The Preparation Of Cellulose Nanocrystals By TEMPO Oxidation With The Synergy Of Ultrasonic

The utilization of natural cellulose fibers has become a growing concern in the world. The preparation of cellulose nanocrystals was the good way of modified cellulose fibers as a new function materials to expand the filed of the utilized natural cellulose fibers, which have attracted great attention in recent years.Cellulose fibers was dispersed in distillated water with TEMPO and sodium bromide. Then, sodium hypochlorite solution was added into the mixture to oxidize cellulose fibers, and the cellulose nanocrystals was directly obtained in the solution after 13.5h. The cellulose nanocrystals was observed by SEM and TEM, the carboxylate content of cellulose nanocrystals was determined by the electric conductivity titration method, and the X-ray diffractor was used to analyze the crystallinity of the oxidized fibers.Cotton linter pulp was oxidized by TEMPO-NaBr-NaClO system with ultrasonic indicated: cotton linter pulp was dispersed in water, and the pulp was oxidized by TEMPO-NaBr-NaClO system with ultrasonic for 13.5h at 25℃, and then the cellulose nanocrystals was obtained directly.Cellulose nanocrystals were 200-400nm in the length, and the width was 5-10nm,the content of cellulose nanocrystals was 1.66mmol/g, which could be stablized the cellulose nanocrystals and well-dispersed in aqueous solutionThe full bleached kraft bamboo pulp was oxidized by TEMPO-NaBr-NaClO system with ultrasonic at 25℃, and then the cellulose nanocrystals was obtained directly after 8h.Cellulose nanocrystals were 400-500nm in the length, and the width was 5-10nm,the content of cellulose nanocrystals was 2.10mmol/g.Microcrystalline cellulose was dispersed was oxidized by TEMPO-NaBr-NaClO system under the condition of ultrasonic for 15h at 25℃, and then the cellulose nanocrystals was obtained, which were 100-200nm in the length, and the width was 10-20nm,the content of cellulose nanocrystals was 1.56mmol/g. The crystallinity of the oxidized microcrystalline cellulose slightly increased in the oxidized with ultrasonic, and the crystallinity was 0.85.These results indicated:1. The TEMPO-NaBr-NaClO system oxidize cellulose fibers with the synergy of ultrasonic that was a efficiently and directly way to obtain cellulose nanocrystals.2. Depending on the crystallinity and the structure of various cellulose fibers, the time of prepared cellulose nanocrystals was difference with the ultrasonic, as well as the scale of cellulose nanocrystals.3. The acoustic cavitation of ultrasonic could help the dissociation of cellulose fibers in the TEMPO oxidation process.