Non-destructive determination of the cross-linking degree of EVA by Raman Spectroscopy

Abstract

The gel content of photovoltaic module encapsulation Ethylene-vinyl acetate (EVA) is usually measured by the Soxhlet extraction method. Due to the destructive sample preparation, long turnaround times, hazardous solvents and the limited precision of results, an alternative crosslinking determination technique for the in-line process control is needed.The general capability of Raman spectroscopy as cross-linking determination method was investigated.EVA foils from two different manufactures were cured to different cross-linking degrees. Solvent extraction was used as reference technique. For the Raman spectroscopic investigation of the degree of cross-linking, residual peroxide peaks from the cross-linking agent in EVA were utilized. The intensity of the peroxide peaks appeared to be inversely correlated to the gel content.