Positron annihilation study of nanoholes and compatibility of EPDM/NBR blends

Blends of ethylene propylene diene monomer (EPDM) and acrylonitrile butadiene (NBR) with and without the compatibilizer polyvinyl chloride (PVC) were investigated by positron annihilation spectroscopy (PAS). In the presence of a compatibilizer, the PAS results show that the size of free-volume hole (Vf) and its fraction (f %) as well as S-parameter have a linear relationship with a negative slope as a function of the weight percentage of NBR suggesting an increased interaction between the blend components. Moreover, Vf, f% and S-parameter show positive and negative deviation from linear additive rule for blends without compatibilizer indicating a two-phase system. The broadening in free-volume hole size distribution by increasing the weight percentage of NBR in EPDM/NBR blend without compatibilizer confirm the incompatibility of the blend. From the filling effect of silica on the free-volume properties of EPDM/NBR (75% /25%) of the above mentioned blends, it has been found that the addition of silica up to 50 phr is the most promising concentration for electrical applications. Furthermore, correlations were established between size and fraction of free-volume hole combined with the electric and mechanical results.