Basic properties of grain by-products and their viability in polypropylene composites

The objective was to study the potential of grain by-products (husk) of grains such as wheat (Triticum aestivum L; German name is Weizen) and rice (Oryza sativa) as reinforcements for thermoplastics as an alternative to or in combination with wood fibres. Prior to composites preparation, the chemical components of fibres such as cellulose, hemi-cellulose, lignin, starch, protein and fat were measured and the surface chemistry and functionality of grain by-products were studied using EDX and FT-IR. Structural constituents (cellulose, starch) were found in wheat husk (W) equal 42%, in rice husk 50% and in soft wood 42%, respectively. Thermal degradation characteristics, the bulk density, water absorption and the solubility index were also investigated. Wheat husk (W) and rice husk were found thermally stable at temperatures as low as 178 °C and 208 °C, respectively. The particle morphology and particle size were investigated using microscopy. Water absorption properties of the fibres were studied to evaluate the viability of these fibres as reinforcements. Polypropylene composites were fabricated using a high speed mixer and an ensuing injection moulding process with 40 wt% fibre. The tensile and Charpy impact strength of the resulting composites were investigated. The tensile elongation at break was found to 75% for wheat husk (W) composites and 23% for rice husk composites better than soft wood composites. Rice husk composites showed 13% better Charpy impact strength than soft wood composites. Due to coupling agent, tensile strength of composites found to improve 25% for soft wood, 35% for wheat husk (W) and 45% for rice husk.

► The potential of rice husk and wheat husk (W) were studied. ► Particle size, chemical contents, thermal and moisture absorption of fibres were evaluated. ► Polypropylene composites were prepared with those fibres and properties were investigated. ► After than the properties were compared with WPC.