This is a single book with Color Photographs which has information related to extraction of dyestuffs from 19 common flowers, weeds, bark or leaves and its application on cotton silk and wool fabrics for textile industry.
The book describes the step wise methodology of extraction, mordanting and dyeing with photos of the actual plants part used for extraction of Natural dye. Shade cards have been incorporated so that the full gamut of colors can be visualized from each dyestuff.
The Author Dr Padma S Vankar, works as Principal Research Scientist, in Facility for Ecological and Analytical Testing (FEAT) at Indian Institute of Technology, Kanpur. She has been engaged in the screening and characterization of newer natural dyes for the past 10 years. She also works in the area of designing synthetic strategies for Eco friendly dyes using microwave heating system. Using innovative technology for natural dyeing has been her main emphasis. The author has conducted several workshops throughout India in order to popularize natural dyeing.
This book is an output of the research on Newer Sources of Natural dyes for Industrial application through the funding received from Ministry of Textiles (MOT) in the year 1999-2000, Department of Science and Technology (DST) for 2003-2006 and from Khadi and Village Industries (KVIC), 2003-2006. Newer plants have been screened, collected, tested them for the type of the color derived from shoot, leaves, bark, flowers or fruits. Isolation of colorants, their spectral analyses and structure elucidation has been one major aspect of the study.
The dye –yielding plants have been listed by their local names and botanical names- giving details of species and genus. Plants have been identified on the basis of their high dye content so that they are economically viable for industrial purpose. With the availability of standardized procedure for utilizing locally available plants/tree products to extract dyes this would help in promoting better and perhaps cheaper use of natural dyes. More than 50 plants were screened from which 25 dye- yielding plants have been enlisted for use as they have yielded consistent results having acceptable fastness properties. The dye extract and dyed fabrics have also been tested for ecofriendliness mainly analyzing heavy metals, residual pesticides, banned amines and formaldehyde.
Dye-ability with these newer sources has been the other aspect of the study. The standardization process for 25 dyes has been documented. This includes method of extraction, application of newer natural dyes in textile dyeing, mordanting methodology, fastness properties and ecofriendliness of these natural dyes have been evaluated and documented. Color measurements –L,a,b values have been assessed. Shade cards have been developed for each dye plant to show the range of colors. Main emphasis has been on usage of forest bio-waste- such as teak leaves, eucalyptus bark and flowering plants.
HISTORY OF NATURAL DYES
Color is one of the elements of
nature that made the human living more aesthetic and fascinating in the world.
They are supposed to be associated with emotions, human qualities, seasons,
festivals and passion in our life. In the past, at dawn of the civilization, the
people tried to ornament their surroundings similar to that of natural colors
observed in the plant, soil, sky and other sources. This gave birth to a new
science of colors from natural origin.
The
art of dyeing was as old as human civilization. From the historical records, it
is learnt that natural colorants were available to people during Greco-Roman
periods. Our Vedas, the Atharveda carries description of natural dyes. The use
of natural dyeing materials is evident with the wall paintings of Ajanta, Ellora
and Sithannvasal and they still demonstrate the efficacy of dyeing craft that
had been inherited from ancient times in India. Ancient Egyptian hieroglyphs
contain a thorough description of the extraction of natural dyes and their
application in dyeing. Further developments extending over many thousands of
years led to rather complicated dyeing process and high quality dyeing.
Natural
dyes have been used since ancient times for coloring and printing fabrics. Until
the middle of last century, most of the dyes were derived from plants or animal
sources by long and elaborate processes. Among these Indigo, Tyrian purple,
Alizarin, Cochineal and Logwood dyes deserve special mention.
Natural
dyes comprise those colorants (dye and pigments) that are obtained from animal
and vegetable matter without chemical processing. Natural dyes fall into three
categories on the basis of their origin:
- Plant/ vegetable Origin
- Insect/ animal Origin
- Mineral Origin
Plant/
vegetable Origin: Colorants derived from root, leaf,
bark, trunk, fruit and flowers of plants. In our country 500 plant species,
which have been identified as useful sources of dyes. Unfortunately most
available publications refer to less than 200 species. Some of the examples of
dye sources are turmeric, mango leaves, mesta calyx, gulmohar, poplar bark and
ratanjot.
Insect/
Animal Origin: Natural substances such as carminic
acid, kermesic acid and laccaic (popularly known as lac dye) obtained from
either exudation or dried bodies of insects namely, cochineal, kermes and kerria
lacca (kerr) respectively are well known and these acid compounds are used for
dyeing purpose from ancient times. These acid compounds particularly carminic
and laccaic acids find limited use for coloring food materials/ products and
cosmetics. Some of the examples of animal dye sources include the urine of cow,
the camel dung, Shellfish and Molluses.
Mineral
Dyes:
The most commonly referred to and used mineral is ‘Geru’ (Redchre) known for
its characteristic shade. Oxides of iron, tin and antimony have been used along
with vegetable or insect dye to obtain the desired shades on fabrics, salt like
copper and iron sulphate are used as auxiliaries in the dyeing/ printing of
fabrics as mordants which not only helps in dye molecule’s adherence but also
gives a gamut of colors with a dye.
Until
the middle of Nineteenth century all the textiles were, if necessary, dyed/
printed with the use of natural products. Naturally, various recipes/ procedures
were in practice in different parts of the country depending upon the
availability of local special vegetable products and stage of local
standardization/ skill achieved by local craftsmen.
Nature
manifests itself in a wide spectrum of rainbow colors. Man-fascinated by her
glory, strove towards harmonizing with her completely. He internalized color by
responding to its vibrations emotionally and externally he drew from her vast
storehouse, to initially paint himself and then to dye the apparel he wore. Thus
started the alchemy of color, and India was forerunner in the art of natural
dyeing-an art perfect during the era of the great Epics.
In the epic period there are frequent references to “PITAMBAR” a
yellow garment used by the gods. Atharveda carries description of natural dyes.
Bhrigu Samhita is written using natural dyes. The references of Ajanta dating as
far back as 1st century A.D. are painted with natural dyes. The later frescoes
evidence the use of colorful garments by men and women alike. Polmey’s
descriptions carry reference to the multicolored flags that fluttered in the
capital.
The
evidence of use of natural dyes during Pre-Muslim and muslim period of Indian
history is much better persevered in the form of dresses, manuscripts and
printings. Some of the records of the court historians (biographers like Firdusi)
are written and illustrated with natural dyes. The palace decoration and the
ceiling of the temples of Hallebid and Bellur (in Karnataka) widely testify to
the mastery of the India craftsman in the use of natural dyes. The colored
exquisite silk and muslin fabrics of India have been found belonging to the
period of 16th and 17th centuries. Thus use of natural dyes is an old age
history since ancient periods. A fragment of coarse madder dyed cotton fabric in
a plain weave, found during the excavation of the ancient Happan sites,
indicates that even the peoples of Mohanjodaro (c. 3000 B.C.) used natural dyes.
Several historical examples found during excavation show, that natural dyes are
used since ancient time.
According
to ‘Mira Roy’ the tinctorical properties of vegetable substances recognized
in the Vedic Period, particularly in Atharvavedic and the succeeding periods
(100 B.C. to 500 B.C.) were Kala or Asikin (possibly indicating Indigo),
safflower, madder and turmeric [Teli et al., 1994].
The
period from the classical age (A.D. 300-700) up to the medieval period (in
Indian history) acknowledges the tinctorial capacity of number of vegetable
substances as well as of metal salts and minerals. The most prized red dyes of
this period were kampillaka (Mallotus Philippinensis), pattanga (Caesaplinia/
Sappan) and jatuka (a species of oldenlandia). In addition of these, some black
dyes came to be known. These were derived from plant substances, like abhaya (Terminala
chebula), amalaka (Emblic myrobalan), nila (Indigofera tinctoria), ayas (Iron),
kesesa (sulphate of iron), turrha (sulphate of copper) and anjana (sulphate of
antimony). Apart from these sakala (a kind of black dye prepared from cow dung)
was also used for this purpose.
The
medieval period (from A.D. 900 onwards) was marked by the discovery of the color
fixation property of tuvari (alum) and processes employed for the extraction of
the coloring principles from the dyestuff. The late medieval period (18th
century A.D.) introduced the application of iron mordant for the fixation of
colors like blue, green and violet and aluminum mordant for the fixation of red
dyestuff.
Hamida
Khatoon Naqvi provides an account of some of the processes employed in dyeing
and printing of cotton fabrics in Mughal India (A.D. 1550-1800). Chakunda
(Cassia tora) was found to be a cheaper substitute for indigo and was fixed by
adding limewater. According to her most of the years, she prepared her own
decoctions. A list of a table from a translated version of 32 selected process
of dyeing and makes an interesting observation about the use of Indigo. She also
gets success in order to get effective alternatives of various costlier
substances. It is observed that it is during the shades of number of colors in
delicate tones come into the field of dyeing and printing with natural dyes.
These were derived from flowers and fruits and added to the basic ranges of
colors consisting of blue (indigo), red (manjistha), black (kalaka), yellow (haidra)
etc.
The
Beauliew manuscripts (C 1734) according to Schwariz provide a brief account of
dyeing for black, red and blue by mordants. Chayroot and indigo were used in
India for cotton painting, obviously to kalamkari work in the coastal region in
the eighteen-century. Machilipatnam, Sri Kalahastiand Tanjavur was some of the
important places for kalamkari work in the eighteen century.
The
manuscript of George Roque’s according to Schwariz the cotton printing centers
of western India in the late seventeenth century [A.D. indicates the use of
roots of saranguy or Al (Morinda citrifolia or Morinda tinctorium)] for dyeing a
beautiful red. In many parts of India the Al root were as cheap substitute for
madder.
Bibhutibhusan
Bandyopadhya’s novel Ichhmati written in Bengali gives a clear existence of
indigo house, organized by the East India Company in the Bengal of that time for
the forcible cultivation of Indigo by farmers for export with the help of local
strong men. There were about seventeen indigo houses mainly in Jessore and Nadia
districts. Their officers marked land owned by farmers especially for the
cultivation of Indigo for export. These seventeen Neel Kuthis (indigo houses),
which were closed down gradually with the appearance of synthetic indigo from
Germany at very cheap rate in the year 1864.
A
collection of 168 specimens of fabrics dyed by indigenous processes were kept in
the Bengal Economic Museum, Calcutta; duplicates of some of the specimens formed
the collection of 108 samples of fabrics dyed with Bengal dyes forwarded by Mr.
Locke to the Secretary of State for India in 1878. These were probably
transferred to the industrial section library of the India Museum, Calcutta.
There is a set of 15 volumes under the name “Specimens of Fabrics dyed with
India dyes by Thos. Wardle”. Many of these colors are not permanent and the
color has faded beyond recognition. Still some of these specimens are good,
while some of the specimens are missing.
With
the influx of synthetic dyes for most of the traditional colors including blue
in the nineteenth century A.D., the use of natural dyes has gradually gone out
of existence from most parts of the country. However, in a few places natural
dyes continued to be used and in some places synthetic dyes are used in the old
process, particularly indigo and alizarin. Some of these places, where natural
dyes continued to be extracted or used in some form or other are Andhra Pradesh
[Devi, 2001], Cuddapah, Uravakonda, Machilipatnam, Sri Kalahasti, Sikkinaikenpet
(Tanjavur district), Balarampuram, Iika, Guleguw, Banhati, Dhanmanka, Ahmedabad,
Begru (Rajasthan) Sangarer, Bharivgarh, Berhampur (Orissa), Kptapad (Orissa),
Imphal, Kadampapi (Manipur) Khensa and Akoya (Nagaland), Darjeeling (Tibtan
refugees), Gangtok and many north eastern hill areas, for small commercial as
well as domestic purpose. There are also many other small places where natural
dye is still used in small scale and in some of the above-mentioned places the
use might have been discontinued in recent years.
A
painting work which is done in different places of India with vegetable colors
is known as kalamkari [Udayini and Jacob, 1988] which is continued still, using
natural dyes till recently, through the efforts of Shri Radha Krishan Naidu.
Natural dyeing processes were reportedly being followed in Balarampuram and
other places in Kerala, and in the parts of Tamil Nadu adjoining Kerala.
In
Padamanabhapuram, 55 kms. from Trivendrum on the way to Kanya Kumari, the
painting on the walls of the Palace there, reported to be in vegetable colors,
indicate that vegetable colors were in use there in the 18th and 19th centuries
A.D. At Dhamadka in Gujarat, dyeing with an inferior type of natural indigo was
no longer practiced.
In
recent years, few enthusiastic people keen on exporting textiles and garments
are endeavoring to revive the processes of natural dyeing particularly because
of the interest shown, in export markets, in the sophisticated fabric in which
natural dyes are used. At a time when natural dyeing process are gradually being
discarded, even in few places where they have been kept alive for so long, and
when it seems clear that this knowledge will also be lost to the country in
course of time, the endeavor of these few people to revive the processes
commercially is praise worthy.
Almost
all the synthetic dyes have their origin from coal tar; many synthetic dyes may
lead to various harmful by-products during their manufacture. A number of azo
dyes, which release carcinogenic harmful amines, have already been banned by
most of the countries [Premi, 1996]. However, the effluent discharged from
dyeing units is also causing lot of concern. Hence, there is an increasing
realization in the textiles industry as well as among the textile consumers to
develop and demand eco-friendly methods of dyeing textiles. Natural dyes offer
an important alternative in these regards, as these are safer in use with
minimum health hazards, have easy disposability, are biodegradable, and can be
used to make compost for agricultural purposes after the had been extracted.
There is a long-time tradition of using natural plant-based dyes in India. The
scientific names of many of these dye-yielding plants lie scattered in classical
references such as Hooker [1876-1897], Watt [1896 and 1908] and a more modern
version of these published in the eleven-volume “Wealth of India”
(1948-1976). Among the more concise references to these plants, mention may be
made of the works of Dastur [1951], Sundararaj and Balasubramanyam [1959],
Maheshwari and Singh [1965] and Santapau and Henry [1973].
A
list of dye yielding plants of India given by Perkin and Everest [1918] was
reproduced Gulati (1949) who also gave corresponding common Indian names for
easy identification of the plants.
In
the excellently produced treatise, Natural Dyeing Processes of India” has
given in the appendices the list taken from Liotard (1881) and also that from
Perkin and Everest [1918]. Mohanty et al. [1987] have also compiled from
available literature on alphabetical list of botanical names in regional
languages, together with a number of illustrations of plants used as dyes and/
or auxiliaries in India.
PROMOTION OF NATURAL DYES
Office
of the Development Commissioner for Handlooms, Ministry of textiles (Govt. of
India), with the help of its branch offices like Weavers Service Center, Indian
Institute of Handloom Technology (IIHTs) and National Handloom Development
Corporation (N.H.D.C.) have been doing a lot, since last few years. But in
recent years serious efforts have been made so as to boost the use of natural
dyes by implementing projects, researches and seminars. It was also felt in
seminars that the extracts of vegetable dyes should be chemically analyzed and
trails shall be made to standardize them after extracting the dyes in the
solution form as the marketable source and make these available in the market.
Since
mostly the locally available natural products were utilized only for coloring
textiles therefore, depending upon local weather conditions, stages of growth of
the vegetable products, their storing conditions and even quality of local water
available for processing, affected the final shades. The variation in tones of
the leaves or flower petals or fruits one sees in one and the same plant species
is the weakness of these natural products. Such a possibility of variation in
final shades is one of the major issues considered in textile coloring.
Apart
from this issue, there were many other problems associated with the use of
vegetable/ natural dyes. Following is the list of some of those problems:
- Non-availability of dye
producing materials due to difficulty of collection.
- Bulk isolation of
dyestuff.
- Standardization of dyeing
procedure.
- Complexity of dyeing
process.
- Reproducibility of shade.
Due
to these problems encountered with natural dyes, the development of synthetic
dyes came into existence. The advent of synthetic dyes dates back to 1856 and
still dominates the entire dyestuff industry. These synthetic dyes have received
faster acceptability due to its ease in dyeing, reproducibility and cost
factors. It was only a decade ago when toxicological effects of dyes during
wearing became more and more known and caused a great concern about the use of
synthetic dyes. In the late 1994, Germany struck a severe blow to dyestuff
industries and subsequently other European countries also executed ban on import
of textiles and garments, colored with a series of azo-dyes made from aromatic
compounds, which are carcinogenic, allergenic and poisonous.
Even after this ban, the textile
processing units are one of the most polluting industries. The dyestuff
industrial wastes in the form of atmospheric gases and wastewaters have been
found to be polluting the neighboring areas. If the examples of the famous
textile processing dominated industrial cities of Pali and Jaipur are any
indication, where because of pollution by industrial wastes even drinking water
in the area was rendered unpotable and majority of the industries had to be
de-registered or closed down. This aspect cannot be neglected in the coming
days.
The
pollution problem is the main inspiration behind the resurge of natural dyeing
materials. Though after the advent of chemical colors, people have got used to
very bright and very fast range of shades, which is still not possible with the
natural dye materials available till date. However, it is always not necessary
or desirable to have only very bright or very fast shades on the cost of nature
damage. The soothing effect of natural shades may at times win over in aesthetic
aspects over the chemical dyestuffs.
People
in general or the present day textile processors in particular are very much
used to the idea of getting their dyes in ready powder form packed in tins/
bags. All the natural products are still not available in this form and hence
these dyers/ printers do not readily come forward to handle these cumbersome
natural products presently marketed in the form of barks, stems, roots, leaves
etc. and not as powders or extract of these products.
These
shortcomings of the natural dyes can be overcome by making the efforts to
streamline the supply channels of natural products and to improve the dyeing
quality of these products. If sufficient research time is allotted to this
subject, recipes could be developed which could bring any of the desired colors
at par with their competing synthetic colors.
Besides
this, many of these natural products have some medicinal or healing qualities
for human bodies. The vegetable indigo gives a cooling effect to the skin even
in hot summer. Myrobalan gives a soothing feeling to the skin. It is also said
to be antiseptic in effect. If systematic studies were undertaken in these
aspects, surely the natural (dye yielding) products would win hands down over
their synthetic counterparts.
Use
of vegetable products for textile coloring at commercial level is, to an extent,
a virgin area nearly seven years ago. In recent years a drive for using natural
dyes is noticed all over the world because in the sophisticated fashion fabrics,
the natural dyes offer pastel color effect, apart from being eco-friendly. The
status of usage of natural dyes world over is enhancing every year. Up till now
more than 500 natural dye sources are known. A very promising crop could be
expected in this field if due efforts are put in for its growth and promotion.
Exploration of plant parts for dye extraction, which are otherwise waste like
bark, leaves and flowers etc., need to be exploited.
India
is primarily an agricultural country. Nature has bestowed India with wide
varieties of vegetables, trees, shrubs and different kinds of grasses, which
provide different natural dyes. In India, some 500 varieties of plants are
available that can yield natural colors. The natural dyestuff manufacturers have
concentrated mainly on manjistha, lac, tissue, pomegranate rind, marigold,
henna, turmeric, catechu and Indian rose.
Natural
dyes are mordant dyes. The mordant is the life for the vegetable colors except
in the case of Indigo. Without mordant no color adheres in vegetable dyeing. It
acts as an agent between the fiber and the color by helping the color and
penetrates into the fiber permanently, and makes it fast. Most of the natural
dyestuffs will not by themselves adhere to yarn or cloth except as a surface
stain which is easily washed away. A mordant, usually of metallic origin
introduced upon the prepared cloth, unites with the dyestuff during the process
of dyeing in the vat, usually under heat to form an insoluble lake.
The
traditional method of dyeing has been to boil the fabric or yarn in dye bath,
till the desired color is obtained. Enormous amount of heat is consumed in terms
of heating the dye bath. Some dyes, which are heat sensitive, cannot be used in
conventional dyeing because prolonged heating decomposes the dye molecules. The
dye uptake by the fabric is also far from exhaustion, as a result fair amount of
dye is wasted, however in case of ultrasonic dyeing, the most advantageous part
is that at low energy dyeing is carried out (mostly at room temperature, no need
for heating the dye bath).
The
use of ultrasonic energy in textile processes is not a new idea, there exists
considerable amounts of literature on the improvement and acceleration of
numerous textile processes with the aid of ultrasound. However, until recently
research into this technology has been limited due to the expenses associated
with the generation of ultrasonic energy. Technological advances in the areas of
inexpensive and reliable ultrasound generators has therefore prompted increased
interest into effects of ultrasonic energy applications in industry. Research is
being conducted into the beneficial effects of ultrasonic energy on dye
application to cotton, wool and other textile fabrics. Dyeing of textiles with
low and high frequency sound waves has been the subject of many studies.
Improved understanding of physicochemical changes caused by sound in dyeing
systems is now known.
The
mechanical agitation causes slight rise in temperature, which helps in dyeing.
Sonicator dyeing is very innovative technique and fuel saver methodology. In
this method ultrasound energy of 20 KHz frequencies is utilized. Sonicator has
high-energy sound waves, which increase ultrasonic cavitations. This releases
considerable amount of energy. Particularly in India, this methodology is
advantageous where energy resources are limited. Even heat sensitive dyes can be
used in sonicator dyeing very comfortably without undergoing decomposition. The
dye uptake is very good in sonicator dyeing. The same bath can be recharged and
reused.
BASICS OF NATURAL DYEING
The
knowledge and use of color or dye on cotton, wool and silk began with the dawn
of the civilization and was first developed in the East, particularly in India.
India has the long rich tradition of colored fabric design. There are many
plants and some animal sources in nature that yield color and can dye fabric,
leather, hair, and other items. Humans started using dyes as soon as they were
discovered; 6000 BC or even earlier. It is not possible to precisely locate the
place of antiquity where dyeing was first known as an art. Evidence leads us to
believe that different civilizations had each its own methods practiced. It is
said that the Egyptians learned this art as early as probably the Indians and
Chinese. In the Medieval period there were certain plants that were heavily
relied on for most colors till the invent of synthetic colors.
Color
was considered by ancient people as a basic necessity as essential as food and
water. The ancient people used exclusively dyestuffs of vegetable, mineral and
animal origin, all easily obtained in their own vicinity. Natural vegetable dyes
have been used in most of the ancient civilizations in different countries e.g.
India, Egypt, Greece, Rome, etc. In India use of vegetable dyes in dyeing,
painting and printing goes back to the pre-historic periods.
In
India, according to the information collected so far, there are nearly 300 dye
yielding plants available. Based on this, 30 raw materials were taken and some
work was done by using these dyes on cotton, silk and wool.
Advantages of Natural Colors/Vegetable Dyes
- Natural dyes bearing
Eco-mark are ecofriendly and acceptable in today’s world
- They are non-toxic &
non allergic, hazard free for skin.
- Fastness can be achieved
by the use of proper mordants.
- They are safe the life,
environment, fuel & time and other investment process.
For
successful introduction of vegetable dyes into technical dyeing processes, some
additional demands have to be fulfilled:
1.
Increase of the number of available vegetable dyes with acceptable
fastness properties suited for one –bath dyeing processes;
- Formation of an efficient
supplier organization which is able to provide a dye-house with standardized
dyes of constant quality and to generate an inventory of suitable vegetable
dyes from application point of view;
- Availability of technical
information about the use of the dyes collected from forest or locally grown
plantation, emphasis be made on production of plant material in sufficient
amounts with modern agricultural methods which would include simple and
environmentally clean extraction methods, suiting the requirement of a
dye-house;
- Determination of
eco-friendliness of the vegetable dyes for suitability for wearing dyed
fabrics;
- Determination of
biodegradability of the waste generated after dye extraction from the plant
sources.
It
is of utmost importance to know the structure of the dye depending on the dyes
structure the mordant and dye uptake is expected. Pretreatments are very
important part of vegetable dyeing.
Natural Dyeing Principles
Application
of natural dyes in today’s scenario makes use of modern science and technology
not only to revive the traditional technique but also to improve its rate of
production, cost effectivity and consistency in shades. It therefore, requires
some special measures to ensure even-ness in dyeing. Many factors have to be
accounted for when one works with natural dyes. They are as follows:
1. Nature of Material to be Dyed
Animal
proteins like wool and silk dye best in acidic conditions and are weakened by
alkaline. If an animal protein is dyed in alkaline conditions, it is best to end
with a diluted vinegar rinse to restore a slightly acidic pH to the fibers
before they dry. Plant materials like cotton, flax, dye best in alkaline (basic)
conditions and are weakened by acids. If cotton is dyed in acidic conditions, it
is best to end with a weak washing soda bath to restore the fibers to slightly
alkaline before they dry.
2. Measurements of Mordants and Dyestuffs
Most
dyeing procedures specify ingredients by weight rather than measure. Recipes
will also specify the amount of fiber to be dyed or the other ingredients will
be expressed as a ratio to fiber weight. This is because the amount of water in
the dye-bath will not affect how strongly the fiber takes color, but the amount
of dyestuff in the dye-bath does. So if one gm of fiber has to be dyed with one
gm of dyestuff and then one wants to reproduce the same color on 5 more gms of
fiber, the amount of dyestuff should be multiplied by 5 times as well. The water
should always be enough to let the fibers move around freely; water quantity
should be sufficient to dip the fabric/fiber properly.
3. Temperature
Different
dyes work better at different temperatures. Most plant dyes benefit from being
heated, but some (i.e. madder) change colors if allowed to boil. Sappan wood
also has a tendency to change color when heated for prolonged hours. Some dyes
work best at lower temperatures (safflower and woad/indigo).
4. Agitation
For
getting even dye uptake, one should move the fibers around as much as possible
in the dye-pot. Unfortunately, when wool is heated and agitated it tends to
felt, so one must be very careful about how much one should move it around. For
most wools, heating and cooling the dye-bath slowly and being gentle while
moving the fibers is necessary to avoid felting.
5. Natural Dyes are Unpredictable
Books
on natural dyeing can predict the range of colors that will most likely be given
from a dye source, but there are so many factors involved in the process that
reproducing a color exactly can be very difficult unless those parameters are
followed strictly. Some reasons for disappointing results could be: insufficient
heat, or too much heat, accidental iron or other metal contamination in the
water, bad growing conditions for the dye-plant, plant harvested at the wrong
time of year, dyestuff allowed to dry out, dyestuff kept in humid conditions,
dyestuff too old and dye obtained from different plantation in terms of climate
and soil conditions. The point here is to list some reasons for failure, which
one would face if one does not get the expected color - the most experienced
dyers in the world get accidental color sometimes. One can over-dye and get the
desired colors.
6. Wet Fibers Look Darker
When
trying to achieve a certain color, it has to be always remembered that the color
when wet will always appear darker and may be disappointing when the fibers dry.
Also, some color will rinse out after rinsing the fibers. Always dyeing to a
darker shade in the dye-pot than what is required. Lifting the fiber out of the
dye-pot to “air” is often good for the dyeing process to check the color.
7. Rinsing
Fibers
should be rinsed after they have been dyed, and some dyes will still bleed for
several washings afterwards. As mentioned above, it is advisable to add some
washing soda to plant fibers or some vinegar to animal fibers to return them to
their optimum pH in the last rinse.
8. Using Natural Dyes
Mordanting
The first step of the actual
dyeing process is mordanting. A mordant is a chemical that, when “cooked”
with the fiber, attaches itself to the fiber molecules. The dye molecule, then,
attaches itself to the mordant. Different mordants give different colors when
combined with the same dye. For example: the dye, cochineal when used with alum
sulfate gives a fuchsia color; when used with tin, the color is more scarlet,
and when used with copper, it is purplish. Mordants except for alum and iron,
are considered toxic and therefore, should be avoided in the preparation of
eco-textiles otherwise the whole exercise will be self defeating. As the
mordants are toxic to the dyer and the disposal of the bath becomes an
environmental problem. Therefore the choice of mordants is limited. Alum and
iron are ideal safe mordants. Other chemicals known as assistants may be used in
addition to dyes and mordants which help in coloration of the fabric in one way
or the other, for example- to change pH and hence the color, sometimes to
brighten the color, to help in the absorption of the mordant metal, or to slow
down the rate of absorption of pigments or for evenness. These include potassium
hydrogen tartrate (cream of tartar), oxalic acid, tannic acid, acetic acid,
formic acid, ammonia, sodium sulphate (Glauber’s salts), sodium chloride
(common salt) and sodium carbonate (washing soda). Treating cotton with tannic
acid is useful as it prepares the fabric for effective absorption of the dye.
Mordants
The
word “mordant” comes from the French “Mord” and mordants can be
described as metallic salts with affinity for both fiber and dyes stuffs and
that improves the color fastness. Even some of the fugitive dyes have been used
successfully with the help of mordants. Dyes are categorized as either
“mordant”or adjective” or “Indirect” dyes. Most of the natural dyes
are mordant dyes except the very few direct dyes and vat dye such as Indigo. The
latter dye needs no mordants.
In
addition to adding substances to a bath for mordanting, the vessel that is used
may itself serve as mordant. The dyers use copper tin vessels to brighten the
color and iron vat to dull the color. To get the effect of alum mordant,
now-a-days aluminum dye pot with a little soda is used. To get the basic
original color of the coloring materials, earthen or stainless steel materials
are advisable.
There
are two processes concerned with the dyeing of most vegetable colors. The first
is mordanting and the second is the actual coloring. The mordanting prepares the
material to be dyed to receive the dye. Mordant should not affect the physical
characteristics of the fiber.
A mordant
must not ‘flatten’ i.e. dull or deaden, the luster of the fiber, but if
anything ‘raise’ or brighten it, for which sufficient time must be allowed
for the mordant to penetrate in the fiber thoroughly. Different mordants give
different color with the same dyestuff. Alum, Iron, Tin, Chrome and Copper
mordants are used commonly.
Mordanting of Cotton
Mordanting
is very important for cotton dyeing. Natural dyeing of cotton is more difficult
than silk and wool. Cotton is not very porous and will not hold the dye stuff
without a more complicated preparation for mordanting, the fiber must be cleaned
first.
Preparation
of alum mordant - To prepare alum mordant, first
alum-powder and cream of tartar are mixed with little boiling water and then
made up with the remaining required water. Stirring is continued well till the
chemicals are dissolved and water should be lukewarm.
The wetted fiber is entered slowly bring the bath to the required
temperature and worked. Dyeing the fiber immediately or it should be dried in
the shade and stored for further use.
Tin mordant
–
Dissolving cream of tartar or oxalic acid in a little quantity of hot water.
When it is thoroughly dissolved, some more hot water is added.
Addition of stannous chloride and mixing well is continued till it
dissolves. The remaining water is added. When it is luke-warm thoroughly
loosened wetted fiber is entered and the heating to required temperature is done
and continued to work for the specified time.
Copper mordant – Dissolving sulphate of Copper in
lukewarm water and remaining required quantity of water is added.
The fiber is entered and worked as tin mordant. If bright colors are
desired cream of tartar may be added in the beginning itself in the copper
sulphate.
Chrome
mordant -
Mordanting with potassium dichromate is best just before dyeing. Dissolving the
potassium dichromate in little warm water and making up the solution with the
rest of required water. When the bath is lukewarm, then similar procedure is
followed as stated above. Care should be taken while handling chrome mordant.
Covering the pot with a lid except when the fiber is worked is necessary to
avoid inhalation. Apart from this chrome is very sensitive to light. If light
falls on any part of the fiber, it will darken the fiber and result in uneven
dyeing. Further procedure should be followed as before.
Iron
mordant -
Dissolving ferrous sulphate with a little warm and addition of
cream of tartar to this and this should be mixed well. Addition of the
remaining total water and entering the fiber and working for the specified time
at specified temperature gives best results.
MORDANTING THE TEXTILE FOR NATURAL
DYEING
The
term mordant is used for chemicals which usually have a metal with a valency of
at least two or more, they can also be other types of compound as well. Natural
dyes also referred as mordant dyes; do not readily adhere to cotton so mordants
are used. Mordants are needed to set the color when using natural dyes.
Different mordants will give different hue color with the same dye. A mordant is
thus a chemical agent, which allows a reaction to occur between the dye and the
fabric. In textiles, mordants are used to fix the color in dyeing or fabric
printing, especially for fabrics of plant origin (cotton). Mordant is added to
the dye source to influence it, it does not serve as a color source on its own.
The fabric is impregnated with the mordant, then during the dyeing process the
dye reacts with the mordant, forming a chemical bond and attaching it firmly to
the fabric. The choice of mordant depends upon the fabric. An alkali mordant,
such as soda ash, works well with cotton, and acid mordant such as vinegar works
well with wool.
Metal
mordants can be defined as a polyvalent metal ion, which forms coordination
complexes with certain dyes. Two types of bonds are involved in the fundamental
reaction between a mordant dye and a mordant. One is a covalent bond with
usually hydroxyl oxygen and the metal atom. The other is a coordinate bond with
the metal with the double bonded other oxygen also referred as “chelation”.
It is possible, however that the formation of dye-mordant complexes involving
several molecules of dye can also form. Varying the amount of mordant with the
dye is a way to exert some control over the change in hue color. The two
commonest metals used in natural dyeing are aluminium and ferric ions both
having valencies of three.
Treatment of fabric before dyeing
After
removing the impurity of fabric then it is treated with 4 % (owf) solution of
tannic acid in water. The fabric should be dipped in tannic acid solution for at
least 4-5 hours. It is squeezed and dried. After mordanting, the fabric is used
for dyeing. Dyeing would depend upon the type of mordanting used. There are
other types of pretreatment used these days, which are ecofriendly. They are
mainly two types:
1.
Enzymes like amylase, trypsin, cellulose and
2.
Polyethylene glycol (PEG).
Both
these types are used as depth improver for dye fixation.
Methods of Mordanting
The
percentage of chemicals and the weight of the material to be dyed are very
important. The details of chemicals to be used for various mordants with their
quantity, fixed temperature is to be maintained, duration of time and the
procedure to be followed after mordanting and before dyeing have to be followed
strictly. There are three ways of mordanting. Mordants and dyes may be applied
in three ways. They are as follows:
Pre-mordanting,
where the mordant is applied first, followed by dyeing.
Post-mordanting,
where the dyeing is done first and then mordanting is carried out.
Simultaneous
mordanting, where mordant and dye are mixed together and applied.
Mordants
are commercially available, commonly in the form of salts from metals such as
chrome, copper, tin, iron and aluminium. These mordants are listed in descending
order of relative toxicity. Other types of mordants which are not metal mordants
are tannins, cream of tartar, baking soda and vinegar. The later two serve to
change the alkalinity and acidity, respectively, of the dye, another property
that influences the final color. Besides metallic salts, tannins and other inorganic
compounds, sometimes oils such as oil of turkey and its type are also used as
mordants. It is often remarked that the addition of a mordant to an appropriate
dye solution results in a very sudden, dramatic change in color. This is due to
the incorporation of the metal atom into the delocalized electron system of the
dye. Metals have relatively low energy levels, so their incorporation into a
delocalized system results in lowering of the overall energy. The absorbance of
the hue and thus its color is related to this phenomenon.
Most
dyers mordant the cloth and then apply the dyes as two separate steps. The
advantage is that the mordant has a chance to “bite” into the fiber, so that
when the color is applied, maximum amount of bonding takes place. Many dyers
turned to natural dyes because they are safe and non-toxic, so it is imperative
to ascertain whether the mordants that are used to fix the dyes are safe or not.
Most of the mordants that are used for natural dyeing are not seriously toxic.
The
better results obtained in case of pre-mordanting with stannous chloride and
ferrous sulphate are attributed to the empty d-orbitals of ferrous and stannic
ions. The mode of binding of dye seems different with iron and aluminium ions.
The
pre-mordanting with ferrous sulphate showed least color discharge after washing
because of the pretreatment of fabric with tannic acid which shows 100% iron
binding efficiency in terms of tannic acid equivalents. The iron binding by
phenolics increases with increasing number of –OH groups. A flavonoid ring B
and a 3’, 4’-dihydroxy group is required for Fe-binding (I) and in case of
aluminium ion binding, the 3-hydroxychromane groups are required as shown in the
structure (II) below.
Cotton
has very low affinity for natural dyes. The tannins play an important role in
cotton dyeing and are largely used for preparing cotton so as to enable it to
retain coloring matter permanently. Most common mordant for cotton is thus
tannin or tannic acid. It occurs in many tannin containing substances,
especially in gall nuts which has about 60-70% tannic acid. The aqueous solution
of tannic acid gradually decomposes on standing by fermentation. Addition of
boric acid inhibits the decomposition. It is also considered as primary mordant
before mordanting the cotton fabric with metallic salts. Treatment with tannic
acid helps the cotton fabric to absorb all types of metallic mordants. The
metallic mordants form complex with the carboxylic groups of tannic acid.
Frequently
the purpose of preparing the cotton fibers with tannin is not so much to fix the
coloring matter, although that is the final goal, as to fix certain metallic
salts such as alum, copper, tin and iron in the form of insoluble tannates. The
metal tannates present on the fabric form insoluble lakes with the natural dyes
during dyeing. A study was carried out to see the effect of mordant on dye
uptake and enhancement of fastness properties. The figure -1 shows that
treatment of the fabric with only tannic acid, tannic acid and alum show gradual
increase in dye uptake, although blank (un-mordanted) fabric shows good dye
uptake but it all washes off thereby showing the importance of mordanting.
STANDARDIZATION OF VEGETABLE DYES
Natural
dyeing has the problem of standardization. In 1971 Rita Adrosko wrote about
vegetable dyes in NATURAL DYES AND HOME DYEING, “Craftsmen are becoming
increasingly enthusiastic about this out-dated and time-consuming process for
one of the reasons that manufacturers rejected it because of difficulty of
standardization. Natural dyestuffs produce offbeat, one-of-a-kind colors. No two
dye lots are identical, each having subtle differences due to impurities
peculiar to the particular plant material used.
The
problem of course with raw botanicals is that the numerous chemical ingredients
that make up plants vary widely. Not only do the variations occur between plants
of the same species, but also from part to part of the same plant so that, for
instance, in madder the dye is contained in the roots, not the leaves. The type
and quantity of chemicals present are affected by such things as soil, species,
weather, time of harvest as well as the part of the plant used. The manner in
which they are stored and processed also has a profound effect. Color varies
greatly with plants grown in different areas, due to mineral content of the
soil, and various other factors of growth.
Dyers
learned by trial and error what to pick and when and where to pick it. They
passed down their knowledge from generation to generation often keeping trade
secrets from outsiders. Dyers, of course, used color as a control. They kept
trying to determine which plant, which part of the plant, which species, what
growing conditions and what time of harvest would produce the color closest to
the one they wanted, but they also had many other variables to worry about such
as the water and utensils used. Dyes prepared in a tin pot give a color
different than the same ones prepared in an iron pot. To obtain the desired
color time after time, the dyer had to know all this. If he didn’t get what he
was looking for, he knew that something was wrong with the raw materials used or
with the manufacturing process and had to figure out what and how to adjust it.
In
an effort to standardize colors, dye plants were often cultivated rather than
gathered wild. Many were grown commercially. In order to get a standard color
from a particular species of dye plant 400 years ago, the farmer would have had
to have worked empirically by selecting & cultivating plants that produced a
dye that got closer and closer to the color he wanted. He would also have had to
have tried growing the plants under different conditions to see what type of
soil, etc. gave the best results. When he reached his goal, he would then have
had to have maintained the results by always growing the same species under the
same conditions using color as his control. By keeping good records and
adjusting the variables, he learned by experience how to obtain the desired
color, but it wasn’t easy or exactly the same each time. Even today it is not
possible to precisely match color from batch to batch, not even with synthetic
dyes.
To
produce fully standardized eco-friendly vegetable dyes from potential
herbal/vegetable resources, evaluation of natural colors for eco-friendliness,
standardization of processes for various textile substrates, large scale
production and development of commercial natural dyes, there are certain
specifications that need to be followed. They are—
Specifications
in terms of:
1
Color,
2.
Appearance,
3.
Optical density
4.
Water soluble matter,
5.
pH of water extract,
6.
Ash content and
7.
Colour component and its tinctorial value
8. Total suspended solid content.
Procedures
for the extraction of coloring matter in aqueous medium has to be standardized
at pilot and bulk scale plant. Shade cards having shades of fabric and dyed
yarns having good light, wash and rub fastness need to be produced for each
natural dye. But still the problem of reproducibility arises. Dye from one
company does not necessarily give the same shade as the same dye from another
company. Comparative study has been carried out for three dyes- 1. Acacia
catechu (Catechu), 2.Rubia cordifolia (Manjistha) and 3. Quercus infectoria(Gall
nut). Table –I shows the
difference in their pH and total suspended solid contents in the dyes supplied
by different companies. The dyes show that UV spectrum, Visible spectrum as well
as FT-IR spectrum shows difference, which goes to show that there is definitely
difference in their optical density, which is the root cause for their
difference in dyeing ability and color. This exercise of standardization was
carried out to confirm this fact.
METHODS OF DYE EXTRACTION
Experimental
trials were carried out in domestic gardens in collaboration with botanists
mainly focusing on the best conditions for the growth of dye plants in regard to
soil and climatic factors. Modern cultivation system for getting maximal dye
yields including optimal seeding and harvesting time, optimal fertilization
procedures were adapted. The utilizable plant parts were subjected to specific
dehydration processes or the dyestuff was extracted as per the given strategy.
The
traditional method used to extract the dyestuffs from all other plants mentioned
earlier, where the plant material is added directly to the dye bath. This has
been used by dyers for centuries and is still used by many dyers in north
eastern states of India.
The disadvantages of this method are:
- The plant material has to
be separated from the textile
- It is not applicable to
modern textile fabrication machines (pumps and spinerettes will be choked)
- Hard plant material such
as madder roots or barks of Cassia, amla are dufficult to extract
- The low density of the
dried material requires high processing volume
Disadvantage has to be solved for use by modern
mills. For industrial use the best method is to provide extracts. Aqueous
extracts are not especially favorable for dye plants such as Parkia, Alkanet and
Tulsi where we have used 50: 50 water : methanol extract for dyeing. The reason
being that flavonoids, anthraquinones
and aglycones are poorly soluble in water and therefore are extracted only
partially. The remaining material always contains a considerable amount of
dyestuffs. A method to extract the dyestuffs from such plants is to boil the
powdered material with methanol for one hour. This method is used for
quantitative determination of the dye content. Also, an alkaline extraction of
madder as a first step gave promising results. Because of their slightly acidic
character flavonoids and anthraquinones are soluble in alkaline solutions and,
after drying, also in water. This method gives good reproducible relations
between the dye content and the dyeing power.
Methodology
1.
Innovative Method for Extraction of dyes: Efficient extraction of
the dye from the plant material is very important for standardization and
optimization of vegetable dyes. Utilizing
a) Soxhlet b) Supercritical fluid
extraction c) Sub critical water extraction and d) Sonicator methods
SCFE
is a two step process, which uses a dense gas as solvent usually carbon dioxide
above its critical temperature (31°C) and critical pressure (74 bar) for
extraction. The natural product is powdered and charged into the extractor.
Carbon dioxide is fed to the extractor through a high-pressure pump (100-350
bar). The extract charged carbon dioxide is sent to a separator (60-120 bar) via
a pressure reduction value. At reduced temperature and pressure conditions the
extract precipitates out in the separator. The extract free carbon dioxide
stream is introduced several times for effective extraction of all the dye
material from the natural product.
Why
SCFE is superior over the traditional solvent extraction of natural dyes?
Firstly it uses a clean, safe, inexpensive, nonflammable, nontoxic,
environmentally friendly, nonpolluting solvent-carbon dioxide (CO2). Secondly,
the energy costs associated with SCFE are lower than the conventional
techniques.
Sub-critical Extractor
GRAPHICAL Subcritical Water Extraction
Subcritical
Water Extraction was performed with some plants to extract natural colorant.
The water was purged with nitrogen to remove dissolved oxygen prior to
the extraction. Deoxygenated water was used in an HPLC pump programmed for a
constant flow of 1–3 ml/min-1. A 10.4 ml µm frit at the inlet and outlet was
connected to a 1 m cooling loop (in ice water) outside of the oven. A pressure
control valve was placed between the cooling loop and the collection vial. The
extraction was carried out in efficient manner.
2.
Innovative Method for dyeing: The traditional method of dyeing has
been to boil the fabric or yarn in dye bath, till the desired color is obtained.
Enormous amount of heat is consumed in terms of heating the dye bath. Some dyes,
which are heat sensitive, cannot be used in conventional dyeing because
prolonged heating decomposes the dye molecules. The dye uptake by the fabric is
also far from exhaustion, as a result fair amount of dye is wasted, however in
case of ultrasonic dyeing, the most advantageous part is that at low energy
dyeing is carried out (mostly at room temperature, no need for heating the dye
bath). The mechanical agitation causes slight rise in temperature, which helps
in dyeing. Sonicator dyeing is very innovative technique and fuel saver
methodology. In this method ultrasound energy of 20 KHz frequencies is utilized.
Sonicator has high-energy sound waves, which increase ultrasonic cavitations.
This releases considerable amount of energy. Particularly in India, this
methodology is advantageous where energy resources are limited. Even heat
sensitive dyes can be used in sonicator dyeing very comfortably without
undergoing decomposition. The dye uptake is very good in sonicator dyeing. The
same bath can be recharged and reused.
Dyeing
with bottom mordant gives more intensive shades than the first single-bath
method. For the second single-bath method the intensity is not very different
but the shade can be changed. Single-bath dyeing gives greater fastnesses than
with a bottom mordant. As after-treatment all dyed textiles were washed with
soap for 30 minutes at 60°C. The soaping will improve fastness to washing.
Dyeing
on an industrial scale was done using several different types of machines.
Depending on the type of textile, up to 400 meters per piece were dyed with the
help of local company. The test showed that all natural textiles can be dyed
with natural dyes without problems using jiggers or jets.
DYEING METHODOLOGY
Color
is one of the elements of nature that made the human living more aesthetic and
fascinating in the world. They are supposed to be associated with emotions,
human qualities, seasons, festivals and passion in our life. In the past at dawn
of civilization, the people tried to ornament their surroundings similar to that
of natural color observed in the plant, soil, sky and other sources. This gave
birth to a new science of colors from natural origin.
Natural
coloring matters are broadly classified in three categories.
- Vegetable origin:
Colorants derived from root, leaf, bark, trunk, fruit and flowers of plants.
- Animal origin: Lac,
Cochineal and kermes have been the principal dye yielding insects.
- Mineral origin: Various
inorganic metal salts and metal oxides
Only
after 1856, the development of synthetic dyes came into existence and still
dominates the entire dyestuff industry. These synthetic dyes have received
faster acceptability due to its ease in dyeing, reproducibility and cost
factors. But in the late 1994, Germany struck a severe blow to dye-stuff
industries and subsequently other European countries also executed ban on import
of textiles and garments, colored with a series of azo dyes made from aromatic
compounds, which are carcinogenic, allergenic and poisonous.
With
the present national and international awareness of environmental ecology and
pollution controls, natural dyes appear to be the ideal choice since they are
chosen from the non toxic lot and can be handled very easily and safely however
it is not so simple, there are some problems encountered in the use of
vegetable/natural dyes as well. The are as following:
- Non-availability because
of difficulty of collection.
- Bulk isolation of
dye-stuff.
- Standardization of dyeing
procedure.
- Color yield.
- Complexity of dyeing
process.
- Reproducibility of shade.
But in the twenty first century maintaining a safe
environmental balance becomes even more important. The co-operation of
individuals, communities and countries to make this happen become a global
necessity and the following properties are often considered to be advantages of
natural dyes.
- They are obtained from
renewable resources.
- No health hazards,
sometimes they act as health cure.
- Practically no or mild
reactions are involved in there preparation.
- No disposal problems
- They are unsophisticated
and harmonized with nature.
- Lot of creativity is
required to use these dyes judiciously.
MATERIALS
Selection of Plant Sources for Dye
Extraction
Color
like so many other attractive elements in nature attracted and continued to
fascinate mankind from the earliest times. They were not content to enjoy color
through their eyes. They wanted to feel it enjoy it intimately with which began
personal adornment. No doubt flowers and leaves served for a while but they
faded and shriveled away shedding their color to use.
India
is an advantageous position since the country holds a rich reservoir of natural
products. Thus started in India a chapter in chemistry, which has over the years
grown into specialized area. Different parts (leaves, bark, seed, flowers, roots
and wood) of number of plants have been reported to yield the dye but a large
number of them hitherto remain unexplored. As the uses of natural dyes do not
cause pollution, it is of immense importance to explore the additional sources
of natural dye from rich flora of our country, which are abundantly occurring
plants. Research work done has led to the new color yielding plants namely Al
(root), Alkanet, Amaranthus (Flower), Balsam (Flower), Babool (Bark),
Bougainvillea (Flower), Canna( Flower), Carthamus (Flower), Catechu, Cassia
fistula (Bark), Cosmos (Flower), Eclipta ( Weed), Eucalyptus (Bark), Gompherena
(Flower), Hibiscus (Flower), Hollyhock (Flower), Lawsonia (Leaves), Nerium
(Flower), Nyctanthes (Flower), Plumeria (Flower), Tectona (Leaves), Terminalia
(Bark) and Tulsi (leaves). It is a
specialized technique of dyeing of the fabric/ yarn of cotton by natural dyes
for the lovely shades using common mordants like alum and salts of iron, tin and
chrome with good wash fastness and light fastness. It is really stands for the
pride and glory of the craft of India as this art of natural dyeing has been in
Indian as this art of natural dyeing has been in Indian culture from a very long
time. Because of the beauty of its results, those who use them, claim that no
chemical dye has that luster the under glow of rich color that delicious
aromatic smell and the soft light and shadow that gives so much pleasure to the
eyes. These colors are alive as all beauty is alive.
EXTRACTION OF COLORANTS
Natural
or vegetable sources like leaves, fruits, seed, bark etc. could be used as such
for dyeing of textile materials. The dye matter has to be extracted in any one
of the following methods.
Ø
Aqueous
extraction
Ø
Solvent
extraction
Aqueous Extraction
Plant part were soaked in water
and heated at 60°C for certain time. The colorant present in plant part were
transferred to the aqueous solution. Then the dye solution extracted from the
sources were filtered and collected.
In
case of balsam for aqueous extract 40 gm flower soaked in 150 ml of water for 2
hours and give dark peach dye extract.
For
Bougainvillea’s extract 5 gm of bracts in 100 ml water, leave for one hour in
sonicator. These bracts give bright magenta color.
5gm of
cassia fistula’s bark powder was taken in 100 ml water, and boiled it.
Extraction takes one hour and gives dark brown color extract.
Dark
yellowish orange extract were obtained from 5 gm of frozen cosmos flowers dipped
in 100 ml water till all dye bleached out from the flowers at room temperature
or on mild heating.
But some
sources give different color in different medium e.g. Bougainvillea. In acidic
medium and basic medium it gives dark magenta and bright yellow respectively.
Solvent Extraction
Sometime
colorants which are present in natural sources do not come in the aqueous
medium. For that case soxhlet was used to extract the natural sources in organic
solvent. Mainly the solvent used was methanol. Plant parts are cut in to small
pieces and were refluxed in soxhlet in methanol till it discharged color. The
process takes 4 – 6 hours. This method was used for balsam, cosmos and tulsi.
5 gm balsam
flower gives deep peach color in 4 hours with soxhlet extraction in methanol.
Dark
yellowish orange extract was obtained from 5 gm flower refluxed with 150 ml
methanol.
5
gm tulsi took 6 hours in soxhlet extraction and give dark green color.
EQUIPMENT USED FOR DYEING AND ANALYSIS OF DYED FABRIC AND THEIR PRINCIPLE
SONICATOR
Model Make: Julabo-SRO5
The
sonicator used is of 20 KHz frequency which is found to be suitable for
introducing cavitations. High energy ultrasonic waves cause cavitations. When
dye bath is irradiated with high energy ultrasonic cavitations occurs which
releases considerable amount of energy and collapse of the bubbles. This
increases with the surface tension at the bubble interface and decreases with
the vapor pressure of the liquid. Since the aqueous dye bath has water, which
has comparatively high surface tension, it is very effective medium for
cavitations. Interestingly cavitations in alcohol solution (methanolic extract
of dye in our case) is considerably high because of increase in vapor pressure.
Here the later plays a dominant role. We thus were interested in looking into
this aspect of dyeing cotton.
ULTRAVIOLET AND VISIBLE SPECTROPHOTO-METER
Model Make: Perkin Elmer, Lambda 40
When
a material is illuminated by light, specific wavelengths are absorbed depending
on the molecular structure present. This is caused by electrons in the ground
state molecule absorbing light energy and moving to an excited state. The
absorption intensity depends on the wavelength and the absorption spectrum
(curve measuring absorption intensity changes accompanying wavelength changes
for monochromatic light illuminating a material) is characteristic of a specific
material. Analyses of materials based on this principle are called
absorptiometry. These analyses can be used for various purposes such as:
- Identification
- Quantitative analyses
- Electronic state analyses
In addition, molecules absorbing light and entering
the excited state later lose energy, through thermal dissipation, collisions
with other molecules, or other processes, and return to the ground state. These
processes are called radiation less transitions and may include the emission of
the absorbed light energy in the form of light. Such re-emission processes
include fluorescence and phosphorescence. Analyses using these phenomena are
called fluorescence photometry.
Bouguer-Beer
law, a basic principle of quantitative analysis, is also called the Lambert-Beer
rule. The following relationship is established when light with intensity Io is
directed at a material and light with intensity I is transmitted. Here k is
proportionality constant. In this instance the value I/Io is called
transmittance (T) and then value I/Io X 100 is called transmission rate (T%).
The value log (1/T) = log (Io/I) is called absorbance (Abs).
T = I/Io =
10-kcl
Abs = log
(1/T) = log(Io/I) = -kcl
As
can be seen from the above formulas, transmittance is not proportional to sample
concentration. However, absorbance is proportional to sample concentration
(Beer’s law) along with optical path (Bouguer’s law). In addition, when the
optical path is 1cm and the concentration of the target component is 1mol/l, the
proportionality constant is called the molar absorption coefficient and
expressed using the symbol å. The molar absorption coefficient is a
characteristic value of a material under certain, specific conditions.
Finally,
stray light, generated light, scattered light, and reflected light must not be
present in order for the Bouguer-Beer rule to apply.
FOURIER TRANSFORM INFRA RED SPECTROSCOPY
Model make: Bruker, Vector 22
The
IR absorption spectroscopy is based on the absorption of infra red radiation by
molecules and is most widely used for the identification of the organic
compounds. The atoms in molecules vibrate constantly in a variety of stretching
and bending motions. The different types of motion are called vibrational modes.
Atoms that are connected by covalent bonds can stretch or bend at natural
resonance frequencies, which depend on the strength or stiffness of the bonds.
C - C
C = C C
º C
1200cm-1
1650cm-1 2150cm-1
The
double and triple bonds are stronger than a single bond and have correspondingly
higher energies of vibration. Similarly, stretching modes have higher energies
than bending modes for the same atoms. These vibrational modes can be excited to
higher energy states, which cause the atoms to vibrate with greater amplitude
that is a greater displacement from their average position. Vibrations can be
excited by increasing the temperature or by absorption of photons of the
appropriate energy. The energies of the vibrational modes are quantized, can be
excited only with discrete amounts of energy. A photon that has the same energy
as vibration is said to be in resonance with that vibration and can be absorbed.
Infrared
radiation, typically 4,000-400 cm-1, is in the energy range that can excite
molecular vibrations to higher vibrational energy levels. When an IR photon of
the same energy as a vibrational mode passes by a molecule, the molecule can
absorb that IR photon. The energy of the photon is converted to greater
vibrational amplitude. Eventually this energy is transferred to the
surroundings, e.g., by collision with solvent molecules, resulting in an
increase in the temperature of the sample. Since different functional groups in
molecule vibrate at distinctly different frequencies, IR spectra are useful for
qualitative identification of molecular compounds.
GAS CHROMATOGRAPH MASS SPECTROMETER
Model make: Finnigan, Fison
The
GC-MS is an analytical instrument combining a gas chromatograph (GC) and a mass
spectrometer (MS). Gas chromatographs have excellent separation capabilities and
achieve a very high degree of separation when using a capillary column. Mass
spectrometers can be used to determine the molecular structure of a substance
from the mass spectrum of the substance. FID and ECD, conventional gas
chromatograph detectors, were only able to provide qualification information of
the retention time. Mass spectrometers excel at qualifying components, and when
used as a detector of gas chromatograph, the mass spectrum data can also be used
at times other than during the retention time, making it possible to perform
peak identification and quantification.
A
mass spectrometer consists of the ion source, quadrupole mass separator, Ion
detectors, and a data-processor. Each of the sample molecules separated by the
gas chromatograph are introduced into the ion source. In the ion source,
thermoelectrons emitted by the filament accelerate to 70eV and collide with the
sample molecules (electron impact ionization method, EI). As a result, an
electron is knocked out of the sample molecules, creating positive charged ions
(molecular ions). At the same time, energy from the electrons is transferred to
the sample molecules, so the molecular ions split, creating positive charged
ions. This process is called “fragmentation”, and the decomposed ions that
result from this process are called “fragment ions.” The molecular ions and
fragment ions formed in this way are pulled from the ion source as an ion bundle
and introduced into the quadrupole mass separator. The quadrupole mass separator
consists of four metal rods (electrodes) that are parallel with respect to each
other. The ion bundle is introduced into the units in the direction of the long
axis. The relative electrodes are charged with a direct current with a 180°
phase shift, and the electrodes are also in a high-frequency electric field. The
mass to charge number ratio (m/z) of the ions that pass through the path between
the electrodes in the direction of the long axis is dependent on the voltage
applied to the electrodes. The ions that can pass through the unit are detected
and amplified in the detector. This information is then converted into electric
signals that are processed by the data-processor.
There
are two methods of measurement used by mass spectrometer, the scanning method
and the selective ion monitoring method (SIM method). With the scanning method,
a specific mass number range is scanned at set intervals to measure the mass
spectrum. This method is used to obtain total ion chromatograms, mass
chromatograms and mass spectrums. With the SIM method, the type of ion to be
measured is set in advance of measurement, and this limitation results in
improved sensitivity. This method is used primarily to quantify trace
components.
CHEMISTRY OF DYE
BASIC CONCEPT OF DYES COLOR
Color
is not an independent phenomenon; it is the human detection and perception of
electromagnetic radiation. Dyes are aromatic organic compounds, and as such are
based fundamentally on the structure of benzene. Benzene appears to be a
colorless fluid. In fact it absorbs electromagnetic radiation just as dyes do,
but it does so at about 200 nm so that we do not see it.
The
perception of color is an ability of some animals, including humans, to detect
some wavelengths of electromagnetic radiation (light) differently from other
wavelengths. Normal daylight, or white light, is a mixture of all the
wavelengths to which we can respond and some to which we cannot, in particular
the infrared and ultra-violet rays. We respond to wavelengths between about
400-700 nm. When an object absorbs some of the radiation from within that range
we see the waves that are left over, and the object appears colored. In reality
this range we see makes up only a very small fraction of the electromagnetic
spectrum.
In
scientific terms there is nothing special about the wavelengths in the visible
range, other than being the major components of sunlight, which are not removed
by the earth’s atmosphere. Their special importance is based exclusively on
the ability of human retinas to respond to them, and to discriminate between
them to a significant degree. These discriminations are what we call color.
Wavelengths
just outside the visible range are considered colorless, even though there is no
substantive difference between them and the limiting wavelengths inside the
range. Some animals (bees, for example) can see these other wavelengths but,
because humans do not, we consider them colorless. The point is that color is a
subjective phenomenon, and thinking of color as something objective is
misleading. For that reason, we should refer to the wavelengths involved rather
than describe the human response to them.
When
some of the wavelengths found in white light are absorbed, then we see what is
left over as colored light. The color that we see is referred to as the
complementary color of the color that was removed. For instance, if the red rays
are removed from white light, the color we detect is blue-green. Blue-green is
complementary to red, and red is complementary to blue-green.
The
perception of color is merely a human evolutionary adaptation to the absence of
some wavelengths in white light. Suppose however, that the same thing happens
outside the range to which our eyes respond. Suppose a chemical removes
radiation, which has a wavelength about 200 nm, as benzene does.
RELATION BETWEEN COLOR AND CONSTITUTION
Like
the physical and chemical properties of organic compounds, there is a definite
relationship between the color and constitution e.g., Benzene is colorless,
whereas its isomer, fulvene is colored. The following theories have been
proposed to explain the observed general relationships existing between color
and constitutions.
a) Witt’s
Theory (Chromophore-Auxochrome Theory)
In
1876 Witt put forward a theory according to which the color of a substance is
mainly due to the presence of an unsaturated group known as chromophores (Greek
chroma - color, and phores - bearing). The important chromophores are:
·
C = C -
·
C = N -
·
C = O -
·
N = N -
·
NO2
·
Quinoid rings
The
compounds possessing chromophores are known as chromogens. The chromopheric
groups are of the following two types.
- When a single chromophore
is sufficient to impart color to the compound. Examples are: -NO, -NO2,
-N=N, =N=N-N, -N=N®O, p-quinonoid etc.
- When more than one
chromophore is required to impart the color, e.g. >C=O, >C=C< etc.
This can be exemplified by various examples. Acetone (having one >C=O as
chromophore) is colorless, whereas biacetyl (with two >C=O) is yellow.
Witt
also pointed out another type of groups, which while themselves are unable to
produce the color, but can deepen it if the molecule possesses a chromophore. To
such group, he called auxochrome (Greek auxein-to increase and chroma-color).
The important auxochrome are: Acidic –OH, SO3H, -COOH; Basic NH2, NHR, NR2
etc.
Since
the auxocromes are capable of forming salts either with a basic or acidic groups
their presence also convert a colored compound (devoid of salt forming groups)
into a dye which must fix permanently to the fiber, i.e., it must be fast to
water, light, soap and laundering, when fixed to the fiber. The permanent fixing
of dye to the fiber is generally due to the formation of chemical bond between
the fiber and the auxochrome. This can best be exemplified by the following
examples.
b)
Armstrong Theory (Quinonoid Theory)
Armstrong
in 1885 suggested that all coloring matters may be represented by quinonoid
structures (p- or o-), and thus believed that if a particular compound can be
formulated in a quinonoid form it is colored, otherwise it is colorless. Some of
the important compounds, the coloring properties of which can be explained on
the basis of this theory are given below.
On
the basis of this theory we can see that benzene is colorless, where as
benzoquinones are colored.
But
the quinonoid theory is not sufficient to account for the coloring
characteristics of all the compounds. For example, iminoquinone and
di-iminoquinone, both posses a quinoid structure even then they are colorless.
On
the other hand, a number of colored compounds are known which cannot be
represented by quinonoid structures, e.g.,
c)
Modern Theory
The
above two theories were discussing the relationship between color and
constitution are found to be only empirical. The next two important theories,
which explain plausibly the relation between color and constitution, require
somewhat theoretical background about the effect of light on the molecule.
- Valence bond theory
- Molecular orbital theory
Valence
bond theory:
The various postulates of this theory are as follows:
Ø
Chromophores
are groups of atoms, the ð-electrons of which may get transferred from ground
state to excited state by the absorption of radiation, thus producing the color.
Ø
Auxochromes
are groups, which tend to increase resonance by interacting the unshared pair of
electrons on nitrogen or oxygen atoms of the auxochromes with the ð electrons
of the aromatic ring. This increase in resonance increases the intensity of
absorption of light and also shifts the absorption band to longer wavelength.
Hence there occurs the deepening of the color. From this it is evident that
increase in resonance must deepen the color and actually it has been found to be
so.
Ø
The
dipole moment changes as a result of oscillation of electron pairs. The
following order has been observed for the case of excitation of different
groups.
Ø
N=O
> C=S > N=N > C=O > C=N > C=C
Ø
Resonance
theory explains the relation of the color and the symmetry of the molecule or
transition dipole of the molecule because as the number of charged canonical
structures increases, the color of the compound deepens. The more the
possibility and longer the path for a change to oscillate in a compound, the
longer wavelength of light will be absorbed and therefore deeper would be the
color of the compound.
Resonance
theory also explains that pure p-nitrophenol is colorless but yellow in alkaline
solution nitrophenol exists as nitrophenoxide ion in which only the charged
structures are contributing to the resonance hybrid and therefore the compound
absorbs light of higher wavelength.
Molecular
orbital theory: According to this theory the excitation of a molecule means the
transference of one electron from an orbital of lower energy to that of higher
energy. These electrons may be s, p or n (non-bonding) electrons. The higher
energy states are commonly known as anti-bonding orbitals. The anti-bonding
orbitals associated with s and p bonds are called s * and p* orbitals
respectively. However, there are no anti-bonding orbitals associated with n
(non-bonding) electrons because they do not form bonds. Chart of the simplest
form, the essential types of energy are given below.
The
electronic transitions can occur by the absorption of ultraviolet and visible
radiation. Although transitions are possible, only the following types are
allowed:
(i)
n®s*
(ii)
n®p* and p®p*
A
s®p* transition takes place when a bonding s –electron is excited to an
antibonding s –orbital, i.e. s*. This type of transition requires a very large
amount of energy as s –electrons are very tightly bond. Hence the compounds
like saturated hydrocarbons which do not have any p or s electrons may undergo
only s ® s* transitions. However, these transitions do not take place by
absorbing in the ordinary ultra-violet region, e.g., ethane absorbs at 135 mµ.
A
n ® s* transition takes place when one electron of a lone pair, i.e., a
non-bonding pair of electrons, is excited to an anti-bonding s –orbitals i.e.,
s*. Compounds having non-bonding electrons on hetroatom like O, N, S etc. can
undergo n ® s* transitions also in addition to the s ® s* transitions. But the
nonbonding, electrons are much more loosely held than the s – electrons.
Therefore, the energy required for n ® p* transitions will be much lower than
that required for s ® s* transitions. Hence the compounds having non-binding
electrons usually absorb in the ordinary UV region. For example, methyl iodide
shows ëmax at 258 mµ while trimethylamine at 227 mµ.
Both
transitions n ® p* and p ® p* are lower energy than both the s ® s* and n ®
s* transitions, and therefore, take place at longer wavelengths. Furthermore, p
® p*transitions are of lower energy than the n ® s* transitions but require
more energy than the n ® s* transitions. Acetaldehyde shows two absorptions,
one at 180 mµ corresponding to a p ® p* transition while the other at 290 mµ
corresponding to a n ® p* transition.
The
various transitions may be arranged in their decreasing order of energy:
s ® s*
> n ® s*
> p ® p*
> n ® p*
CHARACTERIZATION OF NATURAL DYES
Studies
on the analysis/ identification of natural dyes started as early as nineteen
hundred thirties [Pfister, 1935 and Knecht et al., 1893]. A French chemist
Pfister used a micro chemical analysis in which he achieved the result by color
reactions with different chemicals. Abraham et al., 1964 reported a method using
infrared structural analysis. Many workers have used thin layer chromatography
to identify natural dyes in textiles [Karbade and Agarwal, 1985]. UV– Visible
spectroscopic studies were carried out by Schweppe, 1988. Identification of dyes
in historic textiles using chromatographic and spectrophotometric methods as
well as by using sensitive colours reaction was done by Schaffe. A
non-destructive method was reported of faded dyes on textiles fibers through
examination of their emission and excitation spectra. High performance liquid
chromatography (HPLC) has been used [Walker
et al., 1986] to identify synthetic as well as natural dyes.
Various
techniques that are used for characterization of natural dye are given below:
SOLUBILITY STUDIES
Solubility
of extracted dyes is determined in different solvents, extraction is done on the
basis of the polarity e.g. ether, methanol, alcohol, acetone, ethyl acetate,
dilute acid and alkali. The solubility is determined both at room temperature
and higher temperature (50-60°C).
1. Thin Layer & Column Chromatographic Studies
Thin
layer chromatography is a vers
