Butyrated kraft lignin as compatibilizing agent for natural fiber reinforced thermoset composites

Butyrated kraft lignin was added to an unsaturated thermosetting resin, consisting of a mixture of acrylated epoxidized soybean oil and styrene. Composites were made by the Vacuum Assisted Transfer Molding process with varying amounts of butyrated kraft lignin dissolved in the unsaturated resin system. Butyrated kraft lignin improved the interface between the resin and reinforcing flax fibers. SEM images illustrate a clear improvement in the adhesion of the resin to the fibers by showing the fibers fracturing together with the resin, without fiber pullout. Increases in viscosity upon solubilization of butyrated kraft lignin in the unsaturated resin of up to 150% for 10 wt% butyrated lignin however, resulted in the appearance of dry patches in composites made with dense fiber reinforcement mats. These dry spots decrease the mechanical properties of the overall composite. On the other hand, strength improvement is seen for composites made with short wheat straw fibers, which allow for better resin penetration and fiber wetting. The flexural strength increased by 40% for a 5 wt% butyrated lignin addition. Work currently in progress to reduce the negative effects of the viscosity increase by changing the processing conditions, is also described. (C) 2003 Published by Elsevier Ltd.