| As an important member of high performance rubber, silicone rubber isirreplaceable in modern high-tech, aero-space and the other fields. Silicone rubber is akind of polymer with a backbone of Si-O units and side chains of organic groups(primarily methyl),which shows significant differences in structure and performancewith polymers which have a backbone of C-C units. Because silicone rubber is atypical semi-inorganic and semi-organic polymer, has many unique and excellentproperties, both heat resistance of inorganic matter and flexibility of organic polymer.Silicone rubber keeps good performance of cold resistance, electrical insulation andweather resistance, and it is widely applied as elastic materials under high temperatureenvironment due to the most prominent property of thermal stability.However,becauseof the poor mechanical properties of silicone rubber, its scope of application isseverely limited, therefore, it must be modified to enhance its properties.Whiskers as reinforcement materials have attracted considerable attention fortheir perfect properties nowadays. Whiskers are fiber-shaped single crystals. Theyhave large length/diameter ratio, as having relatively small diameter, they avoids thedefects occurring on large crystals. And their atom arranged in highly order, hence theyield strength of whiskers tends to approach the maximum theoretical value. They notonly have high strength, high modulus, heat resistance, wear resistance, light weightand other characteristics, but also exhibit attractive properties in terms of electrical,optical and magnetic.They have been widely used in a series of high-performanceadvanced composites.Recently, owing to their relatively low cost, potassium titanatewhisker reinforced polymer composites have shown promise.The potassium titanate whisker(PTW)/polymethylvinylsiloxane(PMVS)composites were prepared in this paper,and,the effects of potassium titanate whiskeron the rheological properties,vulcanized properties,mechanical properties and thermalstabilities of the heat vulcanized(HTV) silicone rubber were investigated,respectively.The kinetic parameters were evaluated by differential method.Simultaneously,thefracture surface of the composites and the dispersion degree of PTW were observedby means of scanning electron microscopy(SEM). The results showed that the shear viscosity increased when the content of the PTW increased in PTW/PMVS,thecomposites performance for Newton’s fluid in low shear rate,then the shear viscositydecreased with an increase in the shear rate.PTW could accelerate vulcanizationreaction,and improve maximum torque(MH) of the compound.The tensile strength,stress at the elongation of100%and hardness increased with the PTW content.Theaddition of PTW with relatively low volume fraction to silicone rubber would lead toan increase of the thermal stability sharply,for the composite with9vol%of PTW,thethermal decomposition temperature increased about65℃compared with the puresilicone rubber.The composite with12vol%of PTW exhibited better thermalstability,the thermal decomposition apparent activation energy E of it was193.62kJ/mol,higher than that of the composite with fumed silica.In order to improve the compatibility of potassium titanate whisker and siliconerubber, thus it can be uniformly dispersed in the matrix, a silane coupling agentKH570, a titanate coupling agent NDZ101and stearic acid were used to modify thepotassium titanate whiskers. The results indicated that, KH570and stearic acid can bewell tilted on the surface of PTW, modified whiskers changed from hydrophilic tohydrophobic. But only whiskers modified with KH570could better bond with thematrix, and uniformly dispersed in the matrix. The Cross-model parameters increasedin the rheology test, means that the interaction between the filler and the matrixenhanced. The mechanical properties and corrosion resistance of composites have alsobeen improved. However, the modification effects of NDZ101and stearic acid werenot satisfied.In this thesis,the effects of molecular weight and the vinyl content of PMVS onthe properties of the composites were investigated. A shear-thinning behavior of the flowwas observed for all composites. The interaction between PTW and PMVS increasedwith the increase of the molecular weight and vinyl content. In addition, withincreasing molecular weight of the matrix, the higher the degree of vulcanization, aslight increase in the tensile strength, elongation at break decreased, and heatresistance was improved. Similarly, increasing the vinyl content of the matrix, themaximum torque of the composites increased, tensile strength, elongation at break,the heat resistance were all improved.The PTW and SiO2mixed with PMVS together, the effects of PTW on thecomposites were studied when the amount of silica was fixed. The PTW/SiO2/PMVScomposites also showed a shear thinning phenomenon, shear viscosity reduced withincreasing shear rate, and shear thinning phenomenon was more obvious in the high shear rate region. The shear viscosity, shear modulus G’ and the maximum torque inthe vulcanization process of PTW/SiO2/PMVS slightly larger. After heat aging72h at300℃, the PTW/SiO2/PMVS spline performanced thermal aging embrittlement. Afterthermal aging72h, the SiO2/PMVS spline have broken completely. And then add the12vol%PTW, the aged spline intact, and the retention rate of tensile strength couldreached72.5%. The synergistic effect of PTW and SiO2can significantly improve thermalstability of the composites. |
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