Construction of robust siloxane coating for urea-formaldehyde foam and durable hydrophobic mechanism

Urea-formaldehyde (UF) foams with robust siloxane coating were successfully prepared by grafting 3-aminopropyl-terminated poly-(dimethylsiloxane) (APDMS) and using 1, 6-hexanediol diglycidyl ether (HDE) as the bridging molecule. Compared with pristine UF foam and UF-g-APDMS foam, after immersion in water for 7 days, the UF-g-HDE-APDMS foam showed higher durable hydrophobicity with lower water absorption ratio and more integral cell structure. Moreover, for UF-g-HDE-APDMS foam, a large amount of APMDS molecules were grafted uniformly and tightly both on the surface and inside of the foam via strong interfacial interactions promoted by HDE, which prevented the APDMS molecules from falling off UF matrix. Such robust APMDS layer can act as a barrier to retard the water, and thus higher water contact angle and lower sliding angle can be kept during long term immersion for the foam, which was beneficial for reducing the destruction of the cell walls and keeping its structural integrity.