<title>Abstract</title><p>Large amounts of acacia bark residues are produced each day after tannin extraction with hot water, being generally burned. This by-product was chemically characterized and used as filler in polypropylene (PP) composites, considering different particle sizes and concentrations. The materials produced by melt blending had their mechanical and thermal properties evaluated. It was verified that, even containing a significant amount of extractable compounds, the acacia bark particles can produce PP composites with higher impact properties, higher crystallization temperature and higher degradation temperature in comparison to the polymer matrix.</p>

Rice husk is a by-product of rice milling process that usually finds inadequate final disposal (burning, land filling). Thermoplastics composites filled with rice husk flour are materials that offer an alternative for using this agricultural resource viewing the production of low dense materials with some specific properties. In this work composites of polypropylene (PP) and rice husk flour (RHF) were prepared by melt extrusion. Maleic anhydride-modified PP (MAPP) was added as a coupling agent. It was verified that tensile strength decreased with filler loading. The presence of MAPP improved this property showing a strong dependence on the MAPP/RHF ratio (MAPP/RHF = 0.03 produced the best results). The density of the composites slightly increased with filler and coupling agent in comparison to pure PP. The presence of MAPP diminished more than 20% water uptake in highly-loaded composites.