Aligned cellulose nanocrystal composite filament with high tensile strength enhanced by cationic polyacrylamide via flow focusing approach

Abstract

Unsatisfactory macroscopic strength is one of the important reasons that limit the application of cellulose composites. However, the mechanical properties of cellulose composites could be improved by the directional orientation of cellulose nanofibers. In this paper, a five-channel microfluidic chip was designed to fabricate core-sheath cellulose nanocrystal/ cationic polyacrylamide (CNC/CPAM) composite filament. The core spinning solution with high flow velocity promoted the extended arrangement of CPAM in sheath flow. CPAM with long chain structure could not only reduce the electrostatic repulsion between CNCs, but also ensures the fiber orientation by inhibiting the disorderly diffusion of CNCs, thus improving the toughness of the composite filament. The orientation of the composite fiber was studied by wide-angle X-ray scattering, showing an orientation index of 0.725. The mechanical properties of the composite fiber were tested by a universal material testing machine. The tensile strength was 510 ± 20 MPa, which was about 117% higher than that of pure CNC spun fiber, and the elongation at break was also increased by about 70%. The improvement in mechanical properties was attributed to the increase in the content of intramolecular and intermolecular hydrogen bonds. In addition, the demonstrated spinning technology provided a new way for preparing high-performance composite fibers.