Thermogravimetric analysis of poly(3-hydroxybutyrate) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate)

The thermal degradation of poly(3-hydroxybutyrate) (PHB) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) [P(HB-HV)] was studied using thermogravimetry (TG). In the thermal degradation of PHB, the temperature at the onset of weight loss (T-o) was derived by T-o = 0.97B + 259, where B represents the heating rate (degreesC/min). The temperature at which the weight loss rate was maximum (T-p) was T-p = 1.07B +/- 273, and the final temperature (T-f) at which degradation was completed was T-f = 1.10B + 280. The percentage of the weight loss at temperature T-p (C-p) was 69 +/- 1% whereas the percentage of the weight loss at temperature T-f (C-f) was 96 + 1%. In the thermal degradation of P(HB-HV) (7:3), T-o = 0.98B + 262, T-p = 1.00B + 278, and T-f = 1.12B + 285. The values of C-p and C-f were 62 +/- 7 and 93 +/- 1%, respectively. The derivative thermogravimetric (DTG) curves of PHB confirmed only one weight loss step change because the polymer mainly consisted of the HB monomer only. The DTG curves of P(HB-HV), however, suggested multiple weight loss step changes; this was probably due to the different evaporation rates of the two monomers. The incorporation of 10 and 30 mol % of the HV component into the polyester increased the various thermal temperatures (T-o, T-p, andT(f)) by 7-12 degreesC (measured at B = 20 degreesC/min). (C) 2001 John Wiley & Sons, Inc.