Investigation of chemi-crystallization and free volume changes of high-density polyethylene weathered in a subtropical humid zone

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• 作者：Jian Xiong ; Kai Ni ; Xia Liao ; Jingjun Zhu ; Zhu An ; Qi Yang ; Yajiang Huang and Guangxian Li
• 刊名：Polymer International
• 出版年：2016
• 出版时间：December 2016
• 年：2016
• 卷：65
• 期：12
• 页码：1474-1481
• 全文大小：1250K
• ISSN：1097-0126

文摘

The chemi-crystallization and free volume changes of high-density polyethylene (HDPE) exposed to subtropical humid climate of Guangzhou, China, were investigated using Fourier transform infrared spectroscopy, differential scanning calorimetry, wide-angle X-ray diffraction, dynamic mechanical analysis and positron annihilation lifetime spectroscopy. An increase in content of carbonyl groups and significant chemi-crystallization were observed to occur during natural exposure. Chain scission accounted for the chemi-crystallization and would lead to greater crystallizability of the molecules. The reheating DSC run indicated that the crystallizability of the degraded HDPE molecules increased initially with exposure time and then decreased. Positron data showed the new crystals induced by chemi-crystallization indeed had more imperfect crystal structure in comparison with the pre-existing parent crystals, and the free volume located in amorphous regions decreased involving a shrinking of the free volume holes. The shrinkage of free volume holes was correlated with the loss of mobility of HDPE molecules, which was confirmed by the increase of glass transition temperature. The formation of new imperfect crystals might increase the amount of rigid amorphous fraction of HDPE materials, as well as the occurrence of crosslinking reactions of molecules located in the interior of HDPE materials, consequently decreasing the molecular mobility.