Influence of fillers and oil on mill processability of brominated isobutylene‐co‐paramethylstyrene and its blends with EPDM

Milling behavior of brominated isobutylene‐co‐paramethylstyrene (BIMS), and its blends with ethylene propylene diene rubber (EPDM), with special reference to the effect of addition of different fillers, filler loadings and processing oil, was investigated over a range of temperatures in a drop mill operation. The critical nip gap (CNG, at which a front to back roll transition (F‐B transition) occurs, was also measured. Addition of different fillers reduced the value of the critical nip gap and the mill band formation indices for BIMS as compared to the gum polymer, indicating a decrease in the tendency to go to the back roll. The systems containing reinforcing fillers showed a lower value of the critical nip gap, as compared to systems containing low or non‐reinforcing fillers. For different filled blends of BIMS and EPDM, the CNG decreased on increasing the EPDM content, indicating a decrease in the tendency for a F‐B transition. The CNG decreased on increasing the N330 carbon black‐loading, while it increased with the addition of procesing oil. The results were explained in terms of rubber to metal adhension and viscosity of the polymers.