Continuous additive manufacturing of hemp yarn-reinforced biocomposites with improved impregnation method

This study was motivated by the development of new additively manufactured bio-based materials with high performance. Hemp yarn was used in continuous material extrusion additive manufacturing to produce novel hemp yarn-reinforced biocomposites. The hemp yarn was compared to an original hemp/poly(lactic acid) hybrid yarn prepared by commingling before printing as an improved impregnation method. In X-ray micro-computed tomography, the hybrid yarn-based biocomposite exhibited a higher impregnation rate accompanied by a reduced void content, more aligned fibers, and a more homogeneous distribution of the different constituents, resulting in significantly higher mechanical properties during tensile loading with a more brittle behavior compared to the additively manufactured biocomposite based on pure hemp yarn. In addition, superior mechanical performance was obtained while having lower fiber fraction with the use of hybrid yarns, raising awareness about the importance of improving the impregnation of the plant fibers as well as the fiber volume fraction. This original preparation method can provide bio-based materials with enhanced quality and performance, close to those obtained with conventional manufacturing techniques, while making the most of additive manufacturing for sustainable, lightweight, and high-end applications in health or aerospace.