Three-dimensional printing of continuous carbon fibre-reinforced polylactic acid

Abstract

This study investigates how key process parameters in material extrusion (MEX, ISO/ASTM 52900) affect the flexural behaviour and interfacial performance of continuous carbon fibre-reinforced polylactic acid (PLA) composites (CFRTPCs). Continuous carbon fibre (CCF) pre-impregnated with vinyl ester resin were coextruded with molten PLA to strengthen fibre–matrix adhesion. Three-point bending tests and scanning electron microscopy (SEM) were employed to assess the effects of printing temperature, layer thickness, and hatch spacing. Reducing the layer thickness and optimising the hatch spacing improved fibre distribution and interlayer bonding, while printing temperature strongly influenced matrix flow and fibre impregnation; 230 °C provided the most favourable balance. Under the optimised conditions (230 °C, 0.3 mm layer thickness, 0.8 mm hatch spacing), the composites achieved 3.4-fold higher flexural strength and 8.1-fold higher modulus relative to neat PLA. SEM revealed cohesive fracture with minimal fibre pull-out, confirming robust interfacial bonding. Within the framework of the MEX welding model, the chosen parameter set expanded the weld-capable window (time above the glass-transition temperature (Tg) and early high-temperature exposure), thereby enhancing interlayer welding and fibre wetting. These findings highlight the importance of process optimisation and indicate that a hybrid thermoplastic–thermoset interphase improves the structural performance of continuous fibre-reinforced thermoplastic composites.