ADSORPTION OF WHITENING AGENTS ON CELLULOSE FIBERS - MONITORED BY STREAMING POTENTIAL MEASUREMENTS, CALORIMETRY AND FLUORESCENCE

Fluorescent whitening agents (FWA) are used to improve the whiteness o f cellulose fabrics. It is well known but not completely understood th at the fluorescence decreases (chemical and physical mechanisms of dis tinguishing) above a certain FWA concentration c(crit). This reduction of fluorescence correlates very well with the alteration of the adsor ption process studied by calorimetry and zeta potential measurements. The results obtained by these methods indicate that the adsorption mec hanism is different at concentrations below and above c(crit). The red uction of the intensity of fluorescence, the degree of whiteness and t he zeta potential are caused by the adsorption of a second layer of fl uorescent whitening agents. This second layer reduces the zeta potenti al due to a shielding effect and reduces the whiteness and fluorescenc e by a bathochromic shift of the reflection curves. The final effect i s a reduction of the total reflection.