NR/BR-based Tire Sidewall Compounds Ozone-stabilized with Alkylphenol-polysulfide Modified EPDM

Inclusion of ± 30 phr. EPDM rubber has frequently been studied for replacement of 6PPD as ozone-stabilizer for NR/BR-based tire sidewalls. However, cure incompatibility and heterogeneous filler distribution result in poor mechanical properties of such blends. Alkylphenol-polysulfide (APPS) modification of EPDM has been investigated in order to solve these problems. The application of APPS-modified EPDM results in a significant improvement of the tensile, tear and fatigue properties compared to the use of virgin EPDM: the blend properties are equivalent or even superior to those of conventional NR/BR tire sidewalls. A better rubber-carbon black affinity of the APPS-grafted EPDM in the blend can be proven from bound-rubber and carbon black adsorption measurements. The study is complemented with TEM and STEM electron-microscopic characterizations,  which show a much more homogeneous morphology for the NR/BR/APPS-EPDM blends than for the straight NR/BR/EPDM blend. Further, apart from improved co-cure, a significantly better distribution of carbon black may be held responsible for the improvement, particularly into the EPDM-phase.