Atmospheric pressure plasma enhances the mechanical properties of natural fibre-reinforced polyoxymethylene thermoplastic composites

Abstract

The development of sustainable, yet high-performance composite materials necessitates effective strategies to improve compatibility between natural fibres (NFs) and circular thermoplastic matrices. We report atmospheric pressure (AP) plasma treatment as a scalable, interface-engineered approach to enhance the mechanical performance of unidirectional flax fibre (FF)-reinforced polyoxymethylene copolymer (coPOM) composites. FF fabrics were treated using diffuse coplanar surface barrier discharge plasma and processed into high fibre volume fraction (FVF ∼ 61 %) composites via film stacking. Post-treatment surface analysis revealed removal of waxy species and increased oxygen-containing functional groups, reflected by an increased O/C ratio (from 0.48 to 0.74) and elevated total surface energy (from 29.4 to 41.8mJ/m 2 ). The wetting improved significantly, with spreading coefficient changing from − 3.9mJ/m 2 to positive values. At the coupon level, transverse tensile modulus and strength increased by ∼ 67 % and ∼ 23 %, and transverse compressive modulus and strength by ∼ 46 % and ∼ 43 %, respectively. Shear strength (∼23 %) and in-plane shear moduli (∼31 %) were also enhanced. In contrast, longitudinal tensile strength decreased by ∼ 12 % despite a 12 % increase in longitudinal modulus, while failure-envelope analysis indicated an expanded inter-fibre failure domain. Together, the results highlight AP plasma treatment as a roll-to-roll-compatible route to significantly improve off-axis mechanical performance of NF/thermoplastic composites.