Polyamide12-Meta-Composites with Excellent Mechanical Performance, Shape-Memory, Flame Retardancy and 3D/4D Printability

Achieving multifunctional polymer composites that combine mechanical strength, thermal stability, flame retardancy, and shape-memory capability while remaining compatible with additive manufacturing remains challenging. In this work, a comprehensive materials library of fused filament fabrication (FFF)-printable polyamide 12 (PA12) composites was developed using bamboo charcoal (BC), a BC/carbon nanotube (BC/CNT) hybrid, and conventional glass fiber (GF) and carbon fibers (CF). PA12/BC and PA12/BC/CNT composites were compounded, extruded into filaments, and systematically characterized in terms of microstructure, wettability, thermomechanical behavior, flammability, shape-memory performance, and mechanical properties at ambient and elevated temperatures. The BC/CNT hybrid represents the key innovation of this study, enabling a synergistic reinforcement strategy that simultaneously enhances stiffness, strength, damping, thermal stability, flame retardancy, and hydrophobicity while preserving excellent shape-memory behavior. In contrast, GF and CF reinforced composites provide higher stiffness and strength but suppress shape-memory functionality. Extending beyond material development, architected shape-memory polymer meta-composites with honeycomb, honeycomb-circle hybrid, and auxetic geometries were fabricated via 4D printing. They demonstrated shape-recovery, force-regulating behavior and high energy absorption/dissipation under compression. These results establish BC/CNT-reinforced PA12 as a more sustainable and multifunctional alternative to conventional fibre-reinforced systems for advanced additive manufacturing applications.