Researches On Toughning Modification Of Cellulose Nanocrystals Iridescent Films

In this paper,several strategies were adopted to improve the toughness of cellulose nanocrystals(CNC)iridescent film.We used UV-Vis,SEM,AFM,FTIR,XRD,TGA,DMA methods to explore the properties of CNC iridescent films.First,form I CNC suspension was prepared by sulfuric acid,and by vacuum assisted self-assembled methods(VASA)to get uniform color iridescent film.The sonication time have a great influence on the color of CNC iridescent film.The colors of iridescent film have redshift when the sonication time is increasing.The iridescent films still remain iridescent color after the films treated by NaOH solution.The change of crystal form and the decomposition in the NaOH treatment make the iridescent color redshift first then blueshift.The higher crystallinity of form I to a lower crystallinity of form II makes the iridescent film show high toughness.And the thermostability of iridescent film improved a lot because of the elimination of sulfate ester groups in the alkali treatment.We prepared CNC/polyvinyl alcohol(PVA)composite iridescent films by VASA technology.With improvement of PVA content in the CNC/PVA composite films the color of film show redshift tendency in the casting technology to prepare film,however in the VASA technology,the improvement of PVA caused the blueshift of iridescent film,which was caused by the extension of drying process with more polymers in the composite suspension.The composite films still remain their iridescent color after the alkali treatment.The films processed by NaOH solution show high toughness and thermostability similar to the pure CNC films processed by alkali treatment.Nitrile rubber latex(NBR)was added into the CNC suspension to prepare composite iridescent film based on the high elasticity of rubber materials.By casting evaporation technology,we successfully prepared CNC/NBR iridescent film.The addition spherical latex make CNC/NBR composite film form phase separation structure.CNC/PVA iridescent film will lose CNC's self-assembled ability when the mass ratio of CNC/PVA is 1:0.6.However when the CNC/NBR ratio is 1:0.9,the composite film still show iridescent color.And the addition of NBR improves the mechanical properties of composite film,the thermostability of composite film improved a lot because NBR packages the CNC.