Evaluation of different methods to quantify changes in near-infrared spectra of glass fibre reinforced and neat epoxy resin using the example of mechanical strain, moisture and UV radiation

Tesis Energía y Ambiente (maestría) - Instituto Tecnológico de Buenos Aires, Buenos Aires - Karlsruher Institut für Technologie, Karlsruhe, 2024 "Fibre reinforced polymers (FRP) used in outdoor applications are exposed to multiple stressors, including mechanical loads, UV radiation, and moisture. Accurately assessing and predicting their degradation is key to extending their service life, reducing resource consumption, and improving overall safety. This work investigates the changes in near-infrared spectral signatures of glass fibre reinforced polymer and neat epoxy resin samples subjected to tensile strain, UV exposure, and moisture absorption. Three evaluation methods are compared: Peak Shift Analysis, Partial Least Squares Regression combined with principal component analysis, and Two-Dimensional Correlation Spectroscopy. In the experimental procedure, a custom UV chamber and sample holder were developed to ensure reproducible exposure conditions, with NIR spectra recorded at regular intervals over extended periods. Complementary experiments were performed on samples exposed to mechanical strain and moisture absorption. Each evaluation method was then applied to identify spectral regions and absorption bands most sensitive to the imposed stressors. The results demonstrate that Peak Shift Analysis excels under controlled loading conditions, while PLSR identifies critical spectral regions influenced by various stressors. In contrast, 2D Correlation Spectroscopy struggles to provide clear mechanistic insights under complex, overlapping degradation processes. Future refinements in controlling environmental conditions, sample geometry, and exposure durations may further enhance the interpretability and reliability of these methods for assessing and predicting FRP degradation in real-world applications".