Investigation on self-healing, anti-fogging and anti-frosting performances of silica sol modified waterborne polyurethane coatings

Abstract

In this study, a series of silica sol modified polyurethane composite emulsions were fabricated via incorporating silica sol precursor into anionic silanol-terminated polyurethane emulsion, which was obtained via three steps, including (1) reacting excess hexamethylene diisocyanate (HDI) with polybutylene glycol (PBG), 2,2-dimethylhydroxypropionic acid (DMPA), bis(2-hydroxyethyl) disulfide (HEDS) in a stepwise process using dibutyltin diacetate (DBTA) as the catalyst, (2) neutralizing the resulting prepolymer with triethylamine and end-capping with 3-aminopropyltriethoxysilane (APTES), and (3) dispersing the resulting silanol-terminated polyurethane in water under stirring. The reaction products were characterized by fourier transform infrared (FT-IR) spectroscopy, hydrogen proton nuclear magnetic resonance (1H NMR) spectroscopy, Raman spectroscopy and permeation gel chromatography (GPC). The swelling degree and gel content analysis confirmed the formation of crosslinking network in the composite coatings formed after drying the composite emulsions. The self-healing performances of the coatings were investigated by differential scanning calorimetry (DSC), dynamic thermomechanical analysis (DMA), scanning electron microscopy (SEM) and tensile mechanical tests, and the anti-fogging and anti-frosting behaviors of the composite coatings were analyzed by UV–visible spectroscopy, reflectance spectroscopy, water contact angle test and optical photometry. Based on the measurements, the self-healing process, the anti-fogging and anti-frosting mechanism were discussed. At suitable amount of HEDS, this coating exhibited excellent self-healing performances with the self-healing efficiency up to 95.9 % because of the high moving ability of the chains. After self-healing, these coatings displayed the same anti-fogging and anti-frosting properties as those before self-healing. The silica sol component was found to increasing both the polar groups and crosslinking degree, endowing the composite coating with durable anti-fogging and anti-frosting properties.