DETERMINATION OF THE MODES OF ACTION OF A CATIONIC SURFACTANT FOR PROPERTY DEVELOPMENT IN SILICA-FILLED NATURAL-RUBBER COMPOUNDS

Work has been carried out to separate the contributions of a diamine s alt of fatty acid [termed a multifunctional additive (MFA)] of a silic a-filled natural rubber (NR) compound to property development by (1) i mproved filler dispersion from elastomer-filler interface, (2) mastica tion of the NR, (3) modification of the NR-silica interface, and [4] c ross-link density effect. Results have shown that there is a substanti al increase in mechanical properties at equivalent filler dispersion l evel due to the effect of MFA on cross-link density. Between 0 and 0.3 phr of MFA, the enhancement of the mechanical properties is due to im provement in silica dispersion. The addition of MFA accelerates filler disagglomeration and results in reduction of the effective volume fra ction of filler, as agglomerate breakdown releases immobilized rubber. When the level of MFA is more than 0.3 phr, the cross-link density be comes the dominant factor for mechanical property enhancement. However , after the optimum amount of MFA is exceeded, the properties start to deteriorate owing to weak interfacial interaction between adjacent la yers of MFA molecules.