Thermal Characterization of Virgin and Recycled PET

Significance of the topic

Recycled PET plays a critical role in reducing plastic waste, lowering greenhouse gas emissions, and advancing a circular economy by substituting virgin PET derived from fossil fuels. Its thermal properties directly impact processing and performance in fiber manufacturing, making their characterization essential for sustainable material development.

Objectives and Overview of the Study

This study compares the thermal behavior of virgin and recycled PET fibers. Using DSC and simultaneous TG/DTA analyses, it aims to elucidate differences in melting, crystallization, crystallinity changes with repeated heating, and thermal stability under inert and oxidative atmospheres.

Methodology and Instrumentation

Used Instrumentation:

• DSC-60 Plus differential scanning calorimeter with TAC-60i cooling attachment
• DTG-60 simultaneous thermogravimetric/differential thermal analyzer

Experimental Procedures:

• DSC Analysis: Samples (~4 mg) heated from 0 °C to 300 °C at 10 °C/min (first heating), cooled to 0 °C at –10 °C/min, then reheated to 300 °C (second heating).
• Repeated Heating: Six successive DSC heating–cooling cycles on virgin PET to assess crystallinity loss.
• TG/DTA Analysis: Samples (~4 mg) heated from 30 °C to 600 °C at 20 °C/min under nitrogen and air to evaluate decomposition behavior and residual mass.

Main Results and Discussion

• First heating DSC revealed lower melting temperature for recycled PET (≈247 °C) versus virgin PET (≈254 °C), attributed to isophthalic acid units from bottle-derived feedstock.
• Crystallization and second heating melting peaks differed between fiber types, indicating distinct thermal histories and recrystallization behavior.
• Repeated DSC cycles on virgin PET showed a linear decline in melting point, reflecting progressive reduction in crystallinity with each cycle.
• TG/DTA under nitrogen demonstrated similar onset of weight loss (~400 °C) but ~5.7 % difference in final residue between fibers; under air, overall residues matched but secondary decomposition stages varied.

Benefits and Practical Applications

• Thermal property data enable optimization of fiber processing parameters (temperature profiles, cooling rates) to enhance quality and performance.
• Insights support quality assurance in industrial manufacturing and inform control strategies for consistent product characteristics.
• Validation of recycled PET’s performance fosters its adoption in sustainable textile and packaging applications.

Future Trends and Opportunities

Advancements may include coupling thermal analysis with real-time process monitoring, exploring compatibilizers or nucleating agents to stabilize crystallinity, integrating life-cycle assessment for holistic sustainability evaluation, and applying machine-learning models to predict thermal behavior from compositional parameters.

Conclusion

The comparative thermal characterization of virgin and recycled PET fibers revealed key differences in melting, crystallization, and decomposition behaviors. Thermal history and repeated heating significantly influence crystallinity, providing actionable guidance for processing optimization and reinforcing the viability of recycled PET in high-performance and eco-friendly applications.

References

No explicit literature references were provided in the original text.