Supercritical CO2 Forming of TPU Foam Materials:Correlations of Cell Structure,Hard Segment Structure,and Properties
This study meticulously prepared thermoplastic polyurethane elastomer(TPU)foam materials with diverse cell structures utilizing supercritical CO2 physical foaming technology and conducted an in-depth investigation of the systematic relationship between cell structure,hard segment chemical structure,and elastic properties.Through Fourier transform infrared spectroscopy(FTIR),proton nuclear magnetic resonance(1H-NMR),and scanning electron microscopy(SEM),the chemical and microscopic cellular structure characteristics of TPU were comprehensively revealed.Comparative analysis using differential scanning calorimetry(DSC)highlighted the thermal behavior differences between two TPU materials.In addition,the cyclic compression performance and resilience of TPU foam materials were meticulously evaluated and quantitatively analyzed using a universal testing machine and a rebound tester.The results indicate that cell size and density are primarily regulated by saturation pressure,while the expansion ratio is mainly dependent on the saturation temperature.As the saturation temperature increases,the cell size initially enlarges and then diminishes,though the temperature's impact on cell size is relatively limited.The compressive strength of TPU foam is inversely proportional to cell size,and compressive resilience increases as the cell size decreases.The compressive strength of the foam significantly decreases with an increase in the expansion ratio,while the compressive resilience initially rises and then diminishes with an increase in the expansion ratio.The symmetry of the TPU hard segment molecular structure significantly influences mechanical properties,resulting in a maximum increase of 160％and 82％in compressive strength and resilience,respectively,for H-TPU foam compared to M-TPU foam.The findings of this study not only provide insights into the impact of cell structure and hard segment chemical structure on the mechanical properties and resilience of TPU microcellular foaming materials but also offer a theoretical foundation for the industrial fabrication of TPU foam materials with superior performance,cost-effectiveness,and complex functionalities.
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