Estudo da adesão fibra-matriz dos compósitos de poliuretano sem isocianato (NIPU) com fibra da folha do abacaxizeiro

Abstract

In recent decades, vegetable fibers have aroused great interest in the scientific community as they demonstrate a wide potential for application as reinforcement in natural-based composites. One of the main challenges for an effective application of fibers as reinforcement is the physicochemical divergences that they have in relation to polymeric matrices, which hinders interactions at the fiber-matrix interface of composites and compromises their mechanical properties. This work aimed to characterize the interfacial interactions of the reinforcement with the matrix in non-isocyanate polyurethane (NIPU) composites with pineapple leaf fiber (PALF). The fibers were treated by extraction of lipids by Soxhlet and by acid hydrolysis with lemon juice, aiming at the removal of lignin, hemicellulose and other components of the vegetable fiber that hinder its anchorage to the polymeric matrix. Subsequently, the fibers were incorporated into the NIPU to carry out pull-out tests on the composite. The fibers were submitted to the water absorption test and analyzed by optical microscopy, to show the changes caused by the applied chemical treatments. The mechanical properties of the NIPU-PALF composite were obtained through the pull-out test. Water absorption test revealed a significant reduction in the moisture absorption capacity of the fiber after acid hydrolysis, due to the removal of its hydrophilic components. Pull-out test proved the improvement of fiber adhesion to the matrix polymer after acid hydrolysis, increasing the interfacial shear stress of the composite by 18% and the fiber tensile strength by 23.2%. The results indicated that the acid hydrolysis treatment with lemon juice is able to promote a better adhesion of the PALF to the NIPU, without compromising its mechanical properties.