Preparation And Application Of Carboxylated Cellulose Nanocrystal Cholesteric Liquid Crystal And Manganese Composites

Cellulose nanocrystals,extracted from natural cellulose based materials,have emerged as a new class of nanomaterials for polymer reinforcement and nanocomposite formulation due to excellent properties.Owing to easy to modify,good thermal stability and easy to combine with metal ions,carboxylated cellulose nanocrystals have attracted ever increasing attention.However,the common preparation methods of carboxylated cellulose nanocrystals have the disadvantages of tedious process,long time-consuming and low yield,which greatly limits the application and industrial production of carboxylated cellulose nanocrystals.Based on this,a simple,high yield and low cost preparation method with potassium permanganate oxidation was reported in our previous work.Based on this method,the chiral nematic liquid crystals behavior of carboxylated cellulose nanocrystals as well as the preparation and application of manganese doped carboxylated cellulose nanocrystals iridescent films were studied sysmetically in present work.In this work,carboxylated cellulose nanocrystals were prepared by using the potassium permanganate oxidation method.The introduced manganese ions during the preparation process were removed by post-treatment,and eventually the pure carboxylated cellulose nanocrystals suspension was obtained.Upon the concentration of suspension reached 7 wt%,phase separation phenomenon occurred and cholesteric liquid crystals were formed.It is found that the helical pitch of chiral nematic liquid crystals decreases with the increase of concentration.After the evaporation of water in the suspension by natural drying,the cholesteric phase structure can be retained in the solid films,and the carboxylated cellulose nanocrystals iridescent films was obtained.It is worth noting that the film mainly consists of left-handed structure.The carboxyl group is easy to combine with manganese ion,which resulting in that some manganese ion retained and carboxylated cellulose nanocrystals suspension doped with manganese ion obtained.After the ultrasonic treatment of the suspension,carboxylated cellulose nanocrystals iridescent film doped with manganese ion can be prepared by vacuum filtration.Furthermore,the color of the film can be tuned by changing the sonication time.The introduction of manganese ion endows the iridescent film with reversible responsiveness to ammonia atmosphere,and the color variation is visible to the naked eye during the response process.Besides,a composite iridescent film composed of cellulose nanocrystals and manganese oxide was obtained through the ammonia treatment of original manganese ion doped film,which shows a certain decolorization effect on dyes.