GB467160A - Improvement in high viscosity organic esters of cellulose and process of preparing them - Google Patents

Abstract

High viscosity cellulose esters having an acyl content predominately acetyl, are prepared by pretreating cellulose in a bath composed mainly of acetic acid, with or without propionic or butyric acid, but no catalyst, and then subjecting the cellulose so pretreated to esterification in a bath in which the solvent for the anhydride is mainly acetic acid and containing as regards its acyl content 5--23 per cent, preferably 10--20 per cent, butyric or propionic acid or anhydride, and as regards its sulphuric acid catalyst content 4--8 per cent at an esterification temperature of 70--95 DEG F. or with a higher sulphuric acid content up to 20 per cent at a temperature down to about 50 DEG F. It is preferred to employ 6--8 per cent sulphuric acid and a temperature of 70--90 DEG F. By the use of the propionic or butyric acid &c. and a sufficient quantity of sulphuric acid catalyst, adequate adsorption of the latter is obtained initially to prevent degradation of the cellulose and at the same time gelling of the cellulose ester in the esterification bath is prevented. Provided there is present initially sufficient sulphuric acid to inhibit degradation of the cellulose, the remaining sulphuric acid may be added later, slowly and with agitation. The esters obtained which contain a certain proportion of propionyl and butyryl groups, are suitable for the manufacture of artificial silk and as the interlayers of laminated glass. The products have an increased wet strength. Specification 316,593, [Class 2 (ii)], is referred to.