Study on hydrophobic modification of starch-based foam with fumigating and spraying

To enhance water resistance of starch-based foam, based on the porous and irregular surface feature of foam, fumigating hexamethyldisilazane (HMDS) and spraying nano-SiO2/ethanol solution were utilized to enhance hydrophobic properties of the starch-based foam. Homemade starch-molded foams were used for hydrophobic modification studies, the results showed that fumigating HMDS can lead to the formation of "Si-O-C" bonds between HMDS and starch. Additionally, it can form more stable "Si-O-Si" bonds with nano-SiO2 in the original composites, which can better adhere to the surface of the starch foam to effectively create a waterproof barrier layer. On the basis of HMDS fumigation modification, hydrophobicity was significantly enhanced by further spraying of nano-SiO2/ethanol solution. When the mass ratio of nano-SiO2 to ethanol was 6:100, the combination of HMDS and nano-SiO2 was optimal, while making the roughness of the foam surface suitable, at which time, the contact angle reached 155 degrees, the maximum value under this system, indicating that the hydrophobicity was optimal. The fumigation and spraying method can evenly and comprehensively act on the surface of the porous and irregular starch-based foam, which facilitates the waterproof post-treatment process of the industrial application process and has strong practical significance.Highlights Fumigated with HMDS, the starch foam's exhibit some hydrophobic effect. Fumigation followed by spraying is effective in enhancing the hydrophobicity of starch foams. Both the fumigation method and the spray method are suitable for the post-treatment of hydrophobic of starch foams. Hydrophobic mechanism of sprayed nano-SiO2 solution. image