Preparation of cellulose-based optical brightening agent by a two-step one-pot reaction and its application in fiber treatment

Abstract A simple and efficient two-step one-pot procedure for the manufacturing of a cellulose-based polymeric optical brightening agent is demonstrated. The method employs a consecutive in situ activation of two carboxylic acids in a cellulose solution prepared in N,N -dimethylacetamide and LiCl. As an activating agent, 4-toluenesulfonyl chloride was employed. The optical brightening properties were introduced by a 4-hydroxythiazole moiety. These compounds show strong fluorescence over a large range of the visible electromagnetic spectrum. The properties can be largely tuned by reactions at the 2- and 5-position of the thiazole ring. The water solubility of the cellulose derivative is introduced in the second step, by attaching betaine to the cellulose backbone. This cationic moiety allows not only a fast dissolution of the cellulose mixed ester in water, but also an efficient adsorption onto cellulose fibers via electrostatic interactions. After adsorption onto the fibers, the resulting material appears bright white in daylight and shows a strong blue fluorescence when probed under ultraviolet light. The coating process is fast and almost quantitative as absorption and fluorescence measurements reveal, showing no leaching effect. The cellulose mixed ester synthesized is characterized by means of 1D and 2D 1 H- and 13 C nuclear magnetic resonance, infrared-, UV–Vis-, and fluorescence spectroscopy. In addition, elemental analysis and size-exclusion chromatography were performed. The polymeric optical brightening agents presented consists of environmentally benign compounds only and can be considered as a green alternative for traditional low molecular optical brightening agents employed today.