环氧大豆油作为PVC增塑剂的热分解动力学与裂解机理研究

Study on thermal decomposition kinetics and pyrolysis mechanism of polyvinyl chloride(PVC) using ESO as plasticizer

为明确环氧大豆油(ESO)作为PVC增塑剂的热稳定性能和热裂解机理,笔者研究了ESO作为PVC制品增塑剂在热失重过程中的表观活化能变化。结果表明:活化能随失重量增加而升高;添加ESO的PVC材料在热失重50%前活化能的变化情况说明ESO可作为一种稳定剂使用;在高温阶段,两种增塑剂可能发生了复杂的交联反应,从而使得生成物热稳定性提高。采用裂解-气相色谱/质谱联用分析技术分析了ESO作为PVC增塑剂的裂解机理,在温度达到260℃前,多数PVC分子失去氯化氢后生成含有苯环物质,少部分生成含有十二到十六碳的环状烷烃;约10%的ESO裂解生成含有十六和十八碳的脂肪酸,裂解产物与油脂结构有关,脂肪链上碳原子个数越少越易于分解;温度达到480℃时,ESO裂解产物占多数,产物以十六碳的饱和脂肪酸、十八碳不饱和脂肪酸酯类为主。环氧键吸收氯化氢后生成双键,也有少部分生成呋喃结构和羰基结构。植物油脂较易燃烧的原因为油脂受热分解出沸点较低、易燃的脂肪酸和脂肪酸甲酯。研究结果可为优化PVC材料配方与合成新型油脂基增塑剂提供理论基础。

The thermal decomposition kinetics and pyrolysis mechanism of polyvinyl chloride （PVC） using epoxidized soybean oil （ESO） as the plasticizer （PVC/ESO） was studied in this paper. The results showed that the apparent ac- tivation energy （Ea ） increased with the increase of the weight loss. The changes of Ea of PVC/ESO indicated that ESO could stabilized the PVC when the thermal loss was lower than 50%. At high temperature, a more complex cross-linking reaction might occur between the two plasticizers, leading to the higher Ea of PVC products and conse- quently more stable PVC products. The pyrolysis mechanism of PVC/ESO was analyzed by the pyrolysis-gas chroma- tography-mass spectrometry （Py-GC/MS）. At 260~C, the majority of PVC decomposed aslossing hydrogen chloride and generated substances containing benzene ring. A little part of PVC decomposed to cyclic alkanes containing from 12 to 16 carbon atoms. About 10% of ESO cleaved to fatty acids containing from 16 to 18 carbon atoms. The structure of pyrolysis products depended on the number of carbon atoms in the chain of fat acid. The lower the number of car- bon atoms, the easier they decomposed. When the temperature reached 480~C, decomposed ESO accounted for the majority of the pyrolysis products, which were consisted mainly of 16 carbon atoms saturated fatty acids and 18 carbon atoms unsaturated fatty acid esters. Mostepoxy bonds in ESO reacted with hydrogen chloride to form a double bond. Others were converted to furans and carbonyls. In addition, the boiling points of the fatty acids and fatty acid methyl esters generated from the thermal decomposition of ESO were relatively lower, which led them be easy to burn.