Mechanism of Microstructural Change of High-Density Polyethylene Under Different Outdoor Climates in China
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ORIGINAL PAPER
Mechanism of Microstructural Change of High-Density Polyethylene Under Different Outdoor Climates in China Xinyu Tao1 · Jian Xiong1 · Xia Liao1 · Jingjun Zhu2 · Zhu An2 · Qi Yang1 · Yajiang Huang1 · Guangxian Li1
© Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract This work aims to understand the microstructural change mechanism of high-density polyethylene (HDPE) exposed at five national standard natural exposure stations (at Qionghai, Ruoqiang, Lhasa, Qingdao, and Hailar) for four years, which represented the five typical climates over China. It was found that the natural weathering of HDPE was the synergistic result of multi-factors such as temperature, irradiation, oxygen, etc. Based on the carbonyl index, the degradation degree in decreasing order was Ruoqiang, Qionghai, Lhasa, Qingdao and Hailar, but the microstructural change mechanism of HDPE was similar. The molecular structure was modified and mass molecular defects formed such as carbonyl and hydrogen groups during the degradation. The new freed molecular chains released from the amorphous region self-nucleated, and then formed new imperfect crystals because of the suppression of molecular defects. With the deposition of molecular defects, the chemicrystallization ceased. Positron annihilation lifetime spectroscopy indicated the free volume hole shrank continually with exposure time mainly due to the interaction between molecular defects, and a part of amorphous region transformed into crystalline region by chemi-crystallization. In addition, the crystallization and re-melting behavior of degraded HDPE samples had been investigated in order to promote the recycling of waste degraded polymer materials. The results indicated that the crystalline temperature and the second melting temperature decreased with exposure time. Keywords High-density polyethylene · Natural weathering · Microstructural change · Free volume · Positron annihilation lifetime spectroscopy
Introduction Polymer materials have been used in vast areas based on their excellent performance, such as lower specific gravities, easy processing and inertness towards chemical mediator. However, the atoms in the polymer materials are connected by covalent bond and then macromolecular chains are formed. The covalent bond and macromolecular chains are * Xia Liao [email protected] * Guangxian Li [email protected] 1
State Key Laboratory of Polymer Materials Engineering, College of Polymer Science and Engineering, Sichuan University, Chengdu 610065, Sichuan, China
Key Laboratory of Radiation Physics and Technology of Ministry of Education, Institute of Nuclear Science and Technology, Sichuan University, Chengdu 610064, Sichuan, China
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susceptible to outside factors like heat, radiation, oxygen, humidity and rainfall [1]. Thus, polymer materials are easy to degrade during practical service. This phenomenon would cause two major consequences, on the one hand, the degradation of polymer materials could cause its performance failure and then short
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