Influence of Layer Thickness and Extrusion Temperature on the Mechanical Behavior of PLA–Flax TPMS Sandwich Structures Fabricated via Fused Filament Fabrication

Highlights: What are the main findings? Gyroid PLA–flax TPMS sandwiches printed via FFF were characterized in terms of flexure and compression. Flexural behavior was skin-dominated, with best strength at 0.28 mm/200 °C, and ANOVA confirmed the significant effects of temperature and layer height. Compressive behavior was core-dominated, showing cellular collapse with first-collapse stresses of 6.3–8.2 MPa, significantly governed by temperature and layer height (ANOVA). Layer height strongly influenced printing time/energy/CO2, with 0.28 mm providing the best kWh·MPa−1 efficiency. What are the implications of the main findings? Identifies process windows for optimizing TPMS sandwiches under multi-axial loading (skin vs. core-dominated regimes). Supports sustainable, energy-efficient manufacturing of bio-based lightweight components. Triply periodic minimal surface (TPMS) sandwich structures made from PLA, reinforced with flax fibers, offer a bio-based approach to lightweight design, but their performance is sensitive to material-extrusion parameters. This study investigates the combined effects of layer height (0.16, 0.24, and 0.28 mm) and extrusion temperature (200, 220 °C) on the flexural behavior of gyroid-core PLA–flax sandwiches. Six parameter combinations were fabricated by fused filament fabrication and tested in three-point bending to obtain flexural strength and strain at failure. Post-fracture optical microscopy related mesostructure and failure mechanisms to macroscopic response. The highest strength (≈23 MPa) was found at 0.28 mm/200 °C, while the greatest strain at failure (≈0.06 mm/mm) occurred at 0.16 mm/200 °C. Two-factor ANOVA showed the significant main and interaction effects of temperature and layer height on both metrics. Fractography revealed a transition from interfacial delamination at lower temperatures and thinner layers to a more localized, cohesive rupture as interlayer bonding improved with higher temperature and thicker layers. Complementary compression tests revealed a core-dominated cellular collapse, with first-collapse stresses ranging from 6.3 to 8.2 MPa and a significant dependence on layer height and temperature (ANOVA). A gate-to-gate sustainability assessment indicated that layer height dominates printing time, energy demand, and CO2 emissions, with 0.28 mm minimizing energy per unit property. Measured part masses were 4–6% below slicer predictions, consistent with typical FFF porosity. The results provide TPMS-specific process windows that balance mechanical performance and energy efficiency for PLA–flax sandwiches.