Two‐step foaming process for fabrication of flexible polyurethane foam composites with spring‐like air‐layer structure

Abstract

Due to its exceptional mechanical properties, polyurethane (PU) foam has found wide application in various fields. Microcellular foaming not only reduces weight but also enhances the cushioning properties of PU. However, current foaming methods have limitations in improving performance. Therefore, this study aimed to construct spring‐like sandwich‐structured flexible PU foam composites (SFFCs). These composites were prepared using a two‐step foaming method, utilizing a precise amount of polyol and isocyanate as raw materials, at room temperature (28–35°C). In the preparation process, warp‐knitted spacer fabrics (WKSFs) with spring‐like structures were encapsulated in the middle layer, while the top and bottom layers consisted of PUF (flexible PU foam with different ring radius differences) formed through the foaming process of polyol and isocyanate. The study focused on investigating the influence of the ring radius difference (r = 1, 1.5, 2) and the two‐layer layout (staggered, diagonal, overlapping) of the WKSFs on the compression and cushioning properties. The experimental results revealed a significant improvement in the mechanical properties of the PU with the incorporation of WKSFs. Particularly noteworthy was the excellent cushioning performance exhibited by the two‐layer WKSFs sample, RPUS‐1, in the dynamic impact test. RPUS‐1 absorbed 94.3% of the energy and reduced the impact value to 3921 N, which is 848 N (17.7%) lower than that of PU foam. Furthermore, even after 20 cycles of compression testing, the SFFCs retained excellent compressive properties, with the compressive stress only decreasing from 0.34 to 0.19 MPa. In conclusion, this study expands the application of PU in cushioning, demonstrating their potential in providing improved cushioning properties.