摘要
利用差示量热扫描热分析仪(DSC)测得了不同降温速率下聚乙交酯(PGA)的非等温结晶的温度-热焓曲线。分别通过Ozawa法、Jeziorny法和莫志深法对PGA的非等温结晶机理进行了分析。Ozawa法结果表明:在给定的温度范围内,Ozawa法并不适用于描述PGA的非等温结晶行为;Jeziorny法结果表明:不同降温速率下,PGA结晶过程的Avrami指数(n)接近4,PGA非等温结晶为均相成核、晶粒三维增长的过程;莫志深法结果表明:Avrami指数与Ozawa指数的比值(a)基本无变化,动力学参数f(T)随降温速率增加逐渐增大,即在更快的降温速率下,PGA结晶更充分,可获得更高的结晶度。通过Kissinger方程计算得到的PGA结晶扩散活化能为-66.9kJ/mol。
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 to20℃/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/T2 p)and 1/Tp,was-66.9 kJ/mol.
引文
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