The Role of Acid Catalysts in the Manufacture of Cellulose Acetate

INTRODUCTION Commercial processes for the manufacture of cellulose acetate depend on the reaction of an activated cellulose with acetic anhydride using a strong acid catalyst. (i) Activation of the cellulose implies swelling to make internal surfaces accessible to the acetylating agents. (ii) Though many acid catalysts have been considered, only sulphuric and perchloric acids have practical significance. (iii) The acetylation may be conducted in a nonsolvent diluent, whereupon the cellulose triacetate retains the fibrous form of the original cellulose. (iv) The reaction medium may contain a cellulose acetate solvent, e.g. methylene chloride and!or acetic acid. In this case, the progress of the reaction is readily apparent as the acetylated product dissolves in the reaction medium. There are many reasons for desiring to measure the reactivity of a cellulose sample in the acetylation reaction. For example, it would be useful to (a) Compare cellulose samples from different sources. (b) Study the effects of pulping variables. (c) Assess the effectiveness of cellulose activating (swelling) procedures. (d) Study the chemical reaction kinetics to elucidate aspects of the acetylation mechanism. To this end, many investigators have reported aeetylation test procedures. Borgin' ', Blume and coworkers4, Malm and coworkers5, Akim6, Laamanen and Sihtola7, and Frith8 have made significant literature contributions recently in this field. Rosenthal and White have previously reported9 in detail on an optical procedure for quantitative acetylation of cellulose which offers some interpretive advantages over other reported procedures.