KINETIC MODEL OF LIGHT FADING OF DYES ON POLYMER FILM

Abstract

A kinetic model has been proposed to interpret the fading behavior of 1, 2-bis (benzoxazolyl) ethylene, a disperse dye type fluorescent brightening agent, on polymer film.Rate laws are derived on two assumptions that the fading reaction proceeds competitively through isomerization and dimerization reactions and that population of the dye in a hole in the film can be described by Poisson distribution. When one dye molecule is captured in a hole, only the isomerization occurs. On the other hand, when two or more molecules are captured in a hole, the dyes fade through isomerization and/or dimerization reactions.The derived rate laws are solved numerically by assuming the values of kinetic parameters and the number of holes (θ) in the polymer film. Comparison of the theoretical results with the observations suggests that, at high dyeing temperature, the number of holes in the film has to be small, and accordingly the apparent rate of dimerization is large.Characteristic fading curves and other experimental results are reasonably understood by the kinetic model.