosities and low acid numbers.
ST856 must be decidedly different because of the viscosity. The colors
varnishes were, in general, light but were darker when the oil length
longer. Varnishes with low oil lengths were slightly more viscous than
was found that the film thickness of the enamels exerted a significant
influence on the properties of the enamels. The variation in yellowing,
life, and gloss of the enamels with film thickness is shown in Figure
large variations in properties make it necessary to control the
the films of the test enamels as accurately as possible. Three panels
enamel were coated with films 1.9 ± 0.1 mils thick, evaluated, and the
values obtained were reported.
and Gloss Retention.
Gloss values were measured with a photo-volt gloss meter that measured
specular gloss. Practically all declines in gloss occurred during the
hours of baking at 400° F. Enamels attained their ultimate gloss after
hours. Therefore, gloss values of the enamels after baking for 1/2 hour
100 hours represent initial and final gloss. These two values and the
gloss are given in Table 4.
two alkyd-silicone cold-blend mixtures reported (V-20 and V-25) had
gloss retention. This was probably due to increased decomposition of
mixtures in comparison with the polymers and to incomplete homogeneity
gloss rentention of the enamels became worse as the silicone content
decreased and the fatty acid content increased Fig. 3).
Life. In this
investigation, craze life is defined as the length of time in hours
enamel can be baked at the destinated temperature without film failure
cracking, checking, crazing, or loss of film integrity in any way.
is very greatly influenced by the baking temperature. All the enamels
craze lives in excess of 400 hours at 350° F. and less than 3 hours at
Styrene Copolymers in
is becoming an increasingly important raw material for use in organic
coatings. However, at the present time it is not used in coatings as
nor as polystyrene but rather as copolymers with such materials as
drying oils, and most recently with alkyd resins. The volatility of the
and lack of compatibility of the polymer are the principal deterrents
use of these materials as such. The advantages obtained from the
styrene-copolymerized oils and alkyds are faster drying, harder film,
better water and chemical resistance than can be obtained with the
oils or alkyd resins. However, the copolymers of styrene and various
retain some of the sensitivity of polystyrene to certain hydrocarbon
The tremendous production capacity for styrene, resulting from its
use in the synthetic rubber program during the last war, its relatively
cost, and very high degree of purity make it of definite interest for
of the first methods proposed for the reaction of styrene with a drying
disclosed in a British patent in 1931. This describes the
polymerization of an
aqueous emulsion of styrene and tung oil with hydrogen peroxide as
The next development was the use of the solvent method for
styrene and film-forming materials in inert solvents in 1934. This work
investigated further by Wakeford and Hewitt, Wakeford, Hewitt, and
and Wakeford, Hewitt, and Davidson from 1942 onwards in a number of
patents. The mechanism of copolymerization between styrene and various
oils is described by Hewitt and Armitage and the effect of various
studied by Armitage, Hewitt, and Sleightholme. They used as a standard
50 parts solvent, 25 parts oil, and 25 parts styrene without catalyst.
also applied the same method for styrenation of a prepared alkyd;
method requires about 30 hours for reaction.
and Wakeford, Hewitt, and Armitage in 1945 investigated the mass method
copolymerizing styrene and various drying oils. The mass method is much
than the solvent method but only limited amounts of styrene can be
copolymerized and still maintain homogeneous products. In this country
Chemical Company developed a system for obtaining homogeneous products
mass method by replacing part of the styrene with a-methylstyrene. This
combination produced homogeneous products with drying oils containing a
conjugated system of unsaturation. With oils such as linseed and soya,
recommended that blends be made with tung or dehydrated castor oil to
some conjugated unsaturation. However, the use of a-methylstyrene has
found to detract from the fast drying time and also to reduce the
solvents and chemicals. It is obvious that it would be desirable to use
mass method because of its speed of reaction and to avoid the use of
a-methylstyrene, if possible. The present work knows that this may be
first styrenating the fatty acids allowed by esterification with
anhydride and glycerol to produce a styrenated alkyd resin.
of Fatty Acids
copolymerization reaction between styrene and drying oil fatty acids
the type of the fatty acids used. With the conjugated fatty acids, like
and oiticica fatty acids, the reaction is believed to be similar to
between styrene and butadiene in GR-S manufacture. In this case,
joined to butadiene by 1, 4- and 1, 2-additions. With dehydrated castor
fatty acid and isomerized linseed fatty acid (diene value 22 and 20,
respectively) it is believed that there is some polystyrene formed
the copolymer. Armitage, Hewitt, and Sleightholme have stated that
of high molecular weight was not formed, but they had not proved that
polystyrene of low molecular weight was absent. There is every reason
believing that polystyrene of low molecular weight might be present.
linseed fatty acid, where there is a nonconjugated double bond system,
copolymerization reaction does not take place to any appreciable
can be seen from other similar systems such as vinyl chloride
and styrene (conjugated) which does not copolymerized. In general, a
containing a conjugated double bond system will copolymerize with
molecule containing a conjugated double bond. However, Armitage have
suggested that copolymerization with nonconjugated systems might take
the shift hydrogen mechanism in special circumstances.
fatty acids used were those commercially available; tung from Archer
Midland Company and oiticica, dehydrated castor oil, and linseed from
Degreasing Company. Styrene was obtained from the Dow Chemical Company
was found from a few experiments that it was not necessary to remove
Benzoyl peroxide was used as catalyst.
copolymerization reaction between styrene and tung oil fatty acid,
fatty acid, dehydrated castor oil fatty acid, linseed oil fatty acid,
isomerized linseed oil fatty acid was carried out by the mass method.
cases 3% benzoyl peroxide on the weight of styrene was used.
fatty acid and styrene with catalyst were placed in a 4-necked flask
to 145° C. by an electric mantel. Through the central neck a stirrer
seal was attached. In the three side necks were attached a thermometer,
condenser, and an arrangement for withdrawing samples. In the case of
dehydrated castor oil, linseed, and isomerized linseed fatty acids a
funnel was attached in one of the side necks through a Y-bend
styrene catalyst mixture was added slowly to the fatty acid in the
flask. Samples were withdrawn at various intervals of time and the per
styrene which had reacted was determined by removing the unreacted
using vacuum distillation (6 to 8 mm., 40° C.).
amount of styrene which had reacted with the fatty acid was calculated
difference between the known percentage of styrene present originally
percentage found after vacuum distillation. This value was checked from
number determinations. This value was checked from acid number
The ratio of actual acid number to the theoretical of 195 for fatty
indicates the per cent fatty acid present.
value for the per cent styrene in the product as determined by the
distillation method checks rather closely with that obtained by the
of styrene with tung, oiticica, and dehydrated castor oil fatty acids
out using various molal ratios of styrene. The rate of reaction
increased ratio of styrene and the values are plotted in Figure 1. The
corresponding values for per cent styrene reacted and actual and
acid numbers are given in Table 1.
were made to styrenate standard linseed fatty acids but the products
were heterogeneous which is related to the nonconjugated unsaturation
fatty acid. The isomerized linseed acids shown in Table 1 have a diene
20 and consequently produced homogeneous products after styrenation.
styrenated products containing less than about 70% styrene are clear
liquids, with increasing viscosity as the styrene content is increased.
70% styrene content the products are hard resins. These styrenated
mixtures of mutually soluble materials which include the copolymer of
and fatty acid in the largest amount and considerably smaller
polystyrene and free fatty acid.
of Styrenation of Fatty
general average values for rate of styrenation of a series of
plotted in Figure 1; a comparison of these curves shows the slowest
rate for tung fatty acid, a somewhat faster rate for oiticica, and the
rate for dehydrated castor oil. These differences in rate apply at all
of styrene to fatty acid but in each case a faster rate is obtained by
increasing the amount of excess styrene. Fast reaction rates are always
desirable in commercial operations and these may be obtained by using
4-mole ratio or 2-mole ratio of excess styrene.
saving in time would be offset somewhat by the added cost of removing a
quantity of free styrene and by the larger reactor capacity which would
rates for the three fatty acids are in the reverse order from what
expected, from a consideration of the fact that tung contains the
percentage of conjugated unsaturation and dehydrated castor oil
least. This reversal of the order of the rate of reaction may be due to
smooth copolymerization reaction with the tung acids and a relatively
molecular weight product. The ketonic group in the oiticica fatty acid
expected to exert an accelerating effect on the copolymerization
hence a faster rate than the tung acid. In the dehydrated castor oil
reaction there is formed, most probably, some polystyrene in addition
copolymer. Because the rate of reaction for the polymer is faster than
the copolymer, the over-all ratio is higher as shown. Although the
product from the dehydrated castor oil reaction was sufficiently
for normal use in alkyd resins it was not so smooth as the others,
some polystyrene present.
marked difference in rate of reaction and type of product formed could
obtained by varying the manner in which the styrene was added to the
castor oil fatty acid. When the styrene and dehydrated castor oil fatty
are heated together a rapid, exothermic reaction develops when the
reaches 120° C and the product is very viscous and turbid. However, if
styrene is added to the fatty acid at a slow rate the reaction is
the product is clear and apparently homogeneous. This method was
making the styrenated fatty acids for the alkyd resins described later
it yields a homogeneous product with a minimum of polystyrene and a
Studies on Blends of
Polystyrene Glycol and Alkyds in Surface Coatings
as such is not compatible with oil modified glyceryl phthalate resins,
known as alkyds. But, if polystyrene is made reactive by introducing
groups, it can either be chemically reacted or physically blended with
in small amounts. Blending of polystyrene glycol with a drying oil
linseed oil alkyd was investigated earlier’ and significant
improvements in the
film properties of the alkyd were observed. The present work describes
study of film properties of polystyrene glycol blends with nigerseed
castor oil alkyds. Nigerseed and castor oils are of semi- and
oils respectively. Since semi-drying and non-drying oil alkyds do not
they are usually mixed with amino resins and stoved. Therefore,
formaldehyde resin has been mixed with the alkyds and the polystyrene
(inhibitor free), benzoyl peroxide, dioxane, potassium hydroxide,
(all, L.R. grade) were used for the preparation of polystyrene glycol
further purified by precipitation method using benzene and methanol
grade). Butanol, acetic anhydride, and pyridine (all A.R. grade) were
the determination of hydroxyl value of polystyrene glycol.
anhydride, glycerol (both L.R. grade), alkali refined castor and
were used in the preparation of alkyds.
formaldehyde (37 per cent) and n-butanol (all L.r. grade) were used for
preparation of butylated urea formaldehyde resin.
xylene, methanol (all L.R. grade) were used as solvents.
glycol was prepared by free radical polymerisation of styrene using
as initiator and subsequent hydrolysis of benzoate end groups to
groups. The prepared sample had a hydroxyl value of 289.
oil alkyd of oil length 35 was prepared by direct heating of the
alkali refined castor oil, glycerol and phthalic anhydride at
heating was continued until an acid value of about 10 was achieved.
oil alkyd3 of oil length 40 was prepared by the monoglyceride process
litharge (0.1 per cent by weight of oil) was used as a catalyst.
anhydride was added at 180° after monoglyceride formation and then the
temperature was raised to 230°C. The heating was continued until an
of about 10 was obtained.
of butylated urea
urea formaldehyde resin was prepared in the laboratory by reacting 1
with 3 moles formaldehyde (37 per cent solution) at 93° C for one hour
7.5. PH was brought down to 5.5 by adding phosphoric acid and then 2
was added. The mixture was heated with stirring and reaction was
until the calculated quantity of water of reaction was collected
and Stark apparatus. The resin so obtained was clear and water white.
content was adjusted to 60 per cent by adding more n-butanol.
of polystyrene glycol with nigerseed oil and castor oil alkyds were
adding powdered polystyrene glycol to the alkyd with agitation at a
of 100-120°C. Stirring was continued for about 1 hour. The maximum
polystyrene glycol that gave clear miture with each alkyd was
addition to these samples, other samples having lower amounts (about
the maximum amount found compatible) of polystyrene glycol were also
glycol-alkyd blends and plain alkyds
urea formaldehyde resin was mixed with polystyrene glycol-alkyd blends
plain alkyds. Usually, 25 per cent amino resin is mixed with alkyds.
25 per cent butylated urea formaldehyde resin was added to all the
polystyrene glycol-alkyd blends and plain alkyds. In addition to this,
to minimise the use of amino resin, samples containing 10 per cent
urea formaldehyde resin were also prepared. Butylated urea formaldehyde
solution was added to the alkyds and the polystyrene glycol-alkyd
room temperature (25° C) under continuous stirring until a clear
the samples were thinned with xylol to brushable consistency and films
applied on 6in × 2in glass and tin panels. Films of nigerseed alkyd and
polystyrene glycol blends were based at 120° for 40 minutes while the
castor alkyd and its polystyrene glycol blends were baked at 120°C for
minutes. All the baked films were hard, smooth and glossy.
films of all samples were tested for scratch hardness, flexibility and
adhesion, water, acid, alkali and solvent resistance.
composition of various blends of polystyrene glycol and nigerseed oil
castor oil alkyd is shown in Table 1. The amount of urea formaldehyde
mixed with the blends and plain alkyds is also shown in this table. The
physical properties, viz., scratch hardness and flexibility of the
are shown in Table 2. Water (cold and boiling), acid (hydrochloric,
and nitric) and alkali (sodium carbonate) resistance are given in Table
and 5 respectively.
glycol with alkyds
was observed that when a higher proportion of polystyrene glycol was
incorporated into alkyds, a hazy mixture was obtained and polystyrene
separated out on standing. Therefore, the maximum amount of polystyrene
that gave a clear mixture with each alkyd was determined. It was found
per cent and 12 per cent polystyrene glycol was compatible with
alkyd of oil length 40 and castor oil alkyd of oil length 35
hardness test was carried out by using a mechanically operated Sheen
hardness tester in which a hardened needle loaded with one kilogram
moves over the film. All the samples of the polystyrene glycol-alkyd
plain alkyds passed the test showing good scratch hardness.
scratch hardness was also determined in each case by placing increasing
over the hardened needle. Maximum scratch hardness (in grammes) of all
is shown in Table 2. It is clear that scratch hardness of polystyrene
alkyd blends is more than that of plain alkyd and further, it increases
increasing amount of polystyrene glycol. It is so, because large
cyclic (benzene) rings present in polystyrene glycol contribute towards
and adhesion of the dried film was tested on tin panels. The test was
out by bending the tin panel in ¼ in diameter mandrel. All the samples
blends of polystyrene glycol-alkyd and plain alkyds passed the test as
detachment of film from the substrate or crack in the film was
all the films had good flexibility and adhesion. Further, it confirmed
amount of polystyrene glycol blended was compatible with alkyds.
were applied on 6in × 2in glass panels and baked as described earlier.
sides of the glass panels were protected by wax before performing this
The panels were immersed in cold distilled water at room temperature
for 48 hours and were taken out. The dipped portion of the films was
dry and examined for appearance, loos in gloss, change in colour, and
visible damages. It was found that all the samples were practically
Panels were further immersed in water and were examined at regular
was observed that after 10 days, films of both the alkyds showed slight
gloss while the samples of polystyrene glycol-alkyd blends were
unaffected. After 15 days, the alkyds showed considerable loss in gloss
change in colour while the blends having maximum amount of polystyrene
were practically unaffected and samples of the blend having half of the
amount showed a slight loss in gloss.
20 days, the alkyd films cracked. The condition of the film of all
containing maximum amount of polystyrene glycol were still unaffected,
that in the case of nigerseed oil alkyd blends containing smaller
amino resin, a slight loss in gloss was observed. All blends containing
the maximum amount of polystyrene glycol found compatible showed only a
loss in gloss except that in the case of castor oil alkyd blend some
colour was also noticed. It clearly indicates that the incorporation of
polystyrene glycol into alkyd improves the water resistance of the
further, as the amount of polystyrene glycol increases, water
films were also tested for boiling water resistance in order to
above results. The results from Table 3 show that after 2 hours the
water caused loss in gloss and change in colour of plain alkyds except
the case of nigerseed oil alkyd containing lower amounts of amino
cracks were also noticed. Blends containing the maximum amount of
glycol found compatible, showed slight loss in gloss except the castor
alkyd blend having a higher amount of amino resin, where the film was
practically unaffected. Nigerseed oil alkyd blends containing half of
maximum amount of polystyrene glycol showed loss in gloss and change in
while castor oil alkyd blends showed only slight loss in gloss. Effect
boiling water on the films was more significant after 4 hours of
Films of all the plain alkyds were partially removed. Films of
alkyd blends containing smaller amounts of polystyrene glycol showed
Films of all other blends showed only loss in gloss and change in
results again confirm that the addition of polystyrene glycol imparts
water resistance to the alkyds.
this test also, the glass panels of all the samples were prepared as
above and were immersed in 2 per cent solutions of each of sulphric
acid and nitric acid separately at room temperature (25°C). Panels were
out after 24 hours, washed in running fresh water, allowed to air dry
hour, and check for appearance, loss in gloss, change in colour and for
disintegration. It was observed that there was no loss in gloss or
colour in any of the film.
were further immersed in acids and films were checked at a regular
24 hours. Table 4 gives the results of acid resistance on 15 and 20
immersion in the acids. After 15 days of immersion in hydrochloric and
sulphuric acids, films of all the blends were practically unaffected
nigerseed oil alkyd blends containing half of the maximum amount of
glycol found compatible and 25 per cent amino resin where slight loss
20 days of immersion in hydrochloric and sulphuric acids, films of all
oil alkyd blends and nigerseed oil alkyd blends containing maximum
polystyrene glycol were practically unaffected. Nigerseed oil alkyd
containing half of the maximum amount of polystyrene glycol found
showed slight loss in gloss.
effect of nitric acid on the films was more pronounced as none of the
remained unaffected on 15 days of immersion except the castor oil alkyd
containing maximum amount of polystyrene glycol found compatible and
amounts (10 per cent) of amino resin. The result established that, (i)
oil alkyd had better acid resistance than nigerseed oil alkyd, (ii)
resistance of the alkyds improved with the increasing amounts of
glycol, and (iii) samples containing 10 per cent amino resins had
resistance than those containing 25 per cent amino resin.
this test, the glass panels of all the samples were prepared as
and were immersed in 2 per cent solution of each of sodium carbonate
hydroxide separately at ambient temperature (25° C). Panels dipped in
carbonate solution were taken out at a regular interval of 5 days,
running water, dried and the film examined for any visible damages.
sodium hydroxide solution was checked at a regular interval of 2 hours.
shows the results of the alkali resistance.
oil alkyd containing a maximum amount of polystyrene glycol was
unaffected until 20 days of immersion in sodium carbonate solution.
oil alkyd containing half of the maximum amount of polystyrene glycol
slight loss in gloss on 20 days of immersion. The effect on plain
alkyd was more pronounced than that on its blends e.g., the film of
containing higher amounts (25 per cent) of amino resin cracked and the
alkyd containing lower amount (10 per cent) of amino resin show loss in
and change in colour.
Mechanical Properties of
Modified Alkyd Resins
number of investigators have reported on the stress-strain properties
films. It has been found that the tensile strength of paint and varnish
is a more reliable guide to their strength than other tests commonly
as rocker hardness, scratch hardness impact and bend tests. Higher
cross-linking combined with more homogeneity in the polymer film impart
increased rigidity, which increases with increase in tensile strength
decrease in elongation. The load-elongation curve can also be used to
the toughness, hardness and flexibility of the film.
function of oil in oil-modified alkyds is to give the film the
flexibility to withstand the tensions caused by expansion, contraction
bending of the substrate, which could lead to cracking and flaking in
The present work has undertaken to study the effect of the fatty acids
varying chain lengths and degrees of unsaturation present in refined
oil and upgraded sardine oil on the mechanical properties of their
by comparison with those of vegetable alkyd films.
of 66 and 50% oil lengths were prepared by the usual alcoholysis method
refined sardine, upgraded sardine (prepared by directed
linseed, soybean, safflower and dehydrated castor (prepared by the
Sivasamban et al) oils. Free films of the alkyd resins were obtained by
procedure described earlier.
Gardner tensile strength and percentage elongation apparatus was used
determine the tensile strength and percentage elongation of each film.
35 ± 2µ thickness were cut into strips 1 cm wide and 12 cm long. They
fastened to the upper and lower clamps of the apparatus. The length of
strip between the two clamps was maintained at 10 cm without any strain
film. The set screw of the apparatus was locked tight and the motor was
started. The percentage elongation was noted for every reading of the load shown on the scale.
continued until the film was torn, after which the motor was
stopped. Such readings were calculated in kg/cm2 of cross-section, and
load-elongation curves (Figures 1 and 2) were drawn to estimate the
each curve, which indicates the toughness of the film.
strip of film, 10 cm long and 1 cm wide, was used as a torsional
determine the modulus of rigidity. One end of the strip was clipped by
adhesive tape to a rigid support and the other end to the centre of the
rod of calculated moment of inertia. Oscillations were started by
the rod from its equilibrium position by slightly rotating it.
strength of each alkyd film was determined using the apparatus
Vittal Rao et al. The film was held between the two flat flanges of the
apparatus. In the enclosed space, air was compressed at a steady rate
pressure on the exposed area of the film. The pressure at which the
was noted from the mercury manometer attached to the system. The
strength of each film is expressed in terms of the height of mercury in
curves for 66 and 50% oil length alkyd films are shown in Figures 1 and
respectively. Films of long oil alkyds modified with refined sardine
dehydrated castor oils were very soft and tacky and hence their
properties could not be determined. The strengths of alkyd films
these oils have been found, however, to have increased considerably as
oil lengths were reduced to 50%.
striking differences can be observed between the load-elongation curves
sardine fish oil and vegetable oil modified alkyd films. The curves for
oil alkyd films, irrespective of the oil length of the alkyd and
in the oil used, level off near the break points and bend towards the
elongation axis. On the contrary, the curves of both long and medium
alkyd films modified with vegetable oils except DCO are steeper and at
break point they are bent towards the load-axis. From the nature of
curves it appears that sardine oil alkyd films are inherently softer
flexible than vegetable oil modified alkyd films.
and Harris have studied the effect of a sharp molecular weight
blends of such fractions of differing molecular weight ranges on the
properties. They found that the presence of low molecular weight
substance in a
high molecular weight material has a disproportionately deleterious
mechanical properties. It has been observed that the presence of as
10-15% of low molecular weight fraction acts adversely on all
properties, such as tensile strength and folding strength. These
be used to explain the difference in nature of sardine and vegetable
films. Refined sardine oil contains large proportions of less reactive
and mono-un-saturated fatty acid components, mostly of C14 to C18 chain
lengths, along with highly reactive components such as pentaenoic and
acids belonging to C20 to C22 series16. This complex mixture of fatty
components of the oil results in the alkyd resin modified by the oil
blend of polymer units of very wide range of molecular weights,
large proportion of smaller molecular weight units. Hence, in spite of
unsaturation in refined sardine oil (I.V. = 154), its long oil alkyd
softer than the films of corresponding alkyds from safflower (I.V. =
soybean (I.V. = 136) oils (Table 1).
upgraded sardine oil a large proportion of saturated acids has been
consequently its unsaturation has been increased (I.V. = 221)9. The
long oil alkyd modified with this upgraded oil has improved
regard to the tensile strength of the long oil alkyds, the linseed and
alkyd films give the highest values, followed by the films of alkyds
upgraded sardine and safflower oils. The films of alkyds based on DCO
refined sardine oils, as mentioned earlier, were too soft to allow the
strength to be measured. But again, inspite of the high unsaturation of
upgraded sardine oil (I.V. = 221), its long oil alkyd film is more
less tough than that of the corresponding alkyd from linseed oil (I.V.
Here, perhaps, the effect of highly crosslinked large molecular weight
polymers on tensile strength of its film has been reduced because of
presence of the low molecular weight polymer units formed due to the
of large proportion of monoene acids of C14 to C18 carbon chain in
acids in vegetable oils are more or less confined to C18 chain length
containing a small proportion of saturates and monoenes, along with a
C16 acids. Therefore, the alkyds abtained from such oils are expected
contain a very small range of polymer units and to be more homogeneous
to their counterparts from define oils. Thus, the homogenous polymer
alkyds resins from vegetable oils impart higher tensile strengths and
flexibility to their free films as compared to the films of alkyds
sardine oils which are far less homogenous with regard to their polymer
The softness and flexibility of DCO alkyd films can be attributed to
presence of hydroxy acids in conjunction with conjugated diene and
proportion of non-conjugated diene which may result in a mixture of
units ranging from smaller molecular weight to highly crosslinked ones
medium oil length alkyds, the film of upgraded sardine oil alkyd is
found to be
the toughest. Here, the increased amount of glyceryl phthalate alkyd
have perhaps compensated the adverse effect due to less reactive fatty
present in the oil on the mechanical properties of its alkyd film.
to the scheme of Bosch et al, films of medium oil alkyds modified both
sardine and vegetable oils (except DCO) can be classified as tough and
films compared to their long oil alkyd films, as they have higher
tensile strength and percentage elongation (Table 1). The DCO medium
alkyd films can be grouped as softer and more flexible, as they have
values both for tensile strength and percentage elongation. Linseed oil
films are found to be superior in tensile strength in both sets of
values for toughness given in Table 1 more or less confirm the above
conclusions. However, although the medium oil length linseed oil alkyd
the highest tensile strength, in toughness it is less than the medium
length upgraded sardine oil alkyd film, which has the maximum value.
because in the case of high tensile strength with high per cent
Polyblends of Polystyrene
Glycol and Alkyd in Surface Coatings
alkyds enjoy a wide variety of application in surface coatings. They
prepared either by first styrenation of fatty acid (or oil or
and then preparing alkyds or by styrenation after the preparation of
monomer is incorporated into alkyd in order to improve chemical of the
In surface coatings, this is general practice to blend polymers
order to obtain desired film properties (e.g., alkyd — amino) povided
polymers are compatible. However, a polystyrenealkyd system as such is
compatible and a useful composition cannot be obtained by simply
together. But if polystyrene can be made reactive by introducing
groups such as hydroxyl, chloro, carboxyl etc., it can either be
reacted with alkyd or physically blended with alkyds.
in the present work, polystyrene glycol has been prepared and the
its physical blends with alkyd have been reported. The chemical
polystyrene glycol and alkyd will be reported later.
monomer used for the preparation of polystyrene glycol was purified in
monomer was washed with 4 per cent sodium hydroxide solution three to
times followed by washing with distilled water till free from alkalies.
dried over anhydrous sodium sulphate overnight and then decanted off
distilled under reduced pressure.
peroxide (L.R. grade) was used as catalyst in the synthesis of
Alkali refined linseed oil, phthalic anhydride and glycerol were used
preparation of the alkyd. Butanol, acetic anhydride, pyridine (all A.R.
were used for determination of hydroxyl value. Xylene, dioxane, benzene
methanol (all L.R. grade) were used as solvents. Lead and cobalt
were used as driers for the alkyd.
was first synthesised by free radical polymerization mechanism in bulk
benzoyl peroxide. The polystyrene formed contained benzoate and groups,
were saponified by use of alcoholic potassium hydroxide solution.
benzoate formed on heating was removed by filtration and polystyrene
obtained from dioxane solution by precipitation into water. Polystyrene
so obtained is a creamish white solid having an inherent viscosity of
of hydroxyl group in the polystyrene chain was confirmed by determining
hydroxyl value according to ISI specification NO. !S: 548: Part I. The
value of the prepared sample of polystyrene glycol was 289.
of linseed alkyd
alkyd of 50 per cent oil length was prepared by the monoglyceride
the following manner.
and 25 per cent (by weight of oil) glycerol was taken together and
180°C. Litharge (0.1 per cent by weight of oil) was added and
raised to 240°C and heated till monoglyceride formation took place
solubility in methanol). The mixture was cooled to 180°C and phthalic
and the remaining glycerol was added. Temperature raised to 240°C and
for about 4 hours. The product had an acid value of 10.
of polystyrene glycol
blends of polystyrene glycol and alkyd were prepared by adding powdered
polystyrene glycol into linseed alkyd resin and stirring the mixture
one hour. During stirring, temperature was maintained at 100°C.
was observed that polystyrene glycol was not compatible with oil
in all proportions. The maximum quantity of polystyrene glycol that
clear mixture with the linseed alkyd was 20 per cent. Beside this,
containing lower amounts e.g., 5, 10, 15 per cent of polystyrene glycol
also prepared. Film properties of all these four blends and plain alkyd
samples were tested according to Indian Standard Specification (ISS)
101 — 1964 for drying characteristic, scratch hardness, flexibility and
adhesion, water, acid and alkali resistance, and solvent resistance
benzene, toluene and xylene. The colour of all the 5 samples were
Lovibond tintometer using a 1in. cell. Adequate amounts of driers on
of oil content of the resin were incorporated into the samples and
xylene to a brushable consistency. Films were applied on 6in × 20in.
free radical polymerization by benzoyl peroxide, both phenyl and
radical may attack the double bond of the monomer. However, in case of
of styrene, end groups are mostly benzoate and not phenyl groups.
has been established that the termination of two growing radical chains
predominantly by combination, i.e., the radical ends of two growing
combine to give a single molecule with an initiator fragment (i.e.
each end. Use of a high proportion of initiator gives a low molecular
all the above facts in
mind, successful preparation of polystyrene was performed. Benzoyl
used to impart difunctionality in the macromolecule. Polystyrene so
has benzoate end groups. These end groups were saponified by using
potassium hydroxide into hydroxyl ends.
presence of hydroxyl groups in the prepared sample was confirmed by
determination of the hydroxyl value of the sample which comes to 289.
of polystyrene glycol with alkyd
was observed that when higher
proportions of polystyrene glycol were incorporated into alkyds they
mixtures. Beside this, polystyrene glycol had a tendency to separate
the mixture on standing, when it was added in excess.
maximum amount of polystyrene glycol found compatible with alkyd was 20
cent. Further, the molecular weight of polystyrene glycol would play an
important role in deciding the ease and maximum amount compatible with
of linseed alkyd and its polystyrene glycol blends were air dried.
hard dry and tack free times are recorded in Table 1. It was observed
addition of polystyrene glycol into alkyd considerably reduces the
of linseed alkyd. For example, surface drying time of linseed alkyd was
A 5 per cent blend surface dried in 30 minutes while 20 per cent dried
minutes. It clearly shows that the addition of a higher amount of
glycol into alkyd from 5 to 20 per cent (by weight of alkyd) reduces
surface drying time 30 minutes to 15 minutes.
hard dry time of linseed alkyd was 7 hours while its polystyrene glycol
were hard dried in 3 to 4 hours only.
hardness was measured by mechanically operated ‘sheen’ scratch hardness
in which a hardened needle loaded with one kilogram weight moves over
All the samples of the polyblend and linseed alkyd pass the test which
that polystyrene glycol and alkyd have good scratch hardness.
scratch hardness was
determined by placing an increasing load over the hardened needle.
scratch hardness in gramms of polyblends and linseed alkyd are given in
2. From the table, it is clear that polyblends have better scratch
than linseed alkyd because polystyrene imparts hardness to the film.
of the dried film was tested on tin panels. When bending the tin panels
180° C with a ¼in. mandrel, all the samples of alkyd and their blends
polystyrene glycol passed the test, i.e., no detachment of the film
substrate or crack in the film was observed. Thus, the film had good
flexibility and adhesion. Further, it confirms that polystyrene glycol
compatible with alkyd.
the samples were allowed to air dry in a horizontal position for 48
sides of the panels were protected by wax. The panels were immersed in
distilled water at room temperature (30°C) for 48 hours. After this the
were taken out and washed with distilled water and allowed to air dry.
dipped portion was examined after four hours for appearance, loss in
hardness. It was observed that all the samples were unaffected. Panels
further immersed in water and examined at a regular interval of 2 days.
found that films of plain linseed alkyd softened after 8 days while the
of all blends were practically unaffected even after 18 days of
concluded that blend of polystyrene glycol and alkyd have better water
Analysis of the Carboxylic Acid Components of Alkyd
spite of the fact that alkyd resins were introduced some 45 years ago
still the most widely used synthetic paint resins. In Australia, for
1968-69, alkyd resins constituted two-thirds of the total paint resin
production. This may be attributed to the low cost and the suitability
alkyd resin for modification by physical or chemical blending.
resins consist of a back-bone of an aromatic dicarboxylic acid (e.g.,
0-phthalic acid) esterified with a polyhydric alcohol (e.g. glycerol)
fatty acids are joined at the remaining hydroxyl sites. The performance
alkyds as paint resins is largely dependent upon the nature and the
concentration of the unsaturated fatty acid esters present. Various
commercially available vegetable oils such as linseed, soya bean,
sunflower are used in alkyd manufacture (see Appendix B). These oils
the fatty acids, palmitic, stearic, oleic, linoleic and linolenic in
of triglycerides. The last three of these acids contain, in turn, one
three olefinic double bonds (sites of unsaturation). On exposure to
molecular chains crosslink and this results in the “drying” of the
the formulation of an alkyd, a number of factors need to be considered
determine the type and quantity of vegetable oil used. For example, the
concentration of polyenoic acids in the alkyd determines the drying
However, an increase in their concentration renders the resin more
yellowing. Further, the hardness of a paint film is affected by the
of unsaturated fatty acids.
this basis alone, a knowledge
of the fatty acid composition of an alkyd will enable, to some extent,
prediction of its performance.
methods of characterising vegetable oils largely relied on the
iodine values (which is a measure of unsaturation).
ultra-violet spectroscopy has been used in the determination of fatty
vegetable oils, the main instrumental method of fatty acid analysis has
gas chromatography (GLC). The methyl esters of the fatty acids have
to be suitable for GLC analysis and the conversion of vegetable oils
resins to fatty acid methyl esters has been achieved by
and by saponification followed by methylation. Due to the speed and
of the transesterification method compared to the saponification
former method is more appealing. A comparison of the two methods has
little difference in the distribution of fatty acid methyl esters.
Transesterification of lipids with methanolic sodium methoxide has
fatty-acid methyl ester yield of 96 per cent of the theoretical yield
saponification method gave a comparable result.
has a further disadvantage in that it has been observed that after 1h
reaction of linseed oil with 0.5 M methanolic potassium hydroxide, at
followed by methylation of the liberated acids, an extraneous peak
the chromatogram. This peak was attributed to the isomerisation of the
polyenoic acids during saponification.
analysis of the carboxylic acid components in alkyd resins by GLC has
largely confined to a quantitative determination of the fatty acids and
qualitative estimation of the dicarboxylic acids. In this application a
of reagents have been used for transesterification reactions including
methanolic solutions of sodium methoxide, potassium methoxide, lithium
methoxide, boron trifluoride, hydrogen chloride, and diazomethane.
the present work the transesterification technique was evaluated as a
quantitative method for the determination of carboxylic acid
alkyd resins. The use of transesterifying agents was restricted to
solutions of hydrogen chloride, boron trifluoride and lithium methoxide.
fatty acid methyl esters were chromatographed using both
succinate (DEGS) (Fig. 1.) and the Carbowax columns (Fig. 2.) It was
in general, the DEGS column afforded the better resolution. However,
of dimethyl o-phthalate and methyl linoleate was poor on this column,
Carbowax column was found to be superior in this case.
transesterifying agents HCl/MeOH, BF3/MeOH and LiOMe/MeOH were equally
in the determination of the fatty acid derived components of the
(Table 1), soya bean oil (Table 2) and tall oil (Table 3) alkyds which
studied. However, the acidic reagents (HCl/MeOH and BF3/MeOH) gave very
results for the determination of the concentration of the phthalate
components. The basic reagent, LiOMe/MeOH gave a result for the
component which was significantly lower than the concentration
classical methods, or specified for the alkyd resins (Table 4).
the fatty acid distribution of alkyds, varies significantly from the
glyceride oils, (Table 5). The linoleic and linolenic acid content is
lower in the alkyd than in the parent oils. This is particularly
the case of linseed and soya alkyds. In addition, variations occur
alkyds derived from the same oil. A comparison of a long oil length (70
cent oil) linseed alkyd with a medium oil length linseed alkyd (52 per
oil), illustrates this point (Table 6). The long oil alkyd was produced
fatty acid/oil process and the medium oil alkyd by the alcoholysis
(Appendix B). The source of the variation may be due to either the
glyceride oils (Table 7), or to the reaction conditions used in the two
processes. The fatty acid/oil process involves a higher temperature and
the reaction time required for the alcoholysis process. These more
conditions may induce decomposition or polymerisation of the lindeic
liholenic acids thus reducing their concentrations in the resulting
Table 6 shows that the long oil linseed alkyd contains a lower
the two acids in question than does the medium oil alkyd.
effect of reaction time on the methyl ester determination was also
A medium length linseed alkyd was reacted with the LiOMe/MeOH reagent
various lengths of time. The relative proportions of the methyl esters
was found to vary with changes in reaction time. The largest variation
in the formation of dimethyl o-phthalate. The concentration of dimethyl
in the product was determined with respect to the fatty acid methyl
concentration and so the variation with time of the dimethyl
concentration may be due to a difference in rate of transesterification
the aromatic ester and the fatty acid esters. The reaction time also
the individual fatty acid methyl ester concentrations. This may again
be due to
a difference in reaction rate or perhaps side reactions occurred which
the concentration of the more unsaturated fatty acids (Tables 8 and 9).
found that a reaction time of 0.25 hours at reflux was the most
obtaining a reliable determination of the individual fatty acid ratios.
dimethyl o-phthalate determination by this method was not satisfactory
be used as a guide to oil length.
reagents have been examined in the transesterification of alkyd resins,
view to developing a method of determining the concentration of the
acid components present. A 0.5M methanolic solution of lithium
found to be superior to the other reagents used, which were a
solution of boron trifluoride and a methanolic solution of hydrogen
lithium methoxide reagent was used for determining the concentration of
various fatty acids in the alkyd. The vegetable oil used in the
the resin could thereby ascertained. The phthalate content of the alkyd
not be determined accurately by any of the three reagents; however, the
methoxide solution gave a value for the phthalate content which served
guide to the oil length of the resin.
concentrations of the various methyl esters were determined by means of
gas-liquid chromatography using a diethyleneglycol succinate column and
Carbowax 20 M column.
Methods of Analysis of
number of the general references review the methods of analyzing alkyd
compositional analysis of alkyds is complicated by the wide variety of
ingredient combinations that may be encountered. Neither systematic nor
standard methods have been devised, so the analyst must use his
devise methods to fit the product.
chromatography (GLC) has proved effective for the compositional
alkyd resins. The following discussion will cover a few applications of
are credited with the first systematic study pertaining to the
in alkyds. In order to provide a sample with a sufficiently high vapor
pressure, a rapid transes sterification procedure is used to convert
to the methyl esters. Fatty acids from soybean, linseed, or tall oil
identified in the presence of 0-phthalic, isophthalic, fumaric, maleic,
itaconic, succinic, adipic, azelaic, sebacic, diglycolic, pelargonic,
samples are transesterified with lithium methoxide in methanol, except
is necessary to distinguish maleic from fumaric acid, in which case
trifluoride is used instead of lithium methoxide. The methyl esters are
separated on a two-part polyester–Carbowax column, and the relative
times of the individual esters are compared to data obtained from known
Table 1 lists relative retention time data for methyl esters; Esposito
convenient to refer these esters to triacetin, which was given a value
Values are also included for a silicone column.
0.5 N lithium methoxide in methanol by adding pea-sized pieces of
absolute methanol, chilled in an ice bath. Determine the normality by
and add enough methanol to adjust the solution to 0.5 N.
the boron trifluoride reagent by bubbling the gas into absolute
1 ml of the reagent, diluted with methanol, requires 11-12 ml of 0.5 N
potassium hydroxide in methanol.
about 0.3 g of resin in a 125-ml flask and add 15 ml of 0.5 N lithium
methoxide. Attach an air condenser and boil the contents on a steam
bath for 2
min. Remove, cool, and add 5 ml of 6 N aqueous sulfuric acid. Transfer
separatory funnel and dilute to 50 ml with water. Extract with 35 ml of
methylene chloride and then wash the methylene chloride layer with
portions of water. If in soluble methyl esters are present, add
dropwise until dissolved. Remove the solvent on a steam bath. If maleic
fumaric acid is found in the subsequent chromatogram, repeat the
transesterification procedure with a boron trifluoride catalyst using 5
the reagent and a 5-min reflux.
a 5-ml sample along with 0.2 ml of triacetin on a 6-ft
column, and repeat the separation on a 6-ft silicone grease column.
the methyl ester peaks by determining their retention times relative to
triacetin and comparing them to the values in Table 4.
use of columns of different polarity makes it possible to resolve all
dibasic acids and fatty acids commonly found in alkyd resins. Even
fumarate and dimethyl maleate, prepared with the boron trifluoride
are separated. These acids probably rearrange with alkali in a methanol
to give dimethyl methoxy succinate.
choice of the polyester substrate used in the column is not critical
almost any polyester is satisfactory. There is also a wide selection
for the nonpolar column; Apiezon greases, fluorosilicone, and
Figure 1 shows a chromatogram formed by the separation of the methyl
a typical alkyd prepared by transesterification with lithium methoxide.
chromatogram was run isothermally at 180°C on a 9ft × in. OD column of
glycol succinate (EGS) on Gas-Chrom P with a 1-ml sample. The component
were identified by comparing their retention times to known methyl
chromatography is ideal for the qualitative identifications of acids as
remarkedly free of interferences, even from modifying resins.
solvents found in alkyd resin solutions sometimes obscure low-boiling
esters, but these can be removed by drying the sample before the ester
esters do not form methyl esters under the transesterification
but require strenuous saponification, isolation of the rosin acids by
extraction, and methyl ester preparation with diazomethane.
transesterification procedure does not lend itself to quantitative GLC,
the yields of methyl esters are different for individual acids.
appears that the detector response varies for different methyl esters,
calibration with known mixtures is necessary. Nevertheless, studies are
made of the quantitative aspects, and single acids may be determined by
internal standard technique.
has determined phthalic acid quantitatively in alkyd resins as dimethyl
phthalate through an internal standard, and recently, Haken described
determination of benzoic acid and p-tert-butyl benzoic acid. Since
form soluble potassium salts, a saponification mixture of the resin is
evaporated to dryness, acidified, and extracted with ethyl ether. The
acids are methylated with diazomethane and the resulting methyl esters
examined by GLC.
1. Chromatogram of the methyl esters of a typical alkyd.
insoluble potassium salts isolated in the Kappelmeier procedure may be
converted to methyl esters by the same procedure. However, a preferable
is to pass the salts through a column of cation exchange resin in
form, recover the free acid from the eluate, and methylate with
Percival obtained dimethyle esters from polyesters by methanolysis of
latter with a 95:5 methanol–resin dilution, containing about 0.1 g of
methoxide. However, he extended the methanolysis to 18 hr and up to 42
some resins to insure at least semiquantitative results for the
dimethyl esters and glycols. A 12 ft ×
in. OD column, packed with 10 g of SF-96 silicone on 50 g
80, is used with temperature programming from 110 to 180°C at 8°C/min.
suitable response factors and by working with known mixtures, the
be useful for determining the identity of the dibasic acids as well as
ratio in an alkyd.
adducts are difficult to
detect in alkyds and it is even more difficult to recover maleic acid
mixtures. If the maleic anhydride has added to the oil to form an
alkyl-succinic adduct, the fatty acids are recovered and their
weights determined by an acid value. Then the methyl esters of the
acids are subjected to GLC, comparing the chromatogram with those
similar samples of known composition.
Acids. One of the most important applications of GLC is in fatty acid
The first paper on GLC by James and Martin in 1952 was concerned with
acids, and from then to 1958 more than fifty papers dealing with that
were published. Polyester liquid phases, developed in 1958 permitted
separation of long-chain acids in respect to both chain length and
unsaturation, and in particular, the four C18 acids usually found in
or silicone greases (nonpolar phases) separate fatty acids by chain
only, unless used in extremely efficient packed columns or capillary
Silicone gum, SE-30, is less selective and the C18 acids will give but
peak. This is advantageous if separation into chain lengths is desired
there is a question regarding the assignment of a peak.
the unusual wealth of information and the almost universal availability
reliable instrumentation, analysis of fatty acids by GLC is almost
Recent developments, such as temperature programming, dual column
capillary columns, and more sensitive detectors, serve to make GLC more
attractive and versatile, but most of the applications reported have
carried out with thermal conductivity detectors in conjunction with
fatty acid analysis, methyl esters are generally used. They can be
several methods, starting with the resin as did Esposito or more
the fatty acids isolated by the Kappelmeier separation. The
technique is perfectly satisfactory for identifying the fatty acids,
amount is best determined by an actual separation. The American Oil
Society (AOCS) Gas Chromatography Committee has studied esterification
methanol and sulfuric acid, with boron trifluoride and methanol with
diazo-methane, and with 2,2-dimethoxypropane and has recommended the
methanol-sulfuric acid system except with extremely small samples or
hydroxy or epoxy acids which should be methylated with diazomethane.
Only a few
minutes is involved in the preparation of methyl esters by either
acids may be run directly on columns containing polyesters with 1% of
phosphoric acid added to the support for the purpose of inhibiting
and reducing tailing. The resolution is not so good as that obtained
methyl esters so that the extra methylation step is worth the effort.
Method Ce 1–62 has been studied collaboratively and is suitable for
of fatty acids derived from alkyds.
Methylate 2g, or less, of fatty acids by refluxing with 60 ml of 2%
sulfuric acid for 1 hr. Cool, transfer to a separatory funnel, and add
of water. Extract twice with 50-ml portions of petroleum ether (bp
Wash the combined extracts with 20-ml portions of water until free of
dry with anhydrous sodium sulfate, and evaporate the solvent under a
nitrogen on the steam bath.
chromatograph should have an injector port and a detector with an
temperature control. Use a 4–10 ft × in. OD glass, stainless steel,
or copper column packed with 20% polydiethylene glycol succinate on
acid-washed Chromosorb P or W, and operate at a constant temperature
190 and 210°C. The recorder should have 0–1 mV range with 1 sec full
deflection. Use helium as the carrier gas.
temperature of the injector 50°C above that of the column and the
of the detector 25°C higher than that of the injector. Condition the
column by holding at the operating temperature with the gas flowing
steady base line is achieved. Following the manufacturer’s directions,
the gas flow to permit elution of methyl stearate in 30 min or less; an
adjustment of column length may also be necessary, but do not exceed
inlet pressure. Measure the gas flow periodically with a soap bubble
not during a run. Inject a 0.5–4 ml sample, adjusted so that the major
not attenuated more than eight times, and recore the chromatogram,
as necessary. Mark the air peak as zero.
the area of each peak by a convenient method. Identify the peaks by
relative positions on the chromatogram or by reference to a known
methyl esters run under the same conditions. The esters appear in order
increasing number of carbon atoms and of increasing unsaturation for
number of carbon atoms. Total the areas of all peaks and calculate the
percentage of each. For ordinary work, the percentage area of a peak
considered as the percentage of the corresponding component. For more
work, calibration factors should be determined and used to correct for
non-linearity of detector response and for molecular weight
known mixture used for such calibration should have a composition
that of the unknown.