Influence of molecular weight distribution on degradation properties of low density polyethylene by photo-oxidation aging

doi:10.11949/j.issn.0438-1157.20161330

Abstract

Abstract:

In order to analyze the influence of molecular weight distribution(MWD) on photo-oxidation degradation properties of low density polyethylene(LDPE), the materials parameters(chemical structure, thermal stability, average molecular weight, surface morphology and mechanical properties) of LDPE with different MWD index were studied by attenuated total reflection infrared spectroscopy(ATR-FTIR), thermogravimetry analysis(TGA), gel permeation chromatography(GPC), scanning electron microscope(SEM) and mechanical experiments.The results show that the wide MWD of LDPE resulted in an obvious increasing in the degree of unsaturation and chain branching.For the narrow MWD of LDPE, the degree of carbonyl index increased significantly.The MWD had little effect on the behavior of chain breaking.For the high MWD index, the initial thermal decomposition temperature and 5% mass loss corresponding temperature of LDPE decreased faster, and thermal stability was apt to decline.The average molecular weight decreased much intensely and the aging phenomenon of surface microstructure was much severe.The bending strength and impact strength decreased faster, characterized by the loss of the impact strength of LDPE with 6.0 MWD index after 24 d of aging.Analytically, the large average molecular weight and narrow MWD indicated the long molecular chain and less short-molecular chain, and the probability of production of free radical by oxygen contact was also low.So the wider MWD of the PE, the easier of the material aging.

Key words: molecular weight, molecular weight distribution index, LDPE, photo-oxidation aging, chromatography, degradation, oxidation

摘要：

采用衰减全反射红外光谱技术（ATR-FTIR）、热重分析法（TG）、凝胶渗透色谱（GPC）、扫描电子显微镜（SEM）和力学试验比较研究了不同分子量分布指数低密度聚乙烯（LDPE）的光氧老化特性，分析了分子量分布对LDPE化学结构、热稳定性、平均分子量、表面微观形貌和力学性能的影响规律。结果表明分子量分布越宽，LDPE不饱和度增长越剧烈，支化作用增长越显著；分子量分布越窄，羰基指数增长越快；分子量分布对于分子结构的断链行为并无影响。分子量分布指数越大，LDPE起始热分解温度和失重5%对应温度下降更快，热稳定性更容易变差，平均分子量下降更多，表面微观形貌老化现象越严重；弯曲强度和冲击强度受影响更显著，指数为6.0的LDPE老化24 d冲击强度就已丧失。分析认为，分子量越大、分布越窄表明分子链越长、短分子链越少，与氧接触而产生自由基的概率也越小，因此聚乙烯分子量分布越宽，材料越容易老化。

关键词: 分子量, 分子量分布指数, 低密度聚乙烯, 光氧老化, 色谱, 降解, 氧化

CLC Number:

O632.1

DAI Jun, YAN Hua, WANG Xuemei, GUO Junjun, HU Zhide, YANG Jianjian, SANG Lianyong. Influence of molecular weight distribution on degradation properties of low density polyethylene by photo-oxidation aging[J]. CIESC Journal, 2017, 68(1): 408-417.

代军, 晏华, 王雪梅, 郭骏骏, 胡志德, 杨健健, 桑练勇. 分子量分布对低密度聚乙烯光氧老化特性的影响[J]. 化工学报, 2017, 68(1): 408-417.

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