【作者】 许向彬；

【导师】 杨鸣波；

【作者基本信息】 四川大学 ， 材料加工工程， 2007， 博士

【摘要】 以聚烯烃（PO）为主的通用塑料的功能化是当前以及今后高分子材料科学与工程领域领域研究的一项重要研究课题。其中，导电功能是通用塑料最重要的功能化目标之一，其主要实现手段为外加导电粒子。控制导电粒子在体系中的分布和排列方式是获得高性能、低成本的导电高分子复合材料的重要途径，也是导电高分子复合材料的发展趋势。本论文提出利用聚合物共混物加工过程中形态控制方法，使分散相原位成纤，并控制导电粒子选择性分布于原位微纤中，从而简便高效的获得低成本、高性能的导电高分子复合材料。本论文对以PO为主体的炭黑（CB）/聚对苯二甲酸乙二醇酯（PET）/聚乙烯（PE）复合材料在加工过程中的成纤以及所得微纤化复合材料的形态、结构、逾渗行为、对热和有机液体的响应行为等进行了研究，取得了大量有价值的数据和结果。这对丰富和发展复合型导电高分子材料的导电理论和双逾渗理论具有较重要的学术价值，并为开发廉价且综合性能优异的导电高分子复合材料提供新的思路和方法。主要研究成果：（一）导电原位微纤化复合材料的制备、微观形态和性能研究本文采用“熔融预混合—高温挤出热拉伸—淬冷—低温成型”的新型加工方法制备导电原位微纤化CB/PET/PE复合材料，系统研究了复合材料的微纤的形成条件、导电粒子的分布及其电学性能。（1）CB粒子在整个“熔融预混合—高温挤出热拉伸—淬冷—低温成型”加工过程中，均选择性分布于PET分散相中。这可以基于热力学和动力学两方面进行考虑。从热力学角度看来，根据Young’s方程和最低耗散能理论，CB与PET之间界面张力更低，且PET熔体黏度更低，CB更倾向于分布于PET中；而从动力学角度看来，CB与PET首先熔融混合，两者在与PE基体相混合物之前有充足的时间发生相互作用。（2）导电原位微纤化复合体系的成纤性能强烈依赖于CB/PET分散相与PE基体的黏度比。当黏度比小于1时，体系能形成高长径比的原位微纤；当黏度比略高于1时，体系仍然能形成原位微纤，但长径比较低；当黏度比远高于1时，体系无法成纤。在基体材料一定的情况下，黏度比决定于CB/PET分散相黏度。高的CB结构度以及高的CB粒子含量不利于三元复合体系成纤。（3）CB/PET原位微纤在整个体系中形成三维网络结构，而CB粒子选择性分布于PET微纤中，这种特殊的微观结构导致导电原位微纤化CB/PET/PE复合材料的导电逾渗值明显低于普通CB/PET/PE复合材料和普通CB/PE复合材料。（4）CB/PET原位微纤网络对基体的增强作用，使得导电原位微纤化复合材料在降低逾渗值，降低原料成本的前提下，力学强度得以保持。（二）原位微纤表面微结构对复合体系逾渗行为的影响（1）本文对导电原位微纤化CB/PET/PE复合材料的微观结构与逾渗行为的关系进行了深入研究，发现导电原位微纤化复合材料的逾渗行为无法用经典的双逾渗理论进行解释。（2）研究了原位微纤表面微结构对导电性能的影响，并发现原位CB/PET微纤的表面结构是影响三元体系逾渗行为的关键因素。当CB含量低于CB/PET最大堆积密度Φ_max时，微纤表面几乎无CB粒子，由于微纤之间的高接触电阻，三元体系体积电阻率较高；当CB粒子含量超过Φ_max时，微纤表面CB数量迅速增加，微纤之间导电接触点的数量也相应增加；当微纤表面CB浓度超过某值，以致微纤之间导电接触点的数量足以支持整个体系电子传导时，导电原位微纤体系发生逾渗现象。（三）导电原位微纤化复合材料的温度响应特性（1）研究了导电原位微纤化复合材料的温度—电阻效应，发现在升降温热循环初期，导电原位微纤化CB/PET/PE复合材料PTC强度较强，NTC效应很弱。相比于普通CB/PE体系，具有优异的PTC/NTC综合性能。导电原位CB/PET微纤大的尺寸效应是导致升降温循环初期弱的NTC效应的主要原因。（2）经多次升降温热循环或长时间热处理后，导电原位微纤化CB/PET/PE复合材料材料的PTC效应出现大幅度衰减，电阻表现出温度不敏感性，即电阻随温度的变化基本保持稳定。导电原位微纤特殊的表面微结构和微纤本身较大的尺寸是产生该反常现象的关键因素。由于微纤表面具有独特的导体—绝缘体交错分布结构，在升降温热循环或长时间高温热处理过程中，导电网络会因为CB聚集体之间的相互作用而逐渐完善。又由于原位微纤的大尺寸效应，结晶对原位导电微纤网络影响较小，使得高温下形成的更完善的网络在降温过程中能被部分保留下来，从而使PTC效应发生衰减。（3）这种反常的PTC衰减现象对发展一种制备可回收的电性能稳定的热塑性半晶聚合物（SCTP）基导电复合材料的有效方法具有重要意义。（四）导电原位微纤化复合体系的有机液体响应特性（1）对比普通CB/PE复合材料，本论文考察了导电原位微纤化CB/PET/PE复合材料的有机液体响应特性。发现当试样厚度为140 um，测试温度为常温时，导电原位微纤化复合材料的液敏响应强度大大高于普通导电复合材料。这为发展一种高敏感度液敏高分子材料提供了新的思路。（2）研究了复合材料试样厚度对导电原位微纤化CB/PET/PE复合材料液敏响应速率的影响。相比于普通CB/PE复合材料，导电原位微纤化复合材料液敏响应速率对厚度更加敏感。实验发现，有机液体优先浸入PET/PE相界面是导致以上现象的主要原因。（3）导电原位微纤化复合材料的液敏响应速率相比于普通CB/PE复合材料对温度更不敏感。较大尺寸的原位微纤网络对PE分子链的限制作用被认为是导致这种现象的主要原因。（4）研究了导电原位微纤化CB/PET/PE复合材料的液敏PTC现象。发现导电原位微纤化复合材料和普通CB/PE复合材料均表现出显著的液敏PTC现象。经过升降温测试后，两复合材料试样表面均受到溶剂侵蚀。前者由于具有导电微纤网络结构，相比于后者表面受损程度更低，因而电阻率表现出更好的可回复性。（5）导电原位微纤化CB/PET/PE复合材料在液敏性能测试中体现出一种独特的电压诱导电阻率突变现象，这种反常现象为深入研究原位微纤化复合材料在有机液体环境下的导电机理提供了契机。基于本论文的研究内容，可获得如下三种材料的制备技术：（a）含有导电原位微纤网络的聚合物复合材料；（b）电性能稳定的可回收热塑性半晶聚合物基导电复合材料；（c）具有高液敏强度的导电聚合物复合材料。主要原材料可由本论文的导电CB、PET和PE拓展为普通CB、普通聚烯烃以及通用工程塑料，材料品种多、来源广泛、价格较低；制备工艺易于控制；不需添加多的新设备，易于实现工业化。更多还原

【Abstract】 Functionalization of general-purpose plastics (mainly polyolefin (PO)) is one of the most important research subjects in the field of polymer materials science and engineering at the present and in the future. Electrical conductivity is one of the most important functions of the general-purpose plastics. Filling conductive particles is the main route to fabricate this function. Controlling the distribution and arrayment of the conductive fillers in the polymer matrices is an important method to obtain the conductive polymer composites with high performance and low price. It is also the development tendency of the conductive polymer composites. Based on the technologies of controlling morphology during the processing, this dissertation has put forward a simple and effective method to obtain low price and high performance conductive polymer composites.The fibrillation during the processing, morphology, microstructure, percolation behavior, and temperature and chemical liquid response properties of the PO based carbon black (CB)/ poly (ethylene terephthalate) (PET)/ polyethylene (PE) composite were investigated in this thesis. A large quantity of valuable data and results were obtained, which is of importance to develop the conductive theory and double percolation theory of the conductive polymer composites. These results also provide new ideas and methods to prepare conductive polymer composites with low price and excellent balanceable property. The main results are:(Ⅰ) Preparation, microstructure and percolation behavior for the eleetrieaUy conductive in-situ microfibrillar composites The melt mixing -extrusion at high temperature-quenching-cold moulding process was used to prepare the conductive microfibrillar CB/PET/PE composites in this thesis. The formation of microfibrils, the distribution of conductive fillers and electrical properties were systemically studied.(1) CB aggregates are selectively located in the PET microfibfils during the whole melt mixing -extrusion at high temperature-quenching-cold moulding process. This phenomenon can be explained by thermodynamics and dynamics. By the view of thermodynamics, based on Young’s equation and the minimization of the dissipative energy, CB aggregates prefer to locate in PET owing to the two points: (1) the interfacial tension between CB and PET is lower than that between CB and PE, and (2) the apparent viscosity of PET is lower than that of PE at the extrusion temperature. On the other hand, CB was first compounded with PET prior to extrusion and hot stretching. Hence there was sufficient time for CB particles to mix with PET by the view of dynamics.(2) The droplet-fiber transition in the electrically conductive in-situ microfibrillar CB/PET/PE composite strongly depends on the viscosity ratio of CB/PET dispersed phase and PE matrix. When the viscosity ratio is lower than 1, well defined in-situ micro fibrils with high length/diameter ratio can be formed in the system. As the viscosity ratio is slightly higher than 1, micro fibrils can also be formed, but the length/diameter ratio is relatively low. With the further increase of length/diameter ratio, the microfibrils can not be formed when the length/diameter ratio is far higher than 1. The viscosity ratio depends on the CB/PET dispersed phase as the matrix is fixed at PE. High structure CB and high loading of CB go against the formation of in-situ micro fibrils.(3) A special microstructure is formed in the microfibrillar composite, in which a 3D network is formed by in-situ CB/PET microfibrils, and CB is selectively located in the PET dispersed phase. As a result, the percolation threshold of electrically conductive in-situ microfibrillar CB/PET/PE composite is obviously lower than that of common CB/PET/PE and common CB/PE composite.(4) Owing to the reinforcement of the CB/PET microfibrils, the in-situ microfibrillar composites can keep their mechanical strength while reducing the percolation threshold and the cost.(Ⅱ) The role of the surface microstructure of the microfibrils on the percolation behavior of the in-situ microfibrillar composite(1) The relationship between the microstructure and the percolation behavior of the in-situ microfibrillar CB/PET/PE composite was studied in this thesis. It was found that the percolation behavior of the composite can not be explained by the classical double percolation theory.(2) The influences of the surface microstructure of the fibrils on the conductive properties were studied. The surface microstructure of the microfibrils was found to be the key factor affecting the percolation behavior of the ternary composite. When the CB loading is lower than the maximum packing fraction, there are no CB particles on the surface of the microfibrils, resulting in the high contact resistance among the microfibrils, and thus, the volume resistivity of the ternary composite remains high. As the content of CB is beyond the maximum packing fraction, the number of the CB particles dispersed on the fibrils’ surface increases quickly, and the conductive contacts among the microfibrils increase accordingly. When the concentration of CB particles on the CB/PET microfibrils is higher than a critical value, the microfibrils network connected by electrically conductive contact points is able to sustain the electron transmission in the whole system and as a result, the volume resistivity of in-situ microfibrillar CB/PET/PE composite drops sharply and the percolation happens.(Ⅲ) The temperature response properties of the electrically conductive in-situ microfibrillar composite(1) The resistance-temperature effect of the electrically conductive CB/PET/PE composite was studied in this thesis. The composite exhibits a strong PTC effect and a weak NTC effect during the first few heating-cooling cycles. Compared with common CB/PE composite, in-situ microfibrillar composite has excellent PTC/NTC property. The large size effect of CB/PET microfibrils is the origin of weak NTC effect during the early heating-cooling recycles.(2) After ten heating-cooling cycles or after high-temperature thermal treatment for a long time, the PTC effect of the composite exhibits an anomalous strong attenuation. The resistance becomes insensitive to the temperature. That is, the resistant can keep stabilization as the surrounding temperature change. The unique microstructure and the relatively large size of the microfibrils is the key factor of this anomalous phenomenon. Based on the inhomogeneous microstructure of the surface of microfibrils consisting of conductive and insulative areas, during the heating-cooling recycles or the thermal treatment for a long time, the electrically conductive network becomes more stable and more perfect owing to the interacting among the CB aggregates. During the cooling process, the large size of CB/PET microfibrils can effectively protect the conductive network from being destroyed by crystallization. The more stable and perfect conductive microfibrillar network generated in PE melt can, thus, at least partially survive during crystallization, and consequently, the PTC effect attenuates.(3) This anomalous phenomenon is of great importance to develop an effective way is developed to fabricate recyclable semicrystalline thermoplastic (SCTP) based conductive composite with stable conductive properties.(Ⅳ) Chemical liquid response properties of the electrically conductive in-situ microfibrillar composite(1) The chemical liquid response properties of the electrically conductive in-situ microfibrillar CB/PET/PE composite were studied in this thesis, compared with the common CB/PE composite. The intensity of the chemical liquid response for the microfibrillar composite was found to be much higher than that for the common CB/PE composite. A new idea to develop high sensitive chemical response polymer materials can be provided according to this phenomenon.(2) The influence of the sample’s thickness of the composites on the rate of response was studied. Compared with that for common CB/PE, the rate of chemical liquid response for in-situ microfibrillar composite is more sensitive to the sample’s thickness. Preferentially occupying the interface of PET/PE for the chemical liquid was found to be the origin of this phenomenon.(3) The rate of chemical liquid response for in-situ microfibrillar composite is more sensitive to the liquid temperature compared with that for common CB/PE composite. The restriction effect of the microfibrillar network to the PE chains is regarded as the main reason of this phenomenon.(4) The chemical liquid responsible PTC effect of in-situ microfibrillar CB/PET/PE composite was studied. It was found that both the in-situ microfibrillar composite and the common CB/PE composite exhibit strong chemical liquid responsible PTC effect. The surface of these two composites was destroyed during the heating-cooling cycle. Owing to the microfibrils network, the damage of the surface of microfibrillar composite was weaker than that of common CB/PE, resulting in the better reversible properties of the resistivity for the microfibrillar composite.(5) A unique voltage induced saltation of resistivty in the liquid response measurement was found in the in-situ microfibrillar CB/PET/PE composite. It provides a chance to thoroughly study the conductive mechanism of in-situ microfibrillar composite with the chemical liquid surrounding according to this unusual phenomenon.Base on the content of this thesis, three techniques of the preparation of the following blend materials were obtained: (a) conductive polymer composites with electrically conductive in-situ microfibril network; (b) recyclable SCTP based conductive composites with stable conductive properties; (c) high sensitive chemical response polymer composites. The main raw materials in this thesis including conductive CB, PET and PE can be exchanged by common CB, common PO and common general engineering plastics (GEP). For these raw materials, many grades can be chosen, the resource is wide and the price is low. In addition, the processing operation of these materials can be controlled easily, and it does not have excessive requirements for the processing apparatus. Therefore, the industrial manufacturing of these three materials can be successfully carried out.更多还原