Achieving Lightweight and High Shape Recovery EVA-Based Foams through Supercritical Nitrogen Induced Phase Structure Foaming

During the supercritical foaming process, regulation of the foaming behavior is an extremely challenging issue. In this study, polycaprolactone/ethylene vinyl acetate copolymer (PCL/EVA) blends were prepared by mechanical mixing and further foamed by supercritical nitrogen foaming. The precise control of the phase structure of the material was achieved through the adjustment of the blend components, and the mechanisms behind the foaming behavior were further revealed. Scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and mechanical properties were used to investigate the effect of the blend phase structure on the structure and properties of the foams. The results show that the PCL/EVA blend exhibits a sea-island structure with gradually increasing phase sizes at low PCL content (10-30 wt %). Upon increasing the PCL content to 40 wt %, the phase size further increases, tending to form a bicontinuous structure. With the increase of PCL addition, the expansion ratio of the foams was increased from 7.98 to 11.96, the vesicle density was increased from 1.36 × 10⁷ to 4.05 × 10⁷ cells/cm³, and the average cell size was decreased from 66.12 ± 16.35 to 46.44 ± 11.76 μm. The introduction of PCL into the EVA yielded foams with denser cells and a softer texture, which improved the compression permanent deformation (from 2.53 to 0.59%) and the compression resilience (from 95.5 to 96.93%) of the foams. This work provided a new avenue for regulating the foaming behavior of blends and the development of lightweight and high performances for foams.