Thermal degradation of poly(3-hydroxybutyrate) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) as studied by TG, TG-FTIR, and Py-GC/MS

The thermal degradation kinetics of poly(3-hydroxybutyrate) (PHB) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) [poly(HB-HV)] under nitrogen was studied by thermogravimetry (TG). The results show that the thermal degradation temperatures (T-o, T-p, and T-f) increased with an increasing heating rate (B). Poly(HB-HV) was thermally more stable than PHB because its thermal degradation temperatures, T-o(0), T-p(0), and T-f(0)-determined by extrapolation to B = 0degreesC/min-increased by 13degreesC-15degreesC over those of PHB. The thermal degradation mechanism of PHB and poly(HB-HV) under nitrogen were investigated with TG-FTIR and Py-GC/MS. The results show that the degradation products of PHB are mainly propene, 2-butenoic acid, propenyl-2-butenoate and butyric-2-butenoate; whereas, those of poly(HB-HV) are mainly propene, 2-butenoic acid, 2-pentenoic acid, propenyl-2-butenoate, propenyl-2-pentenoate, butyric-2-butenoate, pentanoic-2-pentenoate, and CO2. The degradation is probably initiated from the chain scission of the ester linkage. (C) 2003 Wiley Periodicals, Inc.