Study On The Mechanism In Rubber Nano-reinforcement And Preparation, Structure And Properties Of The Nano-reinforced Thermal Conductive Rubber Composites

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.