Poly(hexamethylene biguanide) (PHMB) is of interest as a bactericide for fabrics. It has affinity for cotton by reaction with the cellulosic carboxylate groups. In this study, the capacity of undyed cotton to absorb PHMB has been determined and compared with cotton dyed with anionic bis(monochlorotriazinyl) reactive dyes. When cotton is dyed with these dyes the absorption of PHMB increases, the dye providing sulphonic acid sites with which the PHMB can react. The reacted PHMB and the percentage fixation of reactive dye were determined and from this the concentration of sulphonic acid on the dyed fibre. In the case of cotton dyed with Procion Yellow H‐E4R, the dye increased the absorption of PHMB to approximately 1.45 mequiv. of biguanide per sulphonic acid group. For Procion Red H‐E3B and Navy H‐ER the figures were 1.18 and 1.00, respectively.

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A number of closely related dyes, each possessing a single β‐sulphatoethyl sulphonyl reactive group and a variable number of sulphonate residues, were prepared and their dyeing behaviour evaluated. As the level of sulphonation of the dyes increased, both fixation efficiency and build up on cotton were reduced. These observations were attributed to increased electrostatic repulsion, between dye and fibre, as the anionicity, or level of sulphonation, of the dyes was increased. In support of this, the build up of a monosulphonated dye with one reactive group, was as good as that of a market leading bireactive disulphonated dye.