Towards coupling agent-free composites made from regenerated cellulose/HDPE by UV radiation-induced cross-linking

This research aims to enhance fibre-matrix adhesion in bio-based fibre-reinforced polyolefins without using adhesion promoters. The primary focus is to establish a cross-linking mechanism between cellulose fibres and polyethylene by applying UV irradiation to a UV-transparent matrix and UV-absorbing fibres. The influence of UV treatment on the composite properties is evaluated by tensile, interfacial and interlaminar shear strength tests. The UV irradiation decreases the critical fragment length in single fibre fragmentation tests, indicating an improved fibre-matrix adhesion. The UV-irradiated composites’ tensile strength and Young’s modulus are found to be ~10% (for 3- and 8-minute irradiation) and ~50% (for 8-minute irradiation), respectively, higher than those of the untreated samples. Furthermore, the UV irradiation leads to an improvement in the interlaminar shear strength by 25%. The variation of the UV-irradiation time (3 min and 8 min) and the comparison of the properties of semi-finished composite sheets and composites also reveal chemical and physical changes in the regenerated cellulose fibres due to heat adsorption. The proposed mechanism of interfacial crosslinking is confirmed by FTIR spectroscopy. The results suggest an approach to overcome poor compatibility between hydrophobic polyolefin matrix and hydrophilic cellulose-based fibres, resulting in adhesive-free bio-based composites.