45—A Study of the Action of Alkalis on Jute

Abstract

Since the alkalis studied, with the exception of caustic soda, exert only a small solubilising effect on the constituents of jute, the action of caustic soda in particular has been investigated. The reaction of caustic soda with jute, which is very rapid in the initial stages, is almost complete after 1 hour, and an increase in reaction temperature above 40°C generally tends markedly to increase the losses in weight. The first extraction has been found to eliminate the major portion of soluble constituents, while subsequent treatments have relatively small effects. A small portion of lignin is solubilised even after a mild treatment, while the hexosan fraction remains practically unaffected by the action of cold caustic soda. A portion of xylan (5 per cent) and polyuronide (1 per cent) appears to be intimately associated in the fibre, and any attempt to solubilise this resistant fraction of the hemicelluloses results in a marked decrease in strength. The shrinkage suffered by jute in concentrated caustic soda is enhanced with increase in the concentration and decrease in temperature. A marked reduction in the wet strength of the yarn occurs even after a mild treatment with alkali, which seems to be attributable to possible changes in the yarn structure brought about by the higher swelling of the individual fibres in water. The dry strength of the yarn tends to decrease slightly with the progressive removal of hemicelluloses by the action of dilute alkali. A marked decrease (49 per cent), however, occurs after a treatment with concentrated alkali at room temperature. After a similar treatment, the loss in strength of single fibres is 25 per cent, while yarn spun from the treated fibre shows only a small reduction in quality ratio (from 76 to 69). The pronounced decrease in the strength of the treated yarn has been attributed to non-uniform distribution of applied load owing to derangement of the fibres in the yarn. The smaller decrease in the case of yarn spun from the treated fibre appears to be due to the greater number of finer fibres being effective in sharing the stress in a unit cross-section of the yarn.