Studies to Determine Critical Characteristics of Thermally Treated Biomass Fillers Suitable for Thermoset Composites

Abstract

Biomass fillers are of interest for thermoset composites due to their lower density and favorable life cycle impact relative to mineral fillers. The purpose of this reported research is to develop a more thorough understanding of the mechanisms of the cure problems historically reported with biomass fillers in thermosets. Biomass fillers heat-treated using a variety of equipment under various conditions were studied using dielectric analysis (DEA), elemental analysis (EA), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC). In addition, mechanical properties and water absorption were measured for bulk molding compounds (BMC) made using the fillers. Kraft lignin had an inhibition effect on the cure of unsaturated polyester resins. Soy hulls heat treated at 500°C also inhibited cure, although untreated soy hulls did not. Extraction studies indicated significant aromatic content that was soluble in toluene in the aggressively heat treated filler, which also inhibited cure. Lower temperature heat treatments up to 249°C did not inhibit cure. With precursor selection considerations and controlled thermal treatments, a biomass filler capable as a 100% volume replacement for mineral fillers in thermoset composites is feasible.