Thermoplasticization of cellulose acetates by grafting of cyclic esters

Abstract

A plasticization method for cellulose acetates (CAs) based on the selective grafting of e‐caprolactone (CL) and L-lactide (LACD) has been developed. The selective‐grafted products could be prepared by ring opening polymerization in the melt state at 140°C using stannous octoate as catalyst, where CAs with remaining hydroxyl groups worked as initiator. Plasticization of CAs by this selective grafting can solve the problem encountered in the previous reports (Yoshioka et al., 1996, 1998) that the bleeding of unreacted monomers and homo‐oligomers from the inside of molded articles to their surface was often found. By using adequate reaction conditions, the grafting reaction proceeded rapidly and could be completed within 10–30 min. LACD is grafted more rapidly than CL onto CAs, producing relatively rigid and brittle products in the earlier stages and elastomer‐like ones in the later stages. Transparent amorphous molded articles were obtainable depending on the reaction conditions. The analysis of the structure of the grafted side chains by means of high resolution NMR spectroscopy showed that, although the grafted side chains are composed of large amounts of e‐oxycaproyl or lactidyl block polymer portions depending on the reaction conditions, a large amount of randomly polymerized parts coexist in the grafted chains, which confer high thermoplasticity, elasticity and amorphous nature to the grafted products obtained.