The main objective of this research was to synthesize a new compatibilisant agent (PVC-g-MA), which was grafted from the maleic anhydride on the PVC chains. The presence of maleic anhydride grafting on PVC was made evident by infrared analysis. PVC-g-MA was used like compatibilisant to solve the problem of the incompatibility between the hydrophobic polymeric matrix (PVC) and hydrophilic fiber (alfa). Composites samples were prepared with different alfa fiber loading (10, 20, and 30 wt %) and incorporating PVC-g-MA (1, 3, and 5 wt %) or PP-g-MA (3 wt %). The tensile properties, the thermal stability and the morphology of the composites were investigated. The result indicated that the PVC-g-MA increased the interfacial adhesion between the fibers and the polymer matrix and this effect was better than that obtained for the maleated-polypropylene-coupled composites. Microstructure analysis of the fractured surfaces of MAPP modified composites confirmed improved interfacial bonding. The addition of alfa and PVC-g-MA increased the thermal stability of the composites. The temperature of degradation of the polymer matrix increased about 16 degrees C in comparison to the noncoupled composite, indicating that PVC-g-MA improved the thermal stability of the polymer. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012