【作者】 毛立新；

【导师】 金日光；

【作者基本信息】 北京化工大学 ， 材料学， 2002， 博士

【摘要】 聚烯烃工业技术进步的关键在于催化剂。九十年代以来，随着茂金属催化剂的问世，聚烯烃工业正在发生又一场技术革命，这场技术革命将对聚烯烃产品产生巨大的影响。 茂金属聚乙烯（简称mPE）是茂金属催化剂用于烯烃聚合工业化最快的品种，其产品主要包括茂金属聚烯烃塑性体和茂金属聚烯烃弹性体两大类。本论文作为中国石化集团公司项目“茂金属聚乙烯结构、性能及加工应用研究”的一部分，以这两大类产品作为研究对象，研究内容包括以下三个部分：（1） 茂金属聚乙烯的结构—形态—性能研究；（2） mPE／LDPE共混合金的流变性能和力学性能研究；（3）PP／POE共混合金的结构—形态—性能研究。研究重点包括两个问题，一是对于mPE和mPE／LDPE共混合金体系，在大量动态剪切流变试验数据的基础上，推导并验证能够同时表征其熔体粘度对剪切速率和温度依赖性的本构方程；二是对于PP／POE共混合金体系，采用JRG—群子统计理论建立群子均匀性标度参数与PP／POE共混合金体系的力学性能之间的关系。 第一部分：茂金属聚乙烯的结构—形态—性能研究 在该部分，本论文借助GPC、FTIR、WAXD、DSC、¹³C-NMR、流变仪、万能试验机等多种先进的分析手段，对茂金属聚乙烯的链结构、结晶结构、结晶动力学、剪切和拉伸流变性能以及力学性能进行了系统的研究，并取得了一些重要的结果。首先，发现茂金属聚乙烯分子结构规整，共聚单体分布均匀，分子量分布窄；其密度和结晶度受支化结构影响较大，在其分子中引入长支链结构，可以得到密度较低，而力学性能较好的聚乙烯产品；在等温结晶和非等温结晶过程中，mPE均倾向于均相成核，并且在等温结晶过程中，mPE的结晶速率较低，而在非等温结晶过程中，mPE的结晶速率受降温速率的影响较小。其次，发现mPE熔体的剪切流变性能和拉伸流变性能均较差，主要表现为其剪切粘度对剪切速率和温度的依赖性较弱，而在拉伸流变试验中则没有出现明显的“应变硬化”现象；通过在mPE分子中引入部分长支链结构或将mPE与少量LDPE进行共混，是改善mPE流变性能的有效手段。其中通过共聚方法在mPE分子中引入非线性长支链结构，对提高mPE熔体粘度对温度的依赖性作用较为明显，而对提高mPE熔体粘度 北京化工大学博士学位论文对剪切速率的依赖性以及对提高mPE熔体强度作用较弱;采用共混方法在mPE体系中引入线性长支链结构，则对提高mPE熔体粘度对剪切速率的依赖性以及提高mPE的熔体强度的作用较为明显，而对于提高mPE熔体粘度对温度的依赖性作用相对较弱。再者，还发现茂金属聚乙烯具有较好的拉伸性能，在拉伸试验中，当拉伸应变大于300%时，其拉伸强度迅速增大，表现出显著的“应变硬化”现象，并且通过观察其拉伸断面形貌发现，其拉伸屈服主要是结晶熔融和再结晶造成的。总之，通过这一部分的研究发现，尽管mPE拉伸性能较好，但是其剪切和拉伸流变性能还有待进一步提高。 第二部分:n1PE/L DPE共混合金的流变性能和力学性能研究 在该部分，本论文以mPE/LDPE共混合金的流变性能和力学性能作为主要研究内容，探索改进mPE加工性能的有效途径。通过研究发现，在n1PE中混入少量LDPE，不仅能够显著降低n1PE的熔体粘度，提高其熔体粘度对剪切速率的依赖性，而且还可以有效地提高mPE的熔体强度，使mPE熔体在拉伸流动中出现显著的“应变硬化”现象。并且随着mPE几DPE共混合金中LDPE含量的增加，共混合金在拉伸试验中的“应变硬化”现象减弱。因此，建议用LDPE改进n1PE加工性能时，LDPE的添加量不宜超过10%。 此外，在大量mPE和mPE/L DPE共混合金动态剪切流变试验数据的基础上，拟合并推导出能够同时反映PE和mPE几DPE共混合金熔体粘度对剪切速率和温度依赖性的本构方程，并且通过分析发现，方程中的Q值对PE和mPE/L DPE共混合金的熔体粘度的剪切速率依赖性影响较大，Q值越大，其熔体粘度对剪切速率越敏感。同时，Q值的大小不仅与PE分子中长链的作用有关，并且还能反映PE熔体在拉伸流动中出现“应变硬化”现象的能力。 第三部分:PP爪OE共混合金的结构一形态一性能研究 在该部分，本论文通过熔融共混的方法研究了五种茂金属聚烯烃弹性体（POE）对均聚型聚丙烯（HO一PP）和共聚型聚丙烯（CO一即）的增韧效果，发现POE对CO一PP和H。一PP表现出不同的增韧效果，其中POE对C。一PP的增韧效果较为明显，其“脆一韧转变”发生在POE含量为0%一10%之间;而POE对H。一PP的增韧效果较差，其 “脆一韧转变”则发生在POE含量为20%一30%之间。此外，当POE含量超过“脆一韧转变”点之后，PP/POE共混体系不仅具有较高的冲击强度，而且还具有较好的流动性，表明POE是即十分理想的抗冲改性剂。与此同时，通过对不同POE含量的Co--PP/POE共混合金的DSC分析发现，POE能够与CO一PP分子中的PE链段形成共晶结构，并且这种作用在POE含量超过20%以后十分明显，因此，Co--PP/P0E共混体系的界面结合力明显高于Ho一即/POE共混体系，这是造成两者冲击性能差异的主要原因。再者，通过观察PP/POE共混体系的冲击断面形貌发现，在增韧的即/P0E冲击断面上同更多还原

【Abstract】 The development of polyolefin industry lies in catalysts. With the birth of metallocene catalysts, a technology revolution has taken place in the polyolefin industry since 1990s, which will have an important impact on the polyolefin products.Metallocene polyethylenes ( mPE ) are the earliest industrialized products catalyzed by metallocene catalyst in the field of olefin polymerization. The so called metallocene polyethylenes have two types named as polyolefin plastomers ( POP ) and polyolefin elastomers ( POE ). The study based on these two kinds of mPE included three parts:The first part was to study the structure, morphology and properties of mPE. In this part, the chain structure, crystalline structure, shear and extensional rheology, and mechanical properties were studied by means of a series of modern analysis technologies such as GPC, FTIR, WAXD, DSC, 13C-NMR, rheometer, and tensile tester and so on. Based on all these experimental data, some important results were obtained. First, mPE had uniform distribution of comonomers and narrower distribution of molecular weight. The branching structure of mPE had an important effect on their density and crystallinity, and mPE with very low density and good tensile properties could be obtained by introducing long chain branches onto the molecular structure of mPE. Both during isothermal and non-isothermal crystallization, mPE were apt to nucleate homogeneously. During the isothermal crystallization, the crystalline rate of mPE was lower than that of common PE. During the non-isothermal crystallization, compared with common PE, the cooling rate had less impact on the crystallization rate of mPE. Second, the sensitivity of the melt viscosity of mPE to the shear rate was poor, and the introduction of long chain branches onto the molecular structure of mPE could improve the dependence of their melt viscosity on both shear rate and temperature. In the extensional rheometric tests, the occurrence of phenomena of ’strain hardening1relied on the structure of linear long chains, and mPE didn’t show the behavior of "strain hardening’, which implied that the melt strength of mPE was poor. Third, compared with common PE, mPE exhibited better mechanical properties. When their tensile strain exceeded 300%, their tensile stress rose abruptly and this meant that the phenomena of ’strain hardening’ occurred. By observing the morphology of fracture surface obtained from the tensile tests, it was also found that the tensile yielding was mainly due to melting and re-crystallization. Overall, although the properties of mPE were excellent, their shear and extensional rheology still needed improving.The second part was to study the rheology and mechanical properties of the mPE/LDPE blends in order to find some effective ways to improve the processibility of mPE. By adding a little amount of LDPE into mPE systems, both their shear and extensional rheolpgical properties could be improved effectively. On one hand, their melt viscosity was decreased a lot and the dependence of their melt viscosity on the shear rate was also increased. On the other hand, phenomena of ’strain hardening’ was observed obviously in the elongational flow of mPE/LDPE blends. In addition, with the increase of LDPE content, the tensile strength of mPE/LDPE blends decreased remarkably, which implied that when LDPE was used to improve the processibility of mPE, 10 percent or lower was the preferable content of LDPE.Based on the data of dynamic shear rheometric tests, a constitutive equation was also proposed, which could characterize the dependence of the melt viscosity of PE and its blends on both shear rate and temperature. It was also found that the value of a in the constitutive equation had an important effect on the sensitivity of melt viscosity of PE and its blends to the shear rate, which was not only related to the effect of long chains, but also could exhibited the tendency of ’strain hardening’ of PE and its blends occurred in the elongational flow. With the increase of a value, the sensitivity更多还原