Improvement of fibre–matrix adhesion in cellulose/polyolefin composite materials by means of photo-chemical fibre surface modification

The mechanical performance of composites made from viscose fibre reinforcement fabrics and PP matrix polymers could be enhanced by photo-chemical surface modification of the viscose fibres. The surface modification was achieved by deposition of UV-polymerized organic thin layers using pentaerythritol triacrylate or diallylphthalate as monomers. The main effects of the photo-chemical modification refer to a decrease in wettability of the highly hydrophilic and water adsorbing viscose fibres and an increase in their affinity towards non-polar substances. Both effects were found to yield an increase in fibre–matrix adhesion and interfacial shear strength, resulting in better impact and tensile properties compared to untreated samples. The experimental composites were slightly inferior with regard to fibre–matrix adhesion and IFSS than established systems using modified matrix polymers such as the maleic anhydride modified PP, but exhibited similar or even improved properties in view of tensile strength and impact behaviour. The latter indicates superior energy transfer by the thin organic layers forming the fibre–matrix interface. Based on these observations, the studied concept of photo-polymerized inter-layers between fibre and matrix can be understood as a biomimetic concept mimicking the graded transitions of natural structures.