by I.R.Anto, PK.Ravi and U.S.Sarma, Proceedings of the International Workshops on Wet Processing 

of Coir 9-9 Dec.1997, Aleppey

One of the components of the FAO-CFC Project at CCRI is to develop a process for softening coir fibre/yarn for the production of diversified coir products like mats/mattings/carpets of supple feel and improved texture on industrial scale.  The literature survey revealed that a lot of indigenous and overseas firms are engaged on manufacture of specialty chemicals which can be used for finishing textile fibre for getting soft and supplements to the final material.  The softeners which were used by earlier researchers for imparting soft and supple feel to textile materials have been identified for treatment of coir.

Though the cost factors stand in the way of their application, it was possible to conduct laboratory level studies for imparting softness to coir fibre/yarn using the textile softens with cooperation from the indigenous and overseas firms.  The change in quality and effluent parameters were also taken into consideration.

 A device has also been designed and fabricated for measuring the relative degree of softness imparted to coir fibre and the flexural rigidity and percentage improvement to softness of treated coir fibre were measured.

Coir fibre is a lignocellulosic, hard vegetable fibre extracted from the husk of coconut. The physical and chemical characteristics of fibreous materials are to a great extent, influenced by the ingredients, constituting the fibre and the nature of the dispersal of these ingredients in the fibre structure, Pure cellulosic fibre like cotton is comparatively soft whereas the coir fibre which contains about 40% lignin, is hard and stiff in nature, Improvement in the feel of the coir fibre could be attempted by two methods (1) by treatment with selected chemicals which can modify the surfare properties of  fibres and thus improve its physical characteristics and (2) by elimination of the incrusting substance to a desirable extent without adversely affecting the other properties.

Earlier reports of J.V. Bhat indicate that modification in the retting of coconut husk to produce a soft and supple fibre, yielded limited success only.

The softening agents may be divided into the following classes:

a)      Emulsion of oils, fats, and waxes

b)      Soaps

c)      Sulphonated oils

d)      Sulphated alcohols

e)      Fatty acid condensation products

f)        Quaternary ammonium compounds.

Fundamentally, the softening depends on the surface application of oils, fats or waxes in one form or another.  These softeners may be applied to impart softness, smoothness, suppleness and flexibility.

Softeners from tallow, oils and the various soaps are still in common use.  Tallow is both cheap and abundant and capable of giving excellent softening under certain conditions, particularly when suitably emulsified.

Alkali transforms the fatty acids into soaps, which in addition to their detergent action, have great value as softeners, the saturated fatty acids are preferred.  Triethanol amine soaps are prepared by mixing molecular proportions of triethanol amine with the fatty acid such as oleic, palmitic or stearic acid.

Sulphonated oils give the best penetration with a fine and soft handle, talow penetrates les and gives a mellow feel, but better results are obtained from the stearic softeners which penetrate least.  The reactive silicone softeners and their derivatives also produce excellent results.

It is reported that a mixture of borax and stearic acid is a very good softener.  Another simple softener is obtained by emulsifying stearic acid with potassium stearate.

The hygroscopic compounds such as chloride of Zn, Ca, and Mg to some extent serve  the purpose of softening through retention of moisture but quite often retain too much moisture and produce conditions which favour the formation of mildew.  Glycerin to the extent of 1 to 2 % on the weight of the material is also used as a softener.

The action-active softening compounds are very good softening agents Eg. Cetyl, pyridinium bromide, Anion-active softeners such as Sodium lauryl sulphate are also reported to be good softening agents.  The non-ionic surface active softeners also have moderate softening properties.

Earlier, Central Coir Research Institute, Kalavoor the research centre of Coir Board, conducted studies to soften the coir yarn by treating the fibre/yarn with dilute caustic soda solution (1% w/v) at 100^o C for 1 to 2 hours.  This yielded a soft material of deep brown colour which required further bleaching to improve its colour.

The treatment of coir yarn with caustic soda solution (20% o.w.m) in cold for 24 hours was observed to soften coir to a considerable extent imparting comparatively smooth and supple feel. The treated material was then kept in 0.3% sulphuric acid solution for half an hour.  Subsequently, the material was washed thrice in cold water and dried in air.  The loss in the weight of coir yarn treated by 20% caustic soda was observed to be 16.25%.  One of the major disadvantages noticed in this process is that, the softened yarn due to its fluffy nature, was not suitable for the preparation of chain beams required for its conversion into coir products like mats/mattings.  The method is not in vogue in coir industry due to the environmental considerations also, as the caustic soda treatment leads to a huge quantity of toxic effluent.

In the Biopolishing process silky softness is imparted to the  material by the action of cellulase enzymes.  There are exo-and endo types of cellulose activities.  The former hydrolyses the cellulose polymer from one end of the molecule and the other breaks the oxygen bridge to form shorter molecular chains.  The cellulase activity depends on surface are, degree of crystallinity, crystalline dimensions, mechanical pretreatment,. Mercerisation and type of cellulase used.  The source of cellulase activity are normally moulds belonging to Tri conderma. Aspergillus and Fusarium genera. Cellulase is produced industrially by fermentation of suitable micro-organisms.  Eg. Cellusoft L. Biosoft, Bactosol CELI etc. The enzymes may be used at a dosage rate of 0.5 to 2.0% (OWF) with a liquor ratio of 5:1 to 15:1 at a pH of 4.5-5.5 and 45 to 55^o C for 30 to 60 minutes.

In the present study, we have concentrated in identifying the softeners so far used for finishing of other textile fibres with a view to applying them on coir. List of overseas and Indian manufacturers are given in Annexure 1 and II

 Materials :

            Details of the materials used are listed in Annexure –III

            Treatment of coir with softening chemicals.

Investigations were made using textile softeners to impart softening characteristics to coir fibre/yarn by dipping in the solution of softening chemicals with specific concentration under appropriate conditions for material to liquor ratio, temperature, time, etc. and the extent of improvement achieved in softness is furnished in Table –I

  EFFECTS OF CHEMICALS USED ON IMPARTING SOFTNESS TO COIR FIBRE/YARN

On examination of the treated coir materials, it was seen that the material treated with X-500 showed better softness compared to Alfalina CS-100 and Silcosoft 100 respectively

Vycome coir yarn was dipped in solutions containing NaOH @ 50g/l,  100 g/l,  150g/l and  200g/l for 30’ with a material to liquor ratio of 1:10 at room temp. Samples of coir yarn from all these solutions were taken out, washed in cold running water thoroughly, till the pH was neutral and dried at room temp. The materials were further dried at 95-100 ^oC to constant weight.  The pH of each solution was noted before and after treatment. On examination of the softened yarn with naOH solution, it was observed that the colour of yarn treated with 15% and 20% NaOH solution in the cold was very dark and dull compared to that of the yarn treated with 5% and 10% NaOH solution.

The data of the breaking load and elongation at break of the softened vycome coir yarn is shown in Table II below.

From the table it is seen that the % weight loss is higher and has a low breaking load oand the elongation at break % is just half for 15% and 20% NaOH solution treated coir yarn respectively than that of 5% and 10% solution treated coir oyarn.  Therefore it is inferred that  the optimum concentration essential for NaOH solution for achieving soft and supple feel without affecting the brightness and breaking load of vycome coir yarn should be between 50 g/l  to 100g/l  ie.5% to 10% (w/v) at m/l ratio of 1:10

The above softened vycome coir yarn were further bleached under hot and cold process using the recipe (a) and (b).

            a) Hydrogen peroxide                          : 8 cc/l

                Sodium Silicate                                 : 5 g/l

            b) Hydrogen peroxide                          : 8 cc/l

                Sodium Silicate                                 : 5 g/l

                Soda Ash                                           : 2 g/l

                Lisapol D                                           : 2 g/l

Recipe (a) was conducted in hot and cold process and recipe (b) in cold conditions only with a treatment time of one hour and boiling temp  for hot process and 16 hours and room temp for cold process respectively.  The  m:l ratio was  1: 10 and pH of the solution was noted before and after each process.

The characteristics of breaking load and EB % of the above bleached yarns are tabulated in Table –III

Table  III: Characteristics of softened Vycome coir yarn bleached with hydrogen peroxide.