Facile fabrication of EVA cellular material with hydrophobic surface, high solar reflectance and low thermal conductivity via chemical foaming

Recently, cellular materials grasp researchers’ attention for the high solar reflectance performance. However, studies on the construction of hydrophobic surface and solar reflectance based on the closed cell structure obtained by azodicarbonamide (AC) foaming are still insufficient. In this work, a series of ethylene-vinyl acetate copolymer (EVA) cellular materials with different foaming ratios were fabricated by chemical foaming. By increasing the weight content of foaming agent AC from 0 to 12 phr, the apparent density of samples reduced from 0.935 to 0.045 g/cm³, while the closed cell size expanded from 0 to 169.49 μm. In contrast with pristine EVA resin, the water contact angle on the internal surface of EVA-AC12 (the sample with AC weight content of 12 phr) enhanced to 145°. Simultaneously, EVA-AC12 possessed the high near infrared reflectance of 80.5% and low thermal conductivity of 0.04 W/m·K, resulting in an excellent passive cooling effect of 18.6 °C than pristine EVA resin. Moreover, the as-prepared EVA cellular material has great mechanical properties. In summary, the EVA soft cellular material with a hydrophobic surface fabricated in this work can be used as self-cleaning passive cooling material.