Surface modification of lignocellulosic fibres in atmospheric air pressure plasma

New applications of lignocellulosic fibres have been driven by numerous factors, including pressure from environmental groups, stringent environmental laws, waste minimisation efforts, recycling and cost reduction initiatives and responsible social awareness. However, the exploitation of such fibres in, for instance, fibre-reinforced composites or in the textile industry is hindered by the presence of waxy layers on the surfaces of lignocellulosic fibres. Many surface treatments are traditionally used to optimise the surface properties of natural fibres. A potential and environmentally sound surface treatment regards the use of atmospheric air pressure plasma (AAPP). The surfaces of various lignocellulosic fibres were modified using AAPP. We investigated the effect of AAPP treatment duration (i.e. 1 min and 3 min) on the surface properties of the lignocellulosic fibres using wetting and electrokinetic measurements. The critical surface tension of the untreated and AAPP-treated fibres was determined from wetting measurements using the capillary rise technique, whereas the changes in the surface chemistry were characterised by means of zeta (zeta)-potential measurements. A slight increase in the critical surface tension of the lignocellulosic fibres was found with prolonged treatment time, with the exception of abaca fibres. The post-treated fibres show a larger degree of hydrophilicity measured from the difference, Delta zeta, in the decay of the zeta-potential measured as function of time, with the exception of hemp fibres. Finally, zeta-potential measurements as function of pH validated the performance of both AAPP treatments.