Study On Anti-counterfeiting Packaging Film Based On Functionalized Nanocellulose

Cellulose Nanocrystal(CNC)suspensions can form films with cholesteric phase liquid crystal structures after self-assembly by evaporation drying,which have unique structural color anti-counterfeiting properties.However,the application of pure CNC films is limited by the lack of flexibility.This thesis focuses on the surface functionalization of CNC by both chemical modification and physical compounding to prepare anti-counterfeit packaging films with good flexibility and adjustable structural color.The main research includes: surface esterification modification of CNC by L-malic acid,regulation of film flexibility and structural color by adjusting the ratio between L-malic acid and CNC,preparation of composite films with different colors by adjusting the content of PEGDA and combining with UV photosetting technology by physical blending of water-soluble precursor polyethylene glycol diacrylate(PEGDA)with CNC suspension,and anti-counterfeit patterned application of CNC/PEGDA composite films using direct ink writing based on polyvinyl alcohol(PVA)inks with different alcohol resolution.The results showed that the L-malic acid esterified CNC(CNC-g-MA)was a rod-shaped nanoparticle with an aspect ratio of about 15,and the absolute value of its suspension zeta potential was above 40 m V with good stability and it can be stored for a long time.When the ratio of L-malic acid to CNC increased to 4:1,the rod-shaped structure of CNC-g-MA particles was not obvious,the chiral nematic structure of the films disappeared,the reflection spectrum was closed to a straight line,and the films had no structural color.FTIR and XRD analysis showed that the esterification modification had little effect on the crystal form and chemical structure of CNC.Thermogravimetric analysis showed that the thermal stability of the esterification-modified CNC-g-MA films became better with the increase of L-malic acid.Mechanical analysis showed that the mechanical properties of the esterified CNC-g-MA films were improved compared with the pure CNC films.It was found that CNC-P/PEGDA composite films with different proportions prepared from eucalyptus bleached sulfate pulp all showed birefringence characteristics under polarized light,and the composite films all showed chiral nematic phase structure,and with the increase of PEGDA content,the reflection wavelength gradually red-shifted,the pitch gradually increased,and the flexibility became better and better,and the improvement was more obvious.The CNC-L/PEGDA composite film prepared from long-staple cotton,when the PEGDA content was less than 40%,has the same trend as the above,and the structural color was obvious,but when the PEGDA content reached 50%,the reflection wavelength was close to a straight line,and the birefringence characteristic disappeared under polarized light,and the composite film did not form a chiral nematic phase structure.The elongation at break of the composite films made from the above two raw materials are 10-60 times higher than that of pure CNC films,and the film flexibility was effectively improved.The watersensitive real-time response characteristics of the patterned composite film were studied by using the PR730 spectroradiometer.The results showed that the water-sensitive color response time of the patterned composite film printed with PVA1788 ink was significantly shorter than that of the patterned composite film printed with PVA1799 ink;Compared with the CNC-P/PEGDA composite film,the CNC-L/PEGDA composite film has a shorter watersensitive color response time and higher reflectivity under the same PVA ink printing.Since the color of the CNC-L/PEGDA patterned composite film changed quickly and was not easy to observe,the CNC-P/PEGDA composite film was then used for anti-counterfeiting patterning using a direct writing printer(DIW).