US1991786A - Manufacture of cellular substances - Google Patents

Description

Patented Feb. 19, 1935 MANUFACTURE OF CELLULAR SUBSTANCES Hedwig Busch, Mannheim, Germany, a ssignor to Zellstofffabrik Waldhof, Mannheim, Waldhof, Germany, a company of Germany No Drawing. Application January 29, 1931, Serial No. 512,216. In Germany February 1, 1930 1 Claim.

The recovery from unbleached or bleached pulp of a pulp rich in stable alkali cellulose (alpha cellulose), by treatment with alkaline media, (as for example, lime, caustic soda, soda, or their mixtures) at ordinary or high temperatures, and if necessary under increased pressure, is known, the content of which in alpha cellulose may, for example, reach or exceed 98%. Such celluloses represent in the completely bleached state, a very white product. They have, however, always the defect in their further treatment into cellulose solutions and shaped objects therefrom, in particular in the production'of cellulose esters, cellulose ethers, and the like, of giving solutions which are coloured more or less strongly yellow. This generally very undesirable yellow colouring is then, as a rule, transmitted to the objects made from the solutions, or to coatings, and the like.

It has been found that both with unbleached as well as bleached pulps, a highly valuable cellulose product is obtained which in further treatment gives extremely light coloured solutions or shaped objects if, in addition to alkaline media, stable alkaline reduction media, as for example sodium sulphite are allowed to act on the cellulose material. Apparently, the reduction medium prevents injurious decomposition reactions, and the formation otherwise easily taking place with alkaline extraction, of brown coloured caramel-like products. This is supported by the observation that even the spent lye of such pulp matter boiled, for example, with soda lye containing sodium sulphite is of much lighter colour than with the pulp boiled with alkali lye alone. The yield in high grade cellulose is also considerably improved with the new process.

Preferably the reduction medium is brought into action at the same time as the alkali.

The process can, for example; be so carried out that unbleached sulphite pulp is boiled under 2 atmospheres for about 1% hours, or under conditions equivalent thereto, in diluted lye which contains about 0.8% sodium hydroxide and the same quantity of sodium sulphite. The cellular matter is then washed and bleached, etc. in known manner. In this way, a cellulose is obtained which contains some 97% of alpha cellulose, and which in further treatment, as for example into solutions of cellulose esters, cellulose ethers, and the like, yield particularly light products, such as could not hitherto be obtained from pulp and which correspond practically completely to those produced from cotton. The same process may be easily extended to a pulp already bleached, in which just as great diflerences result compared with the process Without reduction medium.

Instead of sodium sulphite, other stable alkali reduction media, as for example other sulphites, hydrosulphites, sulphohydrates, aromatic phenols, and the like, may be used.

The boiling of vegetable material of all kinds with comparatively strong caustic soda lyes which contain an addition of alkali-sulphide or sulphite for the purpose of isolating the cellulose, is known. It is here a question of the primary decomposition of the vegetable raw material (wood, bamboo, grasses, reeds) with the recovery of the cell matter. Such cell matters contain in the most favourable case about 88 to 89% of alpha cellulose, and yield on further treatment in solutions or shaped objects products which are more or less strongly yellow in colour. On the contrary, with the new process, it is a question of a process of improvement for which those cellular substances obtained by known processes form the raw material, since by the improved process they are converted into highly valuable celluloses, the alpha cellulose contents of which almost approach that of cotton, and which on further treatment give purely white solutions, and the like.

What I'claim and desire to secure by Letters Patent of theUnited States is:-

A process of preparing wood cellulose for the manufacture of cellulose solutions or plastics, which process consists in boiling wood cellulose under conditions equivalent to substantially 1 hours, under a pressure of substantially two atmospheres, with an alkaline medium containing substantially 0.8% sodium hydroxide and substantially 0.8% sodium sulphite to provide a reducing action in the said medium in the presence of the wood cellulose during said treatment, which cellulose without further preliminary treatment forms cellulose solutions-and plastics that do not become discolored on standing.

HEDWIG BUSCH.