Effects of soy-based oils on the tensile behavior of EPDM rubber

The effects of soy-based oil on the constitutive behavior of EPDM rubber have been investigated. Soy polyols with various hydroxyl numbers as well as unmodified soybean oil have each been incorporated in the EPDM rubber as a partial replacement for petroleum oil. Tensile tests have been performed at low and high rates, and hysteresis and stress relaxation tests have been performed at low rates. It has been found from the tensile tests that the rubber with soy polyol of low hydroxyl number can provide very similar constitutive characteristics as the control. On the other hand, the constitutive characteristics are significantly changed by using soy polyol of high hydroxyl number or unmodified soybean oil. For example, the rubber with unmodified soybean oil elongates substantially up to stretch ratios of 13, which is approximately 100% greater than that of the control. It has also been found from the tensile and hysteresis tests that the soy-based rubbers generally have better energy storing and dissipation characteristics than the control, such as storing more energy while maintaining lower peak stress, for an impact application. The test results indicate the potential for application based tuning of soy rubber properties by selecting an appropriate soy oil/EPDM blend or a polyol/EPDM blend with optimized functionality.