Updated: Sep 10, 2021
Coir is a natural, fruit fiber which is obtained from the husk of the coconut fruit. It is also called as the golden fiber because the color of the fiber is gold. Coir, Cocos nucifera and Arecaceae are the common name, scientific name and plant family respectively.
Coconut tree also referred as the “tree of life’’ which grows in tropical and subtropical countries. It requires the minimum average temperature is at least 72 degrees Fahrenheit and the annual rainfall amount is at least 30 to 50 inches. An extremely healthy coconut tree survive up to 100 years and yield up to 75 fruits per year. Indonesia, Philippines, India, brazil, Srilanka are the top 5 coconut producers in the world. The global production of coir fiber is about 350,000 metric tons.
The yield of fiber mainly depends on season, method of extraction and the quality of fiber produced.
Manufacturing process of coir fiber:
Harvesting and husking: the husks are taken out from the ripe coconuts but the unripe coconuts has to dry. A steel-tipped spike to split the husk from the coconut. About 2000 coconuts can peel manually by a skilled husker in a day. Husking machines can process 2000 coconuts per hour. For fully ripe coconuts fresh water retting is used and for green husks salt water retting is used.
Retting: In this process the coconut husk is soaked in water for 6 to 10 months to promote bacterial action to facilitate separation of fiber. Separation of leathery exocarp from the fibrous mesocarp is known as retting. Breakdown of pectic substances and decomposition of husk’s pulp takes place in this process.
Mechanical techniques has been recently developed to eliminate retting. Ripe husks has to be retted for only 10 days and after that can be processed in crushing machines.
Extraction of fiber: after the process of retting, the husks are taken out from the water and washed to get rid of dirt and mud. Then the outer skin is peeled off and the husks placed on wooden blocks and beaten with a wooden mallet for separating the fiber from the pith. Further cleaning is done to remove the pith and impurities adhering to the fiber.
Commercial varieties of coir fiber:
Mat Fiber(White Fiber): The fine yarn fiber or mat fiber is the finest and longest variety obtained from the retted husks. It is highly resistant to microbial decay.
Mattress Fiber: referred as short fibers. Fiber of inferior quality(shorter, staple fiber)and the mattress fiber obtained by partial retting of husks. It is considered the best fiber for curling prior to the impregnation with rubber latex.
Bristle Fiber: Referred as long fibers. The thicker and coarser variety extracted from dry coconut husks is known as the bristle fiber. Bristle and mattress fiber are often referred to as brown fiber.
Decorticated fiber: Referred as mixed fibers.
Types of coir fiber:
Chemical Composition of coir ( wt. % ) :
Microfibrillar/spiral angle (Deg.): 41-45
Moisture content: 8.0
Properties of coir fiber:
Coir is light, elastic and water resistant and also resistant to mechanical wear.
It degrades between 190 to 230 ͦ c.
Coir is most resistant to chemical and microbial attack due to lignin content. Resistant to acids.
Cross section: polygonal or round.
Its resistance to microbial degradation and salt water is unique.
Length in cm : 15-20
Diameter (mm) : 0.1 to 1.5
Density (g/cc) : 1.15
Tenacity (g/tex) : 10.0
Tensile strength (MPa) : 131 to 175
Young’s modulus (GPa) : 4 to 6
Elongation at break (%) : 15 to 40
Swelling in water (diameter) (%) : 6 to 8.5%
Breaking elongation (%) : 30%
Moisture at 65% RH: 10.50%
Fineness : >50 µm and ˂300 µm
Advantages of coir fiber:
Made from infinitely replenish able resources
Not easily combustible
Easy to clean
Totally static free
Tough and durable
High water retention
Moth and rot resistant
Good insulator of heat and sound
Coir fiber has the advantage of stretching beyond its elastic limit without rupturing, as well as having the power to take up a permanent stretch.
Brown coir fiber is used for making floor mats, doormats, brushes, mattresses, upholstery padding, sacking and horticulture.
White coir fiber is used for making finer brushes, string, rope and finishing nets.
Coir geo textiles have been developed for application towards erosion control, to make use of the positive attributes such as high water absorption, drapability, formation of mini check dams etc.