豆油基聚酯增塑剂的合成及与聚氯乙烯共混性能分析

Synthesis of soybean oil based polyester plasticizer and its property mixing with polyvinyl chloride

为了进一步利用可再生资源植物油代替石油合成化学品，该研究使用豆油和甘油在230℃下合成了豆油单甘脂，将其作为合成聚酯的二元醇组分，与马来酸酐反应，并以异辛醇为封端剂控制分子量，经过酯化和缩合反应合成了豆油基聚酯增塑剂。采用红外光谱、核磁共振和凝胶渗透色谱对该豆油基聚酯产品的结构和分子量进行了表征；将其与聚氯乙烯热塑共混成型，使用转矩流变仪、扫描电镜、热重分析仪、动态热机械分析仪和万能拉力试验机对共混物的扭矩、相容性、热性能和力学性能进行了表征。研究发现：通过单甘脂与马来酸酐酯化缩合反应合成了分子量范围为3000～3500的聚酯产品，该聚酯产品与邻苯类增塑剂复配使用增塑聚氯乙烯，增塑聚氯乙烯在热塑过程中的扭矩从13.4 N·m降低到10.1 N·m；扫描电镜分析表明聚酯增塑剂较好地改善了聚氯乙烯和填料的相容性；增塑聚氯乙烯的热降解温度由254.7℃提高到255.6℃，玻璃化转变温度由55℃降低到42℃；拉伸强度由16.9 MPa降低到9.6 MPa，断裂伸长率由179.6%增加到269.3%，因此该产品可以作为聚氯乙烯的优良增塑剂使用。

The utilization of renewable resources in material application attracts increasing attentions in chemical industry, due to the concern regarding environmental sustainability. Nowadays, most commercially available materials are derived from non-renewable resources. With rapid consumption of fossil oils and dramatic fluctuations in the oil price, there is an urgent need to develop chemical materials from renewable resources. Vegetable oils are considered to be important renewable sources due to the rich varieties suitable for chemical transformation, universal availability and low price, and they are the preferred alternatives by chemical industry. In this study, soybean oil monoglycerides were prepared by the transesterification between soybean oil and glycerol at 220~240℃, then polyester plasticizer based on soybean oil was synthesized from soybean oil monoglycerides and maleic anhydride via direct esterification and polycondensation route. The soybean oil polyester plasticizer was characterized by Gel Permeation Chromatography, FT-IR spectrum and HNMR Spectroscopy. The results showed that the molar mass increased obviously with the extension of reaction time. The molar mass of Mn increased from 3027 g/mol to 3030 g/mol when reaction time was 10 h. And the distribution index was about 1.79-2.10. The blends of soybean oil polyester and polyvinyl chloride （PVC） underwent a melting process. The compatibility, mechanical properties and thermodynamic properties of the blends were characterized by torque rheometer, universal testing machine, thermogravimetric analysis （TGA） and dynamic thermo mechanical analysis （DMA）. The results showed that with polyester content increasing from 10 g to 30 g in PVC blends, the TG curves showed a three-stage thermal degradation process above 80℃. PVC blends were thermally stable in N2 atmosphere. The first-stage degradation at around 80℃-280℃could be attributed to the evaporation of water and small molecules. The degradation in the second stage at around 280℃-470℃was the fastest and corresponding to the formation and stoichiometric elimination of HCl. The last-stage degradation at above 470℃ was attributed to cross linking containing C=C bonds and the degradation of inert filler such as thermal stabilizers. The glass-transition temperature （Tg） decreased from 55℃ to 42℃, and the change of the Tg of PVC blends was in agreement with the common rule the plasticizer can decrease the Tg of PVC. The reason was that the polyester based on soybean oil could interact with PVC molecular and increase the mobility of PVC chain segment. The scanning electron microscope images of the surface of sample-1 plasticized with polyester plasticizer based on soybean oil presented many particles and fractures on the external surface, the particle appearing on the surface was properly the result of some plasticizer excess that was scattered outside the PVC matrix. It caused the eventual migration of plasticizer out of PVC in the processing and using. The SEM images of the surface of sample-3 showed homogeneous and smooth surface. It indicated that the plasticizer was uniformly dispersed in the PVC matrix and surrounded intimately by PVC continuous phase, and there was not a clear boundary between them to be observed. So there was good compatibility between polyester plasticizer based on soybean oil and PVC. The torque of PVC blends decreased from 13.4 N·m to 10.1 N·m, which corresponded to a decrement of 24.6%. The torque decrement could decrease the melt viscosity and would be conductive to thermoplastic processing of PVC blends. The enhancement in plasticization will expand the application range of PVC plasticized with polyester plasticizer materials. This study may lead to the development of new type of PVC plasticizer based on vegetable oil.