Phenolic resins are obtained by the reaction of phenols with aldehydes. The simplest representative of these types of compounds, phenol and formaldehyde, are by far most important. Phenolic resins are mainly used in the production of circuit boards. The development of synthetic resins for surface coating applications has usually followed the use of similar material in the plastic industry. One of the first synthetic resins ever used commercially, both in plastics and in surface coatings was the phenolic resin. Phenolic resins result aldehyde with or without modification. Phenol resin bonded wood materials; particle boards (PB), plywood, fiber board (FB) and glued wood construction element are used for outdoor construction and in high humidity areas because of the high water and weathering resistance of the phenolic adhesive bond and high specific strength. The competitiveness and development of the wood working industry are of utmost importance for the development for thermosetting plastics. This industry is the largest consumer of urea melamine and phenol resins. Phenolic laminates are made by impregnating one or more layers of a base material such as paper, fiberglass or cotton with phenolic resin and laminating the resin saturated base material under heat and pressure. The resin fully polymerizes (cures) during this process. The base material choice depends on the intended application of the finished product. Paper phenolics are used in manufacturing electrical components such as punch through boards and household laminates. Glass phenolics are particularly well suited for use in the high speed bearing market. Other applications of phenolic resins are in chemical equipments, fibers, socket putties, photo resists, tannins, brush putties, etc. Good performance at a reasonable cost has long been an important selling point for phenolic resins, especially in applications such as wood bonding and insulation, where discoloring and other drawbacks can be overlooked because of cost savings. Hence demand of phenolic resins is growing rapidly.
This book basically deals with general reaction of phenols with aldehydes, the resoles, curing stages of resoles, kinetics of a stage reaction, chemistry of curing reactions, kinetics of the curing reaction, the novolacs, decomposition products of resites, acid cured resites, composition of technical resites, mechanisms of rubber vulcanization with phenolic resins, thermosetting alloy adhesives, vinyl phenolic structural adhesives, nitrile phenolic structural adhesives, phenolic resins in contact adhesives, chloroprene phenolic contact adhesives, nitrile phenolic contact adhesives, phenolic resins in pressure sensitive adhesives, rubber reinforcing resins, resorcinol formaldehyde latex systems etc.
The present book covers manufacturing processes of phenolic resins. New entrepreneurs, technocrats, research scholars can get good knowledge from this book.
1. HISTORICAL DEVELOPMENT OF PHENOLIC RESINS
2. RAW MATERIALS
Phenols, Physical Properties of Phenol, Cumene Process (Hock Process), Cresols and Xylenols â€” Synthesis Methods, Alkylphenols, Phenols from Coal and Petroleum, Other Phenolic Compounds, Resorcinol, Bisphenol-A, Formaldehyde, Properties and Processing, Paraformaldehyde, Trioxane and Cyclic Formals, Hexamethylenetetramine, HMTA, Furfural, Other Aldehydes
3. CHEMICAL STRUCTURE
General Reaction of Phenols with Aldehydes, The Resoles, Curing Stages of Resoles, Kinetics of A-Stage Reaction, Chemistry of Curing Reactions, Kinetics of the Curing Reaction, The Novolacs, Decomposition Products of Resites, Acid-Cured Resites, Composition of Technical Resites
4. PHENOLIC RESINS FROM HIGHER
Acetaldehyde, Butyraldehyde, Chloral, Furfural, Acrolein
5. PHENOLIC RESINS FROM POLYHYDRIC
6. REACTION MECHANISMS
Molecular Structure and Reactivity of Phenols, Formaldehyde-Water and
Formaldehyde-Alcohol Equilibria, Phenol-Formaldehyde Reaction under Alkaline Conditions, Inorganic Catalysts and Tertiary Amines, Ammonia, HMTA and Amine-Catalyzed Reactions, Reaction Kinetics of the Base-Catalyzed Hydroxymethylation, Prepolymer Formation, Resole Cross-Linking Reactions. Quinone Methides, Acid Curing, Heat Curing, Phenol-Formaldehyde Reactions under Acidic Conditions, Reaction Kinetics in Acidic Medium, Reaction under Weak Acidic Conditions. â€œHigh-Orthoâ€-Novolak Resins, Novolak Cross-Linking Reaction with HMTA, Reaction with Epoxide Resins, Reactions with Diisocyanates
7. THE PHYSICAL STRUCTURE OF PHENOLIC
Introduction, X-Ray Examination, Electron Microscope Examination, The Isogel Theory of Phenoplast Structure, The Spherocolloid Theory of Phenoplast Structure, Further Swelling Experiments, Development of Structure in A-Stage Resin, General Picture of Phenoplast Structure, Structure of Cast Phenoplasts
8. RESIN PRODUCTION
9. FILLERS FOR PHENOLIC RESIN MOULDING
Types of Filler, Effect of Filler on Impact Strength and Damping, Microscopic Structure of Fillers, Ratio of Resin to Filler, Standard Classification of Phenoplast Molding Powder According to Filler, Properties of Individual Fillers, Cellulose Derivatives, Wood Flour, Walnut-Shell Flour, Cottonseed Hulls, Cellulosic Fibers, Textile By-Products, Proteinaceous Fillers, Carbon Fillers, Mineral Fillers
10. FILLERS AND RESINS FOR LAMINATES
Classification of Laminates, Laminated Phenolic Sheets, Laminated Phenolic Tubes (NEMA Classi-fication), High Strength Paper Laminates, Plastic Bonded Cotton Fiber, Glass Fabric Filler, Resins used for Laminates
11 PHYSIOLOGY AND ENVIRONMENTAL
Toxicology of Phenols, Toxicology of Formaldehyde, Environmental Protection, Waste Water and Exhaust Air Treatment Processes, Microbial Transformation and Degradation, Chemical Oxidation and Resinification Reactions, Thermal and Catalytic Incineration, Extraction Processes and Recovering, Activated Carbon Process, Gas Scrubbing Processes
12. DEGRADATION OF PHENOLIC RESINS BY
HEAT, OXYGEN AND HIGH ENERGY
Thermal Degradation, Oxidation Reactions, Degradation by High Energy Radiation
13. MECHANICAL PROPERTIES OF MOLDED
Introduction, Mechanical Properties Covered, Pheno-plast Properties at Room Temperature, Effect of Degree of Cure on Physical Properties, Tensile Strength, Modulus of Elasticity, Compressive Strength, Flexural Strength, Shear Strength, Bearing Strength, Impact Resistance, Creep and Stress Endurance, Fatigue Resistance, Influence of Temperature on Mechanical Properties, Influence of Temperature on Creep, Theoretical Discussion of Strength Properties of Phenoplasts, Strength-Weight Comparisons with Metals
14. MECHANICAL PROPERTIES OF LAMINATED
Introduction, Mechanical Properties at Ordinary Temperatures, Tensile Strength, Modulus of Elasticity, Compressive Strength, Flexural Strength, Shear Strength, Bearing Strength, Impact Resistance, Creep and Stress Endurance, Fatigue Resistance, Abrasion Resistance, Influence of Temperature on Mechanical Properties, Effect of Resin Content on Mechanical Properties, Effect of Moisture Content of Paper Filler Before Lamination, Effect of Laminating Pressure, Effect of Degree of Cure, Effect of Moisture Content on Physical Properties, Mechanical Properties of Post-Formed Laminates, Tensile Strength, Flexural Strength, Shear Strength, Impact Strength, Water Absorption
15. MODIFIED AND THERMAL-RESISTANT
Etherification Reactions, Esterification Reaction, Boron-Modified Resins, Silicon-Modified Resins, Phosphorus-Modified Resins, Heavy Metal-Modified Resins, Nitrogen-Modified Resins, Sulfur-Modified
16. COMPOSITE WOOD MATERIALS
Wood, Residues of Annual Plants, Adhesives and Wood Gluing, Phenol Resins, Urea and Melamine Resins, Diisocyanates, Lignosulfonates, Bark Extracts, Physical Properties of Composite Wood Materials, Particle Boards, Wood Chips, Resins and Additives, Wood Chips, Resins, Hydrophobic Agents, Fungicides and Insecticides, Flame Retardants, Production of Particle Boards, Chip Blending, Pressing of Particle Boards, Properties of Particle Boards, Plywood, Resins, Additives and Formulations, Production of Plywood, High-Densified Plywood, Fiber Boards, Wood Fibers, Resins and Additives, Production of Fiber Boards, Structural Wood Gluing, Resorcinol Adhesives
17. MOULDING COMPOUNDS
Standardization and Minimum Properties, Composition of Molding Powders, Resins, Fillers, Reinforcements and Additives, Wood Flour and Cellulose Fibers, Asbestos, Mineral Flour, Other Fillers and Fibers, Colorants, Lubricants and Release Agents, Production of Molding Powders, Thermoset Flow, Manufacturing of Molded Parts, Compression Molding, Transfer Molding, Injection Molding, Selected Properties, Thermal Resistance, Shrinkage and Post-Mold Shrinkage, Thermal Expansion
18. HEAT AND SOUND INSULATION
Inorganic Fiber Insulating Materials, Inorganic Fibers and Fiber Production, Resins and Formulation, Properties of Fiber Mats, Phenolic Resin Foam, Resins and Additives, Blowing Agents, Surfactants, Foaming Equipment, Foam Properties, Sound Insulating Textile Fiber Mats.
19. THERMAL PROPERTIES OF PHENOLIC
Introduction, Coefficient of Expansion, Flame Resistance
20. CHEMICAL RESISTANCE OF PHENOLIC
Introduction, Water Absorption, Effect of Reagents, Chemical Applications for Phenoplasts, Resistance to Microorganisms
21. OIL SOLUBLE PHENOLIC RESINS
Introduction, Pure Oil-Soluble Phenoplasts, The Modified Phenoplasts, Reactions of the Phenoplasts with Oils
22. FRICTION MATERIALS
Friction and Wear of Thermosets, Formulation of Friction Materials, Fibers, Fillers, Resins, Manufacturing of Brake- and Clutch Linings, Impregnation Process, Wet Mix â€œDoughâ€ Process, Dry Mix Process
23. PHENOLIC RESINS IN RUBBERS AND
Mechanisms of Rubber Vulcanization with Phenolic Resins, Thermosetting Alloy Adhesives, Vinyl-Phenolic Structural Adhesives, Nitrile-Phenolic Structural Adhesives, Phenolic Resins in Contact Adhesives, Chloroprene-Phenolic Contact Adhesives, Nitrile-Phenolic Contact Adhesives, Phenolic Resins in Pressure-Sensitive Adhesives, Rubber-Reinforcing Resins, Resorcinol-Formaldehyde Latex Systems
24. PHENOLIC ANTIOXIDANTS
25. OTHER APPLICATIONS
Carbon and Graphite Materials, Phenolics for Chemical Equipment, Phenolic Resin/Fiber Composites, Phenolic Resin Fibers, Blast Furnace Taphole Mixes, Photo-Resists, Socket Putties, Brush Putties, Tannins, Ion-Exchange-Resins, Casting Resins
26. TECHNICAL MANUFACTURE OF
Resin Manufacture, Cast Resins, Resin Varnishes, Resin Compound, Molding Powder, Phenoplast Molding Laminates
27. MOULDING TECHNIQUE FOR PHENOLIC
Introduction, Compression Molding, Transfer Molding, Injection Molding, Molding Practice, Preheating
28. MISCELLANEOUS TECHNICAL
APPLICATIONS OF PHENOLIC RESINS
Wood Adhesives, Bonding of Insulating Mats, Resins for Bonding Grinding Wheels, Wood Impregnation, Miscellaneous Adhesive Applications, Brake-Lining Resins, Cross Linking of Thermoplasts, War Uses of Phenoplasts.
29. FOUNDRY RESINS
Mold- and Core-Making Processes, Inorganic Binders, Organic Binders, Requirements of Foundry Sands, Shell Molding Process, Precoated Resin â€œShellâ€ Sand, Shell Sand Properties, Hot-Box Process, No-Bake Process, Cold-Box Process, Ingot Mold Hot Tops
30. INDUSTRIAL LAMINATES AND PAPER
Electrical Laminates, Materials, Paper, Resins, Production of Electrical Laminates, Laminated Tubes and Rods, Cotton Fabric Reinforced Laminates, Decorative Laminates, Filters, Battery Separators
Automotive Coatings, Water-Borne Paints and Electrodeposition, Coatings for Metal Containers, Marine Paints, Shop Primers, Wash Primers, Oil-Modified Phenolic Resin Paints, Printing Inks, Rosin-Modified Phenolic Resins, Other Applications
32. ABRASIVE MATERIALS
Grinding Wheels, Composition of Grinding Wheels, Abrasive Materials, Fillers and Reinforcements, Resins, Manufacturing of Grinding Wheels, Cold Molding Procedure for Non-reinforced Wheels, High-Speed, Reinforced Grinding and Separating Wheels, Compression Molding Process, Snagging Wheels, Fibrous Laminated Wheels, Coated Abrasives, Composition of Coated Abrasives, Abrasive Materials, Adhesives and Coatings, Coating Process, Abrasive Papers, Abrasive Tissues, Vulcanized Fiber Abrasives
33. ELECTRICAL PROPERTIES OF PHENOLIC
Introduction, Theoretical Discussion, Numerical Data on Electrical Properties, Effect of Heating on Electrical Properties
34. ANALYTICAL METHODS
Monomers, Nitrogen and Water, Physical Properties, Reactivity, Chromatographic Methods, Spectroscopy
35. PHENOLIC RESINS AS ION-EXCHANGE
Introduction, Application of Ion Exchange: Theory, Application of Ion Exchange: Types of Processes
Development of Phenolic Resins
July 13 1907 Leo H. Baekeland
applied for his famous heat and pressure patent for the processing of
formaldehyde resins. This technique made possible the worldwide
the first wholly synthetic polymer material (only cellulose derivatives
known before). Even from his first patent application of February 18
was clear that Baekeland more than these predecessors was fully aware
value of phenolic resins. Before his involvement with phenolic resins
had worked on photographic problems with the same intensity. His
developing a fast copying photographic paper known throughout the world
the name Velox gave him the financial independence which allowed him to
his own research laboratory in his home in Yonkers New York. There
1905 he devoted his whole time to the investigation of phenolic resins.
the first patent covering phenolic resins (as substitute for hard
granted to A. Smith in 1899. A. Von Bayer found in 1872 while studying
dyes that phenol reacting with formaldehyde was converted to a
He first noticed that a reddish brown resinous mass was produced during
reaction of bitter almond oil with pyrogallic acid. However nothing was
with this resinous material. Ter Meer A. Claus and E. Trainer continued
experiments. Claus and Trainer obtained a resinous material from 2 mol
phenol and 1 mol of formaldehyde and hydrochloric acid. After the non
phenol was distilled off a soluble resin was obtained with a MP of
However they also could not think of application for this material and
disappointedly it is not possible to crystallize this resinous
Kleeberg continued the experiments after the company Merklin and
brought the formaldehyde on to the market in 1889. Kleeberg obtained a
linked insoluble resin using an excess of formaldehyde and hydrochloric
a vigorous reaction. There was no interest in the product obtained.
laboratory investigations performed by Manasse and Lederer the Bayer
applied for a patent for a process for the production of o and p
hydroxybenzylalcohol but without mentioning a formation of the resin.
obtained an insoluble material from resorcinol formaldehyde and ammonia
catalyst which could be used as an antiseptic. Speier Smith and Luft
first ones to draw the attention to technical applications for curable
resins. Smith in particular pointed out the valuable properties of the
material which did not melt was a good insulating material and could
serve as a
substitute for ebonite and wood. Luft tried to flexibilize the brittle
obtained by Smith by addition of solvents glycerin and organic acids.
recommended the following applications for his plasticized phenolic
proof coatings for fabrics fibers which are carbonized to form
light bulbs acid and alkali resistant vessels billiard balls buttons
amber and corals when colorants and fillers are added. Almost at the
same time the
Louis Blumer Company applied for a patent for the production of
resins as substitutes for shellac. The solid soluble phenolic resins
organic acids as catalysts were the first commercial scale phenolics in
world sold under the trade name Laccain. In February 1903 Henschke
the experiments of Manasse and using alkali hydroxide as catalyst for
reaction obtained an insoluble resin. Further improvements to the
of phenolic resins were made by Fayolle and Story. Story worked without
catalysts. Laire tried to find a substitute for copal and damar by
phenol alcohols. He obtained high melting condensation products which
soluble in low boiling alcohols but which could be dissolved in
Baekeland started with his studies of phenolic resins the following
and formaldehyde are converted to resinous products in the presence of
and alkaline catalysts. These may be permanently fusible and soluble in
solvents or heat curable depending upon the preparation conditions.
resins were already being sold as substitutes for shellac ebonite horn
celluloid. These are colorable can be mixed with fillers and under the
influence of heat shaped in molds into solid parts.
production of molded parts was not yet possible. The heat and pressure
became the turning point indicating clearly the importance of economic
processing techniques for market acceptance. Phenolic resins mixed with
could be hardened in a press or an autoclave which was called
pressure at temperatures above 100 °C in
a considerably short time and without the formation of blisters.
the first Baekeland patent phenol formaldehyde catalysts and fibrous
material were reacted (in the cellulose matrix) at elevated
impregnation of the fibrous material can be improved by application of
and pressure infusible products being obtained only if formaldehyde was
excess. Soon afterwards he reco mmended the impregnation of the
fibers with liquid phenolic resins acid catalyzed resins were being
this stage. According to a patent application by Lebach in February
insoluble and infusible condensation products useful as plastic
be obtained if phenol is reacted with surplus formaldehyde using
basic salts as catalysts. In the same year Baekeland also patented a
for the preparation of phenolic resins using alkaline catalysts
ammonia NaOH and Na2CO3. A patent was granted to him in the USA but not
Germany because of the lack of inventive steps considering previous
publications by Henschke. It was in this patent however that resin
was described for the first time just as it is carried out today
reaction is performed in a closed vessel with a reflux condenser to
loss of volatile materials.
reaction is interrupted when the desired viscosity is obtained.
is performed in a vacuum and can be continued until a solid product
still soluble in alcohols is obtained.
In 1908 the
of phenolic resins at ambient temperatures by addition of strong
acids was reported by Lebach.
1909 Baekeland conducted small scale trials with a few industrial
as result patented numerous applications for phenolic resins till 1909.
compounds can be made of pulverized fusible phenolic resins made in
environment and fillers and molded to a shaped part of high toughness
and chemical resistance.
are excellent binders for abrasive materials.
catalyzed solid resins in organic solvents can be used for valuable
and coatings for food containers.
steam resistant lining materials can be made of phenolic resin
asbestos fibers paper or cloth.
are useful for coating wood yielding a hard and abrasive resistant
high gloss or can be applied as adhesive for veneer facing.
of fiberboards an aqueous wood fiber pulp is mixed homogeneously with
resin. After a drying process similar to that used in the manufacturing
paper the fiber mats obtained are hardened between hot metal plates
1909 at a meeting of the New York Section of the American Chemical
reported for the first time the results of his thorough studies of
resins which he called Bakelite. His report was received with great
by a large audience. He stated his theory that the reaction of phenols
formaldehyde in the presence of catalysts occurs in three phases
a soluble initial condensation product which could be liquid viscous or
and which he called A the formation of a solid intermediary
product which could still swell in solvents and which he designated as
the formation of an infusible and insoluble product C.
suggested calling the liquid curable resin resol the B phase material
the hardened phenolic resin resit while Aylsworth recommended the name
In the same year Baekeland proposed the designation novolak for the
resin indicating the suggested substitution of shellac.
of paper laminates and laminated paper tubes made of liquid or
the manufacture of noiselessly running cog wheels phenolic resin
glues to bond various materials and impregnating resin for coils and
electrical devices were also suggested by Baekeland at this early
low reactivity of o and p cresol was mentioned and recommended as a
delaying the hardening reaction and increasing plasticity. The high
of m cresol had already been mentioned. In another application the use
phenyl and cresyl phosphates was recommended for making PF resins more
flexible. Also tung oil was recommended as plasticizing additive for
impregnating and coating resins and the resin preparation method
further process for manufacturing phenolic resin bonded fiber boards
patented by him in 1915. The phenolic resin solution added to the fiber
precipitated on the fibers by the addition of acidic salts according to
successful preliminary studies the time came to put what had been
practice. After a visit by Baekeland in June and July 1909 to Germany
companies Rutgerswerke AG and Knoll & Co together with
the Bakelite Gesellschaft mbH at Erkner near Berlin on May 25 1910.
the first company in the world to produce synthetic resins. On October
10 1910 Baekeland
founded the General Bakelite Company in the USA and later other
England France Japan and Canada. On March 22 1922 the Bakelite
founded incorporating Redmanol Chemical Products Company and Condensite
Company. This corporation was taken over by the Union Carbide &
Corporation in 1939. The first customers of the German Bakelite Corp.
big electrical companies. They mainly used shellac for the
production of cresol molding compounds was also started. At that time
was preferred to phenol because it was cheaper J. W. Aylsworth a co
the Condensite Company also contributed a lot to the development of
the production of molding compounds. In 1910 he found that novolaks
obtained from 3 mol of phenol and 2 mol of formaldehyde could be very
favourably cured by the addition of hexamethylenetetramine or
are produced by the reaction of phenols with aldehydes. The simplest
representatives of these types of compounds phenol and formaldehyde are
the most important. As an average considering all applications the
of 1 ton of phenolic resin requires approximately 440 kg phenol
about 10% cresols and xylenols) and 220 kg formaldehyde as well as
family of aromatic compounds with the hydroxyl group bonded directly to
aromatic nucleus. They differ from alcohols in that they behave like
and dissolve readily in aqueous sodium hydroxide but are insoluble in
sodium carbonate. Phenols are colorless solids with the exception of
liquid alkyl phenols. The most important phenols are listed in Table
Data regarding the molecular structure of phenols and cresols are
Table 1.Physical properties of some phenols
Physical Properties of Phenol
point of pure phenol at 40.9 °C is considerably lowered by traces of
0.4°C per 0.1% of water. A water content of < 6% renders it
liquid even at
room temperature. To produce phenolic resins a mixture of 90% of
water is preferably used. Above 65.3°C phenol can be mixed with water
ratio. During the cooling period of those solutions which may contain
28 92% of
water two phases are being developed phenol/water and water/phenol.
soluble in polar organic solvents but not very soluble in aliphatic
hydrocarbons. Phenol crystallizes in the form of colorless prisms.
air phenol rapidly develops a reddish color especially if it contains
copper and iron. This happens if phenol is reacted in copper clad or
reactors or if phenolic resins are stored in iron barrels. Additional
and technical data of phenol are listed in Table 2 below
approximately 3% of the world production of phenol was gained from
the synthetic processes the cumene process in the most frequently used.
basic raw materials for the cumene process and thus for the production
phenol are benzene and propylene. To help understand the dependence of
availability and price for phenolic resins on the crude oil situation
material supply is given in Figure 1.
2. Breakdown of benzene and
Phenol Production Processes
process is by far the most important synthetic process for the
phenol and today probably accounts for 90% of the synthetic phenol
the Western world.
A two step
oxidation process based on toluene was developed by Dow Chemical.
Chemical in USA and DSM in The Netherlands are working according to
of halogenated aromatic compounds in 1930 developed by Raschig was
improved to the Raschig Hooker process. The first step the
benzene with hydrochloric acid in the presence of a copper on alumina
at 275 °C is followed by hydrolysis of the chlorobenzene with water
a copper promoted calcium phosphate catalyst at 400 450 °C.
process the oldest one is almost of no importance nowadays.
Process (Hock Process)
phenol synthesis based on cumene was discovered by H. Hock and
published by him
and Sho Lang.
War II the first pilot plant was constructed jointly by Rutgers werke
Bergwerksgesellschaft Hibernia with Hock s assistance. The commercial
production was first developed by the Distillers Co. (GB) and Hercules
required for the Hock process is produced by alkylation of benzene with
propylene by use of a solid phosphoric acid catalyst (UOP Process Eq.
oxidized with oxygen in air in the liquid phase to cumene hydroperoxide
according to reaction (2.3) yielding small amounts of dimethylbenzyl
and acetophenone as by products. The mechanism mentioned in parenthesis
acid catalyzed peroxide decomposition (Eq. 2.4) was postulated by
compound with relatively low vapour pressure is stable at normal
and conditions but decomposes very rapidly under acidic conditions and
temperatures. During the second stage of the process the concentration
and separation of unreacted cumene occur. The concentrated reaction
then converted in a splitting plant by use of sulfuric acid as catalyst
crude mixture of phenol and acetone which also contains a methylstyrene
as a by
product. Then various purification and distillation steps follow. a
Methylstyrene can also be hydrogenated and returned to the process.
CHP is a
potentially hazardous material. Therefore many safety regulations have
observed and safety equipment must be installed in technical plants.
Cresols and Xylenols Synthesis Methods
derivatives of toluene commonly designated as methyl phenols exist in
isomers depending on the relative position of the methyl towards the
group. The molecular configuration is described in Section. The main
cresols was originally coal tar. Today however synthetic processes
based on toluene and phenol. The importance of the petroleum industry
source of cresols and xylenols is relatively insignificant. Starting
toluene the cresols are obtained either by sulfonation by alkylation
propylene or by chlorination. In the sulfonation process the main
the para derivative together with some ortho derivative. In the
process the meta isomer prevails (about 50%) with an approximately
ratio. This route is advantageous for resin grade cresols. The
chemistry of the
toluene alkylation is very similar to the cumene process with
the oxidation step. Toluene is reacted first with propylene in the
A1C13 or other catalysts to obtain a mixture of cymenes. In this
m/p ratio of approximately 2 1 by less than 5% o cymene is reported.
3. Flow diagram of the
cumene process (Drawing Phenolchemie
among the synthetic processes is the production of cresols and xylenols
on alkylation of phenol with methanol. In the gas phase process the
and phenol vapours pass an aluminium oxide catalyst at approximately
under moderate pressure. Mainly o cresol and 2 6 xylenol are obtained.
If 2 6
xylenol is desired as main product which is used for PPO production
oxide is employed as catalyst. The following purification and
accomplished by vacuum distillation for o cresol (99% purity) and
crystallization for 2 6 xylenol (98%). The further purification of 2 6
as needed for PPO is made by counter current extraction with aqueous
hydroxide solution (Pitt Consol). The yield of the gas phase process is
than 90% with regard to the phenol used and more than 85% with regard
operated by Chemische Werke Lowi and UK Weaseling are performed in the
phase. The Lowi process is carried out at 300 350 °C at a pressure of
40 70 bar
Al methylate is used as catalyst. Thus mainly o cresol is obtained.
methanol ratio favors the formation of 2 4 and 2 6 xylenol. By
of xylenols in the presence of phenol the yield of cresols can be
produces o and p cresol of 99% purity 2 6 xylenol of 98% and 2 4
xylenol of 92%
purity by use of zinc bromide as catalyst. The synthesis of p cresol
mainly for BHT or similar antioxidants is also performed by sulfonation
compounds with a saturated carbon side chain containing a minimum of
carbon atoms should be termed alkylphenols. These alkylphenols are
from phenols or cresols by Friedel Craft alkylation with olefins mainly
isobutene diisobutene or propylene. At low temperatures e.g. below 50
substitution predominates o Alkylphenols can be rearranged to p isomers
heating up to 150°C with acid catalysts. High yield of o derivates is
by use of Ca Mg Zn or Al phenoxides as
catalysts at a
temperature of about 150 °C.
area alkylphenols are used for the production of coating resins because
their good compatibility with natural oils and increased flexibility or
cross linking agents in the rubber industry. Other uses include
and phosphoric acid esters.
Phenols from Coal and Petroleum
approximately 1.5% crude phenols mainly phenol (~ 0.5%) as well as o m
cresols 2.3 2.4 2.5
2.6 and 3.5
dimethylphenol is found in coal tar. Phenols are further obtained from
condensates of coke oven gases and waste waters of coal gasification
The extraction is performed either according to the older Pott
process using benzene/sodium hydroxide or according to Lurgi s
process with diisopropyl ether as solvent. The extraction of phenols
tar is performed with diluted sodium hydroxide (8 12%) followed by
precipitation of the crude phenols with carbon dioxide. The flow
diagram of an
extraction plant is shown in Figure 5. The crude phenoxide solution
approximately 0.5% non phenolic components neutral
oils (hydrocarbons) and pyridine bases
which have to be
removed prior to
precipitation mostly by steam distillation.
recommend selective solvents to extract phenol e.g. aqueous methanol
(Metasolvan process). However only Lurgi s Phenoraffin process which
aqueous sodium phenoxide solution as selective solvent has achieved
importance. The selectivity of NaOH is superior to all other
of cresols is the petroleum industry particularly in the USA. During
catalytic cracking process various phenolic compounds are formed.
the recovery of phenolic compounds from coal tar the extraction is
with diluted sodium hydroxide solution. After the separation of the
precipitation with carbon dioxide further treatment follows by
Thereby phenol (BP 181.8 °C) and o cresol (BP 191.0 °C) can be
technically pure immediately.
of m and p cresol is only possible with special chemical or
methods due to the similar boiling points. This is also applicable to
In the urea process the mixture of m and p cresol is heated with urea.
cooling a crystalline addition compound of m cresol and urea is formed.
p cresol when gently heated to 90 °C forms a crystalline addition
anhydrous oxalic acid. m Cresol with sodium acetate results in adducts
solubility. The chemical processes use the differences in the reaction
sulfonation (sulfuric acid process) followed by crystallization and
or the different behaviour in the alkylation with isobutylene
process) and following dealkylation with sulfuric acid.
Other Phenolic Compounds
Nut Shell Liquid (CNSL)
phenolic compound from natural sources is cashew nutshell liquid
liquid from the shells of cashew nuts which grow mainly in Southern
become a useful raw material in the manufacture of special phenolic
be used for coating laminating and brake lining resin formulations.
resins possess outstanding resistance to the softening action of
and high resistance to acids and alkalies.
obtained by a special heat treatment which includes decarboxylation
mixture of mono and diphenols (2.8) with an unsaturated C15 side chain
meta position thereby exhibiting high reactivity towards formaldehyde.
resin the hardening reaction includes polymerization and polyaddition
solid infusible product which in powdered form ( friction dust )
binding power at raised temperatures and is used in brake lining
dihydric phenol (1 3 dihydroxybenzene) is a very interesting
material for the production of thermosetting resins. However it is only
for special applications due to its relatively high price. The reaction
with formaldehyde is considerably higher compared with that of phenol.
of great technical importance for the preparation of cold setting
Resorcinol or resorcinol formaldehyde prepolymers can be used as
compounds for curing phenolic resins. The addition of 3 10% of such
permits shorter cure cycles in particleboard and grinding wheel
Furthermore the adhesion of textile materials e.g. tire cord to rubber
greatly improved by pretreating them with resorcinol formaldehyde resin.
otherwise be used as intermediate material for azo and triphenylmethane
other dyes pharmaceuticals cosmetics tanning agents textile treating
commercial process for the production of resorcinol is the alkali
fusion of m
benzenedisulfonic acid according to the Eq. (2.9).
intermediate stage the disodium salt of the acid is formed. It is then
with sodium hydroxide in a nickel alloy tank. The melt is dissolved in
and the resulting slurry acidified with sulfuric acid. The resorcinol
recovered by counter current extraction and purified by distillation.
with a capacity of 10 000 tons per year each are operated by Koppers
Hoechst West Germany.
used commercially at the present time is the Hock process starting with
by alkylation with propene (2.10).
oxidation is carried out with
air at about 90°C the decomposition with diluted sulfuric acid in
the common name for 2 2 bis (4 hydroxyphenyl) propane. In 1923 the
production of bisphenol A was introduced by Chemische Werke Albert in
the addition of acetone to phenol using hydrochloric acid as a
use for BPA is the production of epoxide resins (~65%) and
Sulfuric acid is used in the newer process because of problems
the volatility and corrosiveness of hydrochloric acid. Sulfur compounds
thioglycolic acid or mercaptans further increase the reaction rate of
catalyzed addition of carbonyl compounds to phenols.
of BPA made by the sulfuric acid process is satisfactory for the use in
resins high purity BPA is needed for the production of epoxy resins and
especially for polycarbonate. This is normally accomplished by
recrystallization from toluene or by crystallization as phenol BPA
the almost exclusively used carbonyl component for the synthesis of
relevant phenolic resins. Special resins can also be produced with
aldehydes for example acetaldehyde furfural or glyoxal but have not
greater technical importance. Ketones are very seldom used.
properties of aldehydes are compiled in Table4.
Formaldehyde Properties and Processing
produced by dehydrogenation of methanol over either an iron
oxide catalyst or over a silver catalyst. Because of hazards in
mixtures of pure oxygen and methanol air is used as oxidizing gas.
used to burn the developing hydrogen.
catalyst is used the reaction mixture of methanol and air is prepared
so as to
be over the upper flammability limit this is reversed when the oxide
is used. Reactor effluent passes to the absorption train where
other condensables are recovered by condensation and absorption in
recirculating formalin streams. The raw formaldehyde solution is then
by stripping out the unconverted methanol. Formaldehyde assay may be
by regulating amounts of water added to the absorber column or by
diluting in storage tanks. Inhibitors are added to retard the formation
paraformaldehyde in storage.
process works with a mixture of iron oxide and molybdenum oxide as
The reaction proceeds at relatively low temperatures between 250 400 °C
up to completion (95 98%). As a side reaction the formaldehyde produced
oxidized to yield carbon monoxide and water (2.12).
4. Physical properties of
Perstorp/Reichhold Montecatini Nissui Topsoe CdF Lummus and Hiag/ Lurgi
processes function in accordance with this method.
the BASF and Monsanto
processes a silver catalyst is used. Here in general methanol is
oxidized and dehydrogenized at 330 450 °C on silver crystals or silver
The BASF process uses a vapour/methanol/air mixture. The conversion is
considerably high at approximately 90%. Silver catalyst processes with
incomplete methanol conversion performed at 330 380 °C have been
Degussa and ICI.
process is based on the direct oxidation of methane with oxygen from
approximately 450 °C and 10 20 bar on an aluminium phosphate contact.
process however has not yet achieved any technical importance.
influence of acids hemiacetals react to form acetals by eliminating
very important reaction is the formation of HMTA from ammonia and
The overall reaction the reaction mechanism is discussed in Section. By
catalytic action of strong bases e.g. sodium hydroxide formaldehyde
disproportionation reaction known as Cannizzaro reaction yielding
formic acid according to Eq. (2.16).
solutions always contain minor quantities of formic acid due to the
reaction generally around 0.05%. The formic acid content can easily be
determined by titration with sodium hydroxide.
Prins reaction may have some importance in modification reactions of
resins with unsaturated compounds. Olefins can react with carbonyl
under non free radical conditions to result predominantly in
alcohols (2.17) m dioxanes(2.18) and 1.3 glycols (2.19).
As in the
hydroxymethylation of phenols the hydroxy methylene Carboniumion CH2 OH
formaldehyde solutions attention should be given to the fact that at
temperatures or higher concentrations paraformaldehyde may separate.
stabilization of aqueous formaldehyde solutions can be achieved with
methanol. Urea melamine methylcellulose and guanidine derivatives are
recommended for stabilization among other compounds. Proper storage
should be of stainless steel iron containers are not suitable.
plastic lining or RP containers may also be used.
formaldehyde is in the production of thermosetting resins based on
6. Breakdown of
As shown in
Table 6 approximately 55% of the total formaldehyde consumption occurs
production of thermosetting resins. Since 30 55% aqueous solutions are
used for resin production it is often the case that the consumers
own small formaldehyde plants which are supplied with methanol by a
central methanol plant. In spite of the high transportation costs for
formaldehyde solutions the relatively small capital investment will be
repayed. For this reason there are about 53 formaldehyde plants in
Europe at the present time with a total capacity of 4.3 million tons
the more reasonably priced component in phenolic resins. As an average
all fields of application about 1.6 mol formaldehyde including HMTA per
phenol are used.
formaldehyde solutions of 30 55% higher concentrated aqueous or
may be used. These solutions are produced by dissolving
water at 80 100 °C by addition of a small quantity (1%) of NaOH or
amines as depolymerization catalyst. It is also possible to concentrate
formaldehyde solutions by adding paraformaldehyde.
7. Specification of a
is a white solid low molecular polycondensation product of methylene
with the characteristic odor of formaldehyde. The degree of
ranges between 10 and 100. Types of paraformaldehyde common in the
contain approximately 1 6.5% of water. The preparation of
performed by distillation of 30 37% aqueous formaldehyde solutions.
to the conditions (temperature time pressure) different types of
paraformaldehyde are obtained. The values in Table show that
is not a defined compound.
8. Properties of
is only very seldom used for resin production because of its high price
compared with aqueous formaldehyde solutions and because of problems
with the exothermal heat evolution. Paraformaldehyde and an acid
be used to cure novolak resins. However the odor and high formaldehyde
make it unattractive. Products obtained are of poorer quality than when
hand paraformaldehyde is used almost exclusively to crosslink
prepolymers e.g. in cold setting structural wood adhesives. Lower
temperatures are adequate because of the higher reactivity of
formaldehyde evolution is greatly reduced. The reactivity of
depends on the degree of polymerization. A fairly accurate reactivity
method is the resorcinol test. This test indicates the period of time
minutes in which an alkaline resorcinol/paraformaldehyde mixture heats
60°C due to the condensation reaction.
rapid commercial growth of the phenoplasts our knowledge of their
structure and of the chemical reactions which take place during curing
meager until recently. The reaction of phenol with formaldehyde leads
formation of a number of products which are difficult to separate and
readily susceptible to resinification by heat or reagents. Consequently
study tended to be unattractive to organic chemists. The difficulty of
problem was recognized by Baeke land who wrote in 1911
It should be pointed out
that we have to deal
here with substances which are amorphous noncrystalline nonvolatile and
be purified in the usual ways. Furthermore in any of these reactions
substances are liable to be produced at the same time. These substances
form solid solutions one with another or with any excess of the
five years however very significant work has been done in the study of
chemistry of the pheno plasts.
GENERAL REACTION OF PHENOLS WITH ALDEHYDES
react with aldehydes to form condensation products if there are free
on the benzene nucleus ortho or para to the phenolic hydroxy group and
length of any of the substituents on the nucleus is not so great as to
steric hindrance. Because of its greater reactivity formaldehyde is by
most widely used aldehyde. For this reason the discussion in this
be confined to reactions with formaldehyde the use of other aldehydes
discussed in later chapter. The discussion in this chapter will also be
to the monohydric phenols that is phenols with only one hydroxy group
for each benzene
phenol with formaldehyde in the absence of any other reagents is very
catalysts are always added to accelerate the reaction. These catalysts
either acids or bases and the nature of the reaction product depends
considerably upon the type of catalyst which is used.
the addition of formaldehyde to phenol is not entirely understood.
suggested in 1894 that the formaldehyde may react in alkaline solution
methylene glycol as indicated in Equation (1) or it may undergo an
addition with subsequent rearrangement of the hemiformal as shown in
(2). The latter suggestion was also made by von Tollens and later by
the idea of the formation of a primary phenolic hemiformal and suggests
the formation of the phenol alcohols may involve tautomeric
the type indicated below
is very unstable and rearranges rapidly to the phenol alcohol because
instability the hemiformal from a phenol has never been isolated.
exact mechanism of formaldehyde addition may be the phenolic hydroxy
activates the benzene ring so that the methylol groups always enter the
in ortho and para positions to the phenolic hydroxy group. When some of
ortho and para positions are occupied the reaction of the phenol
slower when all of the ortho and para positions are unavailable no
takes place. The presence of substituents in the meta position also has
pronounced effect upon the rate of reaction with formaldehyde. Alkyl
the meta position tend to accelerate both the initial condensation and
subsequent resinification. The presence of a hydroxy group in the meta
as in resorcinol greatly increases the reactivity.
the reaction products depends upon the type of catalyst used. When
catalysts are used the primary reaction products are phenol alcohols
called resoles. When acid catalysts are used the primary reaction
apparently also phenol alcohols but these rearrange quickly under the
of the catalyst to give diphenylmethane derivatives to which the name
given by Baekeland in 1909. Because of this important difference the
structure of these two classes of phenoplasts will be discussed
formed when formaldehyde acts upon a phenol in alkaline solution.
alkali may be employed alkali metal hydroxides hydroxides of the earth
as barium or calcium ammonia or quaternary ammonium bases. There is
evidence to indicate that the products formed are not identical when
bases are used especially in those cases where the phenol has several
positions. It is almost definite that ammonia and amines when employed
catalysts enter into the condensation reaction. The nature of the
affect to some degree the position in the ring which is occupied by the
methylol group. For example Auwers states that strong alkalis favour
production of para methylol derivatives. However, not enough work has
to present any definite data on this point.
has shown that from the
condensation of phenol with formaldehyde under alkaline conditions it
possible to isolate a tetramethylol derivative of 4 4 dihydroxy
methane having the probable constitution of Formula I Seebach isolated
product melting at 145°C. by the action of more than three moles of
formaldehyde on one mole of phenol using a little magnesium oxide as a
catalyst. From o cresol the product which is obtained has the
shown in Formula II. From these observations it is concluded that the
condensation takes place in the para position. The existence of the
tetramethylol derivative implies branching of the chains at an early
already been made to the fact that the methylol group enters the ring
para to the phenolic hydroxy group. When more than one such position is
polymethylol compounds are formed. Thus from phenols with three
positions the series of methylol derivatives shown in Formulas III may
formed. In the case of the reaction of formaldehyde with phenol the
all of these alcohols has been confirmed either through isolation of
alcohol itself or of a derivative. The monophenol alcohols saligenin (o
hydroxybenzyl alcohol) and homosaligenin (p hydroxybenzyl alcohol) were
separated and identified was able to prove the presence of the two
by methylation of the phenolic hydroxy group followed by oxidation of
methylol groups to carboxyl. The formation of the trimethylol compound
definitely established by Bruson and McMullen. They condensed three
formaldehyde with phenol in the presence of a strongly basic
secondary amine. With morpholine for example a definite crystalline
at 106 107°C. was formed which had the structure shown in Formula IV.
quantity of dialcohols formed depends upon the ratio of formaldehyde to
even with equimolar ratios some quantities of polyalcohols are formed
of the great velocity of the addition reaction.
to obtain the trialcohol but derivatives may be formed such as the
compound described by Bruson. Stager attempted to isolate the
pure form but failed. As Granger states the addition of the third
formaldehyde becomes very slow as the reaction progresses although it
comparatively rapid in the earlier stages.
Curing Stages of Resoles
which the phenol alcohols condense to resins is very complex. Our
knowledge of the curing reactions will be discussed in detail later in
chapter. For convenience the curing mechanism has been divided into
phases. The three phases are
resin (resole). This
represents the initial condensation product of phenol and formaldehyde.
resin consists mainly of phenol alcohols although it is probable that
condensation has taken place to give methylene ethers methylol
diphenylmethane and perhaps methylenequinone or its polymers. Lebach
this stage resole from the Latin resina (a resinous body) and ol which
to the solubility in alkalis and pointed to the probable presence of
resin (resitol). This
represents the second stage of condensation. The resin is no longer
alkalis because the molecular weight has advanced to such a size that
alkaline salts are no longer soluble. It is partly or even completely
in organic solvents such as acetone or alcohol. Cross linkage however
proceeded very far and the resin is still softened by heat and is
hot although hard and brittle when cold. Lebach called this stage the
resin (resite). This
represents the final stage of polymerization with a large amount of
linkage. The resin is completely insoluble and infusible. Lebach called
It is important to note that
these stages of resin
formation are not clearly defined but pass gradually one into the
has been indicated above even
the A stage resin does not consist entirely of phenol alcohols but
appreciable amounts of higher condensation products. In the B stage
alcohols are still present together with much more highly condensed
appreciable amounts of partly cross linked resins. As will be explained
is probable that methylene ethers are present in this stage. There are
present even in the C stage resin from 3 to 6% of products which can be
by vigorous extraction with acetone.
Kinetics of A Stage Reaction
a great deal is known
qualitatively about the nature of the initial reaction of phenol and
there have been few quantitative measurements on the kinetics of the
Novak and Cech attempted to follow the progress of resinification by a
the refractive index viscosity and bromine value. Another empirical
represented by the work of Holmes and Megson who studied the behaviour
various phenols with a series of catalysts. In their work 0.4 gram mole
phenol was mixed with 0.6 gram mole of 40% formalin and the catalyst
immersed in boiling water. An arbitrary time the resinification time
measured from initial heating to the appearance of a permanent
I shows the resinification time in minutes for various phenols when 0.5
trimethylamine was used as a catalyst. More detailed experiments were
carried out with phenol the three cresols and m 5 xylenol the catalysts
employed were trimethylamine triethylamine pyridine and ammonia. The
curves were roughly hyperbolas of the form
1. Resinification time for
of comparing the catalytic activities of the more common bases m cresol
condensed in the presence of 0.75 g. of each base (except
0.375 g. was used). Table 2 shows the resinification times obtained.
for sodium hydroxide potassium hydroxide and lithium hydroxide when
molecular proportions lie on the same curve.
higher temperatures on the condensation of m cresol was examined by
one mole fraction (27 g.) with one mole fraction of paraformaldehyde
and 2 g. of pyridine in cyclohexanol as a solvent.
2 Relative Activity of
studied the ammonia catalyzed condensation of phenol with formaldehyde.
classified the two general types of reaction as (a) the primary
which phenol and formaldehyde react to form water soluble intermediates
oxymethylene phenol type (A stage) and (b) the secondary reaction in
these intermediates react further by condensation to give water
resinous products. The reaction was studied by measuring the rate of
disappearance of formaldehyde and the manner in which the bromine value
water soluble portion of the reaction mixture varied as the reaction
disclosed that the primary reaction is confined to the interaction of
of formaldehyde with one mole of phenol no formaldehyde reacts with any
intermediates formed. This reaction is apparently of monomolecular
the rate proportional to the concentration of free phenol. The
influence of the
catalyst is complex apparently both hydrogen ions and hydroxyl ions and
probably other ions derived from the catalyst promote the reactions. At
low ammonia concentrations the reaction order changes to one of
bimolecular type which is characterized by a reaction rate proportional
square of the formaldehyde concentration.
reaction seemed to be of monomolecular order the catalyst action was
and similar but not identical to that governing the primary reaction.
alkaline catalysts which are sufficiently active to bring about a
reaction of the same type as that induced by ammonia are unable to
secondary reaction to any extent. When the catalyst was a weak alkali
ammonia phenol did not take any part in the secondary reaction which
limited to the phenol alcohols. Nordlander reported that the
coefficient varied for the two reactions the secondary reaction rate
much more rapidly with the temperature than the primary reaction rate.
very thorough study of the kinetics of the reaction of paraformaldehyde
presence of a number of phenols using triethanolamine as a catalyst. He
determined that the addition phase of the reaction apparently followed
order rate law. Figure 1 compares the reactivities of the various
98°C. The apparent first order rate contants as taken from the slopes
straight lines are listed in Table 3. The introduction of a methyl
group in the
meta position increased the reaction rate by a factor of 2.8. The
of a methylol group as in the case of saligenin depressed the
phenol to about the same extent as a methyl group similarly placed.
indicates that the rate law as experimentally determined for a di or
trifunctional phenol apparently expresses a summation of the rates at
first second and presumably also the third molecule of formaldehyde
3. Effect of Substitution
on Reactivity of Phenols
Chemistry of Curing Reactions
As has been
previously stated very little definite information on the mechanism of
has been available until within the last few years. It was generally
that the phenol alcohols condensed with the elimination of water to
dimensional macromolecules which were cross linked by methylene
However in the case of phenols with three reactive positions the curing
reactions were so rapid and so complex that little progress had been
isolating and identifying compounds from the later stages of the
In order to
overcome these difficulties recent workers have studied the curing
phenols in which one or two of the reactive ortho or para positions are
blocked. In this way only mono or di phenol alcohols can be formed and
insoluble cross linked products in general cannot be obtained. In most
yields of crystalline products are obtained and these products can be
identified and their further reactions studied. It was through this
attack that Zinke Hultzsch von Euler and their respective associates
up our present knowledge of the curing mechanism. As a result of their
has been shown that the phenol alcohol which results from the primary
condensation of a phenol and formaldehyde in alkaline solution
complex series of reactions. The extent to which these various
place depends upon the structure of the initial phenol the temperature
the phenol alcohol is heated and the time of heating. Scheme 1 taken
gives in diagrammatic form the various reactions which a phenol alcohol
undergo on curing. Those compounds which have been isolated in pure
form are in
heavy type. These various reactions will now be discussed in more
2 when a phenol alcohol is heated some formaldehyde is split off with a
regeneration of the original phenol. The phenol then combines with the
unchanged phenol alcohol with the splitting out of water and a
diphenylmethane derivative is formed. A typical reaction of this type
for 4 hydroxy 3 5 dimethylbenzyl alcohol (Eqs. 4a and 4b). The extent
this reaction takes place depends very much upon the structure of the
3 as shown in Equation (5) indicates the formation of dihydroxydibenzyl
When a dialcohol is used as for example the dialcohol from p cresol
ethers are formed as shown in Equation (6). It is apparent that this
is in general the most important primary reaction in the curing of
substituted phenol alcohols. In many cases the dibenzyl ethers form the
single product which can be isolated from the cured reaction mass.
In the case
(2 hydroxy 5 methylbenzyl) 2 hydroxy 5 methylbenzyl alcohol Adler
only the reaction indicated in Equation (7) took place. An analogous
took place when the dialcohol was used but in this case in addition to
linear ether about 6 10% of cyclic ether was formed with the structure
formation appears to take place more slowly in the case of p methylol
derivatives than in the case of the ortho derivatives. Ether formation
retarded by an increase in the curing temperature or by the presence of
When alkalis are present the formation of methylene bridges is
favoured. Thus when
a resole from p tert butylphenol contains alkali it yields on heating a
large quantity of a crystalline product which was identified by Ziegler
cyclic compound VI. It is interesting to note that this compound is
structure to the cyclic ether shown in Formula V.
action of the alkali is to split off formaldehyde from the ether
cyclic methylene compound.
further heating particularly at temperatures higher than are needed to
ether the latter may split off formaldehyde and give a
which is identical with that obtained through reactions 1 and 2.
Reaction 4 may
be written as in Equation (8).
able to show that when phenol alcohols are heated to a certain
water is split off when the temperature is then raised to another
point formaldehyde is split off indicating the beginning of reaction 4.
temperature increase required to initiate reaction 4 over that required
reaction 3 is definite and depends upon the size and nature of the
group. Table 4 summarizes the effect for dialcohols of various para
phenols. The amount of water which is split off is very nearly one mole
every two moles of phenol alcohol (or one mole for every mole of phenol
dialcohol) which reacts. Even under the most favourable conditions
less than one mole of formaldehyde is split off for one mole of the
their best experiment Zinke and Hanus were not able to get more than
of formaldehyde split off. This is attributed either to side reactions
the tendency of formaldehyde to combine further with the
interesting to note that the presence of a free phenolic hydroxy group
required for reaction 4 to take place although a free phenolic hydroxy
not needed for the ether formation (reaction 3). This was shown by
treated the dialcohol from p cresol with p toluenesulfonyl chloride to
tosyl derivative. The latter split off water readily to form chain
this ether was stable and on further heating did not split off
Adler state that neither reaction 3 nor 4 takes place when the phenolic
group is etherified. Thus the monomethyl ether of p cresol dialcohol
unchanged after heating one hour at 160°C. although the free p cresol
resinified quickly at 130°C.
quantities of phenol aldehydes are usually found in the cured products.
has suggested that these may be formed by the thermal cracking of the
dihydroxydibenzyl ethers as shown in Equation (9). The equation also
a nuclear methylated body is formed simultaneously. The quantities of
formed are usually quite small (4%) even from the highly substituted
employed in these experiments and the yield depends upon the nature of
substituent groups on the original phenol. Ziegler have shown that very
considerable amounts of aldehyde are formed upon heating the dibenzyl
3 5 dichloro 2 hydroxybenzyl alcohol (obtained by the action of
2 4 dichlorophenol).
not favour the theory that phenol aldehydes are formed as indicated
points out that the reaction as written would require equimolar
phenol aldehyde and nuclear methylated phenol to be formed experiment
that this is not always the case. Hultzsch therefore prefers to
phenol aldehyde formation as an oxidation reduction action of
The presence of both dialdehydes and monoaldehydes in the curing
products of cyclohexylphenol
dialcohol was confirmed by Mayer through ultraviolet light absorption
In any case it is important to note that aldehyde formation plays only
part in the curing reaction this is particularly true in the case of
phenoplasts where phenols with two or three reactive positions are used.
7 the formation of methylenequinone or quinonemethide is particularly
interesting because it indicates a mechanism by which phenoplasts or at
part of the resin may be formed by polymerization rather than
Baekeland had suggested that polymerization played a part in the
phenoplasts although he offered no definite mechanism. Wohl and Mylo
in 1912 that the polymerization might proceed through the methylene
of the tautomeric form of phenol although definite proof was lacking.
also felt that polymerization played a part in the curing reaction it
interesting to note that these investigators showed that the curing
was catalyzed by treatment of the formaldehyde with ozone whereby
presumably formed. The latter would evidently be catalysts for a
reaction and would be expected to have no effect upon a condensation.
investigators have definitely identified dimers and trimers of
in the reaction products from the curing of highly substituted phenols.
monomer itself has never been identified as it is very unstable and
rapidly. The methylenequinone may be formed directly from the phenol
shown in Equation (10a) or it may be formed by loss of water from the
benzyl ether as shown in Equation (10b).
above indicate only the formation of para methylenequinone but the
compound is also formed when the methylol group is in the ortho
position as is
shown in Equation (11). Generally speaking the course of the reaction
same whether the methylol group is in the ortho or para position
the phenolic hydroxy group.
phenol alcohols it is probable that both reactions shown in Equation
place simultaneously. However the formation of the dihydroxydibenzyl
usually the predominating reaction and this compound is usually formed
temperatures (below 150°C.) it is rather stable at these temperatures
breaks up into methylenequinone at higher temperatures (about 200°C.).
monomeric form of methylenequinone is unstable and polymerizes rapidly
dimers or trimers. The dimer is colored yellow and Pummerer and
attributed to this compound the general formula of cyclic quinone ether
shown in Formula VII. The presence of the quinone nucleus accounts for
FROM HIGHER ALDEHYDES
The discussion in previous
chapter on the chemical
structure of phenoplasts has covered only condensations with
Higher aldehydes are occasionally used in the manufacture of
by far the greatest percentage of these resins is made from
are two reasons for this (1) Condensation with formaldehyde gives in
which have shorter curing times than those of higher aldehydes and (2)
formaldehyde is subject to few if any side reactions in the presence of
condensation catalysts. The latter consideration is important from the
viewpoint. The Cannizzaro reaction is the only side reaction which
to any extent in the case of formaldehyde under Ordinary conditions of
manufacture. This reaction involves the reduction of one molecule of
formaldehyde accompanied by the oxidation of a second and is normally
hydroxide and formaldehyde alone the reaction takes place slowly at
temperature but the velocity approximately triples for every rise of
temperature and is very rapid at 100ºC. The presence of appreciable
of phenols greatly retards the Cannizzaro reaction with formaldehyde
virtually no Cannizzaro reaction takes place even at refluxing
the molar ratio of phenol to alkali is greater than six to one.
most of the higher aldehydes also undergo self resinification when
strong acids or bases. The facility with which such side reactions take
limits the usefulness of the higher aldehydes in the manufacture of
condensed with phenol to form a resin by Baeyer as early as 1872. Fabinyi mixed an excess of
paraldehyde added stannic chloride slowly and formed a dark brown resin
distilled over in part under a pressure of less than 10 mm. The distillate was
crystallized from benzene
and yielded dihydroxydiphenylethane. Lunjak obtained a similar result
hydrochloric acid as catalyst. Claus dissolved two moles of phenol and
of acetaldehyde in ether and passed in hydrochloric acid gas. After removal of the ether a
dark brown resin
was left which could not be crystallized. The ultimate analysis
dihydroxydiphenylethane. Baekeland obtained a similar result. It will be noted that these
were all rather
vigorous chemical treatments.
conditions however initial condensation products may be isolated. Thus
Euler and Gie have shown that in the presence of dilute aqueous
acid at room temperature the primary condensation of acetaldehyde with
produces a carbinol (Eq. 3 a) which then adds another mole of
give the cyclic acetal benzodioxin (Eq. 3 b). When the phenol has two
reactive positions polycondensation can take place with the formation
resins. When the phenol has only one reactive position as in the case
of 2 4
dimethyl phenol treatment with warm hydrochloric acid decomposes the
to yield first an ortho vinyl phenol which rapidly dimerizes to yield
chroman derivative (Eq. 3 c).
In view of
present knowledge on novolacs it seems probable that the acid
phenol with acetaldehyde under technical conditions yields a series of
polymers in which the phenol groups are linked together by ethane
shown in Formula 1. The bridges may occur in a random manner either
or para to the phenolic
hydroxy group. The arrangement in Formula 1 is of course highly
the acid condensation of phenols with acetaldehyde are soluble and
fusible just as are the novolacs. Like the latter the acetaldehyde
resins may be converted to the insoluble resites by alkaline
formaldehyde or by heating with a source of methylene groups such as
hexamethylenetetramine. It is much more difficult to condense
phenol in the presence of an alkaline catalyst because the acetaldehyde
to undergo aldol condensations and self resinification.
Bender studied the condensation of phenol with normal butyraldehyde in
presence of hydrochloric acid. They obtained a resin which on heating
vacuum distillation gave a fairly good yield of
authors concluded that the primary reaction was the formation of 1
hydroxyphenyl n butane which
rearranged on heating according to Equation (4). When heated with
paraformaldehyde an insoluble and infusible resin was obtained from the
resinous condensation product of phenol and butyraldehyde.
studied the condensation of chloral with various phenols in the
sulfuric acid. When phenol itself was added to chloral suspended in
concentrated sulfuric acid an immediate reaction occurred and an oily
separated which rapidly changed to an opaque white solid. The latter
dissolved in alcohol and gave a colorless solution from which no
matter could be obtained. On evaporating the solvent a viscous liquid
which solidified to a colorless transparent resin. The constitution of
latter was not determined.
When a para
substituent was present on the phenol nucleus no resin was obtained.
good yield was obtained of a crystalline compound. For example p
yielded anhydro 5 nitro 2 (b b b trichloro a hydroxyethoxy) b b b
hydroxyethylbenzene. Chattaway postulated that the reaction proceeded
to the scheme of Equation (5). Harden and Reid also condensed a number
phenols with chloral in order to study the bactericidal efficiency of
Of all the
higher aldehydes which have so far been discussed furfural probably has
most commercial importance in the manufacture of phenoplasts. It had
since 1860 that furfural could be condensed with phenols to give
bodies. In 1921 Novotny covered practical details of the condensation
in U. S.
Pat 1 398 146. Trickey Miner and Brownlee studied the condensation in
came to the following conclusions
In the case
acid condensed resins
order to obtain an infusible insoluble
resin the molecular proportions preferably should be slightly in excess
mole of furfural to 1 mole of phenol.
resin obtained when an excess
of phenol is used is soluble in acetone and alcohol and is permanently
resins obtained by the use of
varying amounts of acid as a condensing agent were similar but the time
necessary to complete the reaction varied from two weeks when 0.2% of
hydrochloric acid was used (based on the weight of the total reaction
ten hours in the case of 0.6% acid.
In the case
alkaline condensed resins
order to obtain an insoluble
resin the proportions are preferably about 1.25 moles of furfural to 1
The resins formed by an excess
of phenol are solid and brittle when cold melt easily and are readily
in acetone alcohol and furfural. When heated with enough furfural to
molecular proportions up to 1.25 of furfural to 1 of phenol the resins
over to the infusible state.
condensation of furfural with phenol in dilute acid solution it is
prepare the primary product hydroxyphenyl furyl carbinol as shown by
reaction in Equation (6). The position of the carbinol group has not
established. It appears then that the behaviour of furfural in
condensations is very similar to that of formaldehyde. There are
differences between the formaldehyde and furfural condensation
phenoplasts from furfural have a dark purplish black color which
the yellow or brown color of the phenoplasts made from formaldehyde.
condensation of the phenols with furfural is initially more sluggish
formaldehyde and furfural itself has a marked tendency to polymerize
from polyhydric phenols
The discussion so far has
concentrated upon the
monohydric phenols that is phenols which have only one hydroxy group
nucleus. From the commercial point of view the monohydric phenols are
the most important since they are more readily available and less
The theoretical studies leading to our knowledge of structure have
with the monohydric phenols. monohydric phenols which have been highly
substituted in order to decrease their reactivity. The polyhydric
phenols are in
general much more reactive than the monohydric phenols since the effect
second hydroxy group is to activate the benzene ring further. This is
particularly true in the case of resorcinol where the hydroxy groups
to one another. The resonance produced by this arrangement activates
and para positions of the nucleus as a result the resorcinol resins are
condensed resorcinol and pyrogallol with various aldehydes. When the
was relatively inactive crystalline compounds could be obtained. For
and pyrogallol gave a crystalline product. With resorcinol and
formaldehyde resinous products were obtained. Caro in 1892 condensed an
of resorcinol with formaldehyde in the presence of dilute hydrochloric
product obtained was identified as tetrahydroxydiphenylmethane (Formula
product obtained in a similar manner with pyrogallol was
methylol derivatives of resorcinol by reduction of the corresponding
dicarbomethoxy aldehydes. The compound shown in Formula 2a was stable
sensitive to acids while compound b could not be prepared in a pure
always occurred as a resin. From this time on no studies were made on
structure of the resins from polyhydric phenols until von Euler and
included this type of condensation product in their work.
In the case
hydroquinone it was shown that alkaline condensation with two moles of
formaldehyde gave the dialcohol illustrated in Formula 3a while four
formaldehyde gave the tetraalcohol illustrated in Formula 3b. Both the
tetraalcohols resinified on heating.
with a weak acid the dialcohol quickly resinified to an insoluble
product to which von Euler Adler and Gie ascribe a methylene bridge
condensation of catechol with formaldehyde gave only catechol dialcohol
which the position of the methylol groups was established by von Euler
and Fagerlund according to Formula 4. The catechol dialcohol also
heating. Rosenmund and Boehm prepared the monomethylol derivative of
by reduction of the corresponding aldehyde.
the mechanism or curing of the di and tetraalcohols from hydroquinone
catechol. The dialcohol of hydroquinone apparently went through a
reactions involving ether formation methylenequinone formation and the
formation of methylene bridges. The tetraalcohol of hydroquinone was
particularly interesting. It has no free nuclear positions and hence
diphenylmethane formation cannot take place. When cured at 210°C. it
about three moles of water per mole of tetraalcohol. This indicates
quinone formation in addition to the development of ether linkages as
studied the tetraalcohol from p quinone and showed that at 180°C. it
slightly less than two moles of water indicating the formation of ether
linkages only. Methylenequinone formation could not take place because
phenolic hydroxy group was present. This experiment showed that the
groups conferred a reactivity similar to that obtained when the hydroxy
were present. However methylation of the phenolic hydroxy groups in
hydroquinone tetraalcohol gave a product which was completely stable at
the rate of gel formation in alkaline catalyzed resorcinol formaldehyde
They concluded that the ratio of aldehyde to resorcinol had a marked
upon the curing time as the ratio increased the gel time passed through
minimum and then increased. The position of the minimum gel time was
by the concentration of sodium hydroxide present. Von Euler and co
point out that the methylol derivatives of the polyhydric phenols will
infusible and insoluble resins when reacted with phenols which have
reactive positions though the latter normally give only soluble and
resins. This is because the dihydroxyphenols behave as tetrafunctional
compounds and when combined with the difunctional phenols the
supply a sufficient number of reactive positions to cause the formation
three dimensional cross linked molecules.
great reactivity resorcinol and its methylol derivatives are used
today either as such or in combination with other resins to increase
of curing of phenoplasts. The addition of from 3 to 20% of resorcinol
either decrease the time of cure required at high temperatures or will
curing at relatively low temperatures even at room temperatures.
accomplishing this have been described in British Pat. Shiskov has
chemically resistant resins for coatings may be prepared from 15 parts
phenol to 12 parts of resorcinol. In this proportion the resin hardens
and has physical properties which are only slightly inferior to those
when pure resorcinol is used.
pH and temperature under which reactions of phenols with formaldehyde
carried out have a profound influence on the character of the products
obtained. Three reaction phases have to be considered formaldehyde
phenol chain growth or prepolymer formation at temperatures <
100 °C and
finally the cross linking or hardening reaction at temperatures above
The rate of the phenol formaldehyde reaction at pH 1 to 4 is
the hydrogen ion concentration above pH 5 it is proportional to the
ion concentration indicating the change in reaction mechanism. Two
types are obtained depending on pH.
obtained by the reaction of phenol and formaldehyde in the acidic pH
general the reaction is carried out at a molar ratio of 1 mol phenol to
0.85 mol of formaldehyde. Novolaks are mostly linear condensation
linked with methylene bridges of a relatively low MW up to
approximately 2 000.
These resins are soluble and permanently fusible i.e. thermoplastic and
cured only by addition of a hardener almost exclusively formaldehyde
HMTA to insoluble and infusible products.
obtained by alkaline reaction of phenols and aldehydes whereby the
used in excess. P/F molar ratios between 1 1.0 to 1 3.0 are customary
technical resols. These are mono or polynuclear hydroxymethylphenols
are stable at room temperature and by application of heat seldom of
transformed into three dimensionally cross linked insoluble and
polymers (resits) over different intermediate stages (resitols).
limited storage stability of resols at ambient temperature must be
bridge is thermodynamically the most stable cross linkage. It is
completely cured phenolic resins. Theoretically 1.5 mol of formaldehyde
for the complete three dimensional cross linking of 1 mol of phenol
higher proportion of formaldehyde is used in technical resins. On an
all fields of application approximately 1.6 mol formaldehyde is used.
excess is necessary to meet distinct technical requirements for
efficiency or free phenol content.
condensation monomers have a functionality of 1 to 3 according to the
substitution. The functionality of the aldehydes always has the value 2.
Molecular Structure and Reactivity of Phenols
configuration in solution and crystal structure of phenol is determined
strong inclination to form hydrogen bonds. In the solid state phenol
bonded chains in the form of a threefold spiral. In solution e.g. in
containing small amounts of water trimolecular species Ph3 Ph2 H2O
2 H2O are formed.
a cyclic structure was proposed. 2 Hydroxy methylphenol forms a strong
intramolecular hydrogen bond. The tendency and extent of H bonding of
can be easily detected by NMR chemical shift or by infrared frequency
linear relation between the thermodynamic functions for H bond
pKa values exists. In Table 2 it is shown that alkyl substituted
only a little lower acidity compared to phenol. This is also confirmed
calculated electron densities listed in Table 5. The differences
and cresols are very small. More pronounced is the effect of bulky
in ortho position because of steric factors. Hydroxymethylphenols are
acids than phenol. Phenols in their electronically excited states are
acidic than the ground state molecules as deduced from spectroscopic
group is in the benzene ring plane even for 2 6 di tert butylphenol
meta substituted phenols exist as cis (a) and trans (b) isomers with
of the Table 2. Acidity of phenols at 25 °C.
group is an inductive electron withdrawing (–1) and conjugatively
releasing (+R) group. Both effects favour para substitution. Steric
also decrease the accessability of the ortho positions. In comparison
other activating groups the following order with decreasing activating
in the phenoxide ion is a very strong activating substituent stronger
than NR2 and
more ortho directing than the hydroxyl group. The calculations (Table
indicate clearly the higher electron density of the ortho position
the para position in the phenoxide ion. This differentiation is not so
in the neutral molecules. The direct experimental comparison of phenol
substitution rates with benzene to indicate the relative activating
the hydroxyl group on the benzene nucleus is impracticable because of
extremely large difference in the reaction rates in the order of 10.
phenol reaction corresponds to an electrophilic aromatic substitution
as well as in alkaline environments. It is generally assumed that this
type involves the rate determining formation of a p complex followed by
loss of a proton. The actual pathway of reaction however is much more
complicated with phenols because of solvent interactions and inter and
intramolecular hydrogen bond formation the abnormal and wide variation
/para ratio supports this.
the para position is favoured by polar solvents and acidic conditions
attack on the ortho position is favoured by nonpolar solvents alkaline
and group II metal oxide hydroxide or
In the last
years because of the fast growth of the electronic computers it has
possible to employ more sophisticated quantum theoretical calculations
not only include the p electrons but all valence electrons of large
theoretical calculations have proved to be a powerful tool in
chemistry. One of the most applied semi empirical calculations which
the 1s electron of hydrogen the 2 s 2 px 2py 2pz electrons of carbon is
CNDO/2. This method has been used by Knop for the calculation of the
structure for the ground and the excited singlet and triplet states of
following molecules (Table 3).
density distribution of the neutral molecules is not a sufficient basis
interpretation of the reported kinetic data. This applies especially to
excited states (1st singlet and triplet state). An increased
the electron density distribution is found for the corresponding ions
5). The electron density of the para position in the phenoxide ion is
remarkably higher than that of the ortho position and is therefore a
Formaldehyde Water and Formaldehyde Alcohol Equilibria
by far the most reactive carbonyl compound. In aqueous medium a very
and base catalyzed hydration reaction of formaldehyde to methylene
occurs. The equilibrium indicated in Eq. (3) far on the side of
glycol can be estimated by UV spectroscopy (n p) transition of the
group) by NMR or by polarographic methods.
is found in aqueous solutions as a low molecular condensation polymer.
also obtained by dissolving parafor maldehyde. The concentration of
non hydrated formaldehyde is very low generally less than 0.01%. The
poly methylene glycol in a 40% aqueous solution is indicated in Table 6.
glycol is present as monomer only in very dilute aqueous formaldehyde
(1 2%). The depolymerization of aqueous polyoxymethylene glycol (4) in
presence of acidic and basic catalysts is of importance for the overall
reaction rates for resol and novolak formation.
often present in the P/F reaction. Methanol is present at least in
amounts (~1%) because the formaldehyde production process starts from
In addition it can be formed from formaldehyde during storage by
disproportionation (Cannizzaro reaction). Furthermore methanol may be
because it is very efficient in stabilization of concentrated aqueous
hyde solutions. The chain termination prevents the formation of low
polymers so that precipitation or turbidity will be omitted. Alcohols
with aqueous formaldehyde in a neutral pH to form hemiformals (5).
are not formed under these conditions.
reaction between hydroxymethylphenols and methylene glycol must be
The extent of this reaction with the hydroxymethyl group (6) as well as
the phenolic hydroxyl group (7) has been studied by high resolution NMR
therefore consumed in the P/F reaction also to form hemiformals which
constitute a potential source of formaldehyde and may be detected by
titrimetric methods but is otherwise not more directly involved in the
methylation reaction. This should be a sufficient reason for the
reduction of the reaction rate at rising conversion.
Phenol Formaldehyde Reaction under Alkaline Conditions
between formaldehyde and phenol in the alkaline pH range was first
1894 by L. Lederer and O. Manasse. It is therefore occasionally also
as the Lederer Manasse reaction. At a pH above 5 bis
and tris alcohols are formed as well as
mono alcohols and other compounds. The simplest product of this
hydroxybenzylalcohol (saligenin) was already isolated from the
salicyn by hydrolysis with diluted acid.
Inorganic Catalysts and Tertiary Amines
ammonia and HMTA sodium carbonate calcium magnesium
and barium hydroxide and tertiary
amines are used as catalysts in the alkaline hydroxy methylation
aqueous solutions as used in all technical processes formaldehyde is
methylene glycol. Phenol reacts quickly with alkali hydroxide to form
phenoxide ion which is stabilized by resonance according to Eq.(10)
reaction catalyzed by alkalis C alkylation in ortho and para position
almost exclusively. Meta substitution is hardly not evident.
transition state is stabilized by proton shifting as indicated in the
and (12). This reaction mechanism was recommended for dilute solutions.
monomethylol derivative continues to react with formaldehyde forming
dimethylol and one trimethylol compounds.
the base catalyzed phenol formaldehyde reaction has been thoroughly
and is relatively well understood. In general a second order reaction
found with the exception of the ammonia catalyzed reaction which rather
to one of the first order.
It must be
pointed out however that the actual constitution of the
in the alkaline catalyzed reaction is not yet fully understood. It is
how methylene glycol would react with the phenoxide ion. The
non hydrated formaldehyde is too low to explain the reaction rates.
reaction mechanism was proposed very early by Claisen later by Walker
others. The presence of hemiformals 3.7 in aqueous phenol formaldehyde
solutions has been proven by the means of NMR.
the formation of hemiformals as intermediates followed by a shift of
hydroxymethyl group according to Eq.(15) the absence of the reaction if
phenolic group is etherified was pointed out. This statement however is
correct since the nucleophily of the phenoxide anion is the decisive
in the alkaline hydroxymethylation.
A series of
results indicates that the constitution of the transition state is
more complex than indicated in the Eq. (11). The strongest evidence is
dependence of the ortho/para substitution ratio on the type of
ortho/para ratio decreases from 1.1 at pH 8.7 to 0.38 at pH 13.0. It
recognized that the ortho substitution is considerably enhanced if
hydroxides of the first and second main group along the series.
distinct is the effect of the hydroxides of transition metals. The
substitution is the more favoured the higher the chelating strength of
cation. The directing effect of the Fe Cu Cr Ni Co Mn and Zn ions is
by Peer as formation of chelates as transient compounds according to
(16). Boric acid also has a strong ortho directing effect (17).)
high ortho novolaks if magnesium oxide or zinc oxide are used as
different activity of some of the more frequently used catalysts and
effect on MWD examined by GPC is shown in Figure 1. Identical reaction
conditions have been used for the production of the resols. The
neutralized with hydrochloric acid and the resin analyzed without
distillation. The highest degree of ortho orientation is observed when
acetate is used (Fig. 5) followed by magnesium oxide and tri ethylamine
catalysts (Fig. 1).
interpretation of the orientation and directing effects depending upon
of catalyst must be performed with care. The concentration of any
alcohol in the reaction mixture does not only depend upon the rate of
but also upon the rate of disappearance due to further reaction i.e. it
depends upon the mol ratio of phenol to formaldehyde and the reaction
order of appearance of the individual methylol phenols in the GPC
depends despite of molecular size also on the number of hydroxyl groups
of solvent interaction.
phenolic resin moulding powders
idea of adding filler to a
phenoplast resin in order to produce a combination which could be
satisfactorily originated with Baekeland and was one of his pioneer
contributions to the art. Filler is any substance either organic or
is mixed with a resin to produce a nonhomogeneous mixture which can
subsequently be molded. The filler facilitates the molding process
usually very difficult with pure resin and also improves the physical
properties of the molded article.
the proper filler for a molding powder has an importance which is
only to the selection of the phenoplast resin. The filler is of most
in controlling mechanical and strength properties of the finished
product to a lesser extent it affects the electrical qualities and heat
resistance. The resin is important because it must give the proper flow
proper bond and must also permit curing to a well finished piece in a
reasonable length of time. The exact nature of the resin is important
securing the most desirable electrical properties. This point will be
further in a later chapter.
requirements for a satisfactory filler have been classified into two
and secondary with the idea that the primary requirements are essential
satisfactory molding while some compromise is possible for certain uses
case of the secondary requirements.
classification is as follows
impact and tensile strength
in the molded piece.
specific gravity in the
wetting by resins and dyes
chemical or physical effects
on steel dies and particularly no abrasive effects.
cost and adequate supply.
or low burning
must be readily
obtainable and of uniform quality.
in the molded piece.
color which is retained at elevated
temperatures and in the presence of chemical materials used in the
of the molding powder.
to acids alkalis and
in controlled mesh
size and bulk factor.
TYPES OF FILLER
usually classified primarily according to their general chemical nature
or mineral and then are further divided into subdivisions according to
chemical composition and physical structure.
EFFECT OF FILLER ON IMPACT STRENGTH AND DAMPING
mechanical effect which is produced by different fillers is a change in
impact resistance of the molded plastic. The change in impact
results from an increase in the capacity of the molded specimen to
mechanical shock waves and thus prevent their amplification at certain
through resonance. The ability to absorb mechanical shock waves and
them into heat is known as damping. In order to obtain a high degree of
it is necessary to have a high degree of nonhomogeneity in the molded
is usually best accomplished by the use of fibrous fillers. The filler
must have very high tensile strength so that it may resist the
tensile forces which are created by the shock wave.
1936 studied the effect of damping and pointed out that the increase in
resistance of fiber filled molding compounds was connected with their
damping capacity. De Bruyne has also emphasized the importance of high
capacity in assuring freedom from vibration. On the other hand a high
capacity involves a high energy absorption in the part which is subject
vibration and the energy absorption is necessarily accompanied by the
development of heat which may of itself be destructive to the plastic.
Leaderman has studied the damping capacity by the decrement of free
oscillations using solid cylindrical specimens tested in torsion. Four
of phenoplast molding materials were employed (a) phenol formaldehyde
transparent and unfilled (b) commercial phenoplast molding material
flour filler (c) shock resisting material with a filler consisting of
snippings impregnated with phenol formaldehyde resin and (d) shock
material with a filler consisting of closely packed cords running
the axis of the specimen.
from Leader man shows the rate at which free torsional oscillations
when these four fillers were used. From these data the mean specific
capacity in torsion was computed (in per cent) and is given in Table 1.
illustrate the relation between damping capacity and impact resistance
also contains the approximate impact resistance for these various
measured by the standard A.S.T.M. test.
MICROSCOPIC STRUCTURE OF FILLERS
structure of both cellulosic and inorganic fillers has been examined.
demonstrated that the resilient fibrous fillers vary considerably in
size. In the cellulosic fillers the fibers are frequently split in many
microscopic examination showed that only 20 to 30% of the fibers were
RATIO OF RESIN TO FILLER
resin to filler has a profound effect upon the molding qualities of the
and upon the physical and chemical properties of the molded plastic.
cases in this chapter weight ratios are meant.) When cellulose fillers
employed the molding composition usually contains approximately equal
weight of resin and filler. With this proportion the best general
of molding qualities strength properties and water resistance is
less resin is employed molding becomes more difficult because the
has less flow. Some strength properties such as tensile and flexural
to drop off rather rapidly. Impact strength values usually rise to a
about 30% resin content and then decrease rapidly. However whatever
there may be to this gain in impact strength is offset by the loss in
and flexural strength. Water resistance and resistance to other
decrease as the resin content decreases because the particles of filler
thoroughly covered and protected by a film of resin. For the same
appearance of the piece is poor because the filler particles are
content is increased much above 50% when cellulosic filler is used the
tends to become more difficult because of excessive flow of the
There is not much change in tensile or flexural strength but the impact
strength decreases because the molded piece tends to become more
composition and consequently has less damping capacity.
used which contain much natural resin such as lignin extended wood
redwood flour the ratio of phenoplast resin to filler may be decreased.
natural resin present compensates for the lower quantity of phenoplast
total quantity of resin present in the combination is still
When mineral fillers such as mica or asbestos are used a higher weight
filler is usually employed about 70% filler to 30% resin. These mineral
have a higher specific gravity than the cellulosic fillers and
volume ratio of filler to resin is about the same as in the case of the
STANDARD CLASSIFICATION OF PHENOPLAST MOLDING POWDER
ACCORDING TO FILLER
several standard classifications of phenoplast molding materials in
method of classification is based upon the nature of the filler. Where
cellulosic fillers are used the impact strength of the molding also
the nature of the filler. Such classifications therefore also give an
indication of the strength of the composition. It is important to note
word strength as affected by the nature of the filler applies
impact strength and not to other strength properties such as tensile or
flexural strength. As a matter of fact in so far as phenolic filled
plastics are concerned the tensile strength is scarcely altered in
from wood flour (the weakest of the cellulosic fillers in impact
tire cord (the strongest in impact resistance) while the flexural
increased only slightly.
fillers and resins for laminates
laminated phenoplasts differ from those used in molding powders
that the fillers for laminates are continuous webs rather than discrete
particles. The chemical nature of fillers is quite similar they may be
or linen fabric sisal mat or woven asbestos. More recently woven glass
has become available for applications in which exceptionally high
required. The filler greatly increases the strength properties of the
over those of the pure resin the increase is greater than is obtained
molding powders because of the continuous web which is present. The
the same type of damping effect upon impact waves as has been described
case of molding powders.
in the form of an alcoholic impregnating solution is applied to the
Aqueous solutions however are frequently used particularly in the case
base laminates.. The impregnated sheet which may contain from 25 to 65%
(usually about 40%) is then dried and pressed between metal plates at a
temperature. In cases in which a highly polished finish is required on
surface of the laminate the surface sheets may contain a higher resin
approximately 50%. For standard flat laminates the usual pressing
ranges from 140° to 180°C. and the molding pressure is from 1000 to
Laminated phenoplast tubing may be formed by rolling the impregnated
material upon mandrels between heated pressure rolls and then either
baking or pressing in a heated mold to complete the curing of the resin.
there have been important developments in the molding of laminates into
intricate forms such as seats for airplane pilots air ducts ammunition
similar articles. There are two general methods by which such contoured
laminates may be formed (1) Layers of laminate cut to the proper size
formed in a mold under heat and pressure. The amount of draw or the
contour is usually limited since the base of the laminate will tear if
subjected to too much strain in molding. The molding pressures may vary
high range (1200 to 2000 p.s.i.) down to a low range (100 to 250
Somewhat better strength properties are obtained at the higher
the lower pressures permit the use of cheaper dies and less expensive
(2) By selection of the proper resin and careful control of the curing
during lamination it is possible to produce a flat laminate which can
and reshaped under relatively low pressures. Such a process is known as
forming. It was originally thought that the resin used in bonding the
should be under cured later work has indicated that a fully cured resin
formed just as well and the use of a well cured resin is in fact
filler is a cotton fabric with a weave chosen especially so that some
is possible in two directions. As in the case of low pressure
forming permits the production of relatively large articles with cheap
light presses. A certain amount of draw is possible when molding by
process. The maximum draw may be determined from an index (r/R) which
calculated by dividing the cup radius (r) by the blank radius (R) of
to be drawn. This index should lie between 0.67 and 0.77 for
drawing of laminated phenoplast sheets in thicknesses of from 1/32 to
CLASSIFICATION OF LAMINATES
laminated sheets and tubes are classified according to properties and
functional use which in turn are dependent upon the type of filler.
been the most important single filler used according to Hanson the
industry produces about 70 000 000 Ib. of finished stock per year.
Prior to the
war 80% of this material had paper used as a base this represented an
consumption of 28 000 000 Ib. of paper.
States the National Electrical Manufacturers Association (NEMA) has set
standard classifications for laminates made under high pressure (i.e.
2500 p.s.i.). The standard NEMA grades are listed below. These grades
include recent developments in high strength paper glass fabric and low
pressure laminates. These new materials will be described in separate
Grade X A
paper base laminated material primarily intended for mechanical
where electrical requirements are of secondary importance. Should be
discretion when high humidity conditions are encountered. Not equal to
base grades in impact strength.
Grade P A
base laminated material primarily intended for punching. More flexible
quite as strong as Grade X. Moisture resistance and electrical
intermediate between Grades X and XX
Grade XX A
base laminated material suitable for usual electrical applications.
Grade XXP A
paper base laminated material similar to Grade XX in electrical and
resisting properties but more suitable for hot punching. Intermediate
Grades P and XX in punching and cold flow characteristics.
Grade XXX A
paper base laminated material suitable for radio frequency work for
humidity applications and with minimum cold flow characteristics.
paper base laminated material similar to Grade XXX but having lower
losses and being more suitable for hot punching. This grade has greater
flow than Grade XXX and is intermediate between Grades XXP and XXX in
Grade C A
base laminated material made throughout from cotton fabric weighing
over 4 oz.
per sq. yd. and having a count as determined from inspection of the
plate of not more than 72 threads per in. in the filler direction nor
140 threads per in. total in both warp and filler directions. A strong
material suitable for gears and other structural forms exposed to high
The heavier the fabric base used the higher will be the impact strength
rougher the machined edge consequently there may be several subgrades
class adapted for various sizes of gears and types of mechanical
Should not be used for electrical applications except for low voltages.
Grade CE A
fabric base laminated material of the same fabric weight and thread
Grade C. For electrical applications requiring greater toughness than
Grade XX or
mechanical applications requiring greater resistance to moisture than
Exceptionally good in moisture resistance.
Grade L A
weave fabric base laminated material made throughout from cotton fabric
weighing 4 oz. or less per sq. yd. As determined by inspection of the
plate the minimum thread count per inch in any ply shall be 72 in the
direction and 140 total in both warp and filler directions. For purpose
identification the surface sheets shall have a minimum thread count of
threads per in. in each of the warp and filler directions. Not quite as
as Grade C. Should not be used for electrical application except for
Grade LE A
weave fabric base laminated material of the same fabric weight and
as Grade L. For electrical applications requiring greater toughness
XX. Better machining properties and finer appearance than Grade CE also
in thinner sizes. Exceptionally good in moisture resistance.
Grade A An
asbestos paper base laminated material. More resistant to flame and
more resistant to heat than other laminated grades because of high
content. Suitable for only low voltage applications. Minimum
changes when exposed to moisture.
Grade AA An
asbestos fabric base laminated material. Similar
to Grade A but stronger and tougher.
Minimum dimensional changes when exposed to moisture.
Phenolic Tubes (NEMA
types of tubes rolled and molded. The rolled are oven baked after
mandrels while the molded are cured in molds under pressure. The rolled
are less dense and generally less resistant to moisture than molded
are of uniform strength around the circumference whereas molded tubes
seams which are sources of weakness both mechanically and electrically
in thin walled tubes. Each type has its own particular applications and
X Rolled A
mechanical strength paper base tubing with good punching and fair
qualities. Low power factor and high dielectric strength under dry
XX Rolled A
paper base tubing with good machining punching and threading qualities.
strong mechanically as X Rotted but better moisture resistance. Best
low dielectric losses particularly on exposure to high humidity.
in moisture resistance and machining qualities than X Rolled. Strongest
base except in thin walls. Dielectric strength may be low at molded
paper base grade from moisture resisting standpoint. Good machining and
electrical properties except in very thin wall forms.
C Rolled A
fabric base tubing made from a cotton fabric weighing more than 4 oz.
yd. As determined by inspection of the laminated tube the thread count
not be more than 72 threads per in. in the filler direction. The total
count per inch in both warp and filler direction shall not exceed 140.
tubing is intended primarily for mechanical purposes. Dielectric
relatively low and moisture absorption greater than for other fabric
CE Molded A
fabric base tubing made of same fabric weight and thread count as Grade
Rolled. For use when a tough dense fabric base material is required
electrical properties along with excellent mechanical properties and
resistance to moisture. Dielectric strength may be low at molded seams
in thin walls.
from a fine weave cotton fabric weighing 4 oz. or less per sq. yd. As
determined by inspection of the laminated tube the minimum thread count
inch shall be 72 in the filler direction and 140 total in both warp and
directions. Best concentricity and dielectric strength of any fabric
grade. For use when the seams from a molded tube may be objectionable
the application requires good machining qualities together with good
and mechanical properties.
from a fine weave cotton fabric of the same weight and thread count as
Rolled. Has high density and good moisture resistance. For mechanical
applications primarily when finer machined appearance than with CE
desired or when tougher material than LE Molded is required. Should not
for electrical applications except for low voltage.
from a fine weave cotton fabric of the same weight and thread count as
Molded. Has excellent machining and moisture resisting characteristics.
in electrical applications even under humid conditions when a tougher
than Grade XX tubing is required at some sacrifice of electrical
Dielectric strength may be low at molded seams especially in thin wall
Grade LE Molded is better electrically than Grade CE Molded but not
Strength Paper Laminates
a new type of paper base for phenoplast laminates has been developed
higher tensile strength properties than the usual paper bases. This
filler is not included in the NEMA specifications. This new base was
principally developed because of the need for paper laminates of
strength characteristics in the construction of component parts for
when molded at low pressure ranges (i.e. 50 to 200 p.s.i.). The paper
from Mitscherlich spruce sulfite pulp because with a minimum of
treatment it gives a sheet of paper with exceptionally high tensile
The fibers are laid on the paper machine so that they are largely
the direction of the machine. A thin sheet gives the best results and
weight of the paper is generally held to 35 lb. per ream. For best
gauge of the paper must be uniform in all directions. Although spruce
for the purpose a number of other softwoods yield pulps of about the
characteristics. In place of Mitscherlich pulp that from the Kraft
be used satisfactorily provided the papermaking conditions are altered
When such a
paper is used as a laminate and the plies are all oriented in the same
direction an ultimate tensile strength as high as 35 000 p.s.i. in the
direction of the fibers may be obtained. The strength in the opposite
however is rather low. The paper is usually used by laying the plies in
alternate directions so that the strength properties are substantially
in any direction.
Bonded Cotton Fiber
to prepare a laminate by using as filler cotton fibers which have all
in a parallel direction. The laminate then develops very high tensile
(up to 35 000 to 40 000 p.s.i.) in the direction of the fiber although
strength properties across the fiber are low. Such laminates have been
described by Goldman.
fabric has recently become available as filler for laminates and this
filler is also not included in the NEMA specifications. The grade most
used has the glass fibers running in one direction and is woven
together by a
fine cotton fiber. To obtain equal strength properties in both
laminates are cross banded that
alternate layers of fabric are oriented at an angle of 90° to each
this filler it is possible to obtain an ultimate tensile strength in
neighborhood of 30 000 p.s.i. at room temperature. The high strength is
extent offset by the relatively high specific gravity of the laminate
compared with 1.34 for a paper laminate with comparable resin content.
impact strength of the laminated glass fabric is particularly high the
Izod value at room temperature is 22 ft. lb. per inch of notch as
compared to 1
ft. lb. per inch of notch for the usual paper laminate.
RESINS USED FOR LAMINATES
resins used in laminates are very similar to those used for molding
Where exceptionally good electrical properties are required cresylic
frequently used as the base instead of phenol or some special type of
is added to the phenolic resin. The proportion of resin to filler is
lower than in the case of molding powders it may be as low as 25% based
weight of the finished laminate and usually averages about 40%. Less
be used because less flow is required in the molding operation there are no sharp corners
in the mold to be
filled out by flow of the resin and filler. The effect of the quantity
on physical properties is further discussed in the chapter on the
properties of laminated phenoplasts.
impregnation obtained in paper filler varies markedly with the
complexity of the resin as the molecualr size is reduced an improvement
impregnation is observed. There is considerable difference between the
inpregnation achieved by a low molecular weight resin dissolved in
water and a
more highly condensed resin which must be dissolved in a solvent such
alcohol. The more highly condensed resin does not penetrate the fibers
same extent as the water soluble resin.
In order to judge the risks
connected with the
handling of phenolic resins a clear distinction must be made between
resin prepolymers and cured phenolic resins. Apart from constitutional
characteristics the MW is of great importance regarding the
effects. The physiological activity of phenolic
depends upon the
content of free phenol and formaldehyde. Cured phenolic resins are
harmless. The FDA permits articles molded from phenolic resins to come
contact with food.
Toxicology of Phenols
phenols are protein degenerating and highly toxic. The oral LD50 value
is 530 mg/kg. Human skin which has come in contact with phenol first
white subsequently red and wrinkled a strong burning sensation is
perceived. Longer contact destroys the skin tissue. Solid and liquid
are absorbed by the skin very quickly and cause very severe damage.
with large amounts leads to death through paralysis of the central
system. Minor intoxications lead mostly to damage of the kidneys liver
pancreas. If phenol is inhaled or swallowed local cauterizing occurs
headaches dizziness vomiting irregular breathing respiratory arrest and
failure are the results.
effect of phenol on the human skin is reduced by introduction of
groups (methyl higher alkyl or chloro groups). The neutral molecules
more active than the corresponding ions. The biological activity of
the result of their ability to alter biological structures i.e.
bacterial cell walls. The disruptive effect on cytoplasmic membranes
and cell walls
develops it is believed by the creation of pores large enough to permit
cytochromes to diffuse out. Cresols are similar to phenol in their
less severe in their effects. Chlorophenols are not used for resin
activity of alkyl phenols leads to their concentration on the cell
does not explain the destructive effect to the cells. The bacterial and
anthelmintic action of phenols is also influenced by soaps which are
used to solubilize phenols in water for use as disinfectants.
Toxicology of Formaldehyde
an aqueous solution is a protoplasm poison with a cauterizing and
degenerating effect. The use of aqueous formaldehyde to preserve
biological preparations is well known. Formaldehyde is believed to
bacteria by reacting with the amino groups of proteins which are
changed in nature and action. Formaldehyde in the organism is quickly
to formic acid which is partly separated by the urine.
the form of gas or aerosol the
both is comparable is very irritating to the mucous membranes. The
smell is noticeable even at concentrations below 1 ppm. The MAK value
is 1 ppm.
Formaldehyde is a dangerous material to work with and has received the
rating as phenol.
of formaldehyde up to 10 ppm cause conjunctivitis within a few minutes
as rhenitis with anosmia and pharyngitis. It can be observed that one
used to formaldehyde to a certain extent. At 10 15 ppm dispnoe cough
environmental policies of progressive industrial nations require not
return of used media to the environment in a treated condition but aim
with these media without causing damages or injuries i.e. new
processes must be developed which prevent contamination of the
the first place. An example is the legislation against environmental
contamination in West Germany. Aims and instruments of environmental
are set forth in the Bundesimmission sschutzgesetz . The Technische
zur Reinerhaltung der Luft (Technical Instructions on Clean Air
describes the minimum requirements for plants and their operation and a
limiting values for emissions and immissions. According to these
organic compounds of Class I phenol and formaldehyde amongst others
this class must not exceed a mass concentration of 20 mg/m3 at a mass
0.1 kg/h and more. In order to protect the waterways from contamination
1976 was passed. The
law called Wasserabgabengesetz
1976 includes a scale of fees determined by the quantity of waste water
and the amount of injurious substances (according to the COD and BOD)
water and deposits as well.
levels of phenols in waste water have been established in USA by the
Environmental Protection Agency (EPA) in the Federal Register. These
generally establish phenol levels of 0.1 mg/1 for the Best Practical
Technology Currently Available (BPCTCA) for 1977 and 0.02 mg/1 for the
Available Control Technology Economically Achievable (BACTEA) for 1983.
low concentrations of phenols below 10.000 mg/1 water are fatal for
kinds of fish after 1 3 days. Lower concentrations are at least
deteriorate the taste of the fish flesh considerably so that it is
human consumption. Phenols in chlorinated water lead to the formation
chlorophenols which will impart objectionable taste and odor to water
quantities below 0.01 mg/1.
West Germany the following requirements must be met when waste water is
to flow into the local waters content of free phenols maximum 0.5 mg/1
maximum 30 °C pH 6.5 8.0. Furthermore the total quantity of waste water
to flow in within 24 hours is limited to 75 m.
1 Phenols in Water Threshold
Odour and Taste Concentration and Acute Fish Toxicity
circumstances waste water may be allowed to flow into the municipal
water treatment plants together with the household sewage. In any case
municipal requirements have to be adhered to. In general the waste
be as follows temperature maximum 30 35 °C pH 6.0 9.0 content of
phenol prepolymers maximum 100 mg/1. In addition the composition of the
water must be such that neither the biological processes nor the plant
operation are affected.
solid phenolic waste is also regulated by the federal legislation.
materials containing injurious substances are to be disposed off only
official disposal places. Flammable waste materials are preferably
within the plant in appropriate incinerators. Used phenolic resin
can be disposed off at official disposal places without problems.
results of the behaviour of foundry waste sand at disposal places show
phenol quantities which may be eluted of cured resin bonded sands are
lower than amounts found for household waste under similar
uber gefahrliche Arbeitsstoffe covering the handling of injurious
materials 1975 contains requirements for the rating packing marking and
of dangerous working materials. Dangerous or injurious materials in the
of this regulation are basic and auxiliary materials and their
(blends mixtures and solutions) if they are explosive flammable toxic
to the health caustic or irritating. To indicate these properties
warning symbols are to be put on packaging and containers. The scope of
list is in accordance with the requirements of the European Community
including their alterations and supplements of May 21 1973 as well as
rules and regulations for solvents. Phenols and phenolic resins
solvents methanol propanol toluene and some others which are used to
resinous solutions are also governed by these regulations.
resins containing more than 5% free phenol must be designated poisonous
skull. Phenolic resins containing 1 5% free phenol are considered
to the health and are to be marked with a St. Andrew s cross
Formulations are not considered toxic if the amount of free phenol is
0.2%. The label on the packaging or containers must also show the name
producer and the kind of toxic components and must include warnings of
special dangers involved and safety measurements to be taken.
handling of phenolic resins sensitive persons may succumb to
diseases. To prevent such reaction it is advisable to treat the hands
other parts of the body which might be exposed to phenolic resins with
appropriate protective cream and to wear rubber or plastic gloves
After work hands and arms are to be washed with a special soap and
treated with protective cream.
attention should be given to clean working conditions and effective
in the working rooms. The MAK value (maximum concentration at place of
5 ppm for phenol and 1 ppm for formaldehyde.
Waste Water and Exhaust Air Treatment Processes
universal solutions for waste problems for plants working with phenol
phenolic resins. The choice of the optimum process requires an
analysis of the kind and amount of injurious substances as well as the
structure of the plant and laboratory performance tests. Occasionally a
combination of different processes may be feasible. Such processes are
microbial degradation thermal combustion physical and physico chemical
scrubbing chemical oxidation or resinification reactions and adsorption
Microbial Transformation and Degradation
aromatic compounds is an important step in the natural carbon cycle and
microorganisms eubacteriales pseudomonas actinomyceatas endomicetas
funghi are capable of breaking down aromatic substrates. The essential
required for biological degradation is the conversion of the aromatic
to an ortho or para dihydroxybenzene structure. The enzymes responsible
this hydroxylation have the character of mixed function oxidases or
dioxygenases. The first steps of the three possible oxidative cleavage
reactions of o and p dihydroxy compounds are shown in the formulae
the case of 1 2 dihydroxybenzene ortho or meta cleavage (1 2) may
occur. Ortho and
para hydroxybenzoic acids (3 5) may be formed as intermediates during
degradation of phenolic resin prepolymers.
mono and dicarboxylic acids formed are further converted to 3
acid which is taken up in the Krebs cycle or to fumarate pyruvate
and acetoacetate. After this the degradation to CO2
Certain kinds of
microorganisms are able to live and
cause degradation in water containing up to 1 000 mg/1 of phenol. They
active at temperatures between 25 35 °C. Further essential
prerequisites are a
sufficient content of nutritive substances (N P) and oxygen pH between
and the absence of heavy metal ions (5 mg/1). In order to provide the
substances it is advantageous to treat the waste water together with
sewage. Ammonium phosphate is most frequently used as a nutritive
effectiveness of the biomass increases with time up to a limiting value
biological selection processes take place and the resistance and
ability of some kinds of micro organisms increase. The basin must have
effective aerating and circulating system so that dissolved oxygen is
available in excess. The Unox process uses oxygen instead of air in
reach a higher oxygen level.
degradation is the most used and most effective process for treating
waters containing phenol. Final effluents in the range of 0.1 mg/1 are
reported. In order to ensure that feed and environmental conditions for
biomass are constant properly designed equalization systems are
optimum efficiency. Particular problems arise if plants are operated
discontinuously or 5 days a week.
Chemical Oxidation and Resinification Reactions
oxidation processes phenols are normally destroyed to form intermediate
toxic compounds (not CO2 and H2O)
and so only a certain
decrease in COD will result. The removal of phenol may reach final
less than 1 mg/1 or > 99% according to the ratio of chemicals
peroxide in the presence
of small amounts of iron manganese chromium
and copper salts is an effective
oxidizer of phenols (and other organics). The temperature has little
reaction rate and conversion a pH in the range of 3 5 is most
Hydrogen peroxide may be used to treat concentrated wastes high in
for pretreating of high phenol waste before biological treatment to
uniform phenol levels.
Ozone is a
effective oxidant than hydrogen peroxide. Lower amounts are normally
necessary for complete destruction to carbon dioxide and water. The
of ozone is low operating at pH values of 11.5 11.8 appears to result
preferential oxidation of phenol. Ozone is often used in the final
step leading to very low phenol levels (lower than 0.1 ppm).
hypochlorite or chlorine dioxide which is the oxidizing agent will
phenols to benzoquinones (pH 7 8). At pH above 10 further oxidation to
acid and oxalic acid will occur chlorophenols are not formed. Chlorine
used because of the formation of chlorophenols which are more toxic and
more objectionable taste and odor than the original phenols. Potassium
permanganate or potassium dichromates are also effective oxidants
handling of the precipitated sludge can be a serious problem.
reactions followed by precipitation of the polymeric material can be
waste waters which contain phenol phenol prepolymers and formaldehyde
sulfuric acid or ammonia and reacting at higher temperature. Ferric
aluminium sulfate are recommended as precipitants. The deposits are
most cases. It is customary in the plywood particle board and fiber
industries to acidify the waste waters with aluminium sulfate up to pH
this method the resinous components precipitate almost completely as a
settles well and is filterable especially if the precipitation occurs
elevated temperatures. Afterwards the water must be neutralized with
lime (pH 6.5 8.0) and the calcium sulfate which is formed filtered.
Thermal and Catalytic Incineration
exhaust air by oxidation thermal or catalytic incineration is taken
consideration if the recovery of the solvents is not feasible or
The organic components are oxidized to CO2 CO
and water. The
catalytic incineration occurs at temperatures between 350 400 °C. Metal
however elements of the platinum group on different supports are used
catalysts. Catalysts are very sensitive. Sulfur phosphorus
halogen silicon arsenic
compounds and many others lead to
then catalytic incineration is only preferred if the exhaust air
minor concentrations of organic substances (