Dynamic stress relaxation behavior of nanogel filled elastomers

Long-time stress relaxation behavior of virgin elastomers, chemically crosslinked nanogels and nanogel filled elastomers was studied with the help of a dynamic mechanical analyzer. Sulfur crosslinked natural rubber and styrene butadiene rubber nanogels and nanocomposite gels were prepared and characterized using different methods. These gels were added in to the virgin elastomer matrix at different concentrations. Presence of crosslinked gels in elastomer matrix greatly influenced its stress relaxation behavior. The effect of draw ratio, gel loading and temperature on the stress relaxation behavior of elastomers was investigated in detail. It was found that virgin elastomers displayed extremely long-term relaxation processes and the time required to achieve equilibrium dramatically decreased with the increase in crosslink density in the case of gels. Time-temperature superposition studies revealed that stress relaxation process was accelerated and relaxation time reduced with a rise in temperature. Finally, experimental stress relaxation data were fitted with the empirical Chasset and Thirion equation with good agreement. From the fitting parameters, the characteristic relaxation time and the material parameter were estimated in order to understand the mechanism of the relaxation processes in the gels and the gel filled elastomers.