Formic acid-directed spinning of closed-loop recyclable cellulose/chitosan filaments with moisture response and antimicrobial performance

Cellulose filaments, combining the inherent “green” characteristics of cellulose with the slenderness of fibers, have emerged as alternatives to replace synthetic fibers. Herein, robust cellulose formate/chitosan formate filaments (CCF) were produced from a cellulose/chitosan solution in formic acid (FA) at room temperature via the wet spinning process by coagulating in the alkaline solution, followed by physical stretching to increase crystallinity, orientation, and mechanical strength. The CCF presented excellent mechanical properties with tensile stress of 4.8 and 1.8 cN/dtex in dry and wet states, respectively, attributed to the good miscibility between cellulose and chitosan, and self-assembly force driven by hydrogen bonds and dynamic imine bonds. Upon stimulation of external water, the CCF showed a switchable water-induced moisture response performance, as the hydrogen bonds between cellulose and chitosan could be partially interrupted, and the filaments reformed to recover in consequence. Moreover, CCF can be 100 % recycled by FA dissolution and subsequent spinning, and biodegraded in the natural environment, exhibiting excellent closed-loop recyclability and biodegradability. The fabricated CCF presented strong antimicrobial activity. This work combined with the biodegradable nature of the cellulose and chitosan provides a “green” and “sustainable” strategy for broad applications, including robust biopolymer filaments and beyond. • A green wet-spinning method was proposed to prepare cellulose/chitosan filaments (CCF). • CCF with a high tensile stress of 4.8 cN/dtex was prepared. • CCF showed a switchable water-induced shape memory performance. • CCF can be 100 % recycled by FA dissolution and biodegraded in the natural environment. • CCF presented strong antimicrobial activity against both E. coli and S. aureus.