Comparison of photostabilization in acrylic/urethane and acrylic/melamine coatings containing hindered amines and ultraviolet absorbers

Abstract

The photostabilization chemistry of a two-package acrylic/urethane coating containing a benzotriazole UV absorber and/or a hindered amine light stabilizer has been studied by using FTIR and ESR. FTIR has been used to follow the rate of chemical change on exposure of the coatings to UV light and humidity. The coatings are found to undergo photooxidation and loss of urethane cross-links during exposure. In contrast to melamine cross-linked coatings, humidity plays only a minor role in the degradation of the urethane coating. The addition of a benzotriazole UV absorber reduces the rate of degradation by reducing the rate of formation of free radicals. The addition of hindered amine greatly reduces the rate of oxidation and urethane loss. The hindered amine is significantly more effective in the urethane coating than in similar melamine coatings. ESR measurements of nitroxide concentrations in hindered amine containing coatings reflect the differences in stabilization chemistry. In addition to being more effective, the effective life of the hindered amine stabilizer is also longer in the urethane than in the melamine coating.

Effect of TiO2 pigment type on the UV degradation of filled coatings

“…This general degradation behavior of the EP films is consistent with that reported in the literature. 13,14 The decrease in IR absorbance after 28 days is due to degradation and chalking of the specimens and affects the accuracy of the ATR-FTIR measurements. It is interesting to note that these ATR-FTIR results show that different pigments influence the degradation rate; that is the C-H stretch absorbance data show Pigment H results in the most change, whereas the C=O stretch absorbance data indicate Pigment L results in the most oxidation.…”

Photo-oxidation of acrylic-urethane thermoset networks. Relating materials properties to changes of chemical structure

“…Prolonged UV light exposure results in significant photo-degradation of acrylic-urethane thermosets, ultimately leading the system to fail. This degradation has mainly been characterised using spectroscopic analysis [7,8], and the photochemical weakness has been shown to arise from the urethane linkage [9,10].…”

Ultraviolet-Curable Cycloaliphatic Polyesters Containing Spiroacetal Moieties for Application as Powder Coatings

“…If the T g of the resin is too low, the powder particles can undergo “cold flow” and agglomerate into an unusable mass. Unfortunately, because aromatic groups are strong ultraviolet (UV)-light absorbers, many powder coatings are prone to photo-oxidative degradation. − The absorption of UV-light accelerates the photo-oxidation process, which results in yellowing and degradation of the polymeric binder when used in outdoor applications. ,,− To offset the mediocre UV-resistance of these resins, formulators typically incorporate additives into the coating such as light stabilizers and UV absorbers to minimize photoinduced degradation. − Unfortunately, these additives do not perform indefinitely, can be fairly expensive, and because many of these additives are nonreactive, can migrate out of the film over time.…”