Hemp fiber reinforced thermoplastic polyurethane composite: An investigation in mechanical properties

In this study, the effect of fiber content, fiber length and alkali treatment on mechanical properties of hemp fiber and thermoplastic polyurethane (TPU) composite were investigated. It focused on the correlative effect of rigid hemp fiber and elastomeric polyurethane on tensile and flexural properties. Furthermore, the stress-strain behavior and the fracture analysis of the composite were discussed. To evaluate the influence of fiber length, three different lengths according to critical fiber length were chosen and examined. Interlaminar shear strength (ILSS) test, Fourier transfer infrared spectroscopy (FTIR) and X-ray diffraction (XRD) were conducted to understand the effect of fiber treatment on fiber-matrix interactions and fiber contents. Results presented that by increasing fiber volume content to 40%, flexural strength enhanced 193.24%. Additionally, 15 mm hemp fiber was found to be the optimum fiber length, where flexural strength at 40% fiber volume was further increased to 274.3%. ILSS tests of treated and untreated hemp fibers showed slight difference. However, FTIR spectra, XRD analysis and Scanning Electron Microscopy micrographs indicated the extraction of non-cellulosic materials from the surface in treated fibers, without altering the cellulose structure. It was found that, there are possibilities to balance the flexural properties and tensile properties by hemp fiber and TPU which is not achievable by glass fibers.