The natural protein fibers Silk and Wool possess so many attractive properties that they have always served as quality fibers in the textile industries. Similarly the natural plant fibers like Cotton, Flax, and Ramie etc. have established their own importance in the textile industries. But nowadays regenerated fibers are getting importance in the textile industries like Viscose, Tencel, Modal, Casein, Soybean fiber etc. In the coming years, these fibers are going to occupy the leading positions in the textile manufacturing. As these fibers are having both the properties of natural and synthetic fibers, they are going to have an added advantage. They can easily be blended with both natural and synthetic fibers.
Vegetable protein fibers and groundnuts:
The proteins from which these animal fibers are made come, in the first place, from proteins in the plants that are eaten by animals as food. These plant proteins differ from animal proteins in the detailed structure of their molecules. But all proteins are basically similar in chemical design. All protein molecules are in the form of long threads of atoms. Plant proteins, as well as animal proteins, are therefore able to satisfy the first requirement of a fiber-forming material.
In 1935, Prof Astbury and Prof Chibnall gave an idea to ICI, the UK that fibers can be made by dissolving vegetable proteins in urea and extruding the solution through spinnerets into coagulating baths. The regenerated protein fibers made in the mid-twentieth century were basically developed as a substitute for wool. For the production of protein fiber, the main emphasis was given to the commercial availability and their usefulness for the textile purpose. Theoretically, any protein containing substance may serve as a starting material, and the protein may be extracted from it.
There are four proteins, which are more important as the source for fiber formation.
- Casein fiber from milk.
- Zein fiber from maize.
- Soya fiber (glycinin) from
- Groundnut fiber (arachins) from groundnuts.
- Ardil from
One of the most likely sources of vegetable protein for fiber production was groundnuts, which grow as a staple product in many of the hot, humid regions of the world.
Groundnuts (peanuts, monkey nuts) are used in large quantities as a source of the arachis oil required for making margarine. The meal remaining after removal of the oil contains a high proportion of protein. This protein was regarded as a potentially suitable source of vegetable protein. The nuts contain around 25 % protein and can be good and can be good and cheap resources for protein fiber.
Experiments were carried out and a process was developed for making the groundnut protein fiber which became known as ‘Ardil’. The fiber was first made at Ardeer in Scotland. Commercial production started in 1951.
Production of groundnut fiber:
Groundnuts are cultivated in India, China, West Africa, and southern states of U.S.A. After harvesting, the nuts are shelled or decorticated. The red skins are removed from the shelled nuts, together with foreign matter such as small stones and nails.
There are five main steps to produce Groundnut fiber.
- Extraction of oil to obtain oil-free meal: The nuts, which contain about 50 % of oil, are crushed and pressed. About 80% of the available oil is squeezed out, leaving the oily groundnut meal which is reduced in breaker rolls and passed through flaking rolls. The thin flakes pass via a series of buckets on an endless chain into an extraction plant. As they pass through the plant, the buckets of the meal are subjected to a thorough washing with a solvent (Hexane) which removes the remainder of the Arachis oil.
- Extraction of protein: The extracted meal is heated under low pressure in steam jacketed pans to remove residual solvent. It is then cooled, screened, weighed and bagged.
This special technique for removing oil from groundnut meal was devised to provide protein suitable for fiber production. The groundnut protein is extracted from the meal by dissolving it in caustic soda solution. The residue after extraction is a valuable cattle food. Then acidification of the protein solution precipitates the protein, which is the raw material from which fiber is spun.
- Preparation of spinning solution: The spinning solution is prepared by dissolving the extracted protein in aqueous urea, ammonia, caustic soda and solutions of detergents. Caustic soda is used for dissolution. It is allowed to mature under controlled condition for 24 hours. During the maturation, the viscosity of the solution increases and attains the spinning characteristics. The solids content of the protein is between 12 -30 %.
- Fiber formation: Groundnut fiber is formed by the wet spinning method. The solution of groundnut protein is filtered and pumped to spinnerets, through which it is extruded at a constant rate into an acid coagulating bath. The spinneret holes are typical of 0.07 – 0.10 mm diameter.
The coagulating liquor consists of a solution containing sulphuric acid, sodium sulfate, and auxiliary substances. It is maintained at a temperature between 12-40 deg c.
- After treatments: As the filament is being spun, it is stretched to increase the alignment of the protein molecule. It coagulates to a filament that is weak and flabby when wet and brittle when dry. At this stage, the filament dissolves easily in dilute saline solution and in dilute acid and alkali. After leaving the coagulating bath it is treated with formaldehyde to harden and insolubilize it, and it is then dried and cut into staple fiber.
Properties of groundnut fiber:
|Table 1: Properties of groundnut fiber and its comparison with other major fiber|
|Moisture regain, %||12-15||11.0||14-16||9|
|Resistance to moth/fungus||Resistance to fungus but not to moth||Resistance to fungus but not to moth||Resistance to fungus but not to moth||Resistance to moth but not to fungus|
|Flammability||Burns very slowly||Burns||Burns slowly||Burns|
Groundnut fiber is having a circular cross-section and smooth, slightly striated surface. It is having tensile strength of 8-12 kg/mm2 (11,000-14,000 ib/in2). It does not soften or melt on heating. It chars at 250 deg c. It is degraded by sodium hypochlorite and sodium chlorite bleaches. Good resistance to organic solvents. Maybe dry cleaned without difficulty.
Groundnut protein fibers are generally similar to wool in that they are protein in structure. They do not have the rough scaly surface of wool fibers and do not undergo felting in the way that wool does.
Groundnut protein molecules carry many side chains, and they cannot pack so closely together as the molecules of silk. Groundnut protein yields a relatively weak fiber, which is much more sensitive to moisture than wool.
The blending of groundnut fiber: One of the outstanding characteristics of groundnut protein fiber is soft, wool-like handle. The price of groundnut protein fiber is half the cost of wool fiber. And it is used largely as a diluent fiber which provides wool-like characteristics at low cost. It is used in various worsted units along with wool and polyester. And it is also used with cotton and viscose in various proportions.
Chemical processing of groundnut fiber:
Groundnut protein fiber has different physical and chemical construction from natural protein fiber, care is taken in the following steps.
- Scouring: During scouring the alkali concentration should be less as compared to other textile fibers and the temperature should be less than 98 deg c. Wool type scouring conditions are suitable for 100 % groundnut protein fibers and kier type boiling should be avoided while processing groundnut blended fabrics.
- Bleaching: It should be borne in mind that Sodium Hypochlorite and Sodium Chlorite cannot be used for bleaching of groundnut protein fiber because it causes degradation. Therefore Hydrogen peroxide is the preferred bleaching agent. The dosage has to be decided depending on the quality of Groundnut fiber.
- Dyeing: Groundnut protein fiber is dyed with the same dyes used for dyeing of wool fiber like Acid dyes, Metal complex dyes, Chrome dyes and few Reactive dyes. Dyes are selected according to end uses of fibers and dyeing fastness. The dyeing method is just like dyeing of wool fiber. But the differences in protein structure result in different individual characteristics. In general, the affinity for dyes is higher than that of wool. It can be dyed in form of loose fiber, tops, yarn hank and fabric (both knitted and woven).
Uses of groundnut protein fiber (GPF):
In the 1950s ardil fiber (groundnut protein fiber) was intensively marketed for industrial and domestic uses. Dresses, suits and pajamas were promoted with the slogan ‘Happy families wear clothes that contain Ardil’. Ardil fibers were used as garments, carpets or upholstery. Ardil/Wool blends were used for sweaters, blankets, underwear, carpets and felt. Blends with cotton were used for sports shirts, pajamas, dress fabrics, and blends with rayon for costume and dress fabrics, tropical clothing, sports shirts, and carpets. In course of time, these fibers were subsequently overshadowed by the successful synthetic fibers such as nylon and have been largely forgotten. However, presently more eco-friendly and biodegradable material has been given importance and so the manufacture of these fibers again getting momentum. Groundnut fiber is more commercialized now and it is expected that others will also follow.