Establishing the constitutive relationship between deep eutectic solvents pre-treatment extent, cellulose structure...

Conventional dissolution of cellulose fibers in N-methylmorpholine-N-oxide (NMMO) solution necessitates harsh conditions including high temperature and prolonged dissolution time, frequently resulting in inhomogeneous dissolution and inferior product characteristics. Herein, a facile pre-treatment strategy was developed to remarkably improve the dissolution efficiency by multiple concentration gradients of ZnCl₂/H₃PO₄ solvents. The novelty of this work lies in the establishment of the constitutive relationship between deep eutectic solvents (DES) pre-treatment extent, cellulose structure characteristics, and dissolution efficiency. The gradient concentration of DES effectively disrupts the amorphous region of cellulose, exposing inter- and intramolecular hydrogen bonds and rapidly shortening the dissolution time of NMMO on the cellulose hydrogen bonding network. Moreover, an interesting phenomenon was discovered. After DES pre-treatment, most of the treated fibers appeared hollow phenomenon in polarized light microscopy during NMMO dissolution. The originally intact overall structure gradually disintegrated, taking on the form of a disassembled filament. Therefore, the simultaneous internal and external dissolution accelerated the dissolution efficiency, leading to a reduction in the dissolution time of the optimal sample from 40 to 13 min. By establishing the quantitative relationship between multiple concentration gradients and fiber structural parameters, the regulatory mechanism of fiber structural characteristics on the dissolution behavior was revealed.