EFFECTS OF MULTIFUNCTIONAL ADDITIVE ON MECHANICAL-PROPERTIES OF SILICA FILLED NATURAL-RUBBER COMPOUND

The effects of a diamine salt of fatty acid of general structure RNH(2) + (CH2)(3)NH3 + (R'COO-)(2), referred to as a multifunctional additive (MFA), on mechanical properties of silica filled natural rubber compound have been studied. The mechanical properties have been enhanced by incorporating the MFA. The optimum level of MFA to obtain maximum mechanical properties are in the range of 5-7 phr, approximately two times higher than those which would be needed for monolayer coverage of carbon black with similar total surface area. Swelling test results show a reduction in the solvent uptake with increasing MFA concentration, indicating that the effect on crosslink density is substantial. Silica dispersion, measured by computer-aided image analysis and scanning electron microscopy, also showed a substantial improvement when MFA concentration is increased from 1 to 3 phr. After this level, there is a further but small improvement.