Composites of biomass fibers with hydrophobic polymers like polypropylene (PP) represent material systems with poor or no interfacial adhesion because of the inherent incompatibility between the respective components. Block and graft copolymers can function as compatibilizers to improve interfacial adhesion and provide composites with an improved and unique balance of properties. Various approaches to improving interfacial adhesion with an emphasis on our work on the compatibilization of biofibers (lignocellulosics) with polypropylene is presented. The biofiber-reinforced polypropylene composite was prepared by reactive extrusion. The compatibilizer which is the graft copolymer produced by reaction of maleated polypropylene with the cellulosic component of the biofiber, was generated insitu during reactive extrusion processing. Maleated polypropylene (MAPP) was produced by the peroxide catalyzed grafting of maleic anhydride (MA) on polypropylene (PP) in the extruder. It was subsequently alloyed with the biofiber by use of a catalyst to form covalent bonds between the components. Alternatively, all the processing steps i.e. maleation, graft formation and the alloying were done in a single extruder run. The chemistry occurring during the two reactive extrusion processing modes and its effect on the properties of the resultant materials is discussed.
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