Environmentally Friendly and Zero-Formamide EVA/LDPE Microcellular Foams via Supercritical Carbon Dioxide Solid Foaming

Elastomeric polyolefin foams with excellent mechanical properties, environmentally friendly performance, and cost effectiveness are highly promising. Nevertheless, it is a huge challenge to obtain these advantages in elastomeric polyolefin foams using chemical or common physical blowing agents. Therefore, a strategy was applied to the ethylene–vinyl acetate copolymer (EVA)/low-density polyethylene (LDPE) (EVA/LDPE) system by combining crosslinking, microphase separation, crystallization, and supercritical CO2 (scCO2) solid foaming. Consequently, environmentally friendly EVA/LDPE foams of zero formamide with the desired uniform cellular structure of expansion ratio over 8, average cell size less than 50 μm, and cell density over 109 #/cm3 were obtained. The lightweight EVA/LDPE foams show excellent tensile strength and compression strength, much higher than those of other elastomeric polyolefin foams. The reasons for this are that (1) the introduction of crosslinking and entanglement structures in EVA enhances the viscoelasticity, which is beneficial to bubble nucleation and bubble stability in the foam, and simultaneously improves the mechanical properties of the foam; (2) the existence of LDPE segments in EVA leads to microphase separation, which is beneficial to bubble nucleation; (3) low-temperature solid foaming enhances the mechanical properties of the foam due to the uniform microcellular structure; and (4) scCO2 foaming has zero formamide, which meets the safety requirements and specifications of children's floor mats (T/CTJPA 005-2018).