GB741004A - Improvements in the production of organic acid esters of cellulose - Google Patents

Abstract

Cellulose is esterified with an organic acid anhydride in the presence of sulphuric acid as catalyst and sufficient of a solvent mixture of a lower aliphatic acid containing 2-4 carbon atoms in the molecule and methylene or ethylene chloride, of which 25-80 per cent by weight consists of the lower aliphatic acid, to dissolve the cellulose triester formed. To the primary esterification solution so obtained there is added sufficient water to hydrolyse residual acid anhydride and to provide at least 50 per cent of water (on the weight of the cellulose) for ripening, and all the sulphuric acid in the solution is neutralized. The solution is then heated to 100-190 DEG C. and maintained between these limits of temperature until the cellulose ester has the desired acyl value. The cellulose used may be a mixture of purified cotton linters and pulp from wood, straw, or grasses. The cellulose may be activated by treatment with an aliphatic acid, e.g. acetic acid. The amount of sulphuric acid used as catalyst may be less than 5 per cent, e.g. 0.8-2.5 per cent, of the weight of the cellulose and, if desired, part or all of this may be contained in the acetic acid used in the pretreatment. The sulphuric acid may be neutralized, after completion of the esterification, by means of carbonates, acetates, oxides, and hydroxides of magnesium, zinc, aluminium, and alkaline earth metals. Neutralization may be effected before, during, or after the addition of the water. Before the actual ripening, part of the methylene or ethylene chloride may be removed by distillation. The ripened solution may be thinned by adding acetic acid or acetone before the cellulose acetate is precipitated. In an example, cotton linters are pretreated with acetic acid and then acetylated with 725 parts per cent by weight of a mixture of 300 volumes of acetic anhydride, 140 volumes of methylene chloride, and 200 volumes of acetic acid containing 2 per cent of sulphuric acid (on the weight of the cellulose), the temperature being allowed to rise to 54 DEG C. When a clear solution has formed, 120 parts by weight of water (as 50 per cent acetic acid) are added with magnesium acetate to neutralize the sulphuric acid. The solution is heated in a pressure vessel to 120 DEG C. and maintained at this temperature for 5 hours. The ripened cellulose acetate is precipitated by the addition of water. The parent Specification and Specification 737,566 are referred to.