Relating laboratory and outdoor exposure of coatingsIII. Effect of relative humidity on moisture-enhanced photolysis of acrylic-melamine coatings
Relating laboratory and outdoor exposure of coatingsIII. Effect of relative humidity on moisture-enhanced photolysis of acrylic-melamine coatings
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DOI：
10.1016/s0141-3910(02)00070-8
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发表时间：
2002
影响因子：
5.9
通讯作者：
T. Nguyen;Jon Martin;E. Byrd;Ned Embree
中科院分区：
文献类型：
--
作者：
T. Nguyen;Jon Martin;E. Byrd;Ned Embree
研究了相对湿度在≈0~90%范围内对部分甲基化三聚氰胺丙烯酸类聚合物涂料在紫外光(UV)/50℃条件下湿增强光解的影响。紫外线源是两个1000W的氙弧太阳模拟器，提供波长从270到800 nm的辐射。由干/湿混合空气湿度发生器提供五种不同的相对湿度水平。用傅里叶变换红外透射法测量了在不同的UV/RH条件下涂覆在CaF2衬底上的约10μm厚的涂层的降解行为。在特定相对湿度下，紫外光下的总降解包括四种模式：后固化过程中的反应、特定相对湿度下的暗水解、光解和MEP。实验的设计是为了测量MEP随RH的变化。MEP的速度和幅度均随相对湿度的增加而增大。丙烯酸-三聚氰胺交联损失和涂层氧化的MEP速率在暴露初期增加，然后趋于平稳，但丙烯酸聚合物链段的MEP裂解速率几乎不随时间变化。三聚氰胺-丙烯酸酯结构的两阶段降解归因于涂层的非均相微结构，增强降解的机理是基于水解生成的甲醛分子，它作为生色团吸收紫外光，加速光氧化。
The effects of relative humidity ranging from ≈0 to 90% on the moisture-enhanced photolysis (MEP) of a partially-methylated melamine acrylic polymer coating exposed to the ultraviolet (UV)/50 °C condition were investigated. The UV source was two 1000 W xenon arc solar simulators, which provided radiation with wavelengths from 270 to 800 nm. Five different relative humidity (RH) levels were supplied by dry air/moist air mixture humidity generators. Degradation of coating films approximately 10 μm thick applied to CaF2substrates exposed to different UV/RH conditions were measured by FTIR transmission spectroscopy using an auto-sampling device. The total degradation under UV at a particular RH consists of four modes: reactions during post curing, dark hydrolysis at a particular RH, photolysis, and MEP. Experiments were designed so that changes in MEP with RH were measured. Both the rates and magnitudes of the MEP increased with increasing RH. The MEP rates of the acrylic-melamine crosslink loss and coating oxidation increased during the early exposure stage then leveled off, but the MEP cleavage rates of the acrylic polymer segment were nearly constant with time. The two-stage degradation of melamine-acrylic structure is attributed to the heterogeneous microstructure of the coating, and the enhanced degradation is explained by a mechanism based on hydrolysis-generated formaldehyde molecules, which act as chromophores to absorb UV light and accelerate photo-oxidation.