New process for producing cellulose acetate from wood in concentrated acetic acid

To explore further potential applications of acetic acid pulp, an investigation was conducted to develop a direct method for producing cellulose acetate from wood in combination with atmospheric acetic acid pulping. The process consists of delignification, totally chlorine-free bleaching, and esterification, with the concentrated acetic acid aqueous solution being used as only solvent throughout the process. The acetic acid pulp with kappa number of 30 and ISO brightness of 16 was bleached with 5% ozone on pulp to kappa number of 1.4 and brightness of 61. The resulting bleached pulp was further bleached with peracetic acid to kappa number of less than 1.0 and brightness of 68. The final bleached acetic acid pulp was acetylated with acetic anhydride in the concentrated acetic acid for 45 min to produce cellulose acetate with an apparent degree of substitution (DS) of 2.54. Although the product was lower grade compared with commercially available cellulose diacetate because it was prepared from the chemical pulp but not dissolving pulp, the product was almost soluble in acetone. Eventually, the DS of the acetone-soluble fraction was 2.62. The acetone solubility might be attributed to the original acetic acid pulp that had been partially acetylated during the pulping.