Processing of Mesta fibres in textile industries

Excerpt: ALTHOUGH cotton is highly versatile with properties suitable for apparel, certain properties that are desirable are not available with cotton.

ALTHOUGH cotton is highly versatile with properties suitable for apparel, certain properties that are desirable are not available with cotton. Hence it has become necessary to find out fibres that could bridge the gap between the required and existing properties. One such answer to the problem is provided by mesta which is a bast fibre taken from stalk of the mesta plant. Earlier some research work has been done on some aspects relating to blending of mesta with jute and also jute with viscose. Investigations on blending of jute with mesta fibres have shown that the latter could be a cheaper substitute for the former.

Mesta is a bast fibre, which grows extensively in India and in some parts of Eastern Asia. It is used as a substitute for jute. It is a herbaceous annual plant (lignocellulosic bast fibre crop like jute) believed to be originated from Afro- Asian countries, ranks next to jute in importance (sharing 15% of raw jute-cum-mesta fibre production). Mesta is more adaptive and drought tolerant than jute under diverse conditions of climate and soil. In India (2010-11), area under mesta is around 85 thousand hectares with a fibre production of 6.2 lakh bales ( One bale is equal to 180 kg) Andhra Pradesh (A.P) is a leading state in the country with respect to both area and production which accounts for 30 per cent of the area and 42 per cent of the production. In A.P., mesta is concentrated in Srikakulam and Vizianagaram districts accounting for 98.7% area of total area in the State.

Production of Mesta fibres

The fibre of Mesta is obtained from stem of two species Hibiscus sabdariffa varaltissima and Hibiscus Cannabinus, family Malvaceae. The area, which favours for Mesta fibre cultivation are within the jute belt, the yield of Mesta is high in West Bengal, Bihar, Assam and Tripura. Outside the jute belt, the highest acreage is in Andhra Pradesh and the areas assuming importance are Dandakaranya, Orissa, eastern Madhya Pradesh, Maharashtra, Karnataka and Uttar Pradesh. Other states grow Hibiscus Cannabinus types over small areas, mostly for home consumption. Yield in the drier areas is a less than that in the humid ones.

The favourable climatic conditions are a warm and humid climate suits both Hibiscus sabdariffa and Hibiscus Cannabinus varieties. Both these varieties grow in drier rain fed areas, the latter being more drought-resistant.

In areas with 500-900 mm of rain fed, Hibiscus Cannabinus suits better by virtue of its shorter duration and faster growth. Neither variety can withstand prolonged water-logging. Both the kharif crops and are sown in April-June with the first showers of the monsoon.

Heavy, continuous rains and low temperature are harmful. It is extracted as a bast fibre retting is done in the same manner as in the case of jute, but the low temperature and the paucity of water or both pose a problem. The harvested stems of both Hibiscus Sabdariffa and Hibiscus Cannabinus can be stored under dry conditions for retting next season during the middle of the monsoon. The resulting Hibiscus Cannabinus fibre is better than that of Hibiscus Sabdariffa.

A proper stage of harvesting gives higher fibre yield as well as better quality. If the plants are harvested pre-maturely in early stages, the quality fibre is good but the fibre yield is poor. If the plants are harvested late the fibre yield is better but quality of fibre goes down. The best time to harvest mesta for fibre is when the plants are in 50% flowering. Harvesting is done normally by cutting the plants close to the ground. In some areas the plants of mesta are also uprooted. Such plants take more time to ret and quality of fibre is adversely affected.

After the harvesting the plants are sorted out based on the thickness of the stems followed by bundling of plants in convenient sizes of 25-30 cms in diameter. These bundles kept standing in the field for 2-3 days for shredding of leaves. The shredding of leaves simultaneously helps in shrinking and rupturing of the bark which helps in the entrance of retting microorganisms. Retting in the current season, if possible, is always preferable.

The quality of the Mesta fibre is judged based on almost the same criteria as in the case of jute and the grading is done on the same lines, although the I.S.I. specifications are now due.

Retting

Steep method of retting is very popular in all mesta growing areas. The steep retting consists of bundling of mesta plants after harvesting . The bundles are kept in standing position in 50-60 cms deep water for nearly 3-4 days. This helps in retting of the hard lower portion of the bark. After 3-4 days the standing bundles are laid down in the retting water and slightly drowned (nearly 10 cms) in water with the help of weights made of cement blocks or stones. Care should be taken not to put any weighed material which releases tannin and iron. For hastening the retting process spraying of 1.25 % Urea solution(12.5gm/lt. of water) on mesta sticks is desirable before retting of the bundles. Soon after completion of retting the fibre can be extracted from the sticks by single plant extraction method. The fibre is extracted from a single plant individually, each plant from the bundle is taken out and with the help of fingures the fibre is extracted, washed and kept. The bundles of ret fibre after washing are open and dried on bamboo frames under the sun. After 3 or 4 days the dried fibre is properly assorted and bundled in different grades for marketing of the fibre.

Advanced retting methods

Two improved techniques of microbial retting are developed by Central Research Institute for Jute and Allied Fibres, Baratpur, Kolkata by utilization Microbial retting consortium for efficient retting during water scarcity situation utilizing minimum amount of ground water They are a) Mechano-microbial/ ribbon retting b) Micro-pind microbial retting. a) Mechano-Microbial/Ribbon Retting The power operated bast fibre extractor can extract 25 kg dry fibre ribbons per hour with broken sticks while manually operated Mesta fibre extractor can extract 15 kg dry fibre per hour with unbroken sticks. These ribbons are then treated with the microbial consortium @ 100 ml/10 kg of green ribbons and kept for 1 hour covering with polythene sheet. For small scale, in polythene lined retting tank of 1 M3 size (1m x 1m x 1m) containing 1000 litres of water After Five to seven days, the retting process will be completed b) Micro-pond microbial retting A circular micro pond of 6.5 m floor diameter and 7.5 m top diameter and 1 m deep having 1 m wide earthen embankment lined with polyethylene sheet (800 to 1000 gauge, 30 ft x 27 ft) is sufficient to mesta harvested from 1333.3 M2 (0.13 Hectors) land. The sharp bases of the mesta plants have to be blunted by ramming the bundles on hard surface to avoid damage to the polyethylene sheet. A single layer of straw bundles arranged radially at the bottom of the pond over polyethylene/tarpulin sheet to avoid damage to the polyethylene sheet. Harvested Mesta bundles are arranged radially upto three layers keeping base of the plants towards periphery of the pond. Microbial consortium @ 1 kg/layer diluted in 10 liters of water will be applied to the mesta bundles in the pond. The retting process will be completed with 12- 15 days. The fibre will be with golden yellow colour

Properties of mesta fibres

Mesta is a bast fibre with certain desirable textile properties like good strength, lustre, good microbial and atmospheric resistance. Mesta fibre is not much utilized now in textile sector due to its coarse and stiff nature. Bast fibres are silky lustre, high tensile strength, low extensibility, considerable heat and fire resistance and long stable length, that make it suitable for industrial use. Raw jute/ mesta fibre is mainly used in the industry in the manufacture of packaging materials.

Studies on blending of viscose with jute have revealed that yarn irregularity decreased with increase in the viscose component and also the weaving efficiency and fabric quality showed improvements even with 10% viscose in the blend. Studies on the quality assessment of jute and mesta yarns from their fibre properties show that the tenacity of jute and mesta yarns has been related to bundle tenacity and fineness and the multiple correlation coefficient has been found to be 0.8. The earlier researches evidently point out the importance of mesta fibre with regard to properties. Hence this research attempts to investigate the effect of blending of mesta with cotton. The mesta fibre has been processed separately before blending it with cotton. The process sequence is given below: The blending has been done in the ratio of 70:30 (Cotton: Mesta). Proportion of mesta beyond 30% in the blend created problems in processing.

Mesta fibres presoaked for 24 hours and softened with25 per cent soidum hydroxide had bright colour, more dye uptake followed by zinc chloride, teepol and turkey red oil. Teepol and turkey red oil improved the texture of the mesta fibres followed by sodium hydroxide and zinc chloride. Fibres softened with sodium hydroxide had bright lustre followed by zinc chloride, teepol and turkey red oil. Mesta fibres softened with sodium hydroxide had excellent overall appearance followed by zinc chloride, teepol and turkey red oil. Fibres softened with sodium hydroxide was found to be cheapest and best, compared to all other three chemical softening methods mentioned earlier. Mesta fibres presoaked for 24 hours and softened with25 per cent concentration of chemical gave the best softened effect which was proved statistically also. Fibres softened with sodium hydroxide improved the dye uptake, texture, lustre and absorbency to the desired degree of acceptance at reasonable cost. Hence sodium hydroxide is found to be the best chemical suitable for softening the mesta fibres.

Uses of mesta fibres

Fibre extracted from untreated and vertical-horizontally steeped stalks exhibited significant fibre elongation. The physical characteristics of 80:20 cotton/mesta blended yarn were better than the 100 per cent organic cotton and 60:40 cotton/mesta blended yarns. Moreover, mesta fibres have added strength to cotton yarn and simultaneously decreased the elongation making the blend suitable for knits, curtains and draperies and other household textiles including table & kitchen linen. The softened mesta fibre could be used in handicrafts and textile industries for making furnishings, bulletin board covers, hand bags, carry bags, campcoats, lamp shades etc. By using softened mesta fibres, the aesthetic appeal can be enhanced there by increasing the utility of the products.

Author Details

Dr. N. N. Mahapatra

Business Head ( Dyes ) Shree Pushkar Chemicals & Fertilisers Ltd.