Some aspects of film formation from pigmented latex systems

Film formation from pigmented latex systems consisting of soft (i.e., low T_g) poly(n-butyl methacrylate-co- n-butyl acrylate) [P(BMA/BA)] latex particles and ground calcium carbonate (GCC) pigment particles were studied with an emphasis on the synthesis of functionalized model latex particles and the influence of the carboxyl groups present on the latex particles on the drying kinetics, film surface properties, bulk morphology, and the mechanical properties of the film. A theoretical model was developed, to calculate the maximum (co)monomer feed rate for maintaining a highly monomer-starved condition in semi-continuous emulsion polymerization processes, to synthesize monodisperse carboxylated and non-carboxylated model latex particles and independently control the particle size and degree of carboxylation. The presence of carboxyl groups on the latex particles was found to facilitate the drying rates of the latex/pigment blend films. The carboxyl groups on the latex particles lead to smaller pigment aggregate size in the film and a more even size distribution in the polymer matrix. With higher carboxyl group surface coverage on latex particles, the resulting blend films have a higher surface gloss which indicates a smoother film surface. The presence of carboxyl groups on the latex particles significantly enhanced the Young's modulus and the yield strength of the latex/pigment blend films. Ionic interactions between neutralized carboxyl groups themselves and between neutralized carboxyl groups and pigment particles were proposed to explain these phenomena. A quantitative model was proposed to predict the Young's modulus of the latex/pigment blend films as a function of the carboxyl group coverage on the latex particles. There was a good agreement between the model and the experimental data.