Ionic liquid-catalyzed synthesis of carbon/polyurethane triboelectric nanocomposites with excellent flame retardancy and oil leak detection

A high-carbon (expandable graphite flakes and carbon black)–loaded polyurethane foam (PUF) composite was prepared using a green and efficient ionic liquid (IL) catalyst. The carbon/PUF composite exhibited excellent flame retardancy and was highly versatile for application in oil leak detection and as triboelectric nanogenerator (TENG). The effect of the IL on the foamability of the carbon/PUF composite was thoroughly investigated. The IL promoted the expansion of the carbon/PUF composite and the microcellular pore formation in it, thereby affording a sponge with low density, excellent flexibility, and compressibility. Owing to the presence of high-carbon fillers, the resultant sponge exhibited excellent flame retardancy by (i) avoiding melt dripping after ignition by a butane torch (∼1400 °C, applied for 20 s), (ii) self-extinguishing after torch removal, and (iii) preventing foam collapse. Additionally, it can pass the UL-94 V-0 rating and the critical fire retardancy metrics, i.e., peak heat release rate, total heat release, and total smoke release, were reduced by 73%, 78%, and 92%, respectively. A flame retardant (FR)-TENG was designed using the carbon/PUF composite. The FR-TENG could be attached to the insole of a shoe, generating an output of 36 and 100 V upon walking and running, respectively. This output was sufficient to concomitantly glow 38 LEDs. Interestingly, owing to the oil-induced reversible shape change, the carbon/PUF composite can be used for the fabrication of high-efficiency oil leak sensors to detect oil spills in pipelines and different water environments. This study offers a new perspective for the development of flame retardant and multifunctional foam-based materials.