Desktop printing of 3D thermoplastic polyurethane parts with enhanced mechanical performance using filaments with varying stiffness

3D printing polymers via fused filament fabrication (FFF) exhibits significant advantages such as low cost and high efficiency, thus FFF has become one of the most popular production methods in the 3D printing field. For a printing using a soft filament feedstock, it is important to understand how to optimize its fabrication process when attempting to improve the packing morphology of deposited melt strand and thus enhance the mechanical performance. This work intends to be a step forward obtaining a strategy for high-quality FFF printing without compromising printing efficiency for those filaments with low stiffness as well as low feeding stress. Using a commercial desktop printer, a facile method to reduce the porosity of FFF-printed thermoplastic polyurethane (TPU) parts was proposed by controlling printing parameters using specific TPU filaments with varying hardness. Tensile strength and tear resistance of the printed parts were measured to assess the optimization printing (OP) strategy. Owing to the significant reduction of porosity, less thermal degradation and higher molecular orientation in FFF, the tensile strength and tear resistance of the OP-printed parts were approximately 95% and 126.8% of those of parts fabricated via injection molding, respectively. Compared with the standard printing (SP) method, OP strategy was found to be effective in improving mechanical performance. The mechanism was then analyzed in terms of nozzle moving trajectory and filament loading ratio, with particular emphasis on feedstock in the continuity and stability of melt strand deposition. In addition, the correlation between residual porosity and mechanical performance of FFF-printed parts was established, providing direction for overcoming the practical limitations of FFF printing, thus paving a way to print high-quality elastomeric materials.