New composites based on short melamine fiber reinforced EPDM rubber

Abstract

Melamine fibre is a new category of advanced synthetic fiber having superior heat and flame resistance with decomposition temperature above 350°C. It suitability as a reinforcing fiber for ethylene propylene diene terpolymer, abbreviated as EPDM rubber, where M stands for polymethylene chain, was investigated. It has been observed that tensile strength and stress at 100% strain of EPDM-melamine fiber composites increase with the addition of a three-component dry bonding system, comprising hexamethylene tetramine (hexa), resorcinol, and hydrate silica, abbreviated HRH system. Moreover, the fiber-filled composites anisotropy in stress-strain properties due to preferential of the short fibers along the milling direction (longitudinal), which is substantiated by the results of swelling and fractography studies. Aging causes an increase in the modulus, tensile strength and hardness of the composites. The fractographs show an increase in interfacial adhesion between the fibers and the matrix during aging, which is further confirmed by the reduction in tan peak height of the aged composites during dynamic mechanical studies. Atomic Force Microscopy (AFM) studies reveal the formation of an interphase with the addition of bonding agents and a better fiber-matrix adhesion due to aging. AFM images also confirm the role of dry bonding systems in improving the fiber-matrix adhesion of the aged vulcanizates. The composite modulus has been theoretically calculated using the well-known Halpin-Tsai equation. It is found that in the transverse direction, observed modulus values are greater than the calculated values, while in the longitudinal direction, the experimental modulus values are found to be lower than the calculated values for both unaged and aged composites owing to some degree of anisotropy in fiber orientation.