Solid-state shear pulverization as effective treatment for dispersing lignocellulose nanofibers in polypropylene composites

Lignocellulose nanofibers (LCNFs) were prepared by the wet-disk milling of wood flour and were subsequently used as a reinforcing filler for a polypropylene (PP) polymer matrix. The specific surface area and the smallest fiber width of the LCNFs were found to be 106 m²/g and 20 nm, respectively. Solid-state shear pulverization (SSSP) using a batch-type kneader was performed at a temperature lower than the PP melting point in order to improve the dispersion of the LCNFs in the PP matrix, which also contained 5 wt% maleic anhydride-grafted PP. The SSSP treatment improved LCNF dispersion; this was determined through optical and scanning electron microscopy observations. The improvement in LCNF dispersion after the SSSP treatment increased the Young’s moduli, yield strengths, and toughnesses of the resulting composites. The composites showed higher Young’s moduli and yield strengths that those of the neat PP matrix; this was true in the case of both the tensile and the bending tests. However, the impact strengths of the composites were not significantly different from that of the neat matrix. Finally, the crystallization rate of the PP matrix also increased with the increase in LCNF dispersion.