A deep eutectic solvent with bifunctional acid sites treatment to upgrade a bamboo kraft pulp into a cellulose-acetate grade dissolving pulp

Valorization of non-wood pulp, such as bamboo bleached kraft pulp into high-purity cellulose acetate (CA)-grade dissolving pulp is crucial but challenging in China. Herein, a series of metal salt-based deep eutectic solvents (MSDESs) involving various ZnCl2-urea (U), ZnCl2-glycerol (G), and ZnCl2-lactic acid (LA) are comparatively investigated for this purpose. Thanks to the bifunctional acid sites of Lewis acid ZnCl2 and Brønsted acid LA, the ZnCl2-LA MSDES has the highest acidity (2.62) and interaction affinity to bamboo fibers, leading to the highest efficiency in simultaneous pulp purification and activation. As a result, the resultant upgraded pulp from ZnCl2-LA (DES3-F) features remarkable improvements in purity (from 80.8 % to 93.1 %), intrinsic viscosity (from 897 to 419 mg/L), and reactivity (from 18.1 % to 80.8 %). Moreover, the modified acetate product has a high degree of substitution of 2.84 and a yield of 75.5 %. In short, such a proposed MSDES treatment can offer a promising and alternative approach for the manufacture of high-quality dissolving pulp and its derivatives. [Display omitted] •Metal salt deep eutectic solvent (MSDES) with ZnCl2-based Lewis acid is prepared.•ZnCl2-lactic acid (LA) with bifunctional acid sites features the highest acidity of 2.62.•ZnCl2-LA has simultaneous purification and activation mechanisms for bamboo pulp.•The upgraded acetate-grade bamboo dissolving pulp has a high reactivity of 80.8 %.