MECHANISMS OF PHOTOLYTICALLY INDUCED DEGRADATION

The photolytic oxidation process--attack by sunlight--is perhaps the most widespread form of irreversible degradation in paint films, and is, in large part, responsible for the deterioration of their aesthetic and protective properties. This review considers the photo-oxidative degradation of organic coatings by light. The degradation of polymeric coating binders by ultraviolet (UV) light is a multistage process involving initiation, propagation, and termination phases. The two principal structural results of these degeneration processes are crosslinking and chain scission. Crosslinking tends to increase the hardness, strength, and modulus of the film while reducing its elongation at break. Chain scission leads to molecular weight reduction, depolymerization, reduced glass transition temperature, and loss of low molecular weight reaction products. These processes weaken the film, induce increased water sensitivity, and reduce its tensile strength. Specific degradation reaction pathways are discussed for polystyrene/butadiene copolymers, acrylates, melamine-crosslinked systems, polyurethanes, and epoxy coatings. The absorptive protection and the photolytic degradation of coating film binders containing entrained pigmentation is discussed in the next unit of the series.

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  • Supplemental Notes:
    • Page Range: pp 73, 75-78, 80, 82, 84-86
  • Corporate Authors:

    Technology Publishing Company

    2100 Wharton Street, Suite 310
    Pittsburgh, PA  United States  15203
  • Authors:
    • Hare, C H
  • Publication Date: 2000-3

Language

  • English

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Filing Info

  • Accession Number: 00790586
  • Record Type: Publication
  • Files: TRIS
  • Created Date: Apr 3 2000 12:00AM