Blending of NR/BR/EPDM by Reactive Processing for Tire Sidewall Applications; Assessment of the Blend Ozone- and Fatigue- Resistance in Comparison with a Conventional NR/BR Compound

The NR/BR blend compound formulations for tire sidewall applications contain a set of stabilizers added to prevent degradation mainly due to oxygen, ozone, and heat. 6PPD is the most effective and widely used antiozonant in tire compounds, but is a highly staining material causing a surface discoloration of the tire sidewall. Incorporation of 30 phr EPDM into blends of NR/BR improves the ozone resistance to the required level, without the need of 6PPD. The first two parts of this series have described a reactive processing technique applied to enhance the covulcanization and blend homogeneity, together with their characterization. In the present article, the properties of the NR/BR/EPDM blends prepared by both reactive and straight mixing are tested in comparison with those of equivalent conventional NR/BR compounds. The reactive NR/BR/EPDM blend vulcanizates show excellent tensile strength, elongation at break, tear strength, fatigue-to-failure, and ozone resistance in both static and dynamic conditions. The properties are equivalent or even superior to those of the conventional NR/BR tire sidewall compounds. The simple straight mixed NR/BR/EPDMblend vulcanizates distinctively possess inferior mechanicalproperties compared to those of the reactive mix.