Relating laboratory and outdoor exposure of coatings: II

Effects of relative humidity on photodegradation and the apparent quantum yield of acrylic-melamine coatings
  • Tinh Nguyen
  • Jonathan Martin
  • Eric Byrd
  • Ned Embree
Technical Articles


The effect of relative humidity (RH) from ≪1% to 90% on the photodegradation and quantum efficiency for a partially-methylated melamine acrylic coating exposed to UV/50°C condition has been investigated. The UV source is supplied by two 1000 W Xenon arc solar simulators and the relative humidities are provided by specially designed humidity generators, which control relative humidity in the 0 to 90% range to within <3% of the measured values. Radiation absorbed in the coating and degradation of the films are measured by UV-visible and Fourier transform infrared spectroscopies, respectively. The degradation at a particular RH/UV condition consists of four different modes: reactions taken place during post curing, hydrolysis due to water in the film at a particular RH, photodegradation, and moisture-enhanced photodegradation. Total degradation, hydrolysis, and moisture-enhanced photodegradation increase with increasing RH. At low relative humidities, photodegradation is an important degradation mode but hydrolysis dominates the degradation at high RH levels. Moisture in the film is found to increase the quantum efficiency of acrylic melamine coating photodegradation.


Melamine Coating Technology Outdoor Exposure Relative Humidity Level Apparent Quantum Yield 
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Copyright information

© Springer Science+Business Media 2002

Authors and Affiliations

  • Tinh Nguyen
    • 1
  • Jonathan Martin
    • 1
  • Eric Byrd
    • 1
  • Ned Embree
    • 1
  1. 1.National Institute of Standards and TechnologyUSA

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