Journal Article

Multivariate multiple regression models of poly(ethylene-terephthalate) film degradation under outdoor and multi-stressor accelerated weathering exposures

Bruckman, Laura S., Huang, Wei-Heng, French, Roger H., Burns, David M., Gordon, Devin A.

2018

Overview

Developing materials for use in photovoltaic (PV) systems requires knowledge of their performance over the warranted lifetime of the PV system. Poly(ethylene-terephthalate) (PET) is a critical component of PV module backsheets due to its dielectric properties and low cost. However, PET is susceptible to environmental stressors and degrades over time. Changes in the physical properties of nine PET grades were modeled after outdoor and accelerated weathering exposures to characterize the degradation process of PET and assess the influence of stabilizing additives and weathering factors. Multivariate multiple regression (MMR) models were developed to quantify changes in color, gloss, and haze of the materials. Natural splines were used to capture the non-linear relationship between predictors and responses. Model performance was evaluated via adjusted-R2 and root mean squared error values from leave-one-out cross validation analysis. All models described over 85% of the variation in the data with low relative error. Model coefficients were used to assess the influence of weathering stressors and material additives on the property changes of films. Photodose was found to be the primary degradation stressor and moisture was found to increase the degradation rate of PET. Direct moisture contact was found to impose more stress on the material than airbone moisture (humidity). Increasing the concentration of TiO2 was found to generally decrease the degradation rate of PET and mitigate hydrolytic degradation. MMR models were compared to physics-based models and agreement was found between the two modeling approaches. Cross-correlation of accelerated exposures to outdoor exposures was achieved via determination of cross-correlation scale factors. Cross-correlation revealed that direct moisture contact is a key factor for reliable accelerated weathering testing and provided a quantitative method to determine when accelerated exposure results can be made more aggressive to better approximate outdoor exposure conditions.

• Publisher: Public Library of Science,Public Library of Science (PLoS)
• Subject: Accelerated tests / Additives / Biodegradation / Chemical reactions / Coefficient of variation / Contact stresses / Correlation / Critical components / Cross correlation / Degradation / Dielectric properties / Earth Sciences / Electrical properties / Engineering / Environmental aspects / Environmental changes / Environmental stress / Error analysis / Ethylene / Exposure / Gloss / Haze / Humidity / Kinetics / Laboratories / Light / Longitudinal Studies / Materials science / Materials Testing / Models, Theoretical / Moisture / Multiple regression models / Multivariate Analysis / Photovoltaic cells / Photovoltaics / Physical properties / Physical Sciences / Polyethylene terephthalate / Polyethylene Terephthalates / Polymers / Random Allocation / Regression Analysis / Regression models / Solar cells / Splines / Titanium dioxide / Waste management / Weather / Weathering