Photostabilisation of the ‘‘wood-clearcoatings’’ systems with UV absorbers: correlation with their effect on the glass transition temperature.

The Search for Durable Exterior Clear Coatings for Wood

“…The same benzotriazole UVA used in these studies was also effective at inhibiting the cracking of a clear coating on grand fir and European oak panels exposed to accelerated weathering [56]. This positive effect was thought to be due to the ability of the UVA to modify the elasticity of the coating (Tg) and prevent it from becoming brittle when exposed to UV light and water [56]. UV absorbers are generally added at a level of 1% to 5% to stabilize clear coatings on wood used outdoors or a lower amount can be used if they are combined with a hindered amine light stabilizer (HALS) [57].…”

“…More recently, Forsthuber and Grüll found that the combination of a HALS and UVA was better at restricting the photodegradation of an acrylic clear coating on Norway spruce than a UVA on its own [59]. In contrast to most previous findings Aloui and co-workers found that a combination of HALS and UVA was no better than a UVA at improving the appearance or degree of cracking of a clear coating on oak, and the combination only improved the appearance of the coating on grand fir [56].…”

“…Furthermore, studies by Chang, Chou and co-workers demonstrated that addition of a benzotriazole UVA to clear coats can also decrease the discolouration of the underlying wood as well as that of the clear coat [52,53,55]. The same benzotriazole UVA used in these studies was also effective at inhibiting the cracking of a clear coating on grand fir and European oak panels exposed to accelerated weathering [56]. This positive effect was thought to be due to the ability of the UVA to modify the elasticity of the coating (Tg) and prevent it from becoming brittle when exposed to UV light and water [56].…”

“…The combination of the urethane and the pulverized fuel ash produced a stronger, less extensible film, that failed initially by chalking and then "through the usual mechanism of cracking and delamination of the coating film" [62]. In contrast to these observations, Aloui and co-workers found that transparent cerium or titanium oxide particles were not very effective at improving the performance of a clear coating on oak and grand fir [56], although, in accord with Boxall and co-workers [62], they observed that the inorganic particles reduced the flexibility of the coating [56]. In subsequent research, Aloui and co-workers found that transparent titanium dioxide and iron oxide particles, particularly the latter, were less effective than a UVA or a UVA/HALS combination at restricting the discolouration and cracking of a clear coating on grand fir and oak panels exposed to accelerated weathering [63].…”

Glass transition temperature: Basics and application in pharmaceutical sector

“…Polymers with both amorphous and crystalline region show all the three characteristics. [5] [2,5,10,11] Refractive index [12,13] Dynamic mechanical measurements [8,11] Specific heat measurements [8] Thermo mechanical analysis [11,14] Thermal expansion measurement [12] Micro-heat-transfer measurement [15] Isothermal compressibility [12] Heat capacity [12] Elastic modulus or hardness [12] Broad-line NMR [12,13] …”