【作者】 张恒红；

【导师】 王新；

【作者基本信息】 青岛科技大学 ， 高分子化学与物理， 2011， 硕士

【摘要】 聚合物基PTC导电复合材料是指以聚合物为基体,填充导电粒子制备的具有导电性的复合材料,由于其聚合物原料来源广泛,具有较好的应用性能和加工性能,受到越来越多的关注以及广泛应用。采用两种不相容的聚合物作为基体材料,使导电粒子在两相聚合物中形成“双逾渗”结构:即导电粒子在一相聚合物中形成一个连续结构,而这一聚合物又在另外一相聚合物中形成连续结构,从而形成双连续结构。可以降低导电粒子填充的逾渗阈值,改善材料的PTC性能以及其稳定性。本文选择CB为填充粒子,两种不相容的聚合物高密度聚乙烯(HDPE)和聚碳酸酯(PC)作为基体,采用两种制备工艺:CB母料填充和CB直接共混填充制备三元HDPE/PC/CB复合材料。同时以单一组分聚合物HDPE/CB、PC/CB二元复合体系作为对比,通过电镜、溶剂抽出、动态流变等研究手段对其电性能以及CB的分布状况进行了系统的研究。首先,试验发现由于CB的选择性分布在HDPE相以及两相界面处,优先形成导电通路,三元HDPE/PC/CB复合材料的逾渗阈值要明显低于单一组分HDPE/CB、PC/CB二元复合材料的逾渗阈值,即在低的CB填充量下即具有较低的体积电阻率。通过对HDPE/PC/CB三元复合材料的电阻率～温度性能的测试,发现母料填充的复合试样的PTC强度较高,电阻率重复较好,出现了两个电阻率突增的转变点又称为“双PTC效应”。而直接法制备的试样的PTC强度较小,且只有一个电阻率转变点,重复性较差。这与HDPE/PC/CB中双逾渗结构的形成有很大关系。从热力学和动力学两个方面研究了CB在基体中的分散状况,研究发现,从热力学角度而言,CB粒子倾向于分布在PC相中。采用三氯甲烷对三元复合试样进行选择性抽出PC,计算被溶解掉的PC的量,发现同种HDPE/PC配比下,母料法制备的试样其PC的抽出量明显高于直接法制备的试样,说明母料法试样的双连续性比较高。另外,通过对选择性抽出PC后的试样进行电镜观察,发现母料法中CB主要分布在HDPE相以及两相界面,HDPE相与PC相形成了连续结构。而直接法制备试样的HDPE相没有CB粒子的存在,并且出现了大量的局部团聚现象,CB粒子之间出现了很多的连续的孔洞,为溶解掉的PC原来所在的位置,说明CB主要分布在PC相中,也证实了从热力学角度上得出的CB倾向于分布在PC相中的观点。母料法制备三元试样是先将CB分布在HDPE中,增大了HDPE的黏度,从动力学方面,使得HDPE与PC的黏度相近,更易形成较为理想的双逾渗结构,这也与抽提结果相吻合,同时也进一步证实了母料法中PTC性能优于直接法的原因。利用动态流变方法对二元、三元复合材料进行研究,发现动态流变黏弹函数对填充含量的依赖性较大,从流变学角度表征了不相容体系的三维逾渗网络的形成。低CB填充量下,CB含量对三元HDPE/PC/CB复合体系的黏弹性影响较小,储能模量和复数黏度主要依赖于PC相,损耗模量、损耗因子则主要取决于HDPE的链段运动能力和聚合物的界面相互作用。而在高CB填充量下,母料法与直接法对试样黏弹性的影响不同。更多还原

【Abstract】 The study on Conductive Polymer Composites possessing PTC behavior (Positive Temperature Coefficient) becomes an increasingly popular topic in the world. PTC means the resistivity of Conductive Polymer Composites increases with the temperature increasing.Two different ways were used to prepare HDPE/PC/CB composites in which carbon black (CB) as conductive filler filled in immiscible polymer blends of high-density polyethylene(HDPE)and polycarbonate(PC):direct melt-mixing and using CB master batch. And we also prepared single polymer composites(HDPE/CB,PC/CB) as counterpart. Resistivity,PTC behavior,the dispersion state of CB,and the relationship of morphology,rheology were investigated in this paper.The properties of PTC materials are not only related to the properties of polymers,CB and the interaction between the polymer and CB,but also to the distribution CB filled in polymers.In comparison with single polymer composites (HDPE/CB,PC/CB),the percolation threshold of CB filled in HDPE/PC/CB is about 12%,which is obviously lower than that in HDPE/CB (20%)and PC/CB(22%).The measurement of resistivity~temperature indicated that PTC intensity and PTC reproducibility of composites prepared using CB master batch was better than composites prepared via direct mixing of CB and polymers. The composites prepared using CB master batch had a bi-percolation structure and exhibited a better PTC reproducibility especially for the composite with HDPE/PC ratio 40/60. This depends on the structure of double percolation as mentioned above.SEM showed that HDPE phase and PC phase were bi-continuous in composite prepared using CB master batch; CB mainly distributed in HDPE phase and the interface between HDPE/PC in which the conductive network were easily formed. But CB preferably distributed in PC phase in composites prepared by direct melt-mixing.The dynamic viscoelasticity of CB filled in HDPE/PC/CB composites were investigated. The results indicated that the viscoelasticity of the composites were dominantly influenced by the PC/HDPE morphologies on the case of low CB loading while CB exhibited its effect on the case of high loading.更多还原