Evidence of Plasma-Driven Decomposition of Common Plastics Exposed to an Atmospheric Nonthermal Discharge

A nonthermal, pulsed spark discharge is applied to three polymer powders in Ar and Ar-H2 ${{\rm{H}}}_{2}$ gas mixtures. Hydrogen is introduced to assess plasma-driven decomposition. Gaseous decomposition products, including methane, acetylene, and ethylene, are observed with Fourier-transform infrared (FTIR). Surface modifications are observed on the residual polymer via attenuated total internal reflection-FTIR. Time-averaged rotational, vibrational, and excitation temperatures are characterized in the discharge. The plasma density is found to be around 3x1022 m-3 $3\times 1{0}<^>{22}\unicode{x0200A}{{\rm{m}}}<^>{-3}$, with rotational and vibrational temperatures ranging from 1500 to 2200 K and an excitation temperature of 1-2 eV. While spark properties did not change with either gas composition or polymer composition, it was determined that the addition of hydrogen promoted higher concentrations of gaseous phase products (promoting hydrogenolysis). A spark discharge in an argon and argon-hydrogen mixture provides evidence of plastic depolymerization of low-density polyethylene, polypropylene, and polyethylene terephthalate. Light hydrocarbon products and the resulting polymer surface are analyzed and connected to the discharge properties.image