【作者】 何灿忠；

【导师】 彭政；

【作者基本信息】 海南大学 ， 橡胶学， 2013， 博士

【摘要】 近年来,随着国家节能减排战略的提出和汽车工业向高速、安全、节能、舒适化方向的发展,对轮胎高性能化的要求也逐年提高,这就要求轮胎胎面具有良好的抗湿滑性能,优异的耐磨性、低的滚动阻力特性。轮胎胎面要获得如此全面的特性,必须在橡胶的分子结构及增强结构上有新的突破。众所周知,橡胶分子间的内摩擦损耗和松弛特性是制约其低滚阻和高抗湿滑性能的主要因素,因此通过环氧改性对天然橡胶进行分子结构设计是本论文的研究重点之一,其次橡胶的增强结构高性能化也是轮胎工业者致力解决的难题。无机填料白炭黑以其高补强、低生热的优点而逐渐受到橡胶工业研究者的青睐,但是也具有易团聚、与基体结合差等缺点。因此通过分子结构设计和纳米填料增强的角度来提高白炭黑分散性及其与基体的界面相互作用力并实现节能降耗目标是本论文的另一个研究重点。论文的第一部分,从微观分子结构入手,研究环氧化反应对橡胶结构和性能的影响,在微观结构与宏观性能之间建立有机联系。分析环氧化反应机理及环氧基团的分布情况,探索环氧基团开环反应的机理。发现天然橡胶分子链上发生环氧化反应的同时,存在环氧基团的二次开环副反应,开环产物的结构取决于环氧化的程度,环氧基团在橡胶分子链上呈无规分布的。玻璃化转变温度(Tg),门尼粘度和P0值随着环氧化程度的升高而升高,相反PRI值随环氧化程度的升高而降低。论文的第二部分,采用Py-GC/MS动态跟踪环氧化天然橡胶裂解过程,结合TG/DTG,DTA等分析技术,探索ENR的降解机理。研究发现,与NR相比,ENR的TG曲线往低温方向移动,说明环氧化改性后ENR的热稳定性变差。NRf和ENR的第一步热氧降解机理相同,都为一维扩散；NR的第二步热氧降机理为二维扩散(Valensi方程1。然而,ENR降解机理为三维扩散(Jander方程),表明在NR分子链上引入环氧基团后,ENR的降解变得更复杂。NR的DTA曲线出现了两个放热峰,ENR的DTA曲线出现了三个放热峰,说明ENR的热氧降解过程变得更复杂。Py-GC/MS分析结果可以看出,ENR在低温(350℃)裂解的主要是碳碳单键发生p-断裂,在剧烈的温度条件(550℃)下,产物中有大量的短支链表明ENR的裂解不仅发生了链的p-断裂,还有“拉开链式反应”(unzipping reaction)的分子链解聚。论文的第三部分,我们提出了一种全新的设想：不使用任何偶联剂的条件下,通过环氧化天然橡胶(ENR)分子链上的环氧基团与纳米Si02表面的硅羟基产生强的相互作用力(氢键或是化学键),抑制纳米Si02粒子的团聚,使其均相分散在橡胶基体中,来有效的提高复合材料的性能。在混炼阶段,环氧基团和Si02粒子表面的硅羟基相互作用形成氢键,同时诱导SiO2粒子在橡胶基体中的均匀分散；NR/SiO2共混物在硫化的过程中,环氧基团发生开环反应；开环产物马上与SiO2粒子表面的硅羟基发应,形成稳定的Si-O-C键,并进一步预制了SiO2粒子团聚,促进其在橡胶基体中均匀分散。当SiO2用量低于30份时,ENR/SiO2胶料在0℃具有较高的tanδ值,同时在600C具有较低的tanδ值,滚动阻力和抗湿滑性之间达到较好的平衡；SiO2在橡胶基体中的分散越均匀,力学性能越好,生热性能越低,热氧稳定性越好。论文的第四部分,对ENR/SiO2共混体系进行动态流变学测定,探讨环氧化程度和炼胶温度对高填充体系中粒子的分散以及粒子-橡胶相互作用的影响。发现SiO2粒子在橡胶中的分散状态既与环氧基团的含量有关,又与混炼温度有关。随着环氧化程度的升高,出现payne效益的临界应变(yc)以及低频率(ω)区域1gG’-1gω曲线的斜率值均增大,反映出环氧化改性对SiO2与橡胶基体相互作用的促进以及粒子分散的改善。在低温下(60℃)混炼,环氧基团与SiO2粒子表面的硅羟基间以氢键的形式结合,诱导SiO2粒子在橡胶基体中均匀分散；在高温下(120℃)下混炼,部分环氧基团发生开环,开环产物立刻与SiO2粒子表面的硅羟基反应,形成稳定的化学键结合,SiO2粒子在橡胶基体中更均匀地分散。论文的第五部分,考察ENR作为新型SiO2分散剂对NR/SiO2复合材料微观结构和性能的影响,发现ENR改性NR/Silica复合材料的扭矩差值、结合胶含量和交联密度均随着ENR用量的增加而升高,SiO2粒子的分散变得均匀。ENR起到类似于“偶联剂”的作用,通过硫化网络与NR形成稳定的化学键结合和通过环氧基团与SiO2粒子表面的硅羟基反应,在填料和橡胶基体间建立强的相互作用。SiO2粒子均匀的分散在橡胶基体中,有效的提高了抗湿滑性能,降低了滚动阻力和生热性能。更多还原

【Abstract】 Recently, with the demand of energy conservation and emission reduction in our country and the development of automotive industry in high-speed, security, energy-saving and comfort, there are increased requirements of high-performance tire with good wet-skid resistance, abrasion resistance, and low rolling resistance. It should have new breakthrough in molecular structure and reinforced structure of rubber. It is well known that, the internal friction losses among macromolecular chains and relaxation characteristics are the main factors. Therefore, the design of molecular structure of energy-saving rubber is the one of research focuses. On the other hand, the optimization of reinforced structure of rubber is the problem to be solved. Silica, a high reinforcement and low heat build-up filler, is gradually popular in rubber industry, but it still shows easy-aggregation and weak interaction with rubber matrix. In this paper, we try to improve the silica-sispersion and its interfacial interaction with matrix and achieve the energy-saving and emission reduction through the design of molecular structure and nanoscale filler reinforcement.In the first part, the microstructure and properties of epoxidized natural rubber (ENR) based on micro molecule during epoxidized process were supervised to build-up the relationship between microstructure and macro-properties, which not only verified the epoxidation mechanism and revealed the reason of ENR epoxy ring-open and crosslink of molecule. Two distinct types of ring-opened products were obtained depending principally on the level of epoxidation. The introduction of epoxy groups was found to occur randomly along the molecular chain while retaining NR’s high stereoregularity. The Tg, Po and Mooney viscosity increase as the ENR loading increases. However, the PRI decrease as the ENR loading increases.In the second part, the pyrolysis products of ENR at different pyrolysis temperatures were analyzed by the combination of pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) technique. Thermal degradation kinetics was studied by TGA and DTA. The results showed that, compared to NR, the TG curve of ENR shifted towards low temperatures, indicate that the thermal stability of the ENR-50is worse than that of NR. The pyrolysis of ENR exhibits mainly three exotherms in the DTA curves, means the degradation process of ENR is more complex than that of NR. From the major products of Py-GC/MS, it is found that major reactions during the pyrolysis are affected seriously by the pyrolysis temperature. The chain scission mainly occurred at β position of carbon-carbon single bond. Under drastic conditions, the products of short chain hydrocarbon show that ENR not only undergo main chain-scission but also a chain depropagation reaction by unzipping.In the third part, we proposes a novel way to form an agglomerate-free ENR/SiO2nanocomposite at a low processing temperature by taking the advantages of the "bridge" structure of ENR, where the bone chains with high stereo regularity of ENR are further connected with NR, while its oxygenous functional groups will strongly interact with silanol groups on the SiO2surface via hydrogen bonds. The properties and dispersion mechanism of anocomposites are investigated. During the mixing process, the hydrogen bonds are formed between epoxy and silanol groups, resulting in better dispersion of SiO2nanoparticles. Furthermore, when the composites are vulcanized under a pressure of15MPa at145℃for the respective cure times (tgo) with curing agents, the epoxy groups of ENR chains may occur ring-opening reaction. The ring-opening products will react with the silanol groups on the surface of SiO2immediately to form stable chemical bonds to depress the self-aggregation of silica. The improvement of SiO2dispersion leads to the significant enhancement of thermal properties, tensile strength and wet grip, and reduction of rolling resistance and inner-thermogenesis, demonstrating the great potential in the applications of tyre industry.In the fourth part, rheological properties revealed significant differences phenomenon, depending on the types of matrix and the process temperature. When rubber/silica composite is mixed at60℃, The critical strains (yc) and the slope of plotting logarithm storage modulus (lgG) versus logarithm frequency (lgω) in low ωs range substantially increased, suggesting that the Payne effect becomes weaker and the miscibility between silica filler and natural rubber is greatly enhanced. When rubber/silica composite is mixed at120℃, its viscoelasticity presents a dramatic change, the strain dependence G’ increases while the "Second Plateau" disappears, largely due to the crosslink between rubber-rubber molecules and chemical bonding between rubber and silica. Based on the SEM, and rheological properties analyze, the probable structure evolution mechanism of epoxidized natural rubber/silica composites is proposed.In the fifth part, epoxidized natural rubber as a disperse modifier for silica-filled natural rubber and its impacts on properties were studied. The results show that delta torques, bound rubber contents and crosslink density increase as the ENR loading increases, indicating that ENR not only interact with NR through sulfur crosslink but with silica through hydrogen bonds or covalent bonds. These interactions enable ENR compatible with NR matrix, and play a similar role as silane coupling agent by being grafted onto the surfaces of silica nanoparticles to depress the strong self-agglomerate nature of nano-silica. The improvement of SiO2dispersion and strong rubber-filler interaction leads to the significant enhancement of tensile strength, wet grip, and reduction of rolling resistance and inner-thermogenesis. Due to the formation of new chemical bonds between ENR and silica, the NR filled silica in the presence of ENR transfers much stress with less hysteresis.更多还原