Efficient plant fibre yarn pre-treatment for 3D printed continuous flax fibre/poly(lactic) acid composites

To address the issue of high void contents in 3D printed continuous flax fibre reinforced composites (CFFRCs), an efficient fibre pre-treatment method was proposed to improve the compatibility between plant fibre and resin matrix so that the high-quality manufacturing and excellent mechanical performance were achieved. The surface of flax yarns was treated by silane coupling agents to improve the wettability and interfacial performance. The CFFRCs were then prepared by the customised 3D printing technology, and the mechanical tests were conducted to measure their mechanical properties. It was found that the mechanical properties of the CFFRCs were greatly improved after the treatments which induced very low void contents of less than 1.1%, due to the improved wettability and the interfacial bonding between the flax yarns and resin matrix. The mechanical properties of the CFFRCs prepared by 3D printing in the present work were comparable to those manufactured by compression moulding in literature. Compared with compression moulding and autoclave, 3D printing has lower pressure and shorter time during moulding. So, prior to the preparation of 3D-printed continuous plant fibre reinforced composites, it is necessary to modify the surface of the plant fibres to improve the wettability and the interfacial compatibility, while ensuring the continuity of the yarn. The silane coupling agent can eliminate the hydroxyl group through chemical reaction with the fibre surface, and establish a chemical bond with the matrix. To improve the wettability of the fibre and the interface performance of the 3D printed composites, thereby improving the mechanical properties of continuous flax fibre reinforced composites (CFFRCs) manufactured by 3D printing [Display omitted] •An efficient pre-treatment method for 3D printing is proposed to improve mechanical properties of CFFRCs.•Improved fibre wettability helps to reduce voids in CFFRCs arisen from low printing pressure and twisted nature of yarns.•Mechanical properties of 3D printed CFFRCs are comparable to those by compression moulding in literature.