Analytical approach to degradation structural changes of epoxy-dicyandiamide powder coating by accelerated weathering

Epoxy resin is used for the powder coatings of steel pipes, but paints containing epoxy resins may cause various structural changes, including methyl abstraction, depending on climatic conditions and ultraviolet ray intensity. Structural changes cause the deterioration of various properties. Herein, the degradation mechanism of weathering resistance was analyzed by monitoring molecular structure changes of bisphenol A diglycidyl ether (BADGE)-dicyandiamide (DDA)-cured coating films before and after the Weather-O-Meter test (accelerated weather resistance chamber). DSC(Differential scanning calorimetry), GPC (Gel permeation chromatography), FT-IR(Fourier-transform Infrared spectroscopy), FT-NMR(Fourier-transform nuclear magnetic resonance), and MALDI-TOF MS(Matrix-assisted laser desorption ionization time-of-flight mass spectroscopy) analyses were performed on coated specimens. Structural changes, including epoxy resin oxidation and cross-linking bond breakage, were confirmed while the chain cleavage and crosslinking occurred simultaneously.