Crystallization, melting, and enzymatic degradation of biodegradable poly(butylene succinate-co-14 mol % ethylene succinate) copolyester

The crystal structure and growth kinetics of melt-crystallized poly(butylen e succinate-co-14 mol % ethylene succinate) [P(BS-co-14 mol % ES)] copolyes ter have been investigated at a wide crystallization temperature range of 3 0 to 90 degreesC. By means of wide-angle X-ray diffraction (WAXD), the copo lyester composed of BS and ES units has been identified to have the same cr ystal structure with that of poly(butylene succinate) (PBS) homopolymer, su ggesting that only PBS sequences crystallize while that the ES units are in an amorphous form. On the basis of secondary nucleation theory, two regime s of II and III have been observed and their transition temperature is arou nd 80 degreesC. The spherulitic morphologies of P(BS-co-14 mol % ES) copoly ester developed from banded spherulites to the normal ones without banding extinction patterns as the crystallization temperature increased. The melti ng behavior of P(BS-co-14 mol % ES) copolyester under different conditions has been studied by differential scanning calorimetry (DSC). Four melting p eaks and one exothermal peak on the melting curves were observed during hea ting process, and their origination is discussed. The enzymatic degradation was carried out on the melt-crystallized P(BS-co-l il mol LTC ES) thin fil m by an extracellar PHB depolymerase from Pseudomonas stutzeri and the morp hologies of lamellar crystals before and after degradation have been examin ed by atomic force microscopy (AFM). The results have indicated that enzyma tically degradable ES units exist on the surface of lamellar crystals and a re hydrolyzed by the enzyme, while that the crystalline cores composed of P BS chains are not degraded.