Lignin‐polypropylene composites. Part 1: Composites from unmodified lignin and polypropylene

Abstract Lignin polypropylene composites were prepared in the range of 10–60% by weight lignin content. Blending of lignin with polypropylene resulted in materials with reduced tensile and flexural strength and a dramatic decrease in unnotched Izod impact strength compared to the properties of virgin polypropylene, although moduli (Young's and flexural) were improved. Traditional surface‐treated fillers such as mica and talc performed better than lignin, but when lignin and inorganic fillers were mixed, the strength properties were improved with respect to lignin alone, perhaps because of a better lignin‐filler‐particle interaction and distribution. This could be an alternate approach for obtaining improved strength composites containing large quantities of unmodified kraft lignin. Incorporation of maleic anhydride grafted polypropylene (MAPP) as a coupling agent also improved strength properties, although at high lignin contents (e.g. 60%) there was considerable variability in the tensile strength.