Jute is well known as a very cheap fiber, and its employment in textile industry is consequently both extensive and always increasing. Accompanying this increase is a corresponding one in the amount of old waste jute, which can be employed for the manufacture of paper.
Up to the present time, only very little use has been made of jute for the manufacture of thread and the finer fabrics, because the difficulty of bleaching the fiber satisfactorily has proved a very serious hindrance to its improvement by chemical means. All the methods hitherto proposed for bleaching jute are so costly that they can scarcely be made to pay; and, moreover, in many cases, the jute is scarcely bleached, and loses considerably in firmness and weight, owing to the large quantities of bleaching agents which have to be applied.
In consequence of this difficulty, the enormous quantities of jute scraps, which are always available, are utilized in paper making almost entirely for the production of ordinary wrapping paper, which is, at the best, of medium quality. In the well known work of Hoffmann and Muller, the authors refer to the great difficulty of bleaching jute, and therefore recommend that it be not used for making white papers.
Messrs. Leykam and Tosefothal have succeeded in bleaching it, and rendering the fiber perfectly white, by a new process, simple and cheap (which we describe below), so that their method can be very advantageously employed in the paper industry.
The jute fiber only loses very little of its original firmness and weight; but, on the other hand, gains largely in pliability and elasticity, so that the paper made from it is of great strength, and not only resists tearing, but especially crumpling and breaking.
The jute may be submitted to the process in any form whatever, either crude, in scraps, or as thread or tissue.
The material to be bleached is first treated with gaseous chlorine or chlorine water, in order to attack the jute pigment, which is very difficult to bleach, until it takes an orange shade. After having removed the acids, etc., formed by this treatment, the jute is placed in a weak alkaline bath, cold or hot, of caustic soda, caustic potash, caustic ammonia, quicklime, sodium or potassium carbonate, etc., or a mixture of several of these substances, which converts the greatest part of the jute pigment, already altered by the chlorine, into a form easily soluble in water, so that the pigment can be readily removed by a washing with water. After this washing the jute can be bleached as easily as any other vegetable fiber in the ordinary manner, by means of bleaching powder, etc., and an excellent fibrous material is obtained, which can be made use of with advantage in the textile and paper industries.
The application of the process may be illustrated by an example:
One hundred kilos. of waste jute scraps are first of all treated in the manner usually employed in the paper industry; 15 per cent. of quicklime is added, and they are treated for 10 hours at a pressure of 1½ atmospheres. The scraps are then freed from water by means of a hydro-extractor, or a press, and finally saturated with chlorine in a gas chamber for 24 hours or less, according to the requirements of the case. Every 100 kilos. of jute requires 75 kilos. of hydrochloric acid (20° B.) and 20 kilos. of manganese peroxide (78-80 per cent.).
The jute then takes an orange color, and is subsequently washed in a tank, a kilo. of caustic soda being added per 100 kilos. of jute; this amount of alkali is sufficient to dissolve the pigment, which colors the water flowing from the washer a deep brown. After washing, the jute can be completely bleached by the use of 5-7 kilos. of bleaching powder per 100 kilos.