Preparation and Performance of a Self-Produced High-Molecular-Weight Waterborne Epoxy–Acrylic Emulsion

Abstract

To improve the stability of waterborne epoxy–acrylic emulsions and their comprehensive properties, such as the chemical resistance of coatings, a new research idea is proposed in this paper. First, a series of high-molecular-weight epoxy resins were synthesized with epoxy resin E-51 and bisphenol A (BPA) using benzyl triphenyl phosphine bromide as the catalyst. Then, free-radical graft copolymerization was carried out between the epoxy resin and methacrylic acid (MAA), styrene (ST), and butyl acrylate (BA) using benzoyl peroxide (BPO) as the initiator. This method ensured that the epoxy groups were retained. Finally, the carboxylic acid groups were neutralized with N,N-dimethylethanolamine (DMEA), and a stable aqueous epoxy–acrylic emulsion was obtained by high-speed dispersion in deionized water. The effects of key factors such as temperature, time, the molecular weight and dosage of epoxy resin, the dosage of MAA, the dosage of BPO, and the neutralization degree of the synthesis of emulsions and coating film properties were mainly discussed. The molecular weight and molecular weight distribution of the epoxy resin were determined by gel permeation chromatography (GPC). The epoxy resin and its graft copolymer were analyzed and characterized by Fourier-transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). The particle size and distribution of the emulsions were tested by laser particle size analysis. The morphology of the emulsion particles was observed by transmission electron microscopy. The results showed that the acrylic monomers (MAA, ST, and BA) were grafted onto the epoxy resin. The graft copolymers showed higher glass transition temperatures compared with those of the pure epoxy resin. TGA showed that the graft copolymer started to decompose at a high temperature before the pure epoxy resin did, and the thermal stability was slightly reduced. The prepared emulsions with a particle size of 160 nm had a storage stability of more than one year and showed excellent dilution stability, mechanical stability, and freeze–thaw stability. The emulsions were coated and cured at 150 °C for 1 h with a pencil hardness of 5 H, an adhesion of grade 1, and a flexibility of 1 mm. The water resistance was >60 days, the salt water resistance was >30 days, the acid resistance was >10 days, and the alkali resistance was >5 days.