Flexible, Solution-Processable Electrostatic Discharge Protective Coatings from Upcycled Waste Tire Pyrolysis Char via Sequential Acid-Alkali Leaching

Abstract We demonstrate flexible, solution-processable electrostatic discharge (ESD) protective coatings whose conductive filler is derived from upcycled tire pyrolysis char (TPC), a hazardous residue of end-of-life tire pyrolysis. A three-stage protocol uses 6 M HCl, 4 M NaOH, and 6 M HNO3, each at 80 °C for 3 h, for demineralization, desilication, and surface oxidation, respectively. The contribution is integration of established leaching chemistry with purity tracking and device characterization for one carbon stream. Inductively coupled plasma optical emission spectroscopy showed that the sum of quantified elemental concentrations decreased from 4.92 to 0.076 wt %, approximately 98.5%. Ash decreased from 9.85 wt % on an as-received basis (10.9 wt % on a dry basis) to 0.15 wt %, with Zn, Fe, Ca, and Al below the detection limit (≤5 mg kg−1). The quantified elements other than S, expressed as oxides, account for 79% of the dry-basis ash. The purified char (PTPC) showed a lower Raman D/G ratio (0.27 to 0.22), a 38.5% larger Brunauer−Emmett−Teller surface area, and oxygen-containing surface groups. Surface oxidation and improved interparticle contacts are plausible contributors to performance; their individual contributions were not isolated experimentally. Doctor-blade-coated nitrocellulose-bound films on poly(ethylene terephthalate) (PET) gave approximately 1 kΩ sq−1 sheet resistance and dissipated 99% of a 1 kV contact-discharge pulse in approximately 368 μs. The ink was shear-thinning (power-law n = 0.35). After 1000 bending cycles at a 5 mm radius, resistance increased by approximately 8% on PET and 25% on cellulose paper; PET-supported coatings showed approximately 2% drift after 30 days of ambient aging. Preliminary all-in costs are USD 4.3–7.0 kg−1, including reagents at USD 2.1–3.1 kg−1 with acid-liquor reuse. These estimates and proposed Zn and silica recovery remain unvalidated at pilot scale. The protocol demonstrates a laboratory-scale route from waste char to conductive carbon for flexible ESD protection.