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 clarify effects of hemicelluloses and lignin removal on the morphology and properties of flax fibers, but also to improve fiber quality. The quality of flax fibers was characterized in terms of chemical composition, fineness, whiteness, mechanical and sorption properties. Both treatments, alkali treatment leading to hemicelluloses removal (up to 72 % of hemicelluloses removed) and chlorite treatment leading to lignin removal (up to 96 % of lignin removed), induce a modification of morphology and properties of flax fibers. For 5 % NaOH treatments, as well as all NaClO2 treatments, increase in the crystallinity was observed, while for higher NaOH concentrations, the mercerization phenomenon induces a slight decrease of the crystallinity. Modification with NaClO2 results in fiber fibrillation while modification with NaOH at boiling temperature results in smoother fiber surfaces. Both treatments cause decrease in tensile strength and water retention values, with maximal decrease obtained for NaOH treatment at boiling temperature. Chlorite treatment results in finer fibers having a higher whiteness index compare to alkali modified fibers.