Solubility, Dispersion, and Carbon Adsorption of a Chromium Hydroxyazo Complex Dye in a Styrene-Butyl Methacrylate Copolymer

Abstract

Solid blends consisting of a chromium hydroxyazoaryl complex salt (T-37 dye), Cr[−OC10H6NNC6H3− (Cl)O−]2[NH4], in a styrene-butyl methacrylate copolymer containing carbon black powder were characterized to determine the bulk and interface concentrations of the salt and relate it to the contact charge. The salt has limited solubility both in styrene-co-butyl methacrylate copolymer and in organic solvents. It dissolves up to 1.67 μmol/g in the viscous polymer melt at 190 °C, and the dissolution rate is slow. Solid blends which contain the chromium complex salt in excess of this amount contain phase-separated aggregates of the salt and the size of the aggregates varies with the preparation conditions. The chromium complex salt also adsorbs on the surface of carbon black up to a monolayer coverage. The carbon efficiently extracts the salt out of THF and extracts it slowly out of the polymer melt. This class of compounds has been considered as additives to control the negative charge in polymers, and we also observe that the solid blends (as a 10 μm size powder) develop a negative charge on contact. The charge scales with the amount of chromium complex salt in the blend and further varies depending on the portion of the salt which is solubilized, aggregated, or adsorbed on carbon. The chromium complex salt which is adsorbed on carbon is not active for charging. A second chromium complex salt, TRH dye, was studied briefly and found to be ca. 70 times less soluble than the T-37 dye in organic solvents. This salt can be considered an insoluble material for all practical purposes. These results do not support the various reports in the literature that these salts are highly compatible with styrenic resins and that they must be present in a dispersion for effective charging. © 1991, American Chemical Society. All rights reserved.