Synergistic Thermal-Chemical Modification of Cork for Enhanced Interfacial Compatibility in 3D-Printable TPU Composites

Cork/thermoplastic polyurethane (TPU) composites are promising sustainable materials for FDM 3D printing, but poor interfacial compatibility limits cork loading to ~3 wt%. To address this, a green strategy was proposed: cork powder was thermally treated at 300°C (modifying surface polarity and porous structure) and further functionalized with hexamethylene diisocyanate (HDI) to enhance compatibility. Melt-blended composite filaments achieved 10 wt% cork loading: heat treatment alone improved tensile strength by 20% and elongation at break by ~50%, while 6 wt% HDI addition boosted tensile strength by 42% and nearly doubled elongation. This low-cost, bio-based approach enables flexible, high-performance composites, realizing sustainable high-value utilization of natural materials in additive manufacturing.