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The Influence of Glass-Transition Temperatures of Poly (Ethylene Terephthalate) Films on the Fading Behavior of Fluorescent Brightening Agents

Studies have been made of the dependence of the fading behavior of dispersed-type fluorescent brightening agents in poly (ethylene tetrephthalate) (PET) films on the temperature at which the films have been heat-set and dyed. A measure of the variation in the fading behavior can be given by parameter A, defined as k 2 (1st-order)ɛ/k 2' (2nd-order), as in Hida's equation. This constant decreases with increase in the temperatures of heat-setting and dyeing of PET films. And the rate of fading increases with increase in these temperatures. It is found that the physical state of adsorbed dye on PET films varies with these temperatures. The glass-transition temperatures Tg of heat-set PET films were measured. Tg decreases with increase in the heat-setting temperature. The values of parameter A are related to the difference between the dyeing temperature and Tg (T — Tg ), and so the physical state of adsorbed dye on PET films is considered to be governed by the segmental mobility of polymer chains during dyeing. The variation of the rate of fading and parameter A with the dyeing and heat-setting temperatures of PET films might be explained in terms of the additional free volume.