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

Abstract

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.

Unexpected Susceptibility of Poly(ethylene furanoate) to UV Irradiation: A Warning Light for Furandicarboxylic Acid?

“…Another possible explanation can be found in the removal of the titanium isopropoxide catalyst by precipitation. Slow hydrolysis of this catalyst could lead to the formation of photochemically active titanium dioxide (TiO 2 ) species. , Note that for PET addition of TiO 2 has also been shown to have a beneficial effect on weathering stability. − It is widely believed that polymer dissolution/precipitation results in removal of the polymerization catalyst, and as such it was expected that the precipitated PEF would be virtually free of residual titanium species. However, ICP-MS analyses showed that there is no significant difference in titanium concentration between the reactor grade and precipitated PEF and PET (Table S3), and thus an effect of residual titanium is unlikely.…”

How prenatal cortisol levels relate to grandmother‐mother relationships among a cohort of Latina women

“…MMR modeling was chosen because it facilitates more than one outcome variable to be regressed onto the same set of predictors (Breiman & Friedman, 1997). MMR balances goodness of fit with interpretability because it provides coefficients that reflect the contribution of each term in the model (Gordon et al, 2018). Each MMR model assessed how a domain of grandmother allocare was correlated with Aim 1 outcomes (the 4 domains of mental health) and the Aim 2 outcome, cortisol.…”

Transformative Opportunities from Data Science and Big Data Analytics: Applied to Photovoltaics

“…21,22 PET studied under both outdoor and accelerated lab-based exposure conditions show not just different stages of degradation, but also the synergistic effects of combined stressors since moisture as dew is an important stressor along with temperature and irradiance. 23 In PET degradation, the presence of water leads to synergistic photo-hydrolytic degradation in outdoor exposures, beyond photolytic degradation; simple exposure to humidity alone does not induce this photo-hydrolytic degradation. 21 This is an example where combined effects in a material or complex system are not simply additive, and cannot be studied "one at a time, in isolation" as a hallmark of the scientific method (controlling all other variables when studying the one of interest).…”