Processing of Hemp Fibre Using Enzyme/Fungal Treatment for Composites

Hemp fibres compete very well with glass fibres in terms of their specific strength and stiffness and so can replace glass fibres as reinforcement in composites. Combining them with thermoplastics results in potentially cheap recyclable composite materials. The adhesion between the hemp fibre and thermoplastics such as polypropylene is a major factor in the mechanical properties of the composite. Interfacial bonding can be improved by modifications to the fibres, the matrix or both the fibres and the matrix. The aim of this thesis was to investigate low cost and efficient fibre treatment methods with low environmental impact such as bag retting and white rot fungi, and chelator/enzyme treatments which could be applied to hemp fibre in order to create better bonding fibre for potentially recyclable composite materials. Bag retting was carried out by keeping fresh green hemp fibres in a sealed plastic bag for 1 to 2 weeks to allow natural retting to occur under sealed conditions. For white rot fungi treatments, the dried non-retted hemp fibres were gamma irradiated, and then inoculated with white rot fungi for 2 weeks. Chelator/enzyme treatment was achieved by immersing the fresh green non-retted hemp fibres in solutions consisting of either EDTMP.Na5 (ethylene diamine tetra (methylene phosphonic acid pentasodium salt) or pectinase (P2401) and laccase (53739) for 6 hours. Several characterization techniques, namely wet chemical analysis, Fourier-transform infrared (FT-IR), scanning electron microscopy (SEM), fibre density testing, X-ray diffraction (XRD), differential thermal analysis (DTA) and thermogravimetric analysis (TGA), zeta potential and single fibre tensile testing were used to assess the effect of treatment on hemp fibres. Wet chemical analysis and FT-IR, were used to measure the chemical compounds present in untreated and treated hemp fibres and showed all treatments removed non-cellulosic compounds from hemp fibre. The separation of untreated and treated fibres was investigated by visual inspection. An examination of surface morphology of hemp fibres carried out using SEM revealed that all treated fibres had cleaner hemp surfaces than untreated ones. The fibre density testing showed that the treated fibre had higher density than untreated fibre. XRD was carried out to assess modification of the crystallinity of fibres and the results showed hemp fibre crystallinity index increased in all treated fibres. Differential thermal analysis (DTA) and thermogravimetric analysis (TGA) were used to obtain the activation energies and relative thermal stability of fibres, and indicated that all treatments improved fibre thermal stability. Zeta potential indicated that all treated fibres were more hydrophilic than untreated fibre. Single fibre tensile testing was used to obtain the tensile strength of untreated and treated fibres and it was found that the tensile strength of all treated fibres was reduced. Short fibre composites were produced by extrusion and injection moulding. Fibres, polypropylene (PP) and a maleated polypropylene (MAPP) coupling agent were compounded using a twin-screw extruder, and then injection moulded into composite tensile test specimens. It was found that all fibre treatments increased the tensile strength of composites. White rot fungi Schizophyllum commune (S.com) treated fibre gave the highest tensile strength of 45 MPa, an increase of 28% compared to composites using untreated fibre. Both the single fibre pull-out test and the Bowyer and Bader model were used to determine the interfacial shear strength (IFSS) of untreated fibre and S.com treated fibre composites. The results obtained from both methods showed that IFSS of the treated fibre composites was higher than that for untreated fibre composites. This supports that the hemp fibre interfacial bonding with PP was improved by white rot fungi treatment. The Bowyer and Bader model was also used to calculate the tensile strength of untreated and S.com treated short fibre composites and results closely match the experimentally values