Enhancing the mechanical performance of 3D‐printedbasalt fiber‐reinforced composites using in‐line atmospheric plasma pretreatments

The objective of this study is to investigate the use of an air atmospheric plasma jet for the treatment of sized basalt fibres, used in the fabrication of continuous fibre reinforced polypropylene filaments. The plasma treatments were carried out both at a laboratory scale, as well as in-line during the production of fibre reinforced filaments. The latter was carried out at a fibre processing speeds of approx. 15 metres/second, just immediately prior to the polymer coating of the fibre by extrusion. After the air plasma treatment, the water contact angle of the sized basalt fibre decreased from 86° to < 10°. XPS analysis demonstrated that the treatment yielded enhanced levels of oxygen functionality on the fibre surface. After coating with polypropylene, it was observed that there was consistently more homogeneous polymer layer deposited onto the plasma activated fibre, compared with that on the unactivated control fibre. The resulting polymer filament with embedded basalt fibre was used to fabricate mechanical test specimens by 3D printing (fused filament fabrication method). Both three-point bending tests and short beam strength tests were performed. A comparison study was carried out between test specimens fabricated using sized basalt fibre, with and without the plasma pre-treatment. The flexural modulus and maximum shear stress were found to increase by 12% and 13% respectively, for composite's fabricated using the plasma pre-treated basalt fibres. This increased mechanical strength is likely to be due to an increase in interfacial bond strength between the polymer and fibre, with an associated reduction in the level of air incorporation around the basalt filaments as demonstrated using CT analysis.