UV-visible technique for studying powder coatings and their dissolution

Abstract

UV-Visible (UVV) technique used to monitor powder coating and its dissolution processes from hard latex particles. Three sets of latex coatings were prepared from poly(methyl methacrylate) (PMMA) particles. The first set of coatings was annealed at elevated temperatures in various time intervals during which reflected photon intensity, Irf, was measured. The second set of coatings was annealed at various temperatures in 10 min time intervals during which transmitted intensity, Itr, was measured. Irf first decreased and then increased as the annealing temperature was increased. Decrease in Irf was explained with the void closure mechanism due to viscous flow. Increase in Itr and Irf against time and temperature were attributed to an increase in crossing density at the junction surface. The activation energy of viscous flow, ΔH, was measured and found to be around 8 kcal/mol and the back and forth activation energies (ΔErf and ΔEtr) were measured and found to be around 49 and 53 kcal/mol for a reptating polymer chain across the junction surface. Diffusion of solvent molecules (chloroform) into the annealed latex coatings was followed by desorption of PMMA chains for the third set of films. Desorption of pyrene, P, labeled PMMA chains was monitored in real-time by the absorbance change of pyrene in the polymer-solvent mixture. A diffusion model with a moving boundary was employed to quantify real-time UVV data. Diffusion coefficients of desorbed PMMA chains were measured and found to be between 2 and 0.6 × 10−11 cm2 s−1 in the 100 and 275°C temperature range.