Effect of ozone treatment on the chemical and mechanical properties of flax fibers

The surface of flax fiber is covered by noncellulosic substances, which results in many individual fibers that are bound into bundles. These noncellulosic materials must be removed to extract the usable fiber. In this study, ozone was used to remove the noncellulosic components from the surface of flax fiber. The changing regularity and mechanism of ozone treatment on the lignin content and degree of polymerization (DP) in flax fiber under different operational conditions (pH value, moisture content, ozone feed rate, and reaction time) were fully investigated. Then, the quality of untreated, ozone-treated (ozone 130 mg.L-1.min(-1), 20 min), ozone and acid treated (ozone 130 mg.L-1.min(-1), 20 min, pH 2.0, moisture content 70%) flax fiber were compared. The effect of ozone treatment on the change in strength, elongation, whiteness, copper number, and thermal stability of flax fiber was systematically tested. The results showed that the lignin content, DP, strength, elongation and thermal stability of flax fiber decreased after ozone treatment. The crystallinity, whiteness, copper number and roughness of flax fiber increased after ozone treatment. This phenomenon was more evident after ozone and acid treatment. Simultaneously, scanning electron microscopy (SEM) analysis showed that the noncellulosic components on the fiber surface were partially removed after ozone treatment and were thoroughly separated after ozone and acid treatment. This study could offer guidance into the removal of noncellulose materials on the surface of flax fiber using ozone treatment.