Thermal analyses of poly(3-hydroxybutyrate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate), and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate)

Thermal analyses of poly(3-hydroxybutyrate) (PHB), poly(3-hydroxybutyl ate-co-3-hydroxyvalerate) [P(HB-KV)], and poly(3-hydroxybutyratc-co-3-hydroxyhexanoate) [P(HB-HHx)] were made with thermogravimetry and differential scanning calorimetry (DSC). In the thermal degradation of PHB, the onset of weight loss occurred at the temperature (degreesC) given by T-o = 0.75B + 311, where B represents the heating rate (degreesC/min). The temperature at which the weight-loss rate was at a maximum was T-p = 0.91B + 320, and the temperature at which degradation was completed was T-f = 1.00B + 325. In the thermal degradation of P(HB-HV) (70:30), T-o =0.96B + 308, T-p = 0.99B + 320, and T-f = 1.09B + 325. In the termal degradation of P(HB-HHx) (85:15), T-o = 1.11B + 305, T-p = 1.10B + 319, and T-f = 1.16B + 325. The derivative thermogravimetry curves of PHB, P(HB-HV), and P(HB-HHx) confirmed only one weight-loss step change. The incorporation of 30 mol % 3-hydroxyvalerate (HV) and 15 mol % 3-hydroxyhexanoate (HHx) components into the polyester increased the various thermal temperatures T-o, T-p, and T-f relative to those of PHB by 3-12 degreesC (measured at B = 40 degreesC/min). DSC measurements showed that the incorporation of HV and HHx decreased the melting temperature relative to that of PHB by 70 degreesC. (C) 2001 John Wiley & Sons, Inc.