Mechanical properties of a polyurethane hybrid composite with natural lignocellulosic fibers

Several low-cost hybrid composites composed of polyurethane and renewable natural fibers were developed and analyzed for their mechanical and physical properties. Composites were fabricated by replacing up to 20% w/w of the polyethylene glycol present in conventional polyurethane foams with one and the mixture of three natural fibers: sugarcane bagasse, sisal or rice husk. Prior to composite production, fibers were mercerized with sodium hydroxide and hydrogen peroxide to remove lignin and hemicellulose. A simplex-centroid mixture design model was used to evaluate the effects of the added fibers on composite properties such as resilience, elastic modulus and deformation under permanent compression. Obtained hybrid composites demonstrated up to 32% of resilience, 0.1 GPa of elastic modulus, and 7.32% of permanent deformation. In order to optimize these properties, fiber amounts were adjusted using a quadratic mathematical model, indicating that formulations containing only the rice husk or an 82/18 (% w/w) rice husk/sugarcane bagasse mixture will perform best. The obtained composite is a unique low cost material because is environmentally friendly and has a high potential for applications in shock absorption and padding materials, due its proven good resilience and elastic modulus.