(353b) Upcycling of Recycled Polyphenylene Sulfide into Functional High-Performance Nanocomposites Via Novel Electromagnetic Melt-Processing

The increasing demand for high-performance (HP) thermoplastics in aerospace, automotive, and energy sectors underscores the need for materials that exhibit superior thermal stability, mechanical robustness, chemical resistance, functionality, and lightweight properties.¹ Polyphenylene sulfide (PPS) is widely recognized as one of the most versatile HP thermoplastics due to its exceptional structural integrity under extreme conditions.² However, the widespread use of PPS and other HP polymers has raised concerns regarding their environmental footprint, particularly due to their limited biodegradability and the challenges associated with their disposal.³ As sustainability becomes a central priority in materials engineering, the upcycling of recycled PPS (rPPS) into value-added functional materials represents an important strategy to reduce polymer waste, mitigate resource depletion, and promote a circular economy in polymer processing.¹

Upcycling differs from conventional recycling in that it enhances or maintains the material's original performance rather than degrading it.⁴ While traditional polymer recycling often leads to compromised mechanical and chemical properties due to repeated exposure to heat and shear, upcycling aims to preserve or improve the polymer’s structural and functional characteristics.⁵ Despite the benefits of rPPS reuse, thermomechanical degradation remains a critical challenge during its reprocessing.⁶ Conventional methods such as extrusion, injection molding, and compression molding require prolonged exposure to high temperatures (>300°C), leading to polymer chain scission, molecular weight reduction, and altered crystallinity, ultimately limiting its applicability in demanding engineering environments.⁶ Developing innovative reprocessing techniques that mitigate such degradation is crucial to expanding the utility of rPPS in high-performance applications.

To overcome these limitations, electromagnetic (EM) melt-processing has emerged as a promising alternative to conventional heating methods, offering a rapid, energy-efficient, and selective heating methodology that minimizes polymer degradation.^7,8 Unlike conventional heating, electromagnetic irradiation enables volumetric heating through the direct interaction of the radiation with the electrically conductive and/or dielectric material.⁷ It has been reported that EM heating reduces processing times by up to 90% and energy consumption by up to 70%, making it an attractive method for the sustainable reprocessing of engineering thermoplastics.⁹ However, PPS, like most polymers, is inherently non-conductive and requires strategic modification to enable effective EM heating.

This study explores the upcycling of rPPS into functional nanocomposites using EM melt-processing, facilitated by the integration of carbon nanotubes (CNTs) to create an electrically percolated network that enables EM susceptibility in the “green” polymer. Thus, here, recycled PPS micro-pellets (F0320-MP140 grade, PolyClean Technologies, Inc.) were coated with NC7000 carbon nanotubes (Nanocyl, Belgium) using multiscale dry-state attrition, forming an electrical network that enabled rapid viscoelastic melt flow under 2.45 GHz microwave irradiation at 500 W. Significantly, at CNT loadings as low as 0.1 wt.% (~0.06 vol%), the rPPS nanoformulations exhibited full electrical percolation and electromagnetic susceptibility to microwaves, allowing rapid melt-processing with minimal thermal degradation. The electrical conductivity of the green nanoformulated mixtures at only 0.1 wt% CNT loading reached (1.24±0.74)x10^-5 S/m, and upon EM processing, the HP nanocomposites attained (2.64±0.51)x10^-9 S/m. Additionally, at the 1.5 wt.% loading, the electromagnetic shielding effectiveness (EM SE) measured at 8.2 GHz (X-band) reached 8.27±1.52 dB/mm for the green mixtures, and 3.63±0.60 dB/mm for the resulting EM-processed nanocomposites, demonstrating a balance between EM absorption and reflection. Furthermore, at 0.1 wt% CNT, the tensile strength of the nanocomposites increased to 53.17±3.12 MPa, which is about 14% higher than the host PPS matrix's tensile strength at 46.78±3.77 MPa. At the same loading, the modulus and elongation-at-break of the nanocomposites reached 2554.0±135.9 MPa and 4.17 ± 0.49 %, respectively. These values demonstrate substantial increases of 43% and 26% compared to the stiffness and ductility of the host PPS matrix, i.e., 1781.5±479.3 MPa and 3.31±0.31 %, respectively.

Ongoing investigations are focused on evaluating how EM melt-processing influences the thermal conductivity and crystallinity of rPPS nanocomposites, particularly in mitigating thermal degradation and enhancing their performance for high-temperature applications and electronics. In summary, the findings of this study establish EM melt-processing as a scalable and sustainable approach for upcycling rPPS into functional nanocomposites, providing an innovative pathway toward a circular economy for high-performance thermoplastics. By enabling rapid processing, improving energy efficiency, and preserving material integrity, this work underscores the potential of EM melt-processing in advancing the next generation of sustainable HP polymeric materials.

References

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(8) Madara Mohoppu a, b, Utsab Ayan a, b, Bibek Kattel c, Elliot Hutchcraft c, O. D. M. d; Ahmed Al-Ostaz b, e, Byron S. Villacorta a, b, F. 539h - Facile Manufacturing of Recycled Polyphenylene Sulfide-Based Nanocomposites through Novel Electromagnetic Melt-Processing. 2024.

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