Analysis of Artificially Weathered PET and a Separate PET Hydrolysis Evaluation Using the 4300 Handheld FTIR

Significance of the Topic

This study addresses the critical need for early detection of polymer degradation in photovoltaic applications. Environmental stressors such as light, heat, moisture, and electric fields initiate subtle chemical changes in PET that lead to cracking and physical failure over time. A rapid, non-destructive, on-site analytical method can greatly accelerate the optimization of additive formulations and support maintenance of installed solar panels.

Study Objectives and Overview

The primary goal was to demonstrate that the Agilent 4300 Handheld FTIR analyzer can detect early chemical alterations in PET exposed to accelerated weathering and hydrolysis. Key objectives included:

• Benchmarking additive-free PET response to xenon-arc simulated sunlight.
• Separately evaluating hydrolytic degradation under reflux in water.
• Developing multivariate calibration models to quantify equivalent aging time.

Methodology and Instrumentation

A two-part experimental approach was employed:

• Simulated weathering: Mitsubishi Hostaphan RNK 50 PET films (50 µm) were aged 0, 5, and 10 days in an Atlas XLS+ xenon arc weatherometer (700 W/m2, filter A, 40 °C).
• Hydrolysis: Identical PET films were refluxed in distilled water for 0, 3, 7, 10, and 14 days.
• FTIR analysis: Agilent 4300 Handheld FTIR with interchangeable diamond ATR and external reflectance interfaces. Spectra were acquired at 4 cm⁻¹ resolution, 64 co-adds, over 4,000–650 cm⁻¹.
• Data processing: Partial least squares regression with derivative preprocessing, MSC or SNV, built into MicroLab PC software. Mahalanobis distance used for sample validation.

Main Results and Discussion

The weathering experiment revealed:

• Emergence of oxidation bands at ~1,773 cm⁻¹ (peresters) and ~1,690 cm⁻¹ (aromatic acids), plus broad OH/C–O features at 1,450–1,150 cm⁻¹.
• ATR-based PLS model (five factors) achieved R² = 0.987 for predicting 0–10 days of exposure.
• External reflectance PLS (two factors) yielded similar correlation (R² ≈ 0.99), but ATR spectra offer greater interpretability and surface sensitivity (~2–3 µm depth).
• Bottom surface showed limited oxidation after 10 days, consistent with radical diffusion through the polymer matrix.

Hydrolysis findings:

• Submerged PET exhibited smaller spectral changes focused on aromatic ring vibrations.
• ATR-based PLS model (two factors) produced R² = 0.913 for 0–14 days of hydrolysis.
• Hydrolysis levels were grouped into low (0–3 days), medium (3–7 days), and high (>7 days) degradation categories.

Practical Benefits and Applications

The handheld FTIR approach offers:

• Non-destructive, on-site evaluation of polymer aging in large panels or coatings without sample removal.
• Rapid screening to eliminate suboptimal additive formulations, reducing development costs.
• Color-coded alerts via Mahalanobis distance for critical degradation notifications.
• Capability to assess both photo-oxidation and hydrolytic processes with a single instrument.

Future Trends and Applications

Potential directions include:

• Integration of cloud-based data analytics and predictive maintenance algorithms.
• Extension of handheld FTIR protocols to other polymers, paints, and industrial coatings.
• Development of more advanced chemometric models for multi-stressor environments.
• Miniaturization and ruggedization to support harsh field conditions.

Conclusion

The Agilent 4300 Handheld FTIR spectrometer effectively detects early chemical changes in PET under simulated weathering and hydrolysis. High-performance PLS models enable quantification of equivalent aging time, facilitating rapid optimization of additives and informing maintenance decisions for photovoltaic installations.

References

1. F. Higgins, “Non-Destructive Evaluation of Composite Thermal Damage with Agilent’s New Handheld 4300 FTIR,” Agilent Technologies, Application Note, 2014.
2. ISO 10640:2011(E), Plastics – Methodology for assessing polymer photoageing by FTIR and UV/Visible spectroscopy.
3. S. Junkichi, “Radical Migration as an elementary process in degradation,” Pure & Appl. Chem., Vol. 55, No. 10, 1983.
4. W.J. Brennan, S.J. Shepherd, “Developments in Weatherable Polyester Films For Photovoltaic Applications,” DuPont Teijin Films, 2011.