Role of Carbon Black for Enhancing the Mechanical Properties of Short Aramid Fiber Reinforced Ethylene-Acrylic Rubber

Composites based on ethylene-acrylic rubber and 1 mm short aramid fibers (AF) were developed by varying the fiber content from 3 to 40 phr. At 10 phr short fiber loading, the tensile modulus (10 % modulus) of the neat matrix was around 11 times increased. However, its breaking elongation was decreased from 408 to 58 %. This drastic reduction in the breaking elongation even at a 10 phr fiber loading leads to a brittle failure with inferior toughness. The tensile-fractured surface of the fiber-filled composite showed an intact matrix with no plastic deformation during fiber pulled-out. To solve this problem, carbon black (CB) was used as a toughening agent. Surprisingly, the addition of 20 phr CB onto a 10 phr AF-filled composite enhanced its 10 % modulus in the longitudinal direction by 70 % and also enhanced its breaking elongation from 58 to 351 %. From the morphological analysis, it has been presumed that the addition of CB enhanced the friction between the fiber and the matrix at a very low strain and also facilitate the matrix for a plastic deformation at a higher strain. This enhanced friction between the fiber and the matrix is considered as the improved low strain modulus and the subsequent plastic deformation at a higher strain is responsible for the improved toughness.