Fluorescent Whitening Agents

Wool fabrics can be whitened by treatment with a solution containing both a fluorescent whitening agent and a polymer. After drying, this leads to the distribution of the whitener in a polymer film which surrounds the fibers, Many whitener/ polymer systems lead to good whitening, but few provide white wool of satisfactory stability to light. The nature of the polymer, as well as that of the whitener, influences the photostability of the surface-whitened fabric. The most light- stable systems give surface-whitened fabrics which yellow in simulated sunlight less rapidly than conventionally-whitened fabrics, the difference being very pronounced for exposure in the wet state. This result is attributed to the fact that whiteners cannot sensitize the photoyellowing of wool if insulated from the fiber in a polymer film. Most whitener/ polymer systems give a whitening effect which is durable to laundering but not to drycleaning. However, durability to drycleaning (as well as to laundering) can be achieved by using reactive whitener/polymer systems in which the whitener is covalently linked to a polymer which can be crosslinked at a later stage.