Enhancement of Graphene-Coated Para-Aramid Yarn's Pull-Out Resistance by Laser Pre-Treatment

This study investigates the feasibility of enhancing graphene-coated para-aramid yarn's resistance to pull-out from fabric structures, measured by junction rupture force (JRF), by increasing the fibre surface roughness with nano- and microstructures obtained by laser irradiation and graphene coating. Two types of Kevlar^® KM2 fibre woven fabrics were subjected to continuous wave CO₂ laser processing to investigate the influence of laser power and scanning speed combinations on yarn pull-out force from the fabric structure under fixed laser spot diameter and raster step. Depending on the combination of applied laser parameters, a JRF increase of between 32% and 99% was achieved for laser-irradiated KM2+440 fabric compared to the JRF of untreated fabric. Applying a single layer of graphene coating to the fabric pretreated with optimal laser parameters doubled the JRF increase. When a second layer was applied, the increase tripled, indicating that cumulative effects were produced. As a result of laser treatment, the V2KM2600_laz variant's JRF increased by 27% compared to the unmodified fabric, while the corresponding JRF difference for V3KM2600_laz was statistically insignificant, and any further JRF increase for V3 was only provided by the graphene coating layers. Meanwhile, for the laser-modified V2KM2600_laz, the JRF increase for the first graphene layer reached 56%, and adding a second graphene layer boosted it to 90%. The AFM and SEM imaging studies of the self-organization of nano- and microstructures on the surface of Kevlar^® KM2 fibres allowed us to conclude that irradiation-induced structures formed in the defect-enriched upper nanolayer of the 300-350 nm thick fibre skin, with a thickness of about 8 nm. Therefore, treatment within the examined laser parameter limits does not affect the fibres' core structure.