FORMATION OF ENTANGLEMENTS AT BRUSH-LIKE INTERFACES IN CELLULOSE POLYMER COMPOSITES

Cellulose fibers were grafted with compatibilizing agents, such as maleated polypropylenes of different molecular weights. Steric effects and surface free-energy effects were found to stimulate the stretching of grafted chains away from the cellulose fiber surface, giving rise to a brushlike configuration in a polypropylene (PP) melt. Inverse gas chromatography measurements on modified fibers using a model compound for PP as adsorbate showed that interactions of PP and grafted fibers, which were mainly diffusion-dependent, increased with increasing molecular weight of the compatibilizer. Dynamic mechanical measurements and tensile testing of composites showed that the presence of compatibilizing agents enhanced stress transfer and increased interphase thickness considerably, the most significant effect being obtained for the high molecular weight compatibilizers. Apparently, the longer the grafted chains, the larger the fraction of matrix molecules involved in the interactions and, thus, the thicker the interphase. The improvement of adhesion between treated fibers and PP, as detected by peel testing, was proven to be caused mainly by entanglements formed between compatibilizing agents and PP. (C) 1993 John Wiley & Sons, Inc.