School of Materials Science and Engineering, Sun Yat-sen University, Guangzhou 510275, China.
Ningbo Key Lab of Polymer Materials, Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, Ningbo 315201, China.
Molecules. 2022 Dec 15;27(24):8911. doi: 10.3390/molecules27248911.
High-hardness thermoplastic polyurethane (HD-TPU) presents a high matrix modulus, low-temperature durability, and remarkable abrasion resistance, and has been used in many advanced applications. However, the fabrication of microcellular HD-TPU foam is rarely reported in the literature. In this study, the foaming behavior of HD-TPU with a hardness of 75D was investigated via a pressure-quenching foaming process using CO as a blowing agent. Microcellular HD-TPU foam with a maximum expansion ratio of 3.9-fold, a cell size of 25.9 μm, and cell density of 7.8 × 10 cells/cm was prepared, where a high optimum foaming temperature of about 170 °C had to be applied with the aim of softening the polymer's matrix modulus. However, the foaming behavior of HD-TPU deteriorated when the foaming temperature further increased to 180 °C, characterized by the presence of coalesced cells, microcracks, and a high foam density of 1.0 g/cm even though the crystal domains still existed within the matrix. The cell morphology evolution of HD-TPU foam was investigated by adjusting the saturation time, and an obvious degradation occurred during the high-temperature saturation process. A cell growth mechanism of HD-TPU foams in degradation environments was proposed to explain this phenomenon based on the gas escape through the defective matrix.
高硬度热塑性聚氨酯（HD-TPU）具有高基体模量、耐低温和耐磨性好等特点，已被广泛应用于许多先进领域。然而，高硬度 TPU 微孔发泡的研究鲜有报道。本研究采用 CO2 作为发泡剂，通过压力淬火发泡法制备了邵氏硬度为 75D 的 HD-TPU 微孔发泡材料，最大倍率为 3.9 倍，泡孔尺寸为 25.9μm，泡孔密度为 7.8×106 个/cm3。为了降低聚合物基体模量，需要采用较高的最佳发泡温度（约 170℃）。然而，当发泡温度进一步升高到 180℃时，发泡行为恶化，出现泡孔合并、微裂纹和较高的泡沫密度（1.0g/cm3），尽管基体中仍存在结晶区。通过调整饱和时间研究了 HD-TPU 泡沫的细胞形态演变，在高温饱和过程中出现明显的降解。基于缺陷基体中的气体逸出，提出了 HD-TPU 泡沫在降解环境中生长的机理。
