Nonisothermal Crystallization Behavior of Polyglycolide

The nonisothermal crystallization temperature-enthalpy curves of polyglycolide (PGA) were obtained by Differential Scanning Calorimeter (DSC) at different cooling rates ranged from 2.5℃/min to 20℃/min. The relation of relative crystallinity of PGA and crystallization time at different cooling rates were also obtained as S shape curves, which showed that crystallization rate increased with the increase of cooling rate. Compared with Ozawa method, the Jeziorny method and Mo's method were both successfully applied to describe the nonisothermal crystallization behavior of PGA, respectively. The results of Jeziorny method showed that the Avrami exponent (n) at different cooling rates ranged from 3.72 to 3.96, which was apparently close to 4, indicating that the nonisothermal crystallization of PGA was a process of homogeneous nucleation with three-dimensional growth. The results of Mo's method showed that the ratio of Avrami exponent to Ozawa exponent kept invariant regardless of the change of cooling rate. The kinetic parameter "f(T)" increased gradually with the increasing of cooling rate, revealing higher degree of crystallinity could be obtained at higher cooling rate. The value of activation energy of crystallization of PGA, calculated by Kissinger equation for the linear relationship between ln(φ/T_p²) and 1/T_p, was -66.9 kJ/mol.