The effect of chemical treatment on the properties of hemp, sisal, jute and kapok for composite reinforcement

Two chemical treatments were applied to hemp, sisal, jute and kapok natural fibres to create better fibre to resin bonding in natural composite materi als. The natural fibres have been treated with varying concentrations of ca ustic soda with the objective of removing surface impurities and developing fine structure modifications in the process of alkalisation. The same fibr es were also acetylated with and without an acid catalyst to graft acetyl g roups onto the cellulose structure, in order to reduce the hydrophilic tend ency of the fibres and enhance weather resistance. Four characterisation techniques, namely XRD, DSC, FT-IR and SEM, were used to elucidate the effect of the chemical treatment on the fibres. After tre atment the surface topography of hemp, sisal and jute fibres is clean and r ough. The surface of kapok fibres is apparently not affected by the chemica l treatments. X-ray diffraction shows a slight initial improvement in the c rystallinity index of the fibres at low sodium hydroxide concentration. How ever, high caustic soda concentrations lower the fibre crystallinity index. Thermal analysis of the fibres also indicates reductions in crystallinity index with increased caustic soda concentrations and that grafting of the a cetyl groups is optimised at elevated temperatures. Alkalisation and acetyl ation have successfully modified the structure of natural fibres and these modifications will most likely improved the performance of natural fibre co mposites by promoting better fibre to resin bonding.