Plasma-enhanced continuous carbon fibre melt impregnation process for PA6 matrix tape manufacturing

Research efforts have demonstrated the versatility and effectiveness of plasma surface treatment technology in enhancing the interfacial properties of composites. However, a substantial gap exists in integrating plasma surface treatment technology into scalable composite manufacturing processes. This work utilises a continuous atmospheric pressure plasma jet treatment approach to, for the first time, activate the unsized carbon fibre (CF) surface immediately before melt impregnation with a polyamide 6 (PA6) matrix. At a tape manufacturing speed of 0 . 83 m min −1 , the in-line treatment did not diminish the single fibre tensile strength, while raising the short-beam strength from 33.3 to 48.3 and 75 MPa , through treatments applied to one side and both sides of the tow, respectively. Synchrotron wide-angle X-ray scattering revealed that the fibre-matrix interphase crystallinity remained unmodified by the surface treatment, indicating that the enhanced performance was not facilitated by transcrystalline growth. The constrained PA6 lamellae growth detected by preferential α (200) PA6 reflection orientation was unaffected by the plasma surface modification. Instead, enhanced composite performance arises from intermolecular bonding between the functionalised CF surface and the polar PA6 matrix. Moreover, the immediate melt impregnation step can allow the reaction between radicals on the CF surface and the molten PA6 matrix. These mechanisms lead to substantially enhanced short-beam strength, increased stiffness, and cohesive composite failure. Overall, the introduced approach overcomes the well-known plasma surface modification issue of ageing by embedding the activated reinforcement in the melt impregnation step. • First integration of plasma jet treatment with in-line melt impregnation. • CF/PA6 short-beam strength enhancement up to 125% by plasma surface treatment. • Tow surface treatment from both sides recommended for maximum interlaminar strength. • PA6 constrained lamellae growth detected in the composite tape by synchrotron WAXS.