Coir or coconut fibre belongs to the group of hard structural fibres. It is an important commercial product obtained from the husk of the coconut. Industries based on coir have developed in many coconut producing countries especially India, Tanzania, Kenya, Bangladesh, Burma, Thailand, Sri Lanka, Nigeria, Ghana etc. In India, coir manufacture is a traditional industry, which has taken deep roots in the economic structure of the rural areas in the coastal states. The industry sustains over half a million people and contributes substantial foreign exchange to the national exchequer. India was ranked first among the coconut producing countries of the world until 1921, since then, the position has changed. Indonesia and Philippines have increased their production and India now occupies a third place. These three countries together account nearly 65 percent of the world production (4.5 m mt) out of which India’s share is about 25 percent.
Harvesting and Processing
The fruits are harvested when still green to obtain the best quality coir. Husk usually forms 35.45 percent of the weight of the whole nut, when ripe. Husks from ten to eleven month old nuts have been found to give superior quality fibre possessing a golden yellow colour. The fibre from the husk is extracted on a commercial scale, either by natural retting process or by mechanical decortication.
The process involves soaking of the husks in water preferably saline water for a certain period until the fibre becomes loose and soft. The soaking is done either in pits dug near lagoons or by the sides of backwaters where water flows in and out with the rise and fall of the tide.In some areas soaking is done in enclosures erected in shallow brackish waters with coconut leaves and petioles. After the husks are filled in the soaking pits, nets or enclosures, they are covered with coconut leaves and mud and weighted down to prevent floatation when immersed in water.
During the retting process, the husk becomes soft and a number of substances like carbohydrates, glycosides, tannins and nitrogen compounds are brought into solution. The carbohydrates and nitrogen compounds are acted upon by a great variety of anaerobic organisms, which produce various organic acids and gas. When the fermentation progresses, the temperature of the husk increases, water becomes turbid due to gas formation and frothing, and the pectin in the middle lamella of the husk slowly dissolves subsequently, the rate of fermentation slows done and the water becomes clear without the evolution of gases and the consequent frothing. At this stage, the husks are ready for removal. The period of retting is longer (8-10 months) in saline water and shorter (4-6 months) in fresh water.
Mechanical methods of retting are employed in areas where facilities for natural retting do not exist. Either dry or green husks are soaked in cement tanks for a period varying from a few hours to three weeks and the fibre extracted manually or mechanically. In one method, the husks are first crushed through a series of corrugated iron rollers, a machine called husk crusher. Then the husks are thrown into a retting tank where they undergo fermentation for a minimum period of 72 hours. This process, however, does not yield fibre of spinnable quality as in the case of natural retting, but yields only bristles and mattress fibres.
Various chemical methods have also been developed for the retting of husk. The advantages claimed includes higher yield of uniform quality fibre and a considerable saving of time.
- Nanji Process. The green or dry husks are partially crushed and treated under steam pressure of 36.4-45.4 kg/sq. inch. With sodium sulphate or sodium carbonate containing traces of aluminium sulphate for 1-2 hours . During this process the pith is loosened from the fibre and removed by washing. The fibre obtained is of good quality but slightly darker than that of natural retting.
- Elod and Thomas Process. The crushed husks are immersed in hot water twice. Slaked lime or similar substance is added during the second immersion in order to avoid discolouration. Subsequently, the fibre is extracted mechanically.
- Rowel Process. The crushed husks are subjected to a high steam pressure and the fibre come out loose from the steaming chambers.
- Vander Jaget Process. The husks are first split into pieces. The pieces are than boiled with a weak solution of caustic-soda and squeezed. The compressed fibres are reopened, softened and cleaned. It is claimed that good quality fibre could be produced using this technique in less than two hours.
- Caraan Process. The husk is fermented for four days at 37°C with the aid of the fungus Aspergillus sp., previously isolated from partially retted husks. This process is reported to give 37 percent fibre output.
Extraction of Fibre
After retting, the husks are taken out of water and washed. Outer skin peeled of, placed on wooden blocks and beaten with a wooden mallet for separating the fibres from the pith. After fibres are separated from the pith, these are cleaned and then spread on shade for drying. The fibres spread for drying are occasionally beaten and tossed up with poles to remove the remnants of pith and impurities still adhering to the fibre. For making superior types of fibre, especially for spinning, improved methods exist.
It is estimated that the annual production of coir in India nearly amounts to 1 m mt. Three classes of fibre are recognized in the trade. They are Mat, Curl (toe or mattress)and Bristle fibre. The bulk of fibre produced in the west coast of India is mat fibre. Mat fibre is sometimes used as a substitute for hemp in certain cordages. Curl fibre is obtained mostly from unretted husk and is short; it is used for mattresses or for stuffing upholstery, cushions etc. Bristle fibre, which is coarse and thick, is used for making brushes, and brooms. Bristle fibre is not produced in India, but mostly imported from Sri Lanka.
- Individual fibres are 0.3-1.0 mm long and 0.01-0.0.2 mm in diameter; the ratio of length to diameter being 35. The lumen is medium to large, polygonal-rounded, or elliptic. The vascular bundle is collateral and is surrounded by thick sclerenchymatous sheath. Lignin and hemicelluloses, which form the cementing materials of fibre cells, increase with the age of the fibre and the pectin decreases. As the lignin content increases, the fibre becomes stiffer and tougher.
- Length of the fibre determines its spinnability and commercial utility. Spinnability may be defined as the ease with which textile fibres may be twisted into continuous, uniform yarns, having commercially acceptable properties.
- Fineness of a fibre is usually expressed by its diameter in microns or by the weight of the fibre per unit length- dinier. The compactness and strength of a yarn or cord depends on the cohesion between individual fibres.
- Strength or tensile strength of a fibre is determined by its ability to resist strain or rupture induced by tension , and is a determining factor in the selection of a fibre.
- Elongation at rupture is a criterion of practical value and is an index of the work that could be performed by the fibre within the limits of its breaking load.
- Torsional rigidity. Stresses in the fibre due to twisting and bending or important factors which affect the diameter of the yarn, its ability to snarl, its pliability and elastic recovery from small strains and internal pressures.
The chemical composition of coconut husk and coir fibre:
|Total water solubles||26.00|
|Pectins etc. soluble in boiling water||14.25|
Coir fiber is classified according to its length. Following lengths are commonly visible
- Long fibres (15 cms. And above)
- Medium ( 12-15 cms.)
- Short ( 6-8 cms.)
- Very short (4 cms.)
Coir has been found to be remarkably resistant to both fungal and bacterial decomposition.
Spinning of coir yarn is mainly a cottage industry in India and abroad. It is produced either by wheel spinning or hand spinning or mechanized spinning. Handspun yarn is soft and the twist and thickness are even. Wheel spun yarn has a hard twist; it is stronger and more uniform in size and twist than handspun yarn.
The classification of coir yarn is based on variations of color, twist, pitch, scorage etc. and also area of production like; Anjengo, Aratony, Alapat, Beach, Rope yarn, Parur, Muppiri etc.
Coir yarn is treated with dilute solution of sulphuric acid, which improves its colour and gives a certain amount of brightness for the production of mats, Coir mats, fibre mats, speciality mats, Mattings, rugs, mourzouks, carpets etc.
Dyeing and Printing
Colour and design play an important part in the marketing of coir products. Dyed yarn is exported to Australia for the manufacture of matting. The following dye stuffs are employed in coir dyeing. Chrysodin YS, Bismarck Brown, Methyl Violet, Malachite Green, Magenta, Naphthalene orange, Naphthalene Red, Naphthalene Green etc.
Ropes & Cordages
Coir is resistant to the action of water and has the property of elongation without breaking. By virtue of these properties, coir has long been used for ropes and cordages. Very short (4 cms.)
Uses of Coir
- Besides its main use as floor covering and in rope making, coir fibre finds extensive use as packaging material to protect goods against shock in transport.
- Coir fibre finds its use in the production of activated carbon, artificial horse hair, paper pulp, roofing tiles, writing boards, thermal insulations, high stretch paper, manufacture of olive oil filters etc.
- In Germany, coir is rubberized for making cushion seating for automobiles and railways. The rubberization is brought about by Splashing layers of coir fibre and rubber with the help of a specialized machine.
- Coir yarn has been found to be ideal lead for hop wines which is used in brewery in U.S.A Coir bags are used in tea estates for collecting tea leaves and for transportation: and also for lifting coal from mines.
- Coir yarn is used for making fenders which are attached to ships and boats for preventing collision and shock.
- Coir mats are used for commercial packaging purposes and circular brush mats are used for packing.
- Coir mattings after bituminisation offer possibilities of being used as floor covering in godowns to withstand moisture adsorption by stored goods.
- Rubber backed coir mats are sol-proof, sound absorbent and do not scratch polished floor. Heavy matting made out of thick coir rope is being used for transporting gas cylinder. It is used as a strainer in tube wells in place of wire mesh.
- Hardboards made of coconut husk shorts and coir dusts are durable, smooth, insect proof, fire retarding and water-repellent. They may be sawed, nailed, glued and finished into particular requirement.
- Coir waste has been recently used in the manufacture of Coirolite by incorporating with resins and other ingredients by the usual techniques of plastics manufacture. The powder so obtained is hotpressed to obtain articles of any shape using appropriate moulds. It is a tough and hard material and possesses good strength and electrical resistance.