Preparation And Anti-Counterfeiting Patterning Of Chiral Nematic Cellulose Nanocrystals

Cellulose nanocrystals(CNC)have the advantages of high crystallinity and biocom-patibility.However,until recent years,people began to use the self-assembly behavior of CNC in aqueous solution as a template to prepare functional materials with chiral nematic structure and unique optical properties by blending with suitable precursors.In this thesis,CNC was used as template to synthesize functional materials with chiral nematic structure and their unique optical properties were studied Using Eucalyptus bleached kraft pulp as raw material,cellulose nanocrystals were prepared by sulfuric acid hydrolysis.The self-made CNC and glycerin were mixed to form a composite film with chiral nematic structure.The color of the composite film was adjusted by changing the content of glycerin.On the other hand,waterborne polyurethane(WPU)was prepared,and then CNC and WPU were blended to prepare CNC/WPU composite film with chiral ne-matic structure.The color and strength of CNC/WPU composite film can be controlled by changing the amount of wup added.Finally,the anti-counterfeiting application of CNC/WPU composite film was carried out.Zeta potential and nanoparticle size analyzer show that the average particle size of cellulose nanocrystals is 220 nm,zeta potential value is-32 MV,and the average particle size of WPU is 59.3 nm;XRD analysis shows that the crystallinity of CNC is 88.65%;thermogravimetric analysis shows that CNC has good thermal stability below 250?;CNC suspension has bright rainbow color after drying and film formation,which is obvious un-der polarized light microscope Birefringence effect;scanning electron microscope analysis shows that the cross section of CNC film has the layer structure of cholesteric liquid crys-tal,and there are a lot of porous structures in the cross section of CNC/glycerin composite film,which are caused by the volatilization of glycerin;UV-Vis spectrum analysis shows that with the increase of the amount of glycerin added,the maximum reflection wavelength of CNC/glycerin composite film moves from 200nm to 620nm With the increase of the amount of WPU added,the maximum reflection wavelength of CNC/WPU composite film moves from 250nm to 600nm;when the amount of WPU added is 0.262g,the maximum elongation at break of CNC/WPU composite film is 238.11%;The anti-counterfeiting pat-terning of CNC/WPU composite film was carried out by using Nordson direct writing printer.It is found that the photon pattern has a real-time color comparison reaction in wa-ter.The line width of the photon pattern and the color of swelling in water can be controlled by changing the extrusion pressure of the direct writing printer.