【作者】 谭小华；

【导师】 陈贤益； 王庭慰；

【作者基本信息】 南京工业大学 ， 材料学， 2003， 硕士

【摘要】 聚丙烯是一种应用广泛的通用塑料，具备许多优异的性能。但由于聚丙烯只有线性链结构，软化点与熔点接近，当温度高于熔点后，其熔体强度和熔体的粘度急剧下降，导致热成型、挤出涂布、挤出发泡等加工困难。因此，高熔体强度聚丙烯的研究已成为聚丙烯性能研究的重点。本课题的研究目标是获得长链支化的高熔体强度聚丙烯，掌握制备高熔体强度聚丙烯的相关工艺和技术。课题的技术关键是稀疏长支链接枝聚丙烯的生成以及聚合物降解和凝胶生成的控制。我们选用了2,5-二甲基-2,5-（二叔丁基过氧化）己烷和叔丁基过氧化2-乙基己酸酯两种有机过氧化物作为引发剂，甲基丙烯酸缩水甘油酯、1,6己二醇二丙烯酸酯和季戊四醇三丙烯酸酯三种不同官能团度的丙烯酸酯作为单体。我们通过双螺杆挤出机采用熔融接枝聚丙烯/低密度聚乙烯共混物的方法，来制备具有一定熔体强度的聚丙烯/低密度聚乙烯共混物，来达到提高聚丙烯熔体强度的目的。课题主要研究了引发剂、单体的种类及用量和低密度聚乙烯用量对接枝产物性能的影响，并利用傅立叶红外光谱、差示扫描量热分析、凝胶渗透色谱、拉伸粘度等手段对所得接枝产物的分子结构和有关性能进行了分析和表征。研究结果表明，叔丁基过氧化2-乙基己酸酯引发接枝效果优于2,5二甲基-2,5（二叔丁基过氧化）己烷；1,6己二醇二丙烯酸酯和季戊四醇三丙烯酸酯改性效果显著。产物熔体强度、熔体流动速率随引发剂、单体用量变化明显。引发剂过少不足于完全引发单体接枝时，单体会发生自聚而形成低聚物，使熔体强度降低、熔融流动速率增大。引发剂过多，则会引发严重的聚丙烯降解，从而降低产物分子量，以致产物熔融流动速率较大、熔体强度较小。产物的熔体强度一般随单体用量的增加而增大，但当单体过多，则会生成较多的单体自聚物，反而降低了产物的性能。低密度聚乙烯用量增加时，熔体强度会有所上升，但力学性能会下降。总的说来，熔体强度高的产物冲击强度较高，但拉伸强度和弯曲强度有下降的倾向。接枝物的红外谱图表明丙烯酸酯单体接枝上了聚丙烯大分子主链。差示扫描量热分析结果表明高熔体强度的产物熔融温度上升，结晶温度也有一定程度的提<WP=8>高。凝胶渗透色谱结果显示改性前后分子量及其分布变化很小。高熔体强度的产物拉伸粘度较高，且在拉伸过程中出现了应变硬化效应，这说明产物中已存在长链支化结构。研究表明，反应条件对产物性能有一定的影响。反应温度为190℃、螺杆转速为100rpm的工艺条件对改性最适宜。 对于聚合物降解和凝胶生成的控制研究方面，我们也进行了一定的探索。添加共单体苯乙烯和减小引发剂用量可有效抑制反应体系中聚丙烯的降解。当低密度聚乙烯用量过多时，会生成凝胶。单体用量控制在1份以内，基本不会形成凝胶。更多还原

【Abstract】 Polypropylene (PP) is a general plastic with various fine properties. However, due to its linear chain structure and appropinquity of softening point and melting point, its melt strength and melt viscosity harshly drops with the temperature rising beyond its melting point, which results in the difficulties in thermoforming, extrusion coating, and extrusion foaming. Because of its particular molecular structure, superior properties and huge application potentials, the study on High Melt Strength Polypropylene (HMSPP) has been a field of growing interest for years.The purpose of this work was to obtain long chain branching HMSPP and to investigate the technique of its production process. The hinges of this study included the formation of longer side chains in order to acquire higher melt strength and the control of degradation of iPP and cross-linking side reactions, which may lead to the formation of gel.In this study, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane and tert-Butylperoxy 2-ethylhexyl carbonate were used as initiators, while three types of acrylates with various number of functional groups, namely epoxypropyl methacrylate (GMA), 1,6-Hexanediol diacrylate (HDDA), and pentaerythritol triacrylate(PETA) were used as grafts. PP/LDPE blend was melt grafted by these acrylate grafts in a twin-screw extruder to yield blend with higher melt strength.The effects of initiator type, graft type, as well as LDPE dosage on the blend’s properties were investigated. Methods including FTIR, DSC, GPC and extensional viscosity test were used to test the resulted grafting products in terms of molecular structure and other characters.The results indicated that tert-Butylperoxy 2-ethylhexyl carbonate was a better initiator, while both HDDA and PETA helped to improve the blend’s melt strength. The dosage of initiator and graft also strongly affected the blend’s melt strength and melt flow rate (MFR). Lack of initiator resulted in self-polymerization of the grafts and, therefore, the formation of oligomers, which would bring down the melt strength<WP=10>and increase the MFR. On the other hand, excess initiator had similar effects due to the increasing of PP degradation. Generally, the melt strength would grow with the increasing dosage of grafts to a certain degree, then start to drop because excess grafts would self-polymerize to form oligomers. Adding of LDPE causes the melt strength to grow but the stretching and bending strength to decrease.The IR spectrogram proved that the acrylate grafts had been grafted onto the PP chains. Higher melt strength was always accompanied with higher stretching viscosity and strain gauging during stretching, both of which indicated the existence of branching structure. DSC results showed that higher Tc and Tm coexisted with higher melt strength, while molecular weight distribution almost remain unchanged as indicated by the GPC test.The affecting factors of the graft reaction were also investigated. It was found that process condition of 190℃, 100rpm was optimal for the graft reaction. The increase in dosage of monomer and initiating agent could both improve the graft ratio.Degradation of PP and formation of gelatin were also studied. It was found that adding of styrene and reducing the initiator dosage could effectively minimize the degradation of PP, while gelation occurred when too much LDPE were used. In general, gelation could be avoided by limiting the graft dosage to no more than 1 portion.更多还原