The stress–strain properties of TiO2-filled poly(vinyl acetate) have been studied at filler percentages of 0, 10, 20, 30, and 40% TiO2 over a strain-rate range of 100–5000%/ min at 24°C. Tensile strength, Young's modulus, and offset yield strengths all were found to increase with higher strain rates and higher TiO2 contents. Ultimate elongations decreased with greater TiO2 content and higher strain rates. Shift factors for volume fraction of filler were estimated for tensile properties as function of test rate. Stress relaxation studies have shown a reduction in relaxation times with increasing TiO2 content. Calculations of the out-of-phase Young's modulus were made as a function of filler content employing a box-type of distribution of relaxation times. A possible explanation for the stress–strain behavior observed is that introduction of TiO2 changes the internal viscosity of the system, similar to the effect of temperature. This would also mean that the ultimate properties would be dependent on filler content and strain rate because viscous resistance to chain deformation would be altered. The effect of filler on stress relaxation could be thought of being due to an increase in short-range chain motion.
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