Effect of chemical treatments on the chemical composition and properties of flax fibers

Abstract

Flax fibers were modified with NaOH and NaClO2 under different conditions in order to not only clarify the effects of hemicelluloses and lignin removal on the morphology and properties of flax fibers, but also to improve the fiber quality. The quality of flax fibers was characterized in terms of chem­ical composition, fineness, whiteness, and mechanical and sorption properties. Both treatments, alkali treatment leading to hemicelluloses removal (up to 72 % of the hemicelluloses removed) and chlorite treatment leading to lignin rem­oval (up to 96 % of the lignin removed), induce a modification of the mor­phology and properties of flax fibers. For 5 % NaOH treatments, as well as all NaClO2 treatments, an increase in the crystallinity was observed, while for higher NaOH concentrations, the mercerization phenomenon induced a slight decrease in the crystallinity. Modification with NaClO2 resulted in fiber fibril­lation while modification with NaOH at boiling temperature resulted in smoother fiber surfaces. Both treatments cause a decrease in tensile strength and water retention values, with the maximal decrease obtained with NaOH treatment at boiling temperature. Chlorite treatment resulted in finer fibers having a higher whiteness index compare to the alkali-modified fibers.