Polypropylene/cellulosic fiber composites: Chemical treatment of the cellulose assuming compatibilization between the two materials

The present work deals with the realization of composites with a polypropylene (PP) matrix and cellulosic fibers as reinforcement. In order to achieve a good adhesion with the PP matrix, the modification of different cellulosic fibers has been performed with various chemical functions: carboxylic anhydrides, isocyanates, vinylsulfone, and chlorotriazine systems. All these compatibilizing agents carry an alkyl chain or a PP chain. Grafting is evidenced by infrared and ESCA spectroscopies, and the grafting rates for the different chemicals are determined by microweighing measurements. Modification of the surface characteristics is followed by wettability tests and inverse gas chromatography. Determination of the water sorption isotherm for the treated fibers shows an important decrease in water regain in the case of isocyanate treatments in swelling medium. Enhancement of adhesion between fibers and the matrix is demonstrated by mechanical tests: the interfacial shear stress obtained by the microbond test increases by 70% for cellulosic fibers treated with maleated PP. This may be the result of entanglements between PP chains, but for macrocomposites the effect is much more limited due to the predominance of external factors during development of the composite.