Influence of fiber surface treatment and length on physico-chemical properties of short random banana fiber-reinforced castor oil polyurethane composites

Abstract

The growing global concern in relation to the environment and the preservation of non-renewable natural resources has attracted researchers in different areas seeking to develop new eco-friendly materials and products based on sustainability principles. In this context, the use of plant fibers and polyurethane derived from castor oil in polymeric composites has been shown to be a good alternative. The aim of this study was to evaluate the influence of the fiber volume fraction, fiber length and alkaline treatment on the mechanical and thermal properties of short random banana fiber reinforced polyurethane derived from castor oil. The banana fibers were chemically modified through contact with 10 wt.% sodium hydroxide solutions for 1 h and characterized through Fourier transformed infrared spectrometry (FTIR), scanning electron microscopy (SEM), tensile strength and density measurements. Through the FTIR spectra and SEM micrographs, modifications in the chemical structure and morphology of the treated fibers were observed compared with untreated fibers. Polymeric composites with different fiber volume fractions and lengths were prepared through the hand lay-up process followed by compression molding at room temperature. The composites were analyzed by SEM, dynamic mechanical analysis (DMA), FTIR spectrometry, tensile strength and pull-out tests. The tensile strength and Young’s modulus increased with increasing fiber volume fraction and length for the untreated and treated banana fiber polyurethane composites. On the other hand, the treated banana fiber composites displayed higher tensile strength and Young’s modulus values than the untreated fiber composites, due to the stronger interfacial interactions between the treated fibers and the polyurethane matrix. These effects occurred due to the morphological and chemical changes in the treated fiber surfaces which promote better adhesion between the fibers and the polyurethane matrix.