Interaction between coupling agent and lubricants in wood-polypropylene composites

Commercially available additives and a copolymer system were investigated for their impact on composite morphology and crystallization kinetics. This research focuses on the influence of the coupling agent and lubricants on the crystallization of polypropylene in the bulk and interphase regions and the subsequent spatial distribution of the additives. Differential scanning calorimetry and polarized light microscopy were used to determine kinetic parameters for the crystallization process of the polypropylene in the bulk composite melt and at the wood-polypropylene interface. No differences were found in the kinetics of the crystal formation nucleated on the wood surface and in the bulk polymer by polarized microscopy. Using microbeam Fourier transform infrared spectroscopy, the spatial distribution of lubricants and coupling agents were delineated. Lubricants that tended to interfere with wood-polypropylene coupling dispersed throughout the transcrystalline region around the fiber. In contrast, lubricants with lower degree of interference appeared to be phase separated in the amorphous regions between the crystals. These findings are consistent with calorimetric results that show differences in the quality of the crystals formed by the neat polypropylene.