Triboelectric performance and delayed charge generation in triglyceride–sulfur synthesized from waste sources

Abstract

Sulfur–triglyceride (STG) was synthesized by solvent-free inverse vulcanization of elemental sulfur and waste soybean frying oil and processed by compression molding into flexible 0.5 mm thermoplastic film. The resulting sulfur-rich polymer shows a robust, tribo-negative surface (confirmed by Kelvin Probe AFM and the position in Triboelectric Charge Density series) and was implemented as the negative layer in a vertical contact–separation triboelectric nanogenerator (TENG) operated against stainless steel and selected wearable-relevant counter materials. Under cyclic loading the STG-based TENG exhibits progressive charge accumulation with output stabilization, reaching peak open-circuit voltages up to ~570 V and maximum power densities of ~4.05 mWcm−2 (STG/steel, ~1 MΩ, 14.8 kPa) and ~ 4.9 mWcm−2 (STG/PVAc, ~2.2 MΩ, 14.8 kPa). Systematic parametric tests related to various mechanical pressures, resistive loads, actuation frequencies and contact areas are provided. Device durability was verified by long-term cycling tests up to 105 actuation cycles, demonstrating stable operation without STG degradation. Beyond cyclic loading, post-separation experiments reveal a delayed voltage generation associated with interfacial polarization and charge retention. The results demonstrate that waste-derived STG is a sustainable tribo-negative material providing pressure-, frequency-, and area-dependent power output together with a delayed-charge response associated with interfacial polarization.