A torque rheometer method has been developed to evaluate the melt beha
vior of biopolyesters. The main features of this technique include: (i
) a modified equip ment configuration, so as to maintain the melt temp
erature within +/- 1 degrees C of the set temperature after the first
few minutes of polymer melting and thermal equilibration, and (ii) a k
inetic equation that can be used to determine the melt behavior from t
he torque-time data. Applying this methodology to a poly(3-hydroxybuty
rate-co-3-hydroxyvalerate) copolymer shows that the degradation kineti
cs follow Arrhenius behavior with temperature, that the degradation ra
te increases with increasing shear, and that the activation energy for
random chain scission is independent of shear rate. This effect of sh
ear on the degradation process may be a result of viscous heating. The
degradation rate is increased because of the increased internal energ
y of the polymer chains as a result of the mechanical deformation. The
re is no evidence of direct mechanical degradation. Last, the viscosit
y values obtained with the torque rheometer are consistent with those
obtained by capillary rheometry.