Predictive models of poly(ethylene-terephthalate) film degradation under multi-factor accelerated weathering exposures

Abstract

Accelerated weathering exposures were performed on poly(ethylene-terephthalate) (PET) films. Longitudinal multi-level predictive models as a function of PET grades and exposure types were developed for the change in yellowness index (YI) and haze (%). Exposures with similar change in YI were modeled using a linear fixed-effects modeling approach. Due to the complex nature of haze formation, measurement uncertainty, and the differences in the samples’ responses, the change in haze (%) depended on individual samples’ responses and a linear mixed-effects modeling approach was used. When compared to fixed-effects models, the addition of random effects in the haze formation models significantly increased the variance explained. For both modeling approaches, diagnostic plots confirmed independence and homogeneity with normally distributed residual errors. Predictive R2 values for true prediction error and predictive power of the models demonstrated that the models were not subject to over-fitting. These models enable prediction under pre-defined exposure conditions for a given exposure time (or photo-dosage in case of UV light exposure). PET degradation under cyclic exposures combining UV light and condensing humidity is caused by photolytic and hydrolytic mechanisms causing yellowing and haze formation. Quantitative knowledge of these degradation pathways enable cross-correlation of these lab-based exposures with real-world conditions for service life prediction.

Radiation degradation and stability of PBAT: copolymer of aromatic and aliphatic esters

“…Broad absorption appears to be a superposition of several bands attributed to oxidation products. The shape of the spectrum is very similar to that one presented by Gok et al . for photodegraded PET.…”

“…These species cause yellowing of the polymer due to their strong absorbance and the characteristic long‐wavelength tail in the visible region. Usually, the proposed mechanism starts with hydroxylation of the terephthalic ring, which leads to conjugated aromatic systems through cumulative oxidation …”

Reciprocity and spectral effects of the degradation of poly(ethylene‐terephthalate) under accelerated weathering exposures

“…In this degradation science study, the epidemiological data science approach was applied in a laboratory‐based, randomized, longitudinal study design . Samples of unstabilized PET films (Dupont‐Teijin Melinex 454, 75 μm) were randomly assigned to exposure conditions and followed over time with repeated measurements.…”

Influence of UV stabilizers on the weathering of PETG and PCTT films

“…Introducing a high level of UV photostabilizers to polyester through a co‐extrusion process was found to be useful in making polymers highly resistant to weathering‐induced changes . It was shown that polymer longevity in outdoor applications can be enhanced by using UV photostabilizers based on benzoxazinone, triazines, hydroxybenzophenones, hydroxyphenyl benzotriazole and mixtures, quenchers, and radical scavengers . The chemical family and substituents play a key role in UV absorber properties and performance …”