(539h) Facile Manufacturing of Recycled Polyphenylene Sulfide-Based Nanocomposites through Novel Electromagnetic Melt-Processing

Polyphenylene sulfide (PPS) polymer is at the forefront of materials engineering applications in the aerospace, automotive, nuclear, and energy sectors. PPS offers remarkable thermal robustness, dimensional stability, mechanical strength, and chemical resilience, qualifying it as a high-performance (HP) semi-crystalline thermoplastic. Sustainability awareness and polymer recycling efforts are paramount, and the use of recycled PPS (rPPS) for the synthesis of composites, coatings, and other high-demand applications is of great interest. However, polymer recycling is challenging, and transforming polymeric materials into new forms and products often requires high-temperature and/or mechanical micronizing processing steps which reduce their molecular weight. Specifically, reprocessing rPPS into new products via extrusion, hot-pressing, injection molding, or pultrusion, requires an extra thermomechanical degradation step that may last as long as a few minutes at temperatures > 300°C using conventional heating techniques. Such thermomechanical history changes the fundamental polymer properties through degradation pathways.

Electromagnetic (EM) heating offers a softer process alternative to conventional heating when reprocessing rPPS, reducing degradation. EM heating of materials offers up to a 90% faster processing and as high as 70% reduction in energy consumption. The localized interaction of EM radiation with electrically conductive or dielectric materials enables efficient volumetric heating, which, if controlled, may lead to less degradation. However, PPS, like most polymers, is not conductive. We have previously demonstrated that EM viscoelastic melt-processing of thermoplastics is possible if polymer pellets are coated with conductive nanoparticles creating an electrical network that gives EM susceptibility to the polymeric phase, enabling heating upon EM irradiation.

In this study, we apply EM-induced melt-processing of rPPS by the inclusion of graphitic nanoparticles to enable fast and facile manufacturing of PPS nanocomposites. In this investigation, multiscale attrition coating of rPPS micro-pellets (PPS F0320-MP140 grade by PolyClean Technologies, Inc.) was carried out with Nanocyl NC7000 carbon nanotubes (CNTs), which exfoliates and configures a percolated electrical network within the formulated micro-pellets. Such a network is EM susceptible enough for the fabrication of segregated HP nanocomposites via EM melt-processing. Our findings prove that even with nanoparticle loadings as low as 0.3 wt.%, rPPS formulations were fully percolated, witnessed by seconds-fast melt-processing by EM radiation (2.45 GHz) of 500 W. The effects of micro-pellet particle size and nanoparticle concentration on the electrical percolation, transport properties, and EM susceptibility behavior were assessed. At 0.3 wt.% CNTs, the volume electrical conductivity reached semiconductive-range values of 1.35±1.23x10^-3 S/m and 2.12±1.15x10^-5 S/m for the formulated micro-pellets and the EM processed nanocomposites, respectively. Furthermore, at 1.5 wt.% CNT loading the EM susceptibility of the materials measured as electromagnetic shielding effectiveness (EM SE) at 8.2 GHz (X-band) yielded as high as 8.27±1.52 dB/mm (i.e., absorption: 6.34±1.08 dB/mm, reflection: 1.93±0.45 dB/mm, conductivity: 1.47±1.39x10^-2 S/m) and 3.63±0.60 dB/mm (i.e., absorption: 2.43±0.40 dB/mm, reflection: 1.20±0.23 dB/mm, conductivity: 1.29±1.16x10^-3 S/m) for the formulated micro-pellets and the EM processed nanocomposites, respectively. This novel processing approach not only promises a leap in processing speed and energy savings but also offers the potential development of microwave-based innovative and environmentally friendly thermoplastic manufacturing and recycling processes. In this opportunity, for the first time, the use of electromagnetic energy to induce fast viscoelastic melt-processing in a high-performance thermoplastic for the manufacturing of nanocomposites and their unique transport properties will be reported and presented.