Study On The Structure And Properties Of ENR And Its Nano Reinforced Material Specially For High Performance Tyres

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.