GB706522A - Production of organic acid esters of cellulose - Google Patents

Abstract

Cellulose containing less than 5 per cent. of its weight of water is subjected to pretreatment in two stages, and then to esterification with an organic acid anhydride, the first pretreatment stage being effected with a lower aliphatic acid in the presence of 4-9 per cent. of water (calculated on the dry weight of the cellulose and including water already contained in the cellulose) for a time of at least 2 minutes, and the second pretreatment stage being effected with further lower aliphatic acid containing 3-15 per cent. (calculated on the dry weight of the cellulose) of an esterification catalyst for a time of at most 15 minutes. The lower aliphatic acid is one containing 1-4 carbon atoms in the molecule. The cellulose may be purified cotton linters or wood pulp or it may be derived from bamboo, reeds, grasses, straws, jute, esparto, seed hulls or bark. It may be pretreated in the form of loose fibres or in sheet, strip or board form. Formic, acetic, propionic or n-butyric acid or a mixture of these may be used for the pre-treatment. The first stage of pretreatment may be carried out at 25-55 DEG C. and the amount of lower aliphatic acid may be 15-75 per cent. of the weight of the cellulose. In the second stage of pretreatment the amount of aliphatic acid may be 1-6 times the weight of the cellulose. The esterification catalyst used is preferably sulphuric acid. After the pretreatment, the cellulose is esterified with an organic anhydride, with or without additional quantities of lower aliphatic acid and catalyst. The esterification may be carried out in 15-30 minutes or less. In an example, cotton linters which have been dried until they contain 0.3 per cent. by weight of water are treated by spraying with 35 per cent. of acetic acid containing 6 per cent. of water, based on the weight of the cellulose, and allowed to stand for 3 minutes. They are then sprayed with 300 per cent. of acetic acid containing 15 per cent. of sulphuric acid, based on the weight of cellulose. After 3 minutes, the cellulose is introduced into 220 per cent. of acetic anhydride and the esterification proceeds to completion in 15 minutes. Specification 683,648 is referred to.