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‐hydroxybutyrate‐co‐3‐hydroxyvalerate) [P(HB–HV)], and poly(3‐hydroxybutyrate‐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 (°C) given by To = 0.75B + 311, where B represents the heating rate (°C/min). The temperature at which the weight‐loss rate was at a maximum was Tp = 0.91B + 320, and the temperature at which degradation was completed was Tf = 1.00B + 325. In the thermal degradation of P(HB–HV) (70:30), To = 0.96B + 308, Tp = 0.99B + 320, and Tf = 1.09B + 325. In the thermal degradation of P(HB–HHx) (85:15), To = 1.11B + 305, Tp = 1.10B + 319, and Tf = 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 To, Tp, and Tf relative to those of PHB by 3–12°C (measured at B = 40°C/min). DSC measurements showed that the incorporation of HV and HHx decreased the melting temperature relative to that of PHB by 70°C.