Tire rubber particles were mixed randomly with short sisal fibers and hot pressed. Sisal fibers were used as received, mercerized, and mercerized/acetylated. The fibers were characterized by scanning electron microscopy (SEM), thermal gravimetry analysis (TGA), infrared spectroscopy (FTIR), water sorption, and mechanical properties. Thermal stability of the mercerized/acetylated fibers improves (from 200 to 300degreesC) with respect to the raw fibers, and water sorption is similar to20% smaller than for the raw and the mercerized fibers. Tensile strength is unchanged after the chemical treatments. Water sorption, mechanical properties, and SEM evaluated the performance of the tire rubber composites. All composites showed enhanced elastic modulus; increase is dependent on fiber load. Smallest water sorption was obtained in composites with the mercerized/acetylated fibers. With these fibers at 10% load, the best results were obtained with the smaller tire rubber particles (320 mum) and at 5% load with the bigger (740 mum) tire rubber particles. Both composites showed similar to50% increase in tensile strength when compared to similar composites with raw fibers. SEM of the surface of fracture showed that the adhesion between fiber and rubber was enhanced after both chemical treatments. (C) 2003 Wiley Periodicals, Inc.89925072515