3D printing of continuous flax fibre reinforced biocomposites for structural applications

Highlights: • Fused Filament Fabrication of Continuous flax fibre/PLA biocomposites was performed. • Microstructure of filaments and printed samples was characterized. • Longitudinal and transverse mechanical behaviour and properties were evaluated. • Outstanding longitudinal mechanical properties were obtained compared to current printed biocomposites. -- Abstract: Recently, interest has been increasing in natural fibres as composite reinforcing fillers for polymer-based filaments manufactured with the Fused Deposition Modeling (FDM) process, despite their moderate mechanical properties compared to pure polymer. An innovative way was proposed in the present work to optimize the mechanical properties of biocomposites. It was based on novel continuous flax fibre/PLA (cFF/PLA) composite filaments made with a customized co-extrusion process and printed with a simple and affordable printing machine. The microstructure of the printed cFF/PLA biocomposite evidenced a homogeneous distribution of yarn within the cross section, while the twisted flax yarn led to fibre-rich areas at mesoscale. The cFF/PLA showed tensile modulus and strength values that exceeded the only available published result on continuous natural fibre printed composites by >4.5 times. Tensile properties were in the same range as those for continuous glass fibre/PolyAmide (PA) printed composites, paving the way for the use of biocomposites in structural applications. Their weakest point was their transverse properties that remained poorer than similar flax/PLA thermocompressed composites.