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Accelerated Weathering Tests for Sealants Presentation

June 7, 2011

The AAMA Sealants for Installation Task Group met on June 6 at the National Summer Conference, with Norma Searle, Ph.D. presenting on accelerated weathering tests for sealants.

Attention was paid to prime weathering factors such as spectral emission of the radiation source, absorption of the incident wavelengths by materials, wavelength sensitivities of the material to the absorbed wavelengths, and the effects of temperature, moisture or other weathering factors on processes initiated by the absorbed wavelengths.

Searle went into great detail regarding the following eight fundamental principles in the weathering of materials:

  1. Only wavelengths absorbed by a material can cause damage.
  2. Materials differ in the wavelengths they can absorb.
  3. The wavelengths absorbed are determined by the relation between the absorption properties of the material and the wavelengths emitted by the source.
  4. The shorter the wavelength the higher the energy, and thus the greater its ability to break the stronger chemical bonds.
  5. Degradation is initiated by bond breakage. The bonds broken depend on the strength of the bonds in relation to the wavelengths absorbed.
  6. The number of bonds broken increase with the intensities of the absorbed wavelengths responsible for bond breakage.
  7. The extent of degradation is determined by the number of bonds broken and subsequent reactions promoted by heat, moisture, the presence of oxygen and other weather factors as well as by mechanical movements during exposure.
  8. Mechanisms of degradation and type of failure are determined by the type of bonds broken and the secondary reactions that follow. Therefore, the mechanism and type of degradation will often vary with the type of light source used for the exposure. 

The discussion included weathering related to AAMA’s finishes standards for vinyl, fiberglass and aluminum. In order to predict the service life of a material, Searle believes it is important to identify an unacceptable product, compare stabilities of products and maintain quality control.

To view Searle's presentation and others from the Summer Conference, visit the Members Only section of the AAMA website.

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