Coir is a lignocellulosic hard fibre with a very high content of lignin 40% and high extensibility which distinguish it from other cellulosic fibres. The advantages of natural lignocellulosic fibre include acceptable specific strength properties, low cost, low density and biodegradability. Coir has remarkable stretching properties besides possessing high resistance to attack from microorganisms because of its impervious nature. The realization of the deleterious effects of synthetics and environmental concern has increased the demand for coir.
Lignin is the main constituent of coir fibre responsible for its harshness, dark color and branching patterns. Lignin is closely associated with cellulose and hemicellulose in hardening and strengthening .Lignin provides protection to cellulose from degradation, as lignin itself is extremely resistant to chemical and biological degradation only a few microorganisms are able to mineralize it. Lignin degradation is a rate limiting step of carbon recycling .Thus lignin forms a barrier against microbial destruction by protecting the readily assimilable polysaccharides. The white rot fungi (Basidiomycetes) have the ability to degrade lignin e.g. Phanerochaete chrysosporium .Lignocellusoic resources exposed out doors undergo photochemical degradation caused by ultraviolet radiation. This degradation take place primarily in the lignin component it is responsible for the characteristic color changes. Poor photo stability of coir fibre by photo degradation is one of the disadvantages for production of good coir yarn and Products. There fore biobleaching and biosoftening seems to be very important for making diversified end products from fibre.
The mechanical extraction of coir is an acceptable alternative to fibre production by conventional methods (Retting). The greatest disadvantage of the mechanically extracted fibre is inconsistent color and harsh texture.The application of biotechnology may be well adopted for coir softening and brightening.
New environment friendly methods for fibre production having the potential to produce more consistent quality of fibre are of interest. As lignin is main constituent of coir responsible for its stiffness, microbes that selectively remove lignin with out loss of appreciable amount of cellulose are extremely attractive. Biosoftening of unretted coir fibre is more advantageous than the retted fibre.
Improvement in the feel of the coir fibre can be achieved by two methods
1. By treatment with selected chemicals which can modify the surface properties of the fibre and thus improve its physical characteristics.
2. By elimination of the incrusting substance to a desirable extent with out adversely affecting the other properties.
Chemical methods employed for softening and bleaching using compounds like Chlorine, Caustic soda are not environmental friendly. Unlike the weak chemically softened fibre, microbial treatment will produce soft, white fibres having better tensile strength and elongation properties.
Biobleaching of coir
The biological method of bleaching/brightening ie using effective microbial enzyme that is able to remove the lignin from the fibres. Now it can be done by bacterial and fungal cultures especially by using xylanase of fungal origin.Other biotech agents that could be used for this purpose are ligninase and hemicellulase. By the degradation of xylan from the fibre surface using xylanases, lignin can be more easily removed.Partial delignification of the fibre does not affect the strength of the coir fibre. Thus using selective strains of microorganism and an environment friendly method, superior quality fibre can be produced.
Xylanase - causes increased permeability and allows passage of lignin to come out of the fibres e.g. Aspergillus niger
Ligninase - can degrade lignin into its sub products. e.g. Pleurotus sajor-caju
Biosoftening of coir
As lignin is the main constituent of coir responsible for its stiffness ,microbes that selectively remove lignin with out loss of appreciable amounts of cellulose are extremely attractive in biosoftening .Biosoftening aims to achieve a bio-polishing effect with the use of specific microorganism,with selected enzyme specificity towards cell wall component.Biosoftening of unretted coir fibre is more advantageous than the retted fibre .This bring about softening ,thinning and bleaching of the fibre and avoids the use of chemicals there by minimizing pollution.Basidiomycetes fungi can be useful to recover soft and white fibres. The process is more efficient in degrading lignin and toxic phenolics. Phanerochaete chrysosporium, Pleurotus eryngii, Ceriporiopsis subvermispora were found to degrade lignin efficiently without any appreciable loss of cellulose yielding good quality fibre ideal for dying. The raw fibre treated with Psudomonas putida and Phanerochaete chrysosporium produced better softened fibre.
In coir sector, process efficiency can be achieved by means of using biotechnological tools i.e. by altering the genetic make up of a particular strain for a desired purpose using genetic engineering techniques. Thus we can produce an improved strain having better characteristics. There fore special techniques have to be formulated to explore the possibilities of enzymatic quality improvement of coir fibre.There by we can minimize the environmental issues related to the coir industry.
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Doing research in coir