Characterization of ethylene-based encapsulants and their degradation products after damp heat exposure by XPS
Sprache des Vortragstitels:
Polymer Meeting 15
Sprache des Tagungstitel:
Polymer meeting 15 in Bratislava
X-ray photoelectron spectroscopy (XPS) is a well-established technique for characterizing the surfaces of polymeric materials, which are of utmost importance for the encapsulation of photovoltaic modules. About 1 Mio tons of ethylene-vinyl acetate copolymer (EVA) is currently used for PV modules. Hence, high quality of EVA encapsulants as well as in-service reliability of EVA and upcoming less-polar substitution materials has to be ensured. A specific objective of this study was to assess the potential of XPS for elucidation of the copolymer structure of EVA. Therefore, well-defined EVA grades with different vinyl acetate (VA) comonomer content were characterized by XPS. Moreover, the XPS data were corroborated by Fourier-transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC). It was clearly shown that the VA content of EVA could be quantified by XPS in a highly reliable manner.
A further objective of this study was to elucidate the damp heat induced degradation mechanisms of various encapsulation materials in double glass modules. Therefore, EVA, polyolefin elastomer (POE) and thermoplastic polyolefin (TPO) double glass laminates were aged for up to 10,000h in an environmental chamber. The specimens were delaminated by compressive shear testing at 60°C. The fractured surfaces were investigated by XPS and FTIR. Degradation products were discernible after already 1000h of damp heat exposure. While EVA revealed Na acetate degradation products, Na carbonate was ascertained on the fractured POE surfaces. The XPS results indicated an accumulation of Na salts close to the interface of the polymeric encapsulant and low-iron solar glass.
Interestingly, less degradation products were confirmed on the fractured surface of TPO glass laminates, which failed in a more cohesive manner within the TPO encapsulant.