Pull-out and other evaluations in sisal-reinforced polyester biocomposites

Although sisal fibers have been used by several authors, the Brazilian variety has not yet been thoroughly characterized. In this work the surface of sisal fibers was modified by treatment with NaOH or N-isopropyl-acrylamide solutions. Lignin content and density of fibers are reduced with the chemical treatment and the N-isopropyl-acrylamide treatment causes a significant reduction in moisture absorption. Tensile tests of NaOH (0.25, 0.5, 1, 2, 5, and 10% w/w) and N-isopropyl-acrylamide (1, 2, and 3% w/w) treated fibers were carried out and a reinforcement effect of the sisal treated with 2% solutions was observed. TGA measurements showed that with the NaOH treatment the fiber becomes more thermally resistant. SEM micrographs and crystallinity index of sisal indicated how different treatments alter the fiber surface. Pull-out tests in polyester resin were performed, evidencing that all treatments were effective in improving interfacial adhesion. The best results were obtained with the 2% N-isopropyl-acrylamide treatment. The main advantages of pull-out tests is that without considering composite processing variables, good performance sisal/polyester composites may be selected before their laborious and material-consuming preparation step.