低密度聚乙烯热氧老化特性

Characterization of the Degradation Behavior of LDPE after Artificial Thermo-Oxidative Aging

采用衰减全反射傅里叶红外光谱(ATR-FTIR)、差示扫描量热法(DSC)、连续自成核退火热分级技术(SSA)和力学测试等手段研究了人工加速热氧老化环境条件下低密度聚乙烯(LDPE)微观结构和宏观性能的变化。结果表明:随着老化时间的延长,分子结构产生羰基、羟基等含氧基团,通过ATR-FTIR测得的结晶度在老化期间由于断链的影响,表现出先增加后减小的趋势,熔融特征温度和氧化诱导温度变化不明显;拉伸强度和拉伸模量呈现下降趋势。亚甲基结晶序列长度(MSL)为98的片段先增长后急剧减少,先增长主要是由于链段中烷基自由基的重组,这将导致分支的减少和更长亚甲基结晶序列长度片段的形成,而断链和包括系带分子的分子链的氧化导致了亚甲基结晶序列长度为98的片段随后的减少。

The changes to the microstructure and macrostructure of low density polyethylene （LDPE） in artificial thermo- oxidative environment have been investigated by Attenuated Total Reflection Infrared Spectroscopy （ATR-FTIR） , Differential Scanning Calorimetry （DSC） , Successive self-nucleation and Annealing （SSA） thermal fractionation and tensile tests. The results showed that during the aging period, the concentration of carbonyl and hydroxyl groups increased. Crystallinity obtained from ATR-FTIR during degradation exhibited a rapid increased and then decreased due to chain session. The variation of the melting characteristic temperature and oxidation induction temperature were not obvious while the tensile strength and tensile modulus reduced gradually. During thermo-oxidative degradation there was an initial increased followed by a rapid decreased in the relative fraction of segments with an average MSL of 98. The initial increased in the fraction of segments with an average MSL of 98 was attributed to alkyl chain recombination which would result in an overall loss of branches and the formation of chain segments with high MSLs. The latter decreased in the fraction of segments with an average MSL of 98 was consequently attributed to chain session and oxidation of chains including tie-molecules.