From process to performance: Fused Granular Fabrication of Flax/PP biocomposites

This study explores the influence of Fused Granular Fabrication (FGF) parameters on the mechanical performance and microstructural features of flax fiber-reinforced polypropylene (Flax/PP) biocomposites. Layer height, nozzle temperature, and printing orientation were systematically varied, and their effects were analyzed using tensile testing, Digital Image Correlation (DIC), Scanning Electron Microscopy (SEM), and Differential Scanning Calorimetry (DSC). Results show that a layer height of 0.6 mm provides an optimal compromise between mechanical properties, printing efficiency, and process stability, with performance statistically similar to 0.4 mm but superior to larger layer heights (≥0.8 mm). Nozzle temperature exhibited a non-monotonic effect: insufficient fusion and porosity at 170–190°C reduced strength, while improved interfacial bonding at 210°C yielded the best properties, followed by degradation at 220°C due to fiber oxidation and reduced crystallinity. Printing orientation strongly influenced tensile behavior, with ±45° delivering the most uniform stress distribution and highest strength, whereas 90° showed poor interlayer bonding. Overall, FGF enables the fabrication of natural fiber biocomposites with competitive strength-to-weight performance. These findings demonstrate the potential of Flax/PP composites for sustainable engineering applications in automotive and construction sectors, while providing guidelines for further optimization and broader use. • Flax/PP biocomposites were fabricated by fused granular fabrication (FGF). • Printing temperature, layer height, and raster orientation strongly affected tensile properties. • Optimal tensile performance was achieved at 210 °C within the tested range. • Porosity, fiber oxidation, and matrix crystallinity jointly governed mechanical behavior. • Integrated DIC, SEM, and DSC analyses revealed structure–property correlations.