【作者】 王振华；

【导师】 张立群；

【作者基本信息】 北京化工大学 ， 材料科学与工程， 2010， 博士

【摘要】 橡胶因其特有的高弹性,常被用作制备动态条件下使用的制品。由于橡胶是热的不良导体,动态条件下产生的大量生热无法及时导出,热量积聚产生的高温对橡胶制品的性能以及使用寿命有巨大损害。本文首先在炭黑填充丁苯体系的研究中首次发现了橡胶增强中的逾渗现象,深入探讨了橡胶复合材料纳米增强的机理及影响因素；然后从增强导热角度出发,提出了解决橡胶制品动态生热问题的新思路。根据纳米增强机理,选用纳米级导热填料如纳米氧化锌、纳米氧化铝等制备了新型增强导热橡胶复合材料,对其结构与性能进行了系统研究,并与传统增强填料填充体系进行了横向比较。在论文的第一部分中,通过研究不同粒径的炭黑补强丁苯橡胶体系中炭黑用量对丁苯橡胶复合材料拉伸强度的影响,首次发现并提出了橡胶增强中存在着类似于橡胶增韧塑料的逾渗行为,而在纳米氧化锌填充三元乙丙橡胶体系中也发现了相同的现象,且与橡胶复合材料中的模量逾渗以及导电逾渗的逾渗阈值明显不同。进一步的研究发现,这种效应来源于纳米填料增强橡胶的机理,纳米增强剂粒子在拉伸过程中诱导产生橡胶分子链的平行伸直链结构可能是其对橡胶产生显著增强的主要原因。采用FT-IR和分子模拟等方法对拉伸过程中橡胶分子链取向进行表征,结果发现纳米粒子的加入明显提高了分子链取向程度。通过均匀分布理想模型计算出纳米粒子在橡胶复合材料中的理论粒子间距,发现了橡胶增强逾渗中临界粒子间距(CPD)无法归一的问题。采用对临界粒子间距和临界粒径(CMPS)的主要影响因素进行细致深入的研究,从理论上解释了橡胶增强逾渗中临界粒子间距无法归一的原因,并结合实验结果对橡胶增强填料的临界粒径给予了新的诠释。此外,通过对橡胶增强影响因素的进一步探讨提出了一些新的观点。在论文的第二部分和第三部分中,首次提出了增强导热填料的概念,并从增强导热的思路出发首先研究了纳米氧化锌大量填充三元乙丙橡胶(EPDM)复合材料的结构与性能,以期有效地解决由于内部温升积聚带来的制品寿命缩短问题。结果表明,与微米氧化锌相比,纳米氧化锌在赋予橡胶复合材料优异导热性能的同时还具有更为良好的补强效果,而由于纳米氧化锌粒子在橡胶基体中团聚严重使其动态力学性能较差。为了改善纳米氧化锌在复合材料中的分散,我们采用了硅烷偶联剂Si69预处理以及原位改性的方法。使用FT-IR对Si69改性前后的纳米氧化锌粉体进行表征的结果表明,表面改性后的纳米氧化锌粒子表面出现了来自Si69分子的新基团,如1090cm-1出现了硅氧键的伸缩振动峰等,证明了Si69分子确实与粒子发生了化学反应并接枝到了纳米氧化锌粒子表面。通过研究Si69预处理以及原位改性对纳米氧化锌复合材料结构与性能的影响发现,Si69原位改性的纳米氧化锌复合材料中填料粒子与橡胶基体之间分散效果更好,显著提高了复合材料的力学性能,尤其是动态力学性能,而表面改性对复合材料导热性能方面影响并不大。由于纳米氧化锌密度很大约为5.6g/cm3且难以分散,我们进而研究了密度较低的纳米氧化铝填充EPDM复合材料的结构与性能。结果表明,纳米氧化铝橡胶复合材料的导热性能更优异,补强效果较好,动态力学性能不好。Si69原位改性对纳米氧化铝复合材料同样可以有效地改善了填料与橡胶基体之间的界面作用,显著提高了复合材料的力学性能,尤其是动态力学性能,而对导热性能方面影响不大；相比之下,使用SA湿法预处理并没有改善填料与橡胶之间的相互作用,反而使纳米氧化铝粒子团聚现象加重,使复合材料的力学性能明显下降。通过与传统增强填料炭黑N330、白炭黑进行横向对比发现,经过Si69原位改性的纳米氧化锌复合材料以及纳米氧化铝复合材料在导热性能以及动态力学性能方面均具有十分明显的优势,并且具有良好的补强效果,如纳米氧化铝复合材料的拉伸强度为12.9MPa,其导热系数比传统填料填充体系高约44%,而压缩疲劳生热低约50%。纳米氧化锌与纳米氧化铝作为新型增强导热填料,具有良好的补强效果、生热低且导热好等特点,很可能可以有效地解决由于内部温升积聚带来的制品寿命缩短问题。更多还原

【Abstract】 Due to the peculiar high elasticity, rubber products usually work in the dynamic serving conditions. Since most rubber materials have the low thermal conductivity, the generated heat is accumulated, leading to the local high temperature. As a result, the high temperature aggravates the utilized properties and decreases the service life greatly. In this paper, there are two parts:(1) The percolation phenomenon in rubber reinforcement was found for the first time in the various grade carbon black filled styrene-butadiene rubber (SBR) systems. And afterwards the mechanism and influence factors of nano-reinforment in rubber composites were investigated, which had significant theoretical guidance in designing the novel rubber nanocomposites. (2) On purpose of solving the dynamic heat build-up and heat-accumulation problem in rubber composites, we put forward a new strategy. The nano-reinforced and thermal conductive rubber composites were prepared by employing a kind of nano-sized thermal conductive filler such as nano-zinc oxide (ZnO) or nano-alumina (A12O3), and improving the nano-filler dispersion through suitable methods. The structure and properties of novel nanocomposites were investigated systematically, and further compared with the traditional reinforcing fillers filled system.Firstly, the percolation phenomenon in rubber reinforcement was found for the first time in investigating the influence of carbon black volume fraction on the tensile strength of SBR composites, which was similar to the one in rubber toughened plastics system. Additionally, the same percolation phenomenon in rubber reinforcement was found in nano-ZnO reinforced ethylene-propylene-diene monomer (EPDM) systems, and the percolation threshold was significantly different from the percolation thresholds of Young’s modulus and electrical conductivity. Further investigation indicated that the percolation in rubber reinforcement should be derived from the mechanism in rubber nanoreinforcement. Nano particles induced the rubber chains like the random coils to form the parallel-stretched chains structure among the particles during the stretching, which would strengthen the rubber matrix powerfully. The orientation of stretched rubber chains was characterized by using Fourier transform infrared spectroscopy (FT-IR) and molecular dynamic simulation. The experimental results suggested that nano particles could induce the rubber chains to form the oriented stretched chains significantly. The theoretic particle-particle distance in rubber composites was calculated by using the uniform distribution model. We found the critical particle distance (CPD) values of various grade carbon black filled composites were different from each other. Further investigation in the influence factors of CPD and critical minimum particle size (CPMS) answered the question of different CPD based on the nanoreinforcement theory and gave some novel explanations about the CPMS of reinforcing fillers. Moreover, some new ideas and suggestions were presented through discussing the influence factors of rubber reinforcement.Secondly, the concept of nano-reinforcing thermal conductive filler was put forward for the first time. According to the new strategy of nano-reinforcement and thermal conduction, preparation, structure and properties of novel nano-sized thermal conductive fillers such as nano-ZnO and nano-Al2O3 filled EPDM composites were investigated, on purpose of extending the serving time of rubber products. The experimental results indicated that nano-ZnO filled composites performed well in good thermal conductivity and better mechanical properties by comparisons with micro-sized ZnO filled systems. However, bad dispersion in nano-ZnO filled composites aggravated the dynamic mechanical properties. For improving the dispersion state of nano-ZnO particles, the silane coupling agent Si69 was used during various treatments:pretreatment and in-situ modification. The FT-IR spectra of nano-ZnO particles untreated and treated by Si69 showed that some new characteristic peaks appeared in the spectrum of treated nano-ZnO particles, which should be associated to the parts of Si69 molecules. For example, the stretching vibration band of silicon-oxygen bond was observed at 1090cm-1, which suggested that Si69 should be likely to graft on the surface of nano-ZnO particles through the chemical reaction. Study on the influences of Si69 pretreatment and in-situ modification on the structure and properties of nano-ZnO filled composites indicated that in-situ modification improved nano-filler dispersion in EPDM composites more obviously, endowed the composites with better mechanical properties, especially the dynamic properties. Surface modification influenced little on the thermal conductivity of composites. As a result of the high density up to 5.6g/cm3 and hard-dispersed property of nano-ZnO particles, structure and properties of nano-Al2O3 filled composites were investigated further. The results indicated that nano-Al2O3 improved the thermal conductivity greatly, better than nano-ZnO. However, mechanical properties were a little worse than nano-ZnO composites. Furthermore, influences of in-situ modification with Si69 and SA wet-pretreatment on the properties of nano-Al2O3 filled composites were as well investigated. Assisted by in-situ modification with Si69, the interfacial interaction between rubber matrix and nano-Al2O3 particles were enhanced effectively, and the mechanical properties (especially dynamic mechanical properties) of the nano-Al2O3 filled composites were improved obviously, without influencing the thermal conductivity. In comparison, SA pretreatment aggravated the mechanical properties because of more agglomerates in composites. By comparing to the traditional reinforcing fillers, such as carbon black N330 and silica, in-situ modified nano-ZnO and nano-Al2O3 filled composites exhibit excellent performance in mechanical (static and dynamic) properties as well as much better thermal conductivity. For example, in comparison with N330 carbon black filled composites with the similar volume fraction, tensile strength of nano-Al2O3 filled composites was up to 12.9MPa, about 44% higher in thermal conductivity, and more than 50% lower in compression heat build-up. In general, our work indicated that nano-ZnO and nano-Al2O3, as the novel nano-reinforcing thermal conductive fillers, endowed the rubber composites good reinforcement, low heat build-up and excellent thermal conductivity, which seemed more suitable to prepare rubber products serving in dynamic conditions, with the longer expected service life.更多还原