Colored Polymer Microparticles through Carbon Dioxide-Assisted Dyeing

A new procedure is described for dyeing polymer beads using liquid carbon dioxide as a plasticizer to facilitate transport of dye into the particle phase. Aqueous latexes consisting of monodisperse polystyrene particles with surface-grafted poly( N -vinylpyrrolidone) were dyed with Sudan Red 7B using CO 2 at 25 °C and 310 bar. Adding CO 2 to the headspace above the latex resulted in some dyeing of the polymer, but better results were obtained by forming an emulsion of CO 2 in the aqueous latex phase. Emulsions were formed with both a fluorinated and a hydrocarbon-based surfactant. It was found that the carbon dioxide emulsion greatly enhances the transfer of dye into the polystyrene without altering the size or morphology of the particles.