Flax fiber-chitosan biocomposites with tailored structure and switchable physicochemical properties

A facile and sustainable synthesis of unique flax fiber composites (FFCs) is reported, where raw flax fiber (FFR) was immobilized with variable chitosan content. FFCs were structurally characterized via TGA, XRD, SEM analysis, and spectroscopy (IR, NMR, and Raman mapping). Physicochemical characterization of FFCs enabled estimation of the point-of-zero-charge (PZC), solvent swelling at variable pH, dye adsorption with Rose Bengal (RB) and Methylene Blue (MB) to characterize the surface chemistry of the composites. This study is a first reported example that highlights the unique structure-property relationships of FFC materials and the role of electrostatic interactions between the pristine fiber substrate and chitosan. FFCs with incremental chitosan content display the following trends: i) greater solvent swelling at variable pH (350% for FFCs and ca. 100% for FFR and commercial absorbents), ii) two-fold enhanced adsorption of RB (FFC 0.5 to FFC 2.0) and iii) 1.5-fold decreased adsorption of MB (FFC 2.0 to FFC 0.5). The unique "switchable" sorption properties of the FFCs toward solvent and dyes was revealed upon facile and noncovalent immobilization of chitosan on FFR. The sustainable composites reported herein offer a potential adsorption-based technology suitable for filter-based applications in "smart textiles" to biomedical sorbents for wound healing.