| Abstrakt: |
When jute is treated with the chemical reagents employed in textile purification and bleaching processes the lignin, hemicellulose and other incrusting substances are attacked and to some extent removed. The greater the extent of this removal the more is the strength of the jute diminished, particularly when the material is tested in the wet state. Removal of substantially all the lignin with retention of hemicellulose, or of hemicellulose with retention of lignin, results in low wet strength although dry strength is but little affected. Treatments that result in the partial removal of both these incrustants usually reduce both dry and wet strength, although in hot alkaline steeps such as are given in peroxide bleaching, where fibre swelling can occur and there is no pronounced removal of incrustants, dry strength may be increased above the original value owing to the closer setting of fibre on fibre that occurs as a consequence of swelling and subsequent drying. Boiling under moderate pressure with sodium hydroxide solution removes substantially all the hemicellulose but little lignin, whilst treatment with acid chlorite solutions and then neutral sulphite liquor removes the lignin but not the hemicellulose. The incrustants in jute resemble in their behaviour the starch size on a low-twisted sized cotton yarn and while they themselves have little tensile strength they contribute in marked manner to the strength of the jute by cementing together the ultimate cellulose fibre bundles on which the strength fundamentally depends. In oxidation treatments commonly employed in technical bleaching they appear to have a protective action on the cellulose. Alkaline hypochlorite has mainly an oxidising, and acid hypoclilorite a chlorinating action on jute, and use of the latter in conjunction with a pressure boil with sodium hydroxide and a final oxidation bleach with alkaline hypochlorite promotes attack and removal of lignin and fairly readily allows pure white cellulose to be isolated. If the preliminary chlorinating treatment is not given, more drastic boiling at high pressure is necessary and more than one boil may be required. The characteristics of the jute cellulose are such as to suggest that the product can be used satisfactorily for the manufacture ot viscose, cellulose compounds and white papers. The " browning " of bleached jute that occurs when this material is exposed to sunlight can be prevented only when the conditions of purification are such as to ensure that no lignin remains, and it appears that lignin itself is the product responsible for the browning effect. [ABSTRACT FROM AUTHOR] |
