Surface characterization of natural fibers; surface properties and the water up-take behavior of modified sisal and coir fibers

The influence of fiber surface modifications like dewaxing, alkali treatment and methyl methacrylate grafting on the thermal and electrokinetic properties of coir (coconut) and sisal fibers has been investigated. Additionally scanning electron microscopy was performed to follow changes in the fiber surface morphology. Electrokinetic properties were measured using the streaming potential method. The measured time dependence of the ζ-potential offers the possibility to characterize the water up-take, i.e. the swelling behavior of natural fibers. The investigated natural fibers, as expected, contain dissociable surface functional groups as verified by measuring the pH-dependence of the ζ-potential. The influence of fiber surface modifications on the ζ-potential was compared to the influence of fiber surface modifications on measured (tensile and flexural strength) mechanical biocomposite properties. The ζ-potential measurement is a very efficient technique to investigate the various changes effected by different surface modifications, which are necessary to improve the compatibility of such natural fibers and polymer matrices for making eco-friendly and low cost composite materials.