Characterization Study Of Thermal Viscoelastic Damping Properties Of EVA Reinforced Silicone Rubber Composities

Silicone rubber(MVQ)is a vibration damping material,which can improve the human machine working environment.However,The damping factor of single silicone rubber is low especially over room temperature range is poor,the effective damping temperature range is narrow and lower than room temperatureln this paper,MVQ/ethylene vinyl acetate copolymer(EVA)composites with different composition ratios were prepared by melt blending method.The vulcanization process,physical and mechanical properties,damping properties,rheological properties and crystallization characteristics were studied systematically.The present research is as follows:1.The capillary rheometer was used to study the extrusion rheological properties and wall slippage of EVA and MVQ/EVA composites.The results showed that the viscosity of MVQ/EVA increased with the content of EVA content.The change of viscosity of EVA and MVQ/EVA with temperature was analyzed by Arrhenius model.It was found that the viscous activation energy of MVQ/EVA=100/40 is higher than that of pure MVQbut lower than that of EVA at the same shear rate.At the same temperature,the wall slip velocity of EVA and MVQ/EVA increases with shear stress.Mooney model was used to calculate wall slip velocity,it was shown that adding more EVA in silicone rubber tenders the easier ocurrance of wall slip corresponding to lower critical shear stress.2.The effect of EVA on the vulcanization processand structure of silicone rubber was studied by rubber processing analyzer(RPA).The results show that the higher the content of EVA in MVQ/EVA composites,the smaller the equilibrium torque value at the end of vulcanization of silicone rubber corresponding to thelonger positive vulcanization,indicating that the addition of EVA hinders the vulcanization process of silicone rubber.During RPA strain scanning,the larger the strain is,the smaller the storage modulus(G')of MVQ/EVA composites is,showing a significant Payne effect.Its G' increases with the content of EVA content exhibiting that It shows that EVA plays an important role in reinforcing MVQ.According to the fitting results of Kraus model,the fitting parameter value m of the vulcanizate is larger than that of the rubber compound,which shows that EVA dispersion in the MVQ is more uniform and the reinforcing effect is more obvious under a certain temperature and pressure.3.The on-line monitoring of the formation process of the damping cross-linked network of MVQ/EVA composites was carried out using ultrasonic-no-rotor-curing rheometer.Ultrasonicalwave can be used to characterize the vulcanization process of MVQ/EVA composites,which was proved by comparing the variation of the wave speed and torque value.In order to satisfy the on-line inspection of composite,ultrasonic-PVT device was used to study the effect of pressure and temperature on the wave speed and product specific volume of the MVQ/EVA composite during vulcanization.It was found that at the same pressure and temperature,the sound velocity decreases with the increase of EVA content at the end of the curing process.Under the same pressure,the higher the temperature,the higher the specific volume and the lower the wave velocity in the compsite with the sane EVA content.At the same temperature,the higher the pressure,the smaller the specific volume and the higher the wave velocity in the compsite with the sane EVA content.The quantitative relationship between wave velocity and specific volume was fitted in line relationship.Thus,the specific volume of the MVQ/EVA composite material can be estimateat any vulcanization temperature in production when wave is inspected.4.The crystallization process of EVA and MVQ/EVA was studied by DSC.It was found that the crystallization temperature and initial crystallization temperature of EVA in the unvulcanized rubber were not changed obviously compared with that of pure EVA.The crystallization peak temperature and initial crystallization temperature of EVA in vulcanizates are significantly reduced;In the non-isothermal crystallization,the vulcanized and unvulcanized silicone rubbers all play a heterogeneous nucleation effect on EVA,but silicone rubber particles both will impede the growth of EVA crystals.The non-isothermal crystallization activation energy of EVA and MVQ/EVA calculated by the Kissinger equation shows thatthe crystallization activation energy of EVA in vulcanizates of MVQ/EVA is larger when compared with pure EVA.The crystallinity and crystallization activation energy of EVA phase in vulcanizates is higher than the one in the unvulcanized rubber.5.The effect of EVA content on mechanical properties and damping performance of MVQ/EVA was studied by using RPA and dynamic mechanical thermal analysis(DMA).The results show that the addition of more EVA can significantly improve the hardness,modulus and tear strength of MVQ when the tensile strength and elongation at break are still high remaining within the MVQ requirements.The temperature range of pure silicon rubber loss factor greater than 0.1 is-42??-28?.When 40 parts of EVA is filled in MVQ/EVA,the maximum loss factor is increased from 0.125 to 0.18,and the effective damping temperature range is-23? to 37?.This clearly broadens the effective damping temperature range and can be applied to higher temperature damping and noise reduction cases.