Skinless Polyphenylene Sulfide Foam with Enhanced Thermal Insulation Properties Fabricated by Constructing Aligned Gas Barrier Layers for Surface-Constrained sc-CO₂ Foaming

A solid skin layer inevitably forms on the foam surface for supercritical carbon dioxide (sc-CO 2 ) foaming technology, leading to deterioration of some inherent properties of polymeric foams. In this work, skinless polyphenylene sulfide (PPS) foam was fabricated with a surface-constrained sc-CO 2 foaming method by innovatively constructing aligned epoxy resin/ferromagnetic graphene oxide composites (EP/GO@Fe 3 O 4 ) as a CO 2 barrier layer under a magnetic field. Introduction of GO@Fe 3 O 4 and its ordered alignment led to an obvious decrease in the CO 2 permeability coefficient of the barrier layer, a significant increase of the CO 2 concentration in the PPS matrix, and a decrease of desorption diffusivity in the depressurization stage, suggesting that the composite layers effectively inhibited the escape of CO 2 dissolved in the matrix. Meanwhile, the strong interfacial interaction between the composite layer and the PPS matrix remarkably enhanced the heterogeneous nucleation of cells at the interface, resulting in elimination of the solid skin layer and formation of an obvious cellular structure on the foam surface. Moreover, by the alignment of GO@Fe 3 O 4 in EP, the CO 2 permeability coefficient of the barrier layer became much lower, and the cell density on the foam surface further increased with decreasing cell size, which was even higher than that of the cross section of foam, attributed to stronger heterogeneous nucleation at the interface than the homogeneous nucleation in the core region of the sample. As a result, the thermal conductivity of the skinless PPS foam reached as low as 0.0365 W/m·k, decreasing by 49.5% compared with that of regular PPS foam, showing a remarkable improvement in the thermal insulation properties of PPS foam. This work provided a novel and effective method for fabricating skinless PPS foam with enhanced thermal insulation properties.