Effect of preswelling and ultrasound treatment on the properties of flax fibers cross-linked with polycarboxylic acids

This paper presents the investigation of sorption and mechanical properties of single flax fibers (fiber bundle) cross-linked with polycarboxylic acids (PCA; citric acid [CA] and 1, 2, 3, 4-butanetetracarboxylic acid [BTCA]). The improvement of the chemical modification performance was carried out by pre-treating of the fibers with sodium hydroxide and ultrasound (US). Thus, the purpose of the investigations was to determine whether the sorption and mechanical properties of the cross-linked fibers would be enhanced by a preswelling and US treatment before the application of PCA. The effect of cross-linking PCA with cellulose molecules on flax fiber properties was determined by measuring and comparing the properties (fineness, tenacity, and elongation at break; breaking twist; moisture absorption; and water-retention value) of untreated and modified flax fibers. The test results indicate that treatment with PCA undoubtedly changes the tested properties: water retention values decrease while the resistance to tenacity increases. The observed changes are the result of structural alterations in fibers. Fourier-transform infrared (FT-IR) spectra confirmed that cross-linking between the carboxyl groups of acids and the hydroxyl groups of cellulose occurs due to the esterification reaction. Preswelling and US treatments have increased the accessibility of cellulose in flax fibers, and cross-linking was achieved with less fiber damage, whereby US proved to be a more successful pre-treatment.