Effect of surface modification on morphological, mechanical and thermal conductivity of hemp fiber: Characterization of the interface of hemp –Polyurethane composite

The study focuses on the effect of alkaline and silane treatment of hemp fibers on mechanical and thermal conductivity. Hemp fibers were treated with sodium hydroxide solutions at different concentration, and then analysed by infrared Fourier transform spectroscopy, the X-ray diffraction, mechanical tensile test; and a scanning electron microscope. The alkali fibers were subsequently treated with silane solutions and then analysed by the same techniques. Analysis results showed that the most changes caused by this treatment are, the elimination of a certain amount of lignin, wax and oils spanning the cell wall of the fibers and the transformation of some quantity of alpha to beta cellulose. These changes are at the origin of improvement on tensile strength and young's modulus of about 39% and 23% respectively when the concentration of treatment reaches 8%. This modification revealed a strong increase in the Interfacial adhesion of the fibers-polyurethane composite from 1.26 MPa for untreated fibers up to 3.18 for the alkali fibers and 5.16 for silane fibers. Moreover, the measurement of the thermal conductivity has proved that the chemical treatment increase the fibers thermal conductivity from 42.22 mW/m°K for untreated fibers to 47, 92 mW/m°K for the alkali fiber at 8%.