Segmental relaxations and other insights into filler‐mediated interactions for carbon black‐filled polybutadiene rubber

The role of interaction with filler particles in modifying segmental relaxations of elastomers is still not fully clear. This work examines the glass and melting transition of unvulcanized and vulcanized polybutadiene rubber filled with carbon black. It is found that for uncured rubbers, the calorimetric glass and melting transition temperatures are unaffected by the presence of carbon black, without invoking the concept of restricted chains near filler. In quenched vulcanizates, the increment in segmental relaxation with filler loading is detected, which is attributed to the reduction in chemical crosslink density caused by filler agglomeration. On the other hand, the crystalline part constrains the molecular motion in amorphous regions such that the glass transition temperature is raised when the crystallinity is large. This study reveals that the only effect of carbon black is to influence chemical crosslinks through filler networking and then change in segmental relaxations is detectable. No differences in calorimetric glass and melting transition were found even though the presence of a large quantity of the bound rubber. For the vulcanizates, the greater polymer mobility with increasing filler loading was attributed to the reduction in chemical crosslink density caused by filler agglomeration.