A hybrid pre-treatment method for flax fiber: Effects of chemical treatment on fiber diameter

In contrast to conventional alkaline or chlorite bleach treatment of fibers, a hybrid chemical treatment was applied to assess its influence on flax fiber diameter and physiochemical properties. The natural variability in flax fiber diameter presents challenges for uniform dispersion and bonding in composite materials. To address these limitations, a sequential alkaline–chlorite (hybrid) treatment was explored to improve fiber separation and reduce the fiber diameter variability. Herein, two traditional modification methods, alkaline (sodium hydroxide) and bleach treatment (chlorite-bleach), were applied individually and in sequence with a comparison of their effects. Treated flax fibers were characterized by their mechanical properties, wet chemical composition, spectroscopy (IR, Raman), microscopy (optical, electron), thermal gravimetry (TGA), zeta-potential, and solvent swelling in water. The spectral results reveal that the alkaline treatment removed hemicellulose and pectin, whereas the chlorite-bleach treatment was more effective for the lignin, pectin, and hemicellulose removal. Moreover, the hybrid treatment led to a significant (∼86 %) reduction in average fiber diameter, with a marked improvement in the fiber size uniformity (standard deviation reduced from 49 % to 3 %). The hybrid treatment method contributes toward a more effective treatment methodology due to its enhanced fiber size reduction and its more uniform size distribution. In contrast, the chlorite-bleach treatment yields greater tensile strength fibers via a simpler, single-step process that requires less chemical. These features are envisaged to significantly affect the physicochemical properties of flax fibers for development of advanced bioproducts. • Flax fibers were treated with a sequential alkaline and chlorite-bleach process. • The dual treatment (alkaline+chlorite) improved fiber uniformity and fineness. • The dual process yielded narrower and more uniform diameter flax fibers. • The study reveals a simple pre-treatment process to tailor fiber properties. • The dual process enables valorization of industrial crop fibers for potential bioproducts.