Preparation And Properties Of Cellulose-based Anti-counterfeiting Materials

Cellulose is a kind of renewable natural polymer with abundant reserves.As the basic unit of cellulose,nanocellulose possesses numerous fascinating properties including excellent mechanical properties,unique optical properties and good biocompatibility,which make them have great application potential in the field of optical encryption and anticounterfeiting materials.At present,nanocellulose-based anti-counterfeiting materials have some problems such as unfriendly preparation process for the environment,poor mechanical properties,limited optical encryption methods and anti-counterfeiting functions,which greatly limit their development and application.In this paper,high-performance cellulosebased anti-counterfeiting materials were prepared through different green processes and material systems,which not only solved the above problems,but also demonstrated their related applications as optical encryption devices and anti-counterfeiting functional materials.The main research contents are as follows:(1)Cellulose nanofibers(CNFs)were assembled with Cd Te quantum dots in an orderly manner by the interfacial polyelectrolyte complexation(IPC)spinning method,and cellulose-based fluorescent fibers were prepared.The effects of Cd Te quantum dots with different fluorescent colors on the structure and properties of the fibers were systematically investigated,and the fibers were woven into fluorescent labels to explore their potential applications in the fields of concealed fabrics and optical anti-counterfeiting materials.The results showed that the fluorescent fibers exhibited highly oriented structure and excellent mechanical properties,which tensile strength could reach the highest(761.52 ± 8.31)MPa.The fluorescent labels made of the fibers could be hidden in white textiles under natural light,and exhibited obvious photoluminescence phenomenon after being irradiated by ultraviolet lamps,showing good optical encryption performance and application potential as fluorescent anti-counterfeiting fabrics.(2)In order to broaden the application fields of cellulose-based anti-counterfeiting materials and improve their optical encryption properties,cellulose nanocrystal(CNC)films with optically active structural colors were obtained by evaporation-induced self-assembly(EISA)method,and the polyhydroxyethyl acrylate(PHEA)was intercalated by in-situ polymerization method to improve the toughness of CNC films.By adjusting the content of PHEA,the toughening mechanism of PHEA on CNC films and the evolution law of structural color were explored.The results showed that the addition of PHEA could significantly improve the toughness of CNC film.When the ratio of CNC to PHEA is 1:1,the film has the highest elongation at break(12.62 ± 0.58)%,which is nearly 10 times higher than that of the film with the ratio of 1:0.1.In addition,the films could reflect left-handed circularly polarized light to generate structural color,which gradually changed from bluegreen to orange-red with the increased of PHEA content,that were expected to be used in color anti-counterfeiting materials and optical encryption devices.(3)In order to further improving the optical encryption performance of the films,multicolor tunable circularly polarized fluorescence(CPL)films were prepared by EISA method with CNC as the host and Cd Te quantum dots as the guest.By adding waterborne polyurethane(WPU)to improve the brittleness of the films and regulating the maximum UV absorption wavelength,the change rule of the CPL signal of the films were explored.The results confirmed that the maximum absorption wavelength of the films gradually red-shifted with the increased of WPU content.When the maximum absorption wavelength was close to the fluorescence emission wavelength,the CPL signal of the film was the strongest.Besides,the addition of Cd Te quantum dots exhibited little effect on the films structure and mechanical properties.Therefore,the prepared cellulose-based structural color/fluorescence films possessed good mechanical properties and dual optical encryption properties,which provided a new idea for the research and development of chiral optical encryption devices and anti-counterfeiting functional materials.