Novel polypropylene–cellulose composites using polyethylenimine as coupling agent

Novel cellulose reinforced polypropylene composites were obtained using polyethylenimine (PEI) as a coupling agent. Samples of bleached eucalyptus Kraft pulp were sprayed with aqueous solutions of PEI and extruded with isotactic polypropylene, and the tensile properties of the resulting composites were measured. The use of PEI as a coupling agent allows significant increases of both tensile strength and elongation at break. In order to understand the nature of the coupling action of PEI, the composite materials were studied using scanning electron microscopy and diffuse reflectance FTIR spectroscopy. The analysis reveals that the amine groups of PEI react with carbonyl and carboxyl groups, produced during the processing of the composites at elevated temperatures, to form imines and amides. These strong bonds, generated in the interfacial region of the composite, contribute to explain the coupling action of PEI.