Significant reinforcement of polypropylene/wood flour composites by high extent of interfacial interaction

Polypropylene (PP)/wood flour/fiber (WF) composites with strong interfacial compatibility were prepared, and properties of the composites were studied. First, the wood fiber was surface modified by alkali treatment—this process is also termed as fibrillation that creates rough surface, cavities, and much interspace between smaller fibrils. Then multi-monomer grafted copolymers of PP (MPP-St) and PP wax (MPPW-St) were synthesized. The so synthesized MPP-St/MPPW-St well compatibilized the interfaces of the PP/alkali-treated WF (TWF) composites. Mechanical property and water resistance results demonstrated that synergistically compatibilized PP/TWF composites had a better performance than composites compatibilized by MPE-St or MPPW-St separately, uncompatibilized composites, and PP/untreated wood flour (UWF) composites. The interfacial structures of all these composites were characterized by scanning electron microscopy. A three-dimensional mold was constructed to reveal that MPP-St affords a strong interfacial interaction between PP and rough surface of treated fiber, while MPPW-St supplements the interfacial interaction by permeating into the interspace between smaller fibrils of alkali-treated fiber. The mold fitted the results very well.