Multifaceted Evaluation of Changes in Physical Properties of Recycled Plastics by Advanced Recycling Process and Influencing Microstructural Changes (Part 2): Example of Application to Simulated Degraded Polypropylene

Importance of Topic

The rapidly growing volume of plastic waste presents a major environmental and economic challenge. Advanced recycling processes that restore or enhance the mechanical and thermal properties of polymers are critical for creating sustainable circular economies. Multifaceted analytical techniques enable a comprehensive understanding of how novel recycling treatments affect polymer microstructure and bulk performance.

Study Objectives and Overview

This application note investigates the effect of an advanced recycling process on simulated degraded polypropylene (PP). Building on earlier work with polyethylene, the study aims to correlate changes in mechanical properties—strain at break, elastic modulus, impact energy—with microscopic features such as polymer entanglement, crystallization behavior, molecular orientation, and chain conformation. A combination of static and dynamic tensile testing, indentation hardness, calorimetry, scanning probe microscopy and infrared imaging provides a holistic evaluation.

Methodology and Instrumentation

The following techniques and instruments were employed:

• Static tensile testing: AGX-V2 Autograph universal tester with TRViewX non-contact extensometer
• High-speed tensile testing: HITS-TX impact tensile machine with displacement gauge
• Microhardness: DUH-210 dynamic ultra micro hardness tester (Berkovich indenter)
• Differential scanning calorimetry: DSC-60 Plus (10 °C/min, N₂ atmosphere)
• Scanning probe microscopy: SPM-Nanoa Nano3D mapping mode (adhesion and topography)
• FTIR mapping: AIRsight infrared microscope with IRXross transmission mode

Main Results and Discussion

Static and high-speed tensile tests showed a significant increase in strain at break and break energy after advanced recycling, accompanied by a modest decrease in elastic modulus and indentation hardness. DSC cooling curves revealed a lower crystallization onset temperature, indicating suppressed chain mobility and increased entanglement. FTIR chemical imaging demonstrated a higher ratio of helical to parallel chain conformations, consistent with enhanced relaxation and entanglement. SPM adhesion maps of cryo-sectioned specimens showed a more uniform microstructure, suggesting that the advanced process mitigates orientation effects from injection molding.

Benefits and Practical Applications

The combined analytical approach provides deep insight into how advanced recycling treatments influence both microstructure and mechanical performance of PP. This knowledge supports optimization of recycling protocols, quality assurance in manufacturing recycled materials, and design of durable, high-performance polymer products.

Future Trends and Potential Applications

Emerging trends include integration of in-line spectroscopic monitoring with machine learning for predictive process control, extension of multifaceted evaluation to mixed-plastic streams, and development of real-time nanomechanical sensors to assess polymer entanglement dynamics during recycling.

Conclusion

This study confirms that an advanced recycling process can substantially improve the toughness and ductility of degraded polypropylene. The multifaceted evaluation framework effectively links mechanical property enhancements to microstructural changes, guiding future innovation in sustainable polymer recycling.

Reference

Present and future of waste plastics: plastic resource circulation in sustainable society, The Japan Institute of Energy, p. 147.