Approach to fabricating thermoplastic polyurethane blends and foams with tunable properties

Thermoplastic polyurcthane (TPU) has been widely used in many applications because of its broad property range. In this paper, twin screw extrusion was used to produce TPU blends with tunable properties; the foamed samples were produced by microcellular injection molding (a.k.a. MuCell). Multiple tests were performed to confirm the miscibility and tunability of the blends. Fourier transform infrared spectroscopy (FTIR) was used to verify the presence of soft and hard segments in the three blends. Differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA), combined with scanning electron microscopy (SEM), confirmed that soft and hard TPU were miscible at ratios of 2:1 and 1:2, but immiscible at a ratio of 1:1. Rigidity increased while the shape recovery rate decreased with increasing hard TPU content. The blend ratio influenced the foaming morphology as well as other mechanical properties of the foamed samples. Decomposition, as investigated by thermo- gravimetric analysis (TGA), and degradation, as measured in a phosphate buffered saline (PBS) solution, were also studied. It was found that TPU or blends with more hard segments decomposed and degraded faster.