Synthesis and biodegradation of starch-graft-poly(hexylene adipate)

Poly(hexylene adipate) (PHA) was synthesized by the direct condensation of hexandiol and adipic acid with p‐toluene sulfonic acid as a catalyst, dimethyl benzene as a solvent. The terminal carboxyl group of the polyester was then converted to acyl chloride by a solution of SOCl2 in toluene. The degree of acylation (DA) was very much dependent on the molecular weight and the type of the other terminal group of the PHA (hydroxyl or capped with an ester group). A high concentration of SOCl2 increased DA, but the scission of the polyester chain was observed. The graft reaction of the acylated PHA with starch was carried out in dried dimethyl sulfoxide. The results show that the percentage grafting (G) and graft efficiency were determined by several factors, including the weight ratio of the reactants, reaction temperature, and molecular weight of PHA. Biodegradation tests in both the laboratory and the natural environment indicated that the degradation rate of starch‐g‐PHA was much faster than that of PHA. For example, the weight loss of PHA was 1.3% after 36 days of natural soil burial, whereas the weight loss of starch‐g‐PHA (G = 39.1%) reached 28% after the same time period. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 848–854, 2003