Selective adsorption of zwitterionic viscose fiber treated with sodium chloroacetate and hyperbranched polyethylenimine

Anionic modified viscose fiber (AVF) was prepared by using viscose fiber (VF) as raw material, sodium hydroxide as catalyst and sodium chloroacetate as modification reagent. The COOH content of anionic viscose fiber was 109.25 mmol/kg. Anionic viscose fibers were modified with branched polyethylenimine (HPEI) at 140 degrees C hydrothermal environment using a high-pressure reaction kettle. Zwitterionic viscose fibers (AVF-g-HPEI) with different amino and carboxyl contents could be obtained by changing the ratio of the two modified reagents. Increasing HPEI dosage resulted in amide group content of zwitterionic viscose fibers ranging from 0 to 108.35 mmol/kg. The zwitterionic viscose fibers were characterized by IR, SEM and XPS. IR analysis showed that zwitterionic viscose fiber was successfully prepared. SEM analysis showed that the reaction mainly occurred on the surface of the fiber, and the fiber structure was not changed. XPS analysis demonstrated that with the HPEI dosage increasing nitrogen elements on the surface of zwitterionic viscose fiber increased significantly. Dye adsorption experiments indicated that (1) AVF-g-HPEI could selectively adsorb the anionic dye or the cationic dye (such as methyl orange and methylene blue) from the mixed solution after the pre-treatment with pH 4.5 or pH 10.5 solution, respectively, (2) the dyes adsorbed by zwitterionic viscose fiber could be desorbed in the aqueous solution of pH 4.5 or 10.5, respectively and (3) the desorption ratio of AVF-g-HPEI remained above 0.85 after eight cycles.