Rynno Lohmus

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.

The study continues the authors' previous research on The Impact of CO₂ Laser Treatment on Kevlar^® KM2+ Fibres Fabric Surface Morphology, using direct laser surface texturing of polymers. SEM and Confocal microscopy image analysis of Kevlar^® KM2+ 440D and 600 are performed to analyze the results. In the course of the study, the surface topography of Kevlar^® KM2+ fabric is optimized by adjusting the continuous wave (CW) CO2 laser parameters so that it increases the surface roughness before graphene coating and resistance to yarn pulling out of the fabric without destroying the unique structure of Kevlar® KM2+ fibres. Experimental study measurement data indicate an increase in surface roughness by 50%, and a set of laser parameter variants has been obtained that allows increasing the yarn pulling out force of KM2+ woven fabric from the fabric in the range from 50% to 99%, compared to untreated fabric. The results obtained are potentially applicable for the production of composite materials against projectile fragmentation.