结晶度对高密度聚乙烯热氧老化特性的影响

研究了结晶度对高密度聚乙烯(HDPE)在110℃人工热氧老化条件下老化特性的影响,分别采用力学实验、衰减全反射红外光谱技术、凝胶渗透色谱、扫描电子显微镜和X射线衍射技术比较了不同结晶度HDPE的热氧老化特性,研究了结晶度对聚乙烯力学性能、化学结构、相对分子质量、表面微观结构和晶体结构的影响规律。结果表明,结晶度越高,HDPE拉伸强度、拉伸模量和弯曲模量下降越快,抗冲击性能提高;不饱和度增长越剧烈,支化作用和断链作用更明显,羟基指数增长更快,且区别主要集中于老化后期;相对分子质量分布下降越快;表面微观形貌老化程度越严重;主要晶面衍射角和晶胞参数变化越显著。结晶度越高,HDPE缺陷也就越多,在热氧环境中越容易发生氧化,老化现象更严重。

Degradation Properties of High Density Polyethylene by Thermo-Oxidation Aging as a Function of Crystallinity

The degradation properties of high density polyethylene(HDPE) after 110 C artificial thermo-oxidation aging as a function of crystallinity were investigated.The variations of mechanical properties,chemical structure,molecular weight,surface microstructure and crystal structure were evaluated for different aging time by mechanics experiment,attenuated total reflection infrared spectroscopy (ATR-FT-IR),gel permeation chromatography (GPC),scanning electron microscope (SEM) and X-ray diffraction (XRD).The results show that the higher degree of crystallinity in HDPE results in faster decrease in the tensile strength,tensile modulus and bending modulus and more significant change in the chromatic aberration,while the impact property improves.The degree of unsaturation and hydroxyl index increase significantly,the chain branching and chain breaking are more obviously mainly concentrated in the latter part of aging.The molecular weight distribution decreases faster,the aging degree of surface microstructure is more severe,crystalline structure and cell parameters change more significantly.The higher crystallinity increases flaw in HDPE,which facilitates oxidation in thermo-oxidation environment and the aging phenomenon is more severe.