LLDPE和HDPE的非等温结晶动力学

Non-isothermal crystallization kinetics of LLDPE and HDPE

采用差示扫描量热法实现了不同降温速率条件下线型低密度聚乙烯(LLDPE)和高密度聚乙烯(HDPE)的非等温结晶,通过Jeziorny法和莫志深法研究了二者的非等温结晶动力学。结果表明:随着降温速率的增加,LLDPE和HDPE的结晶温度降低,结晶速率加快,而由于发生熔融重结晶现象导致熔融温度变化不大;LLDPE因短支链位阻效应导致晶区不完善,LLDPE结晶和熔融温度、结晶速率均低于HDPE;随着降温速率的增加,LLDPE和HDPE都从多维复杂晶体向低维简单晶体转变;分子链结构不影响二者成核机理和晶体结构;莫志深法和Jeziorny法的研究结果一致,即HDPE较LLDPE更易结晶。

The non-isothermal crystallization of linear low density polyethylene（LLDPE） and high density polyethylene（HDPE） were observed respectively at different cooling rates by differential scanning calorimeter. The non-isothermal crystallization kinetics of both LLDPE and HDPE were studied by Jeziorny equation and Mo Zhishen method. The results show that with the increase of the cooling rate,the crystallization temperature of LLDPE and HDPE fall,and crystallization accelerates,while the melting temperature varies little due to the melting-recrystallization. The steric effect of short branches in LLDPE has led to the imperfect crystalline,the crystallization and melting temperature as well as the crystallization rate of LLDPE are lower than those of HDPE. The crystal structure of LLDPE and HDPE have changed from multi-dimensional and complicated crystalline to low-dimensional and simple crystalline with the increasing cooing rate. The structure of molecular chains has no bearing on the nucleation mechanism and crystalline structure. The results obtained by Jeziorny method is identical with that of Mo method,that is,it is easier for crystallization in HDPE than in LLDPE.