By: K. A. Vijay Kumar and M.K. Vittopa
The South India Textile Research Association, Coimbatore - 641 014
Coir is natural vegetable hard fibre, extracted from the exocarp of the fruit of Coconut palm, Cocos nucifera (Linn). These fibres are widely cultivated in the tropics, particularly in India, Srilanka, Malaysia, Indonesia and Philippines. However India and srilanka are the main producers of Coir in the world1.
Coir fibres are largely used in the manufacture of Yarn, Cordage and wide range of furnishings such as mats, mattings, rugs, carpets, cushioning, insulation and packaging materials. The physical characteristics and chemical compositions2 of coir fibre are provided in table 1 and table 2 respectively.
Due to the presence of high quantity of lignin, coir fibre is very hard. Because of the relatively lower Length/Breadth ratio*, spinning of coir fibres is rather difficult. Hence, softening of coir fibres is necessary to enhance their spinnability. Some research studies were conducted earlier to improve the softness of coir fibres. Padmanabhan C.V.3 had tried with oil and water, Bhat J.V. et.al4 had used micro organisms and Prabu G.N.5 had used some organic & inorganic chemicals, to improve the flexibility of coir fibres. In all these techniques flexibility of coir fibres has improved to some extent, but the improvement was not found sufficient to enhance the spinnability of coir fibres substantially.
Earlier, SITRA has conducted extensive trials on softening of pineapple leaf fibres (PALF) towards enhancing its spinnability6. Studies were also carried out to improve the spinning quality of jute by the action of enzymes and other bio-agents7.
Hence, the present study has been conducted to achieve substantial reduction in the rigidity of coir fibres through appropriate softening which is essential for coir spinning.
* L/B ratio of cotton : 1300
L/B ratio of Pine Apple Leaf Fibres : 450
Softening of Coir Fibres
Physical and Chemical Impurities present in Coir Fibres
Mechanically extracted & retted coir fibres were tested for the Length Distribution and presence of physical and chemical impurities using Analytical Methods9,10. The results are given in Table 3.
Mechanically extracted coir fibres have physical & chemical impurities to the tune of 25%. However, in retted coir fibres, the extent of impurities is around 18%.
Several softening trials were carried out using different chemicals & enzymes on Coir fibres. The softening chemicals and softening parameters are chosen with reference to the composition and the properties of coir fibres. Some of the important trials under taken are briefly described in the table 4.
Spinning trials were carried out for coir / jute and coir / sisal blended materials (30 / 70, 40 / 60 and 50 / 50) using the entire chemical and enzyme treated fibres in modified jute flyer spinning system8. Based on the performance of the spinning trials, following softening treatment was found optimum for coir fibres.
Name of chemical : Caustic Soda (Sodium Hydroxide)
Concentration : 10%
Time : 1 hr.
Temperature : Boiling
After caustic boiling, the fibres are washed, neutralised, treated with Magnesium Chloride (to retain the softness imparted to the fibres) and then dried.
SITRA has developed a simple method to test the rigidity of coir fibres using the newly developed method, chemically softened coir fibres as well as untreated coir fibres were tested for their rigidity. The method of determination of rigidity in the new method is shown in Fig.1.
40 mm length of coir fibre (L) is mounted in a frame and a 20 mg of weight is placed at the base. The weight (W) is displaced slowly towards the free end of the fibre. For deviation of 3 mm (i.e. d) from original position, the displacement ��"á� is noted and the same is expressed as rigidity (mm).
Results and Discussions
Effect of Softening on Rigidity of Coir Fibres
The softened and untreated coir fibres are tested for rigidity by using SITRA��s method and the results are shown in the figure 2.
The results show that the rigidity of coir fibres reduced due to chemical softening by about 70%.
Chemically softened coir fibres were also tested for flexural rigidity using the classical Ring Loop Method. The result of flexural rigidity of coir fibres, obtained using Ring Loop Method is as follows.
Flexural Rigidity (gf.cm2)
Before Softening: 1.0793
After Softening : 0.4611
It is discernible from the above result that chemical softening reduces flexural rigidity of coir fibres by around 60%. These results compare favourably with those obtained regarding flexibility of coir fibres assessed using the newly developed SITRA method.
Effect of Softening on Fineness of Coir Fibres
Both mechanically extracted and retted coir fibres tend to become finer (Figure 3) by about 5% due to chemical softening. This may be due to the removal of some of the impurities present in the fibre during chemical softening.
Effect of Softening on Breaking Elongation of Coir Fibres
The effect of softening on breaking elongation of coir fibre is shown in Figure 4:
It is clear from the figure that chemical softening tends to improve breaking elongation of coir fibres, though marginally. This phenomenon of improvement in flexibility, fineness and breaking elongation may be due to the removal of lignin, swelling of fibre and increased moisture content.
1. Treating coir fibres with Caustic soda and after treatment with Magnesium chloride help to soften Coir fibres.
2. SITRA has developed a new method to measure the rigidity of plant fibres like coir, sisal etc.
3. Treating coir fibres with Caustic Soda at a concentration of 10% for a period of one hour (at boil) reduces and after treatment with Magnesium chloride the rigidity of coir fibres by as much as 70%.
4. Results on fibre rigidity obtained using the newly developed SITRA method, compares favourably with that obtained in the classical ring loop method.
5. Chemical softening of coir fibres shows a tendency y to reduce the linear density of the fibres and to improve the breaking elongation.
The authors are thankful to Dr. Arindam Basu, Director, SITRA for his guidance during the progress of this project. Thanks are also due to Mr. Debasis Chattopadhyay, Senior Scientific officer, Spinning Division, SITRA for his guidance through out the course of this work.
1. Robert R Frank
Bast and other plant fibres, Woodland publishing limited, Cambridge, 2005, P. 299
Coir-Its extraction, properties and uses,Council of Industrial Research, New Delhi, 1960, P. 18
3. Padmanabhan C. V.
Coir- Fibre to Fabric Part II Process of manufacture, Coir, Vol.4, No.1, 1960, P. 14
4. Bhat J. V., Kuntala K. G., Parimala Varadarajan and Prabhu G. N.
Softening of Coir Fibre, Coir, Vol.17, 1973, P. 21-26
5. Prabhu G. N.
A review of the chemistry and the Chemical Technology of Coir Fibre Part II Preliminary Treatments - Softening and Bleaching, Coir, Vol.1, No.4, 1956, P. 11
6. Indra Doraiswamy and K.P. Chellamani,
Pineapple Leaf Fibres, Textile Progress, Vol. 24, No.1, 1993,
7. Indra Doraiswamy et al,
Bast and Other Plant Fibres, The Textile Institute, Manchester, 2005, p. 24
8. Indra Doraiswamy and K.P. Chellamani,
Science and Technology in the Manufacture of Jute Products, SITRA, Coimbatore, 2004, p. 27
9. IS 9308 (Part 1 - 3) : 1993, Specification for Mechanically
Extracted Coir Fibre
10. IS 898 : 1999, Specification for Retted Coir Fibre
11. Morton W.E & Hearle J.W.S.
Physical Properties of Textile Fibres, Textile Institute, Manchester, 1997, p. 403
About the author:
SITRA --The south Indian Textile Research Association,
P.B.No.: 3205, Coimbatore Aerodrome Post,
Coimbatore - 641 014,
Tamil nadu, India.
Phone : 91 - 422 - 2574367-9,
Fax : 91 - 422 - 2571896,
Email : email@example.com
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