【作者】 张春晖；

【导师】 郑强； 上官勇刚；

【作者基本信息】 浙江大学 ， 高分子材料， 2011， 博士

【摘要】 作为一种高性能聚烯烃材料,抗冲共聚聚丙烯(IPC)因其具有的优良强度和抗冲性能在多种工业领域得到了广泛应用。由于丙烯和乙烯单体在共聚阶段其结构序列的多样性,IPC的组成和结构呈现特殊的多重性和复杂性；同时,作为一种“反应合金”,IPC熔体表现出了独特的流变行为。由于组成、链结构、组分间相容性及相形态等均可能对多相多组分材料的最终性能产生重要影响,且流变行为直接反映材料的加工性能,研究IPC的微结构和动态流变行为对于调控材料性能、发展最优加工理论具有重要的理论价值和应用指导意义。本文采用多种测试和表征方法,系统地研究了IPC的链结构、组成、组分间相容性和相形态,并从微结构与形态角度出发,改进了经典模型并提出了新的相结构模型,同时对IPC的动态流变行为进行了深入讨论。此外,还制备了IPC和高密度聚乙烯(HDPE)热压复合材料,并对其界面焊接性能进行了研究。论文研究取得了如下的主要结果：1.利用温度梯度萃取分级的方法将IPC分级为三个级分：F50,F100和F125。热分析的结果表明,三个级分分别对应着IPC中的三种主要成分,即乙烯丙烯无规共聚物(EPR),乙烯丙烯嵌段共聚物(EbP)和丙烯均聚物(HPP)。发现IPC及其F100级分均具有三个玻璃化转变,且IPC中各级分的转变温度和IPC所表现的相应组分的转变温度存在差异,表明IPC中各级分间存在着一定的相互作用。对各级分进行共混和连续自成核退火(SSA)处理,发现IPC中EbP/HPP级分间可形成PP共晶,而EPR对EbP的结晶起到明显的稀释作用。这些结果表明,EPR/EbP和EbP/HPP中组分间均具有良好的相容性,同时也证明了EbP对EPR和HPP具有增容作用。2.通过对IPC相形貌的观察,结合链结构分析及相容性分析结果,提出了改进的多层核壳分散相模型。其中,EPR组成分散相的壳结构,富PP的EbP相分布在EPR和HPP基体之间,充当两组分的增容剂；而富PE的EbP相分布于EPR内部,形成分散相的核结构。对IPC中三种级分进行溶液共混及热处理(热压制样),制得了具有类似IPC原始试样核壳分散相结构的共混试样,发现各组分在一定条件下可通过类似自组装的过程形成复杂的核壳结构,证明了IPC的多层核壳相结构具有很强的热力学稳定性。3.研究了IPC及其级分的动态流变特性,发现IPC在低频率区域表现出类固性行为,即动态储能模量(G＇)对频率(ω)在双对数坐标下作图得到的曲线在低ω区域呈现“第二平台”现象。对IPC三种级分的动态流变行为的研究发现,各级分间在G＇及复数粘度(η*)上表现出明显差异,这主要是因为分子量和分子链链长不同所致。EPR和HPP级分的lgG’-lgω曲线符合线性粘弹性,呈现出均相体系的特征；而EbP则在低ω区域呈现出“第二平台”,表现出非均相体系的特征。研究了IPC中HPP/EPR溶液共混物的流变行为,证明IPC中HPP与EPR之间存在的相分离足以使得IPC产生“第二平台”现象,EbP未在其中起到关键作用。4.采用热压法制备了具有高焊接强度的IPC/HDPE复合材料。研究结果表明IPC和HDPE存在着较强的分子间相互作用,且IPC中的可结晶PE分子链可对HDPE的结晶行为产生显著影响。对IPC/HDPE熔融共混物的相形态研究发现,HDPE倾向于同IPC中富PE的EbP分子链结合以形成新的分散相结构,HDPE和EbP组分之间良好的相容性。IPC/HDPE热压复合材料的高焊接强度来自于HDPE中的乙烯分子与IPC中富PE的EbP之间的共晶作用。更多还原

【Abstract】 As a polymer alloy, impact polypropylene copolymer (IPC) is prepared by two step polymerization. Due to having good strength and impact toughness, IPC has been widely used in many industries. The diversity of the arrangement of propylene and ethylene units during the copolymerization step leads to an extremely complex composition of IPC. In addition, as a multi-component and multi-phase material, the IPC melt exhibits the characteristic rheological behavior. Considering that the performances of IPC strongly depend on its microstructure and composition, and the rheological behavior can reflect the processing property of the IPC, the study on the structure and rheological behaviors are necessary to optimize its performances and develop the optimal processing theory. In this dissertation, the chain structure, compatibility and morphology of IPC were studied and a phase model of IPC was put forward. The dynamic rheological behavior of IPC and its fractions were discussed. Furthermore, an IPC/HDPE (high density polyethylene) laminate was prepared by hot press and the high weld strength between IPC and HDPE was studied.The IPC was fractionated into three fractions (F50, F100 and F125) by means of temperature-gradient extraction fractionation. The thermal behavior of these three fractions was studied by modulated differential scanning calorimeter (MDSC) and dynamic mechanical analysis (DMA). The results show that these three fractions correspond to three main components of IPC, i.e. ethylene-propylene random copolymer (EPR), ethylene-propylene block copolymer (EbP) and propylene homopolymer (HPP), separately. It was also found that both IPC and EbP fraction (F100) present three glass transition peaks, and the glass transition temperature of EPR in IPC sample is remarkably lower than that of pure EPR fraction (F50) due to the existence of EbP component with special structure in IPC. Furthermore, by using successive self-annealing (SSA) technique, cocrystallization occurring between the polypropylene chains in EbP fraction and in HPP fraction was found for solution-mixed EbP/HPP blends, and it is believed that there exists a dilute effect of EPR on the crystallization of EbP fraction for the solution-mixed EPR/EbP blends. Accordingly, it can be inferred that EbP fraction has good compatibility with both EPR and HPP fractions, and it confirms that the compatibilization effect of EbP fraction in IPC is good.Based on electronic microscopy observation and results of chain structure analysis, a modified multi-layer core-shell phase structure model was put forward for IPC. In this model, the HPP component and EPR component were believed to be the matrix and the main dispersed phase respectively, and depending on its chain structure, the EbP component could form the core, the layer or the bridges connecting the core and EbP layer. It was found that even this multi-layer core-shell structure is completely destroyed, it can be rebuilt by thermal treatment, with a way analogous to self-assembly process. This indicates that the multi-layer core-shell structure is stable in thermodynamic to some extent.The dynamic rheological behavior of the melts of IPC and its three fractions were examined. The results shows that the dynamic storage modulus (G’) of IPC exhibits "pseudo solid-like" phenomenon behavior at low frequency (ω). This result indicates that the IPC melt is endowed with a characteristic of heterogeneous phase. The differences in the G’and complex viscosity (η*) among the fractions of IPC appear dramatic, which are probably induced by the large variance of the molecular weight and the length of the molecular chains among the fractions. The EPR and HPP fractions present the fine linear viscoelasticity, implying that these fractions are homogeneous system. Moreover, the dynamic rheological behavior of the EbP exhibits "pseudo solid-like" behavior at lowω, meaning that this fraction is a heterogeneous system. On the other hand, the’second plateau’can be observed in low co region for the HPP/EPR blends when the proportion of the EPR is the same as the proportion of EPR in IPC, suggesting that the "second plateau" in IPC results from the phase-separation between HPP and EPR, and the existence of EbP is not a key factor in the generation of "second plateau" for IPC.The IPC/HDPE laminate was prepared and the peeling test result showed that the welded joint strength of the laminate is high. The thermal analysis results indicated that there exist some interactions between IPC and HDPE, and the crystallizable PE component in IPC could affect the crystallization of HDPE. On the basis of the morphological results of IPC/HDPE blends, it is suggested that HDPE tends to stay with the PE-rich EbP chains in IPC to form the dispersed phase, indicating the good compatibility between HDPE and EbP components of IPC.更多还原