PLA/芳基取代酰肼类成核剂共混物等温结晶动力学

Isothermal Crystallization Kinetics of PLA/Aryl Substituted Hydrazide Compound Blends

采用芳基取代酰肼类化合物成核剂(NA)对聚乳酸(PLA)进行改性,利用转矩流变仪制备PLA/NA共混物。通过差示扫描量热分析仪研究成核剂含量对共混物的熔融结晶性能、等温熔融结晶和等温冷结晶动力学行为的影响。熔融结晶行为测试结果表明,PLA样品结晶度低,存在冷结晶过程;加入成核剂后,减弱冷结晶过程,提高了PLA/NA共混物的结晶度。等温熔融结晶动力学结果表明,随着结晶温度的升高,结晶速率常数Zt降低,半结晶时间t1/2增大;加入成核剂后,结晶速率常数增大,半结晶时间减小。未加成核剂的Avrami指数n为3左右,加入成核剂后,n值稍有降低。等温冷结晶动力学结果表明,随着冷结晶温度的升高,结晶速率常数增加,半结晶时间减小;加入成核剂后,结晶速率常数增加,半结晶时间减小。未加成核剂时,n值为3左右;加入成核剂后,n值减小,在1~2之间。利用Arrhenius方程求出PLA/NA共混物样品的熔融结晶和冷结晶活化能;随着成核剂含量的增加,熔融结晶活化能绝对值减小,冷结晶活化能绝对值增加。

Polylactic acid(PLA)was modified by aryl substituted hydrazide nucleating agent(NA),and PLA/NA blend was prepared by torque rheometer.The effects of nucleating agent content on the melt crystallization properties,isothermal melt crystallization and isothermal cooling crystallization kinetics of the blend were studied by differential scanning calorimetry.The results of melt crystallization show that the PLA samples have low crystallinity and cold crystallization process.After adding nucleating agent,the cold crystallization is weakened,leading to an increase in the overall crystallinity of the PLA/NA blends.The results of isothermal melting crystallization kinetics demonstrate that the crystallization rate constant(Zt)decreases and the half-crystallization time t1/2 increase with the increasing of crystallization temperature.However,after incorporating nucleating agent,both parameters show an opposite trend increases values for rate constant and decreases values for half-crystallization time.Without any nucleating agent present,the Avrami index n has a value around 3,this value slightly decreases upon addition of nucleating agent.The results of isothermal cold crystallization kinetics show that the crystallization rate constants increase and the half-crystallization time decrease with the increase of cold crystallization temperature.The crystallization rate constants increase and the half-crystallization time decrease after nucleating agent is added.When no nucleating agent is added,the n value is about 3,and when nucleating agent is added,the n value decreases between 1 and 2.The activation energies of melt crystallization and cold crystallization of PLA/NA blends are calculated by Arrhenius equation.With the increase of nucleating agent content,the absolute value of activation energy of melt crystallization decreases and that of cold crystallization increases.