Bleed fastness of fluorescent whitening agents in mass whitened paper

Paper samples mass whitened with fluorescent whiteing agents (FWAs) of three different types (di-, tetra-, and hexasulfonated derivatives of 4,4'-diaminostilbene-2,2'-disulfonic acid) were examined for bleed fastness in five different eluents. Fluorescece intensity was measured by a sensitive spectrofluorimetric technique instead of the usual visual assessment. The degree of bleed obtained from each of the FWAs tested was less than 0.4mg/600 cm2 of paper surface area. The FWAs were applied at a normal concentration of use i.e. 0.05% active substance. FWAs with a high degree of sulfonation tend to bleed in aqueous solvents, and those with a lower degree of sulfonation in alcohol solutions. In aqueous acid solutions the degree of bleed was very low in all cases (0.04 mg/600 cm2 of paper surface area). In fatty solutions there was no bleed at all. The limit of detection was 3mug/600 cm2 of paper surface area, with an accuracy of +/-15%.