Dr. N.N. Mahapatra President, Business Development, Colorant Ltd. 3225, Phase IV, G.I.D.C. Vatva, Ahmedabad-382445, Gujarat, India
NATURAL fibres are greatly elongated substances produced by plants and animals that can be spun into filaments, thread or rope. Woven, knitted, matted or bonded, they form fabrics that are essential to society.
Like agriculture, textiles have been a fundamental part of human life since the dawn of civilization. Fragments of cotton articles dated from 5000 BC have been excavated in Mexico and Pakistan. According to Chinese tradition, the history of silk begins in the 27th century BC. The oldest wool textile, found in Denmark, dates from 1500 BC, and the oldest wool carpet, from Siberia, from 500 BC. Fibres such as jute and coir have been cultivated since antiquity.
While the methods used to make fabrics have changed greatly since then, their functions have changed very little: today, most natural fibres are still used to make clothing and containers and to insulate, soften and decorate our living spaces. Increasingly, however, traditional textiles are being used for industrial purposes as well as in components of composite materials, in medical implants, and geo- and agro- textiles.
Ropes and cordage made from coconut fibre have been in use from ancient times. Indian navigators who sailed the seas to Malaya, Java, China, and the Gulf of Arabia centuries ago used coir for their ship ropes. Arab writers of the 11th century AD referred to the extensive use of coir for ship ropes and rigging.
A coir industry in the UK was recorded before the second half of the 19th century. During 1840, Captain Widely, in co- operation with Captain Logan and Mr. Thomas Treloar,founded the known carpet firms of Treloar and Sons in Ludgate Hill, England, for the manufacture of coir into various fabrics suitable for floor coverings.
Total world coir fibre production is 250,000 tonnes (250,000 long tons; 280,000 short tons). This industry is particularly important in some areas of the developing world. India, mainly in Pollachi and the coastal region of Kerala State, produces 60% of the total world supply of white coir fibre. Sri Lanka produces 36% of the total brown fibre output. Over 50% of the coir fibre produced annually throughout the world is consumed in the countries of origin, mainly India. Together, India and Sri Lanka produce 90% of the coir produced every year.
Coir is extracted from the tissues surrounding the seed of the coconut palm (Cocos nucifera), which is grown on 10
million ha of land throughout the tropics. There are two types of coir: brown fibre, which is obtained from mature coconuts, and finer white fibre, which is extracted from immature green coconuts after soaking for up to 10 months.
The coir industry is fully developed only in India and Sri Lanka, but economically important in Brazil, Indonesia, the Philippines and Vietnam. Coconuts are typically grown by small-scale farmers, who use local mills for fibre extraction.
Globally, about 500 000 tonnes of coir are produced annually, mainly in India and Sri Lanka. Its total value is estimated at $100 million. India and Sri Lanka are also the main exporters, followed by Thailand, Vietnam, the Philippines and Indonesia. Around half of the coir produced is exported in the form of raw fibre. Smaller quantities are exported as yarn, and as mats and matting.
Harvesting and husking of coir
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 color. The fibre from the husk is extracted on a commercial scale, either by natural retting process or by mechanical decortication.
Fig.1 : Husking of coir by Machine.
Dr. Mahapatra, C. Col FSDC (U.K), C. Text FTI (Manchester), F.T.A, F.I.C., F.I.E is a B.Sc (Tech), UDCT, Mumbai, M.Sc and PhD, Utkal University, Orissa and MBA I.M.M. Kolkata.
Dr. Mahapatra is having 31 years of experience in textile industries in India and abroad. He has worked in all big textile houses in various senior capacities. He has implemented many new technologies which have given benefits to the Textile Industries. He is a Senior Member of AATCC, Life Member of IIChE, UAA, ICS, ISCA, IEA, IASF; Patron Member ACTI (India) Ahmedabad. Widely traveled, he has contributed more than 225 papers in textile journals having international circulation and presented more than 36 technical papers in various seminars/ conferences in the country and abroad. He has written 4 books (Textile Dyes & Dyeing; Textile Technology; Textile Processing & Textiles and Environment). Presently he is working as president, Business Development, Colorant Ltd, Ahmedabad.
He has been appointed as Vice-Chairman, Textile Association of India, Central Office and was Chairman of Western India section of Textile Institute, Manchester (WISTI)
Retting of coir fibre
Retting is a curing process during which the husks are kept in an environment that encourages the action of naturally occurring microbes. This action partially decomposes the husk's pulp, allowing it to be separated into coir fibres and a residue called coir pith. Freshwater retting is used for fully ripe coconut husks, and saltwater retting is used for green husks.
- For freshwater retting, ripe husks are buried in pits dug along riverbanks, immersed in water-filled concrete tanks, or suspended by nets in a river and weighted to keep them submerged. The husks typically soak at least six months.
- For saltwater retting, green husks are soaked in seawater or artificially salinated fresh water. Often this is accomplished by placing them in pits along riverbanks near the ocean, where tidal action alternately covers them with sea water and rinses them
10 months, although adding the proper bacteria to the water can shorten the retting period to a few days. Fig 2: Retting of coir fibre
- Mechanical techniques have recently been developed to hasten or eliminate retting. Ripe husks can be processed in crushing machines after being retted for only seven to 10 days. Immature husks can be dry milled without any retting. After passing through the crushing machine, these green husks need only be dampened with water or soaked one to two days.
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 fibers spread for drying are occasionally beaten and tossed up with poles to remove the remnants of pith and impurities still adhering to the fibre.
Fig 3: Extraction of coir fibre
Green coconuts, harvested after about six to 12 months on the palm, contain pliable white fibres. Brown fibre is obtained by harvesting fully mature coconuts when the nutritious layer surrounding the seed is ready to be processed into copra and desiccated coconut. The fibrous layer of the fruit is then separated from the hard shell (manually) by driving the fruit down onto a spike to split it (dehusking). A well-seasoned husker can manually separate 2,000 coconuts per day. Machines are now available which crush the whole fruit to give the loose fibres. These machines can process up to 2,000 coconuts per hour.
The fibrous husks are soaked in pits or in nets in a slow- moving body of water to swell and soften the fibres. The long bristle fibres are separated from the shorter mattress fibres underneath the skin of the nut, a process known as wet- milling. The mattress fibres are sifted to remove dirt and other rubbish, dried in the sun and packed into bales. Some mattress fibre is allowed to retain more moisture so it retains its elasticity for twisted fibre production. The coir fibre is elastic enough to
twist without breaking and it holds a curl as though permanently waved. Twisting is done by simply making a rope of the hank of fibre and twisting it using a machine or by hand. The longer bristle fibre is washed in clean water and then dried before being tied into bundles or hanks. It may then be cleaned and 'hackled' by steel combs to straighten the fibres and remove any shorter fibre pieces. Coir bristle fibre can also be bleached and dyed to obtain hanks of different colours.
The immature husks are suspended in a river or water-filled pit for up to ten months. During this time, micro-organisms break down the plant tissues surrounding the fibres to loosen them — a process known as retting. Segments of the husk are then beaten by hand to separate out the long fibres which are subsequently dried and cleaned. Cleaned fibre is ready for spinning into yarn using a simple one-handed system or a spinning wheel.
Researchers at CSIR's National Institute for Interdisciplinary Science and Technolog y in Thiruvananthapuram have developed a biological process for the extraction of coir fibre from coconut husk without polluting the environment. The technology uses enzymes to separate the fibres by converting and solubilizing plant compounds to curb the pollution of waters caused by retting of husks.
Because coir is high in sodium and potassium, it is treated before use as a growth medium for plants or fungi by soaking in a calcium buffering solution; most coir sold for growing purposes is pre-treated. Once any remaining salts have been leached out of the coir pith, it and the coir bark become suitable substrates for cultivating fungi. Coir is naturally rich in potassium, which can lead to magnesium deficiencies in soilless horticultural media.
Coir does provide a suitable substrate for horticultural use as a soilless potting medium. The material's high lignin content is longer lasting, holds more water, and does not shrink off the sides of the pot when dry allowing for easier rewetting. This light media has advantages and disadvantages that can be corrected with the addition of the proper amendment such as coarse sand for weight in interior plants like Draceana. Nutritive amendments should also be considered. Calcium and magnesium will be lacking in coir potting mixes, so a naturally good source of these nutrients is dolomitic lime which contains both. The addition of beneficial microbes to the coir media have been successful in tropical green house conditions and interior spaces as well. However, it is important to note that the microbes will engage in growth and reproduction under moist atmospheres producing fruiting bodies (mushrooms).
Bristle coir is the longest variety of coir fibre. It is manufactured from retted coconut husks through a process
called defibring. The coir fibre thus extracted is then combed using steel combs to make the fibre clean and to remove short fibres. Bristle coir fibre is used as bristles in brushes for domestic and industrial applications.
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 color and gives a certain amount of brightness for the production of mats, Coir mats, fibre mats, especially mats, Mattings, rugs, mourzouks, carpets etc.
Dyeing and Printing
Color 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 dyestuffs are employed in coir dyeing. Chrysodin YS, Bismarck Brown, Methyl Violet, Malachite Green, Magenta, Naphthalene orange, Naphthalene Red, Naphthalene Green etc.
Chemical Composition of Coir Fiber
- Pectin's and related Compound......03.00%
- Water soluble...........05.25%
Properties of coir fibre
Coir fibres are found between the hard, internal shell and the outer coat of a coconut. The individual fibre cells are narrow and hollow, with thick walls made of cellulose. They are pale when immature, but later become hardened and yellowed as a layer of lignin is deposited on their walls. Each cell is about 1 mm (0.04 in) long and 10 to 20 µm (0.0004 to 0.0008 in) in diameter. Fibres are typically 10 to 30 centimetres (4 to 12 in) long. The two varieties of coir are brown and white. Brown coir harvested from fully ripened coconuts is thick, strong and has high abrasion resistance. It is typically used in mats, brushes and sacking. Mature brown coir fibres contain more lignin and less cellulose than fibres such as flax and cotton, so are stronger but less flexible. White coir fibres harvested from coconuts before they are ripe are white or light brown in color and are smoother and finer, but also weaker. They are generally spun to make yarn used in mats or rope.
The coir fibre is relatively waterproof, and is one of the few
natural fibres resistant to damage by saltwater. Fresh water is used to process brown coir, while seawater and fresh water are both used in the production of white coir.
Coir fibres measure up to 35 cm in length with a diameter of 12-25 microns. Among vegetable fibres,coir has one of the highest concentrations of lignin, making it stronger but less flexible than cotton and unsuitable for dyeing. The tensile strength of coir is low compared to abaca, but it has good resistance to microbial action and salt water damage.
Coir is a material which is widely used to overcome the problem of erosion. When woven into geotextiles and placed on areas in need of erosion control it promotes new vegetation by absorbing water and preventing top soil from drying out. Coir geotextiles have a natural ability to retain moisture and protect from the suns radiation just like natural soil, and unlike geo-synthetic materials, it provides good soil support for up to three years, allowing natural vegetation to become established.
The waste product from milling the coir is peat or pith which makes for high quality mulch and fertilizer. Coir peat compost developed from coir waste is an excellent organic manure and soil conditioner applicable to agricultural
Physical Properties of Coir Fiber
- Length in inches..............6-8
- Density (g/cc)...............1.40
- Tenacity (g/Tex)..............10.0
- Breaking elongation%..............30%
- Diameter in mm...............0.1 to 1.5
- Rigidity of Modulus..............1.8924 dyne/cm2
- Swelling in water (diameter)..............5%
- Moisture at 65% RH..............10.50%
Uses of coir fibre
Red coir is used in floor mats and doormats, brushes, mattresses, floor tiles and sacking. A small amount is also made into twine. Pads of curled brown coir fibre, made by needle-felting (a machine technique that mats the fibres together), are shaped and cut to fill mattresses and for use in erosion control on river banks and hillsides. A major proportion of brown coir pads are sprayed with rubber latex which bonds the fibres together (rubberised coir) to be used as upholstery padding for the automobile industry in Europe. The material is also used for insulation and packaging.
The major use of white coir is in rope manufacture. Mats of woven coir fibre are made from the finer grades of bristle and white fibre using hand or mechanical looms. White coir also is used to make fishing nets due to its strong resistance to saltwater.
In horticulture, coir is a substitute for sphagnum moss because it is free of bacteria and fungal spores. Coir is also useful to deter snails from delicate plantings, and as a growing medium in intensive glasshouse (greenhouse) horticulture.
Coconut coir from Mexico has been found to contain large numbers of colonies of the beneficial fungus Aspergillus terreus, which acts as a biological control against plant
Coir is also used as a substrate to grow mushrooms. The coir is usually mixed with vermiculite and pasteurized with boiling water. After the coir/vermiculite mix has cooled to room temperature, it is placed in a larger container, usually a plastic box. Previously prepared spawn jars are then added, spawn is usually grown in jars using substrates such as rye grains or wild bird seed. This spawn is the mushrooms mycelium and will colonize the coir/vermiculite mix eventually fruiting mushrooms.
Coir is an allergen, as well as the latex and other materials used frequently in the treatment of coir.
Coir can be used as a terrarium substrate for reptiles or arachnids.
It is used in products such as floor mats, doormats, brushes, and mattresses. Coir is the fibrous material found between the hard, internal shell and the outer coat of a coconut. Other uses of brown coir (made from ripe coconut) are in upholstery padding, sacking and horticulture. White coir, harvested from unripe coconuts, is used for making finer brushes, string, rope and fishing nets.
Traditionally the coconuts were left to cure in water for several months (or in brine for a longer period for white fibres) then the coir was extracted. However with technology there is an increased use of coconut husk defibering machines.
Typically, white coir spun into yarn is used in the manufacture of rope and, thanks to its strong resistance to salt water, in fishing nets. Brown coir is stronger and more widely used than white coir. Applications include sacking, brushes, doormats, rugs, mattresses, insulation panels and packaging.
Recognition of coir for sustainable vegetation and erosion control arises from the fact that it is an abundant, renewable natural resource with an extremely low decomposition rate and a high strength compared to other natural fibres. Coir is woven into thick textiles which are applied like blankets on the ground in erosion prone areas. Geotextiles made from coir are durable, absorb water, resist sunlight, facilitate seed germination, and are 100% biodegradable. These blankets have high strength retention and a slow rate of degradation meaning they last for several years in field applications.
Coir is widely used in the upholstery industry, and it is a healthy substitute for processed synthetic rubber. It is also used as a combination with natural rubber and is used for filling up mattresses, automobile seats, sofas, settees, and seating systems. European automobile producers upholster cars with pads of brown coir bonded with rubber latex. Coir is used for insulation and finds application in panels, cold storages, food industry, etc.
A substitute to plywood, coir ply is an innovative product that when is added together with resin and limited pre-treated timber veneers. In India the product has been well accepted by the market as an alternative to plywood. Substituting coir for other timber products could also save a substantial amount of tropical trees being logged for this purpose.
Coir ply has all the properties of phenol-bonded ply with the added strength of fibre reinforced phenol bonding. It has high degrees of surface abrasion resistance and resists contraction/expansion due to variations in temperatures. White coir spun into yarn is used in the manufacture of rope (at left) and, thanks to its strong resistance to salt water, in fishing nets.
Brown coir is used in sacking, brushes, doormats, rugs, mattresses, insulation panels and packaging. In Europe, the automobile industry upholsters cars with pads of brown coir bonded with rubber latex.
Geotextiles made from coir mesh (at left) are durable, absorb water, resist sunlight, facilitate seed ger mination, and are 100% biodegradable.
Coir peat (right), a residue of milling, is gaining economic importance as mulch, soil treatment and a hydroponic .