Thermal degradation kinetics of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate)

The degradation kinetics of poly(3-hydroxy-butyrate-co-3-hydroxyhexanoate), a member of the Nodax family of polymers, were investigated using transient constant shear rate and dynamic time sweep rheological tests. The rate of chain scission at several times and temperatures was correlated with viscosity data and verified using molecular weight determination of the degraded samples. The experimental results show that the molecular weight and the viscosity of Nodax decrease with time over the range of temperatures that were studied (155-175 degrees C). The degradation kinetics, which exhibited first-order behavior, were determined as a function of the flow history and thermal history. An apparent activation energy of 189 +/- 5 kJ/mol for thermal degradation was found by modeling variations in the rate with temperature using an Arrhenius law model. (c) 2005 Wiley Periodicals, Inc.