Pulp fiber-reinforced thermoset polymer composites: Effects of the pulp fibers and polymer

In this study, composites were fabricated with four types of pulp fibers and two types of thermoset polymers. Four pulp fibers included hardwood and softwood high-yield pulp (HYP), Kraft pulp, and Whatman cellulose fibers and two polymers included unsaturated polyester (UPE) and vinyl ester (VE). FTIR and TGA results showed the chemical differences among the four pulp fibers and confirmed the existence of lignin on the HYP pulp fibers. The two HYP fibers were more compatible to the UPE resin, while the Kraft and Whatman cellulose fibers were more compatible to the VE resin as indicated by the tensile properties. Lignin on the two HYP fibers acted as a natural coupling agent for the natural fiber and the more hydrophobic UPE resin. The two cellulose-rich pulp fibers performed better when the VE resin was used. Composite storage moduli were significantly improved as compared with those of the neat UPE and VE resins. Only a slight increase in glass transition temperature was noted for the composites.