Developing flame-retardant lignocellulosic nanofibrils through reactive deep eutectic solvent treatment for thermal insulation

The global consensus to pivot to a more sustainable lifestyle and achieve greater atom economy calls for not only sourcing advanced functional materials from biomass but also accomplishing high feedstock utilization with green and low-toxic reagents; yet, the multi-constituent nature of biomass with complex hierarchical structure makes this target difficult to meet. This study focused on the high-yield conversion of low-cost, coarsely pretreated biomass via reactive deep eutectic solvent (DES) pretreatment into lignocellulosic nanofibrils (LCNF) with high aspect ratio (up to ∼ 103) and high sulfate ammonium functionalization (up to 3.53 mmol/g). The aqueous suspension of LCNF exhibited high viscosity and superb colloidal stability. Such LCNF can be directly processed into highly porous aerogel with low apparent density, good mechanical properties, satisfactory thermal insulating performance (κ ranged 31.0–31.6 mW/m∙K) that is comparable to commercial petrochemical-based insulators. Moreover, the surface sulfate ammonium functionalized during DES pretreatment endowed LCNF with intrinsic flame retardancy and self-extinguishing property. Taken together, a facile valorization strategy is developed to convert low-cost renewable resources into functionalized nanofibrils at a high yield, which serve as an intrinsically flame-retardant platform material for thermal insulation applications.