Rubber composites with very high moduli at low elongation, high elongation at break and high ultimate
breaking strength have been developed. The matrix was acrylonitrile butadiene rubber (NBR) and the
hybrid (fibrous and particulate) reinforcements were short, fine pineapple leaf fiber (PALF) and carbon
black. The amount of PALF was fixed at 10 parts (by weight) per hundred of rubber (phr) while that of
carbon black was varied from 0 to 30 phr. Uniaxial NBR composites were prepared. Tensile strength,
elongation at break, modulus and tear strength of the hybrid composites were characterized in both
longitudinal (parallel to the fiber axis) and transverse (perpendicular to the fiber axis) directions. The
addition of carbon black causes the slope of the early part of the stressestrain curve to increase and also
extends breaking to greater strains. At carbon black contents of 20 phr and above, the stressestrain
relation displays an upturn at high elongations, providing greater ultimate strength. Comparison with
the usual carbon black filled rubber shows that the composite behavior at low strains is determined by
the PALF, and at high strains by the carbon black. This high performance PALF-carbon black reinforced
NBR shows great promise for engineering applications.