Measurement of UV-Degraded Polymer Materials Using a Thermal Analyzer

Importance of the Topic

Exposure to ultraviolet (UV) radiation leads to chemical and physical deterioration of polymer materials such as polypropylene and polyethylene. Monitoring these changes is crucial for ensuring long-term performance of plastic components used outdoors, in automotive, construction, and packaging industries.

Objectives and Study Overview

This study aims to characterize the effects of UV exposure on polypropylene (PP) and polyethylene (PE) using a combination of spectroscopic and thermal analysis. Key goals include:

• Assessing chemical structural changes via Fourier transform infrared spectroscopy (FTIR).
• Evaluating shifts in melting behavior and heat of fusion by differential scanning calorimetry (DSC).
• Tracking changes in decomposition onset and thermal stability with simultaneous thermogravimetric (TG) and differential thermal analysis (DTA).

Methodology and Instrumentation

Sample Preparation:

• Plate-like PP and PE specimens (~1 mm thickness) cut into 3 cm squares.
• Irradiation with UV light for 0, 50, 100, and 550 hours.
• Subsamples for DSC/DTG were further reduced to ~1 mm³ and weighed (~5–7 mg).

Experimental Conditions:

• DSC: DSC-60Plus with TAC-60i electric cooling, 20→200→20→200 °C at 10 °C/min under N₂.
• Simultaneous TG/DTA: DTG-60, room temperature to 600 °C at 10 °C/min under N₂.
• FTIR: Measurement of characteristic absorption bands (O–H, C=O, C–O–C) to monitor oxidation.

Main Results and Discussion

Polypropylene (PP):

• FTIR revealed increased intensity of O–H, C=O, and C–O–C bands with longer UV exposure, indicating oxidative degradation.
• DSC first and second heating cycles showed melting peak shifts from ~170 °C down to ~158 °C and broadening of the transition.
• TG/DTA data indicated decomposition onset decreasing from ~439 °C to ~425 °C as irradiation time increased.

Polyethylene (PE):

• FTIR changes were less pronounced than in PP, showing minor oxidation signals after prolonged exposure.
• DSC first heating peaks remained largely unchanged; second heating displayed subtle endotherm variations.
• TG curves demonstrated a slight drop in decomposition onset temperature from ~464 °C to ~460 °C.

Benefits and Practical Applications of the Method

• Non-destructive probing of surface versus bulk degradation without isolating layers.
• Complementary insights: FTIR identifies chemical oxidation, while DSC and TG quantify thermal property shifts.
• Applicable to quality control and service-life prediction of UV-exposed polymer products.

Future Trends and Potential Applications

• Integration of thermal and spectroscopic data with advanced data analytics and AI for predictive modelling.
• Development of in situ monitoring tools combining micro-FTIR imaging and micro-DSC for real-time degradation tracking.
• Expansion of spectral libraries and coupling with mechanical testing to correlate molecular changes with macroscopic performance.
• Use of accelerated weathering chambers and near-infrared precursors to refine lifetime estimates.

Conclusion

UV irradiation causes oxidative degradation in PP and PE, manifested by altered infrared absorption signals, lower melting points, broadened transitions, and reduced thermal stability. The combined use of FTIR, DSC, and TG/DTA provides a comprehensive toolkit for evaluating polymer deterioration, enabling informed material selection and durability assessment.

Reference

No specific literature references were provided in the source document.