Effect of carbon black addition and its phase selective distribution on the stress relaxation behavior of filled thermoplastic vulcanizates

摘要

The long term mechanical behavior of thermoplastic vulcanizates (TPV) based on polypropylene (PP) and ethylene propylene diene terpolymer (EPDM) and different types and concentrations of carbon black (CB) has been characterized by means of stress relaxation experiments. Evaluation of the relaxation curves was carried out using the two-component model allowing a division of the initial stress into different stress components which are caused by different networks available in TPV. The discussion focussed on the background of the stress components, which are originated by the CB addition, the non-relaxing stress components σ _∞~(CB) (polymer-layer), and σ _∞~(cb)(network), as well as the relaxing stress components Δσ ~(CB)(polymer-layer) andΔσ ~(CB)(network) It was found that the concentration and type of CB as well as the phase specific CB distribution strongly affect the non-relaxing and relaxing stress components. Up to a CB concentration of 9% in the EPDM phase the composite behaves as a thermo-rheologically simple material because the impact of CB addition on the a-relaxation of the crystalline PP phase is still negligible. A master curve was created by the horizontal shift of the relaxing stress curves Δσ ~(Comp)(t) to a reference curve. At higher local CB loadings the additional relaxation processes induced by CB addition overlap with the arelaxation, thus, no master curve could be made in that case.