Combustion Separation Enables Repeated Recycling of Carbon Nanotubes from Ultra-lightweight Materials: Implications for Sound-Absorbing Applications

Abstract

Carbon nanotubes (CNTs) are costly and energy-intensive to manufacture, making their recovery from single-use ultra-lightweight materials (ULMs) important for sustainable carbon-resource recycling. We show that solvent-free combustion separation, which exploits the thermal-stability difference between CNTs and a cellulose nanofiber matrix, enables CNT recovery over three successive fabrication−combustion−recovery cycles. X-ray photoelectron spectroscopy, Raman spectroscopy, and thermogravimetric analysis show that CNT crystallinity is largely preserved despite progressive sodium impurity accumulation and reduced thermal stability. Critically, sound-absorbing ULMs fabricated from the recycled CNTs retain acoustic performance equivalent to that of pristine CNTs, confirming the practical viability of this recycling route.