Colored polymer microparticles through carbon dioxide-assisted dyeing

A new procedure is described for dyeing polymer beads using liquid carbon d ioxide as a plasticizer to facilitate transport; of dye into the particle p hase. Aqueous latexes consisting of monodisperse polystyrene particles with surface-grafted poly(N-vinylpyrrolidone) were dyed with Sudan Red 7B using CO2 at 25 degrees C and 310 bar. Adding CO2 to the headspace above the lat ex resulted in some dyeing of the polymer, but better results were obtained by forming an emulsion of CO2 in the aqueous latex phase. Emulsions were f ormed with both a fluorinated and a hydrocarbon-based surfactant. It was fo und that the carbon dioxide emulsion greatly enhances the transfer of dye i nto the polystyrene without altering the size or morphology of the particle s.