(181e) Electromagnetic Processing of Graphitic Nanoparticle-Based Thermoplastic Nanocomposites

Due to intricate conductive and dielectric loss mechanisms, electrically conductive nanoparticles may undergo significant heating (e.g., ~ 2000°C) when exposed to microwave radiation^1,3. Due to their suitable intrinsic impedance, graphitic carbon nanoparticles (e.g., carbon nanotubes, nanofibers, graphene, etc.) may exhibit a very strong absorptive response to microwaves to the point of enabling fast electromagnetic (EM) processing of thermoplastic nanocomposites (TPNCs)⁴. Nevertheless, such carbon nanoparticles may excessively heat polymeric matrices during such a EM processing, which may lead to polymer degradation⁴. In contrast to this, it is hypothesized that graphitic carbon nitride (g-C₃N₄) nanosheets, with semiconducting characteristics^5,6, may display a more controllable heating response, enabling its use as an effective nano-reinforcement and microwave absorber⁶ that, in turn, permits an adequate and easier EM processing of its TPNCs³.

In our previous research, this novel and alternative EM processing method was used to develop TPNCs that exhibited a unique combination of high transport and mechanical properties not achievable by conventional processing (e.g., hot pressing, extrusion, etc.)^3,4,7. This time, our focus is on a new set of polyolefins (Propolder FPP4040 and Fipolder FHP005040 by TWO H Chem Ltd) and polyetheretherketone (PEEK, Victrex 150XF) matrices, the latter being a high-performance thermoplastic that is difficult to process using conventional techniques (i.e., requiring temperatures of more than 350 °C). For this study, we have in-house synthesized the graphitic carbon nitride (g-C₃N₄) nanosheets using the methodology described by Majdoub et.al.⁵.

The formation and retention of an electromechanical network of nanoparticles around the polymeric micro-pellets, achieved by multiscale dry-mixing formulation methods, make the green mixtures electromagnetically susceptible, and is responsible for an exceptional combination of properties as well as excellent dispersion and homogeneity^{2, 3}. We found that green formulations as low as 0.5 wt% loading can be successfully processed with EM radiation of 2.45 GHz within a few seconds of irradiation^3,4,6. We have identified the role of materials factors such as the polymeric particle size, the size distribution, viscosity, and nanoparticle concentration as influential parameters on the electrical percolation threshold behavior of the mixtures. In addition, such factors were determining on the subsequent electromagnetic susceptibility and absorption of the green mixtures, the electrical conductivity, the microstructure, and the mechanical properties of the thus formed TPNCs. For instance, TPNCs prepared with 0.5wt% carbon nanotubes (NC7000 Nanocyl) and polypropylene (Propolder FPP4040) displayed satisfactory electromagnetic susceptibility to be processed in less than 120 seconds, and a through-thickness volume electrical conductivity of 3.73±1.77x10^-8 S/m and 7.38±3.69x10^-10 S/m, for the green mixture and the microwaved TPNCs, respectively. Moreover, the mechanical properties (ISO 37 Type 4) of the TPNCs at 0.5 wt% displayed a modulus of elasticity, a tensile strength, and a ductility of 1.49±0.16 GPa, 32.58±2.36 MPa, and 56.82±0.41%, respectively. Therefore, in this study we intend to present the latest progress on this alternative processing method and the electrical, electromagnetic, and mechanical responses generated by the formed network of nanoparticles at selected concentrations in the TPNCs.

References

(1) Al-Saleh, M.; Sundararaj, U. Electromagnetic Interference Shielding Mechanisms of CNT/Polymer Composites. Carbon N. Y. 2009, 47, 1738–1746. https://doi.org/10.1016/j.carbon.2009.02.030.

(2) Fakirov, S. Polymer Nanocomposites: Why Their Mechanical Performance Does Not Justify the Expectation and a Possible Solution to the Problem? Express Polym. Lett. 2020, 14, 436–466. https://doi.org/10.3144/expresspolymlett.2020.36.

(3) Villacorta, B.; Karunarathna, M.; Ayan, U. R. (259h) Next-Generation of Thermoplastic Nanocomposites Via Electromagnetic Processing | AIChE Annual Meeting (2022) | Materials Engineering and Sciences Division.

(4) Villacorta, B.; Zhu, Z.; Truss, R.; Larsen, A.; Solomon, G. Method for Fabricating Carbon Nanoparticle Polymer Matrix Composites Using Electromagnetic Irradiation. 2022. US 11512180 B2.

(5) Majdoub, M.; Amedlous, A.; Anfar, Z.; Jada, A. Engineering of H-Bonding Interactions in PVA/g-C3N4 Hybrids for Enhanced Structural, Thermal, and Mechanical Properties: Toward Water-Responsive Shape Memory Nanocomposites. Adv. Mater. Interfaces 2022, 9 (14), 1–13. https://doi.org/10.1002/admi.202200170.

(6) Green, M.; Liu, Z.; Smedley, R.; Nawaz, H.; Li, X.; Huang, F.; Chen, X. Graphitic Carbon Nitride Nanosheets for Microwave Absorption, Materials Today Physics, 2018, 5, 78-86. https://doi.org/10.1016/j.mtphys.2018.06.005

(7) Ryan, E.; Truss, R.; Villacorta, B. Feasibility Assessment and Optimization of the Fabrication of Carbon Nanotube/Polyolefin Composites Using Microwave Irradiation, University of Queensland. 2015.