Oak sawdust and hazelnut shells as fillers for a polyester thermoset

Composites made from a styrene cross linked unsaturated polyester resin and vegetable particles (oak sawdust and milled hazelnut shells) were prepared. The influence of the particle's chemical treatment on the final properties of the materials was investigated. The fillers were modified by a simple alkaline treatment or by further addition of acrylic acid to the hydroxyl groups of the lignocellulosic materials. The modification changed the chemistry of the particles as determined by infrared spectroscopy. Three-point bending tests were performed on the composites filled with the different sawdust batches and with untreated milled hazelnut shells. The modulus was maximum for the composite made with alkaline treated sawdust. However, the ultimate strength as well as the displacement were best if the fibers were acrylic acid treated. Composites made with milled shells showed the lowest ultimate properties.