Shelf-Stable Bingham Plastic Polyurethane Thermosets for Additive Manufacturing

This study presents an innovative three-dimensional (3D) printing method for fabricating hybrid-hardness polyurethane (PU) thermosets via direct-ink writing (DIW). This method features an unprecedentedly long pot life of at least 16 months for uncured material, achieved by employing internally blocked polymeric uretdione as the isocyanate source. This innovation not only extends pot life but also broadens the preprint processing temperature range. Surface-modified fumed silica, used as a rheology modifier, ensures the maintenance of the Bingham fluid characteristics. Rigorous evaluations, including differential scanning calorimetry (DSC), tensile tests, scanning electron microscopy (SEM), optical microscopy (OM), and micro-computed tomography (μ-CT), verify the material's uniform and nearly isotropic structure, devoid of defects. Dynamic mechanical analysis (DMA) reveals that these 3D-printed PUs withstand processing temperatures up to 240 °C. The practical application of this technology is demonstrated through the successful 3D printing of a shoe sole, showcasing the ability to incorporate regions of varying hardness and highlighting the versatile property customization of this method.