Effects of lignin on the volume shrinkage and mechanical properties of a styrene/unsaturated polyester/lignin ternary composite system

A pristine lignin and chemically surface modified lignin were used as a low profile additive and reinforcing filler for unsaturated polyester (UPE) resin. The chemical modification for pristine lignin was confirmed by FT-IR and SEM/EDX. Two different styrene/unsaturated polyester/lignin ternary composite series were prepared by using the pristine lignin or allyltrimethoxy silane (VPS)-modified lignin (VPS-lignin) to investigate volume shrinkage behavior and the mechanical properties of the UPE composites according to the lignin filler contents. The tensile and impact properties of the UPE composites showed that VPS-lignin/UPE composites performed better than the pristine lignin/UPE composites due to improved interfacial adhesion between the lignin filler and UPE matrix. However, the results of the volume shrinkage behavior in the UPE composites showed that the pristine lignin was more efficient than the VPS-lignin due to the many micro-voids formed from poor interface adhesion between them.