The aggregation of triphenodioxazine reactive dyes in aqueous solution and on cellulosic and nylon substrates

Monomer¯dimer equilibriums of triphenodioxazine (TPDO) reactive dyes with vinylsulfone anchors (PVS-TPDO) and monochlorotriazine anchors (MCT-TPDO) were investigated in water, in aqueous organic solvent, and on a cellulosic substrate. The aggregation tendency of PVS-TPDO in water was promoted by the addition of neutral electrolyte and suppressed by that of 1-methyl-2-pyrrolidone (MP). The dimerization constants, K, for PVS-TPDO were estimated in water and in aqueous sodium chloride solution; PVS-TPDO showed also aggregation on a cellulosic substrate. The apparent value of K on dry cellulose was two orders of magnitude smaller than that in water, and was increased by about ten times by water. The aggregation of PVS-TPDO in aqueous sodium chloride solution was suppressed by the addition of both MP and poly(vinylpyrrolidone). Four TPDO dyes examined showed the same order of aggregation tendency on cellulosic and nylon substrates as that in aqueous solution.