Biodegradable natural composites. II. Synergistic effects of processing cellulose with PHB

This article reports on the synergistic effects observed during the processing of cellulose with bacteria‐produced polyhydroxybutyrate (PHB). Cellulose fibers processed with PHB‐melt exhibited defibrillation as shown by SEM. Microscopic studies of extracted fibers demonstrated that a dramatic fiber‐size reduction occurred during processing. The size reduction was related to the degree of processing, which, we believe, depended on the amount of crotonic acid produced during thermal degradation of PHB. Size exclusion chromotography (SEC) studies of PHB samples thermally treated under well‐defined conditions showed a decrease in molecular weight as a function of treatment time. The samples processed with and without cellulose were analyzed for their molecular weight, and the processing of cellulose was found to contribute to a greater amount of chain scission, plausibly caused by local overheating as a result of shear forces developed during processing. Thermogravimetric studies performed isothermally on PHB under various temperatures gave correlations between the amount of volatile products and the molecular weight reduction of PHB. These findings confirmed our hypothesis on in situ formation of acid during melt processing of PHB and hydrolysis of cellulose fibers by such an acid during compounding.