Thermal Oxidation and Structural Changes of Degraded Polyethylene in an Oxygen Atmosphere
Thermal Oxidation and Structural Changes of Degraded Polyethylene in an Oxygen Atmosphere
复制标题
氧气气氛中降解聚乙烯的热氧化和结构变化
DOI：
10.1080/00222348.2010.516687
复制
发表时间：
2011-01-01
影响因子：
1.4
通讯作者：
Yang, Ming-Bo
中科院分区：
文献类型：
--
作者：
Huang, Hui-Juan;Wang, Quan-Bing;Yang, Ming-Bo
对高密度聚乙烯（HDPE）进行高温本体热处理，得到降解聚乙烯，然后将降解聚乙烯置于氧气气氛中，在160 ℃下进行不同时间的氧化反应，得到一系列聚乙烯降解氧化产物。采用红外光谱、化学滴定、凝胶色谱、差示扫描量热等方法研究了聚乙烯降解氧化产物的结构变化。氧化产物分子链中引入了羟基、羧基、酯基等官能团，且随着氧化时间的延长，羧基数目急剧增加。在氧化过程中，分子链的断裂以及组合反应，如酯化，导致数均分子量（（M（n））/bar）降低，重均分子量（（M（w））/bar）和分子量分布增加，以及每个分子链的羧基数的初始增加和稳定。值得注意的是，氧化主要发生在弱键附近，主要是末端乙烯基不饱和度。因此，与降解的聚乙烯相比，氧化产物的熔融和结晶行为几乎没有变化;即使当氧化时间长达4小时时，熔融和结晶温度的下降也小于3 ℃。这些结果可能为开发定制的低分子量聚合物奠定了基础，这些聚合物可以直接使用，也可以在烯烃官能团的化学修饰后使用。
High-temperature bulk thermolysis of high density polyethylene was performed to obtain degraded polyethylene, which was then left in an oxygen atmosphere for oxidation reaction at 160 degrees C at different oxidation times, yielding a series of polyethylene degradation-oxidation products. Using infrared spectroscopy, chemical titration, gel chromatography, and differential scanning calorimetry, the structural changes of the polyethylene degradation-oxidation products were investigated. Hydroxyl, carboxyl, ester, and other functional groups were introduced into the molecular chains of oxidation products, and the number of carboxyl groups sharply increased with increasing oxidation time. The breaking of molecular chains as well as combination reactions, such as esterfication, during the oxidation process lead to decrease of number-average molecular weight ((M(n)) over bar) and increase of both weight-average molecular weight ((M(w)) over bar) and molecular weight distribution, and an initial increase and leveling off of the carboxyl number per molecular chain. It is noteworthy that oxidation occurred primarily near weak bonds, mainly terminal vinyl unsaturations. Thus, compared with degraded polyethylene, the oxidation products showed little changes in the melting and crystallization behaviors; even when the oxidation time was up to 4 hr, the drop in the melting and crystallization temperature was less than 3 degrees C. These results might lay a foundation for exploring tailored low molecular weight polymers to be used just as they are or after chemical modifications of olefinic functions.