Tack and green strength of filled blends of bromobutyl and EPDM rubbers

Effect of fillers on tack and green strength of blends of EPDM and bromobutyl rubbers has been studied. The fillers used are carbon black and china clay. Test temperature and mode of mixing are varied. Tack increases with the addition of carbon black and china clay. The highest value of tack strength is achieved when the loading of filler is 50% in each phase or all in EPDM phase. The tack strength of filled blends decreases with an increase of test temperature. Tack index, a ratio of tack strength divided by cohesive strength measured under the same geometry, also decreases with test temperature. It has been found that tack strength (Ga) of filled blends is proportional to the contact time (t) and varies as t1/2 or t1/4. Green strength of carbon black filled mixes is much higher than that of china clay filled mixes. The green strength falls with a rise of temperature in both cases. Green strength of carbon black filled mixes increases with the increase of bromobutyl content in the mix. China clay mixes show a reverse trend.