Produced from plant renewable resources, cellulose nanofibres are an emerging class of sustainable materials with favourable mechanical properties. Once carboxylated, they can be used even more widely thanks to the possibility of surface chemical modifications. However, the current fabrication processes for carboxylated cellulose nanofibres (C-CNFs) either require harsh reaction conditions or severely impair the high aspect ratio of products, resulting in low yields, environmental impacts and poor practical value. Here we address these limitations by using a hydrated multi-carboxylic acid deep eutectic solvent comprised of only choline chloride, citric acid and water to produce ultrafine and fairly long C-CNFs. The resultant C-CNFs possess fine diameters of ~3.4 nm, high aspect ratios up to 2,500, a high carboxyl content of 1.5 mmol g⁻¹ and a high mass yield of 90.12%. Superior stability of the C-CNFs suspensions even at high concentrations allows for easy storage, transportation, processing and utilization. Moreover, the solvent exhibits a tenfold increase in its reusability, thereby highlighting its recyclability and economic viability. We further show large-scale production of C-CNFs for preparing large-area, high-performance structural materials. These unique advantages open a new avenue to the production of functional C-CNFs at an industry compatible scale.

纤维素纳米纤维由植物可再生资源制成，是一类新兴的可持续材料，具有良好的机械性能。一旦羧化，由于可以进行表面化学修饰，它们的用途甚至可以更广泛。然而，目前羧化纤维素纳米纤维（C-CNF）的制备工艺要么需要苛刻的反应条件，要么严重损害产品的高长径比，导致产量低、环境影响大、实用价值差。在这里，我们通过使用仅由氯化胆碱、柠檬酸和水组成的水合多元羧酸低共熔溶剂来生产超细且相当长的 C-CNF，从而解决了这些限制。所得的C-CNF具有~3.4 nm的细直径、高达2,500的高长径比、1.5 mmol g ^-1的高羧基含量和90.12%的高质量产率。即使在高浓度下，C-CNF 悬浮液也具有出色的稳定性，易于储存、运输、加工和使用。此外，该溶剂的可重复使用性提高了十倍，从而突出了其可回收性和经济可行性。我们进一步展示了 C-CNF 的大规模生产，用于制备大面积、高性能结构材料。这些独特的优势为以行业兼容的规模生产功能性 C-CNF 开辟了新途径。