DES-separated bamboo lignin-reinforced DES gels with high conductivity, strength, flexibility, and environmental stability

Abstract

Lignin can significantly promote gel formation and enhance the properties of the resulting gels due to its rigid structure and abundant functional groups. Herein, high-purity (91.28%) lignin with a low and uniform molecular weight (M_w = 4071 g mol⁻¹, M_n = 2770 g mol⁻¹, PDI = 1.46) was effectively separated from natural bamboo using deep eutectic solvents (DESs). The obtained DES-separated bamboo lignin (DESL) was dissolved in different DES systems, including betaine/ethylene glycol (Bet/EG) DES and choline chloride/ethylene glycol (ChCl/EG) DES via a green and mild one-pot approach to fabricate two kinds of DES gels, Fe-L-GO/PAA and L/PAA, respectively. The abundant active sites and dispersibility of DESL enabled the formation of a dense and uniform hydrogen-bonded network within both Fe-L-GO/PAA and L/PAA. This network enhanced the polymeric structure of two gels, thereby significantly improving their conductivity, toughness, and stability. Meanwhile, the phenolic hydroxyl groups of DESL improved the long-term and repeatable adhesion of gels, while its aromatic structures endowed the gels with UV resistance. These properties extended the service life of the gels. Among the two gels, Fe-L-GO/PAA exhibited a higher tensile strength of 246.3 kPa and a lower glass transition temperature of −117.4 °C, making it suitable for use in flexible electronic devices at low temperatures. Moreover, L/PAA achieved a higher conductivity (7.41 mS cm⁻¹), elongation at break (712.9%), and compressive strength (2.5 MPa). These properties satisfy the requirements for accurate electrical signal transmission for flexible electronic materials under large-scale deformation. In general, this study extracted high-quality bamboo lignin using DES and employed it to fabricate green DES gels, which exhibit outstanding performance outdoors or in harsh environments.