Characterizing the weathering induced degradation of Poly(ethylene-terephthalate) using PARAFAC modeling of fluorescence spectra

Poly(ethylene-terephthalate) (PET) film is widely used in photovoltaic module backsheets, for its dielectric breakdown strength, and in applications requiring high optical clarity. PET degrades under exposure to ultraviolet (UV) irradiance, heat, and moisture, which leads to loss of optical clarity and performance properties. To study the weathering driven degradation of PET films, three grades of PET, including unstabilized and stabilized grades, were exposed to three types of accelerated weathering exposure. Fluorescence excitation-emission matrix (EEM) spectra were collected after predetermined exposure intervals. Parallel factor analysis (PARAFAC) was applied to the resulting spectra to decompose the fluorescence data into individual fluorophore components and monitor their relative concentrations over time. EEM-PARAFAC was used to identify and distinguish between the formation of monohydroxy-terephthalate and dihydroxy-terephthalate units in PET over time under the UV-light bearing accelerated exposures. The relative concentrations of these fluorophores were found to increase, while the relative concentration of the PARAFAC component assigned to PET was found to generally decrease. ATR-FTIR was used to support findings from EEM-PARAFAC. Results were also used to assess the impact of additives (UV stabilizer and TiO2) on degradation. •PET forms hydroxy-substituted terephthalate units under UV exposure.•A three component parallel factor analysis model can capture degradation phenomena.•Model interpretation reveals impact of composition and weathering parameters.•Parallel factor analysis results build upon previous PET degradation studies.