Further studies of discoloration of EVA encapsulant in photovoltaic modules

Studies of discoloration of ethylene vinylacetate copolymer-based encapsulant in service-aged photovoltaic modules, reported in 1995, showed that conjugated C=C double bond formation due to deacetylation of vinyl acetate is not the cause of discoloration. It was concluded that the color is most likely due to the additive system. These conclusions have been substantiated by further results utilizing x-ray photoelectron spectroscopy, resonance-enhanced Raman spectroscopy, infrared spectroscopy, and by attempts to chemically react possible C=C double bonds. In addition, changes in additives have practically eliminated color in laboratory aging while the original formulation (A9918P) developed a deep amber color under the same conditions. The new studies have also demonstrated the presence of keto carbonyl C=O in discolored service-aged EVA encapsulant, which is believed to be due to oxidative degradation of the ethylene CH2-CH2 portion of EVA.