The investigation of TPU molecular structure regulation and supercritical fluid foaming behavior

The molecular structure of TPU plays a crucial role in the performance of supercritical fluid foaming, yet the regulation mechanism remains unclear. This study systematically investigates the effects of molecular structure regulation on foaming performance by varying the amounts of diols, triols, and soft segment content. Methods such as GPC, melt index testing, DSC, and SAXS were employed to analyze the foaming performance of different TPU structures in terms of melt strength, phase separation structure, and crystallization behavior. The results show that TPUs synthesized with PBA as the soft segment exhibit higher melt strength and a greater degree of phase separation, leading to a higher foaming expansion ratio and a wider foaming window. Introducing small-molecule triols to regulate the crosslinking degree of the soft segments results in increased melt strength and foaming expansion ratio, as well as a broader foaming window with higher crosslinking. As the soft segment content increases, the TPU soft segment phase interval broadens, causing a decrease in melt strength and foaming ratio but promoting an expansion of the foaming window. Overall, the study reveals that the regulation of TPU molecular structure significantly influences supercritical fluid foaming performance and provides valuable theoretical guidance for the process.