Cellulose acetate production from Finnish hardwood and softwood dissolving pulp

Abstract

Cellulose acetate pulp was produced from viscose-grade, unbleached and bleached hardwood dissolving pulps and bleached softwood dissolving pulp. The raw materials were purified by cold caustic extraction and elemental-chlorine free bleaching. Initially, pulp purification was optimized for all of the pulps. The unbleached hardwood pulp was purified with cold caustic extraction, bleached with D0-EOP-D1-P bleaching sequence and then acetylated. The same acetylation and bleaching conditions were applied for all the samples. The resulting cellulose acetate quality had a complex relation to the quality of raw material and extent of purification. The most cost-effective CCE was obtained with 5% consistency, 30 min reaction time, and 30 °C 70 g/L NaOH. Transmission and yellowness of the cellulose acetate solution for the most successful hardwood sample were 50 % and 0.29 respectively and for the most successful softwood sample 40 % and 0.26. The corresponding values for cellulose acetates prepared from the commercially available acetate-grade pulps were 78 % and 0.27 for hardwood and 73 % and 0.35 for softwood. The produced cellulose acetate quality was mediocre even when the purification was on an excellent level due to several factors affecting the acetylation process; some of the main reasons are probably extensive degradation of the fibers due non-optimal raw material with too low degree of polymerization. The result of the experimental work was the production of a low-quality acetate pulp from hardwood and softwood viscose pulps by cold caustic extraction and, in the case of unbleached pulp, by additional ECF bleaching.