Abstract:

Foaming materials with gradient structure are widely studied due to their innovative structural design and potential multifunctionality. In this work, thermoplastic polyurethane (TPU) was used as the research object. High-ratio TPU foaming materials with gradient cell structure were prepared by primary temperature rising foaming and secondary depressurization foaming, and the influence mechanism of foaming conditions was explored. Microscopic morphology characterization showed that when the foaming time is relatively short, gradient foaming materials with larger cell sizes on both sides and smaller cell sizes in the middle can be prepared due to the temperature gradient existing in the polymer matrix. As the foaming time is prolonged, uniform foaming materials would be prepared due to the reduction of temperature difference. The mechanical properties of TPU foaming materials are tested. The results show that the energy loss coefficient of the gradient foaming materials is slightly higher compared with the uniform foaming materials. However, the relative difference between the two decreases with the increase in foaming expansion ratio. Moreover, the gradient foaming materials have lower hardness and higher resilience rate, demonstrating excellent cushioning performance and resilience at high foaming expansion ratios. This paper provides theoretical basis and practical guidance for optimizing the preparation process of TPU foaming materials and is of great significance for the realization of high-performance and lightweight development of TPU.

Key words: temperature rising foaming, cell structure, thermoplastic polyurethane elastomer, supercritical fluid, mechanical property, polymer processing, foam

摘要：

具有梯度结构的发泡材料因创新结构设计和潜在多功能性受广泛研究。本工作以热塑性聚氨酯（TPU）为研究对象，通过一次升温发泡与二次卸压发泡制备了具有梯度泡孔结构的高倍率TPU发泡材料，并且探究了发泡条件影响机制。微观形貌表征显示，当发泡时间较短时，因基体中存在的温度梯度，可制得两侧孔径大、中间孔径小的梯度发泡材料，延长发泡时间则因温差降低制备出均匀发泡材料。力学性能测试结果表明，相较于均匀发泡材料，梯度发泡材料能量损失系数略高，但两者的相对差值随着发泡倍率的增高而降低，且具有更高的回弹率和更低的硬度，展现出高发泡倍率下优异的缓冲性能和回弹性。这为优化TPU发泡材料制备工艺提供了理论基础和实践指导，对TPU实现高性能、轻量化发展具有重要作用。

关键词: 升温发泡, 泡孔结构, 热塑性聚氨酯弹性体, 超临界流体, 力学性能, 聚合物加工, 泡沫