Atmospheric air pressure plasma treatment of lignocellulosic fibres: Impact on mechanical properties and adhesion to cellulose acetate butyrate

We report on the effect of atmospheric air pressure plasma (AAPP) treatment on the mechanical properties and interfacial behaviour of different lignocellulosic fibres to cellulose–acetate–butyrate (CAB), as an example for a renewable polymer. The impact of the AAPP treatment on the properties of abaca, flax, hemp and sisal fibres was studied by scanning electron microscopy and single fibre tensile tests. Single fibre pull-out tests were performed in order to determine the effect of AAPP on the apparent interfacial shear strength (τIFSS) of the (modified) fibres to CAB. After AAPP treatment, the tensile strength, Young’s modulus and elongation at break of the lignocellulosic fibres reduced drastically and deteriorated further with extended treatment. The heat generated during the plasma treatment causes dehydratation of the fibres and the etching effect of plasma degrades their macrofibril structure. A goodness-of-fit analysis shows that the tensile strength of the pre- and post-treated fibres approximate a normal distribution. The interfacial shear strength (IFSS) increases for flax, hemp and sisal fibres after 1 min AAPP treatment duration, but decreases with prolonged treatment time for abaca and sisal fibres. The increase in τIFSS after short AAPP treatment (1 min) is due to the introduction of functional groups, cleaning of contaminant substances that hinder the adhesive process and enhanced surface roughness, which favours mechanical interlocking between the fibres and the matrix. Extended AAPP treatment seems to have induced weak boundary layers on the surface of the fibres, which reduced the IFSS to CAB.