Broom fibers have been used as reinforcement for the conventional polypro- pylene (iPP) and a maleate modified one (iPPMA). A conventional alkaline treatment and a steam explosion extraction process were applied to obtain the cellulosic material from broom branches. Composites were prepared by melt mixing materials with differ- ent weight percentages of broom fibers. Also ternary blends (iPPMA/iPP/broom fibers 5/45/50 wt) were obtained to examine the possibility of utilizing the maleate polypro- pylene as a compatibilizing agent. The fibers and the composites were thermally, mor- phologically, and mechanically characterized. Water absorption tests, to examine the behavior of these materials in wet conditions, were also performed. Particular attention was addressed to the study of the fiber/matrix interfacial adhesion. The results showed that the iPPMA-based composites, reinforced with alkaline extracted broom fibers, present specific mechanical properties competitive with those of the homologous poly- propylene-based materials reinforced with short glass fibers. The ternary blends gave similar properties to those of the corresponding whole iPPMA-based composites. It is considered that the esteric linkage between the cellulose {OH, and the maleic anhy- dride groups grafted on the polypropylene backbone is greatly responsible for the simi- larity in the properties. In spite of better adhesion observed in the samples reinforced by the steam-exploded fibers, less improvement of the mechanical properties was observed, owing to significant damage of the structure of the fibers during the steam explosion process. A general decrease of mechanical properties is observed in normal polypropyl- ene-based composites. The results are also supported by the water absorption tests: whereby the iPPMA-based composites showed good capability to return their dry prop- erties when kept in an oven after wetting for many days. q 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 1077-1089, 1998