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Investigation of chemi‐crystallization and free volume changes of high‐density polyethylene weathered in a subtropical humid zone
Author(s) -
Xiong Jian,
Ni Kai,
Liao Xia,
Zhu Jingjun,
An Zhu,
Yang Qi,
Huang Yajiang,
Li Guangxian
Publication year - 2016
Publication title -
polymer international
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.592
H-Index - 105
eISSN - 1097-0126
pISSN - 0959-8103
DOI - 10.1002/pi.5241
Subject(s) - crystallization , high density polyethylene , differential scanning calorimetry , materials science , amorphous solid , polyethylene , crystal (programming language) , volume fraction , volume (thermodynamics) , composite material , polymer chemistry , chemical engineering , crystallography , chemistry , thermodynamics , programming language , physics , engineering , computer science
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. © 2016 Society of Chemical Industry