The effect of high crystallinity of pulp in the preparation of cellulose acetate film with iodine as a catalyst

In this study, acetic anhydride and iodine were used as acetylating agents to produce cellulose acetate (CA) from cotton linter-dissolving pulp (LDP). The conditions for acetylation, as well as the crystallinity and reactivity of LDP with high cellulose purity, were investigated and compared with our previous research on low-grade pulp. The properties of the CA, including yield, degree of substitution (DS), differential scanning calorimetry (DSC) analysis, and film characteristics were examined. The results reveal that LDP due to its high cellulose purity (98%) and higher crystallinity, has significantly fewer low-degree polymerization (DP) chains than wood pulp, resulting in a higher molecular weight. Acetylation of LDP required more catalysts due to the reduced accessibility of hydroxy groups, leading to variable yields and degrees of substitution (DS) depending on iodine consumption and acetic anhydride ratios. Therefore, acetylation using a large amount of iodine as catalyst (8% of the pulp), adapted well to different types of pulp. Mechanical testing indicated that while increased catalyst usage initially improved film strength and transparency, excessive iodine led to degradation, reduced mechanical properties, and increased brittleness. These findings suggest that both high and low-purity pulps can be effectively utilized for CA film production, potentially reducing costs in industrial applications. Overall, this study demonstrates the flexibility of the acetylation process when iodine is used as a catalyst.