Investigating the effect of methacrylic acid on the properties of waterborne epoxy-acrylate core-shell emulsion, film and coating

Waterborne coating has recently become a trend in research, with extensive studies focusing on waterborne epoxy-acrylate (WEA) emulsion. However, the understanding of the role of methacrylic acid (MAA) in the core-shell structure, affecting film and coating performance, is still limited. Here, we investigate the effect of MAA addition on the properties of the WEA core-shell emulsion, film and coating. The WEA core-shell emulsion was synthesized through semi-continuous emulsion polymerization and subsequently cast into WEA film. Two types of crosslinking systems were established by introducing MAA to either the shell layer (interlayer crosslinking) or the core layer (intralayer crosslinking). The interlayer crosslinking provides a high crosslinking density (7.01 × 10−4 mol cm−3), involving the crosslinking of polymer chains between the core and shell layers. Consequently, the film has a compact structure and high modulus (489 MPa) but low elongation at break (3.20 %). Conversely, the intralayer crosslinking has a low crosslinking density (1.59 × 10−4 mol cm−3). Hence, the film has a loose structure and low modulus (0.38 MPa) but high elongation at break (225 %). This occurs because it involves crosslinking with the polymer chains within the same layer, resulting in reduced compatibility between the layers. The inclusion of MAA enhances the clarity in discerning two glass transition temperatures (Tg). Lastly, the stability (shelf-life) of the WEA emulsion remains unaffected by the MAA, with the decisive factor being the presence of the oxirane ring in the Epoxy (EP). We believe that this finding can significantly contribute to a better understanding of the role of MAA in crosslinking systems within WEA core-shell coatings for researchers.