Composites consisting of high density polyethylene (HDPE) reinforced with randomly oriented chopped Twaron fibers (both fluorinated and nonfluorinated) show a significant increase in mechanical and thermal properties. To increase the better fiber matrix adhesion, the Twaron fiber is surface fluorinated using elemental fluorine. The surface of the Twaron fiber becomes very rough and the diameter of Twaron fiber increases from similar to 12 to 14 mu m after fluorination. The composites were prepared using solution method to overcome the damage of the fiber. The tensile strength and the Young's modulus increases with increasing fiber content. The tensile strength and modulus of modified fiber (fluorinated Twaron fiber) composites is much higher than nonmodified fiber composites indicating that there is better mechanical interlocking between the modified fiber and the matrix. Thermal properties obtained from DSC and DTA-TG analysis of the fluorinated fiber composites are also improved. Contact angle measurements, as well as the surface energy measurements, indicate that the composites are more wettable and is maximum for fluorinated fiber composites i.e., surface energy for fluorinated fiber composites is highest. Crystallinity is also higher for fluorinated fiber composites. (C) 2007 Wiley Periodicals, Inc.