High strength and transparent polyvinyl alcohol/nanocellulose film with encoding fluorescence properties

Fluorescent anti-counterfeiting films have garnered significant attention due to their advantages of tunable emission, strong concealment, high difficulty of imitation, and good processability. In this work, two zinc sulfide quantum dots (ZnS QDs) with different fluorescence wavelengths were loaded to construct polyvinyl alcohol (PVA)/cellulose nanofiber (CNF) composite films with encoding anti-counterfeiting fluorescence properties. By controlling the loading ratio of the two ZnS QDs, coded signals with different fluorescence intensity ratios at emission wavelengths of 400 nm and 600 nm were achieved. The fluorescence intensity ratio of the film can be adjusted between 1.3×105 to 1×10-4, resulting in a wide range of blue to orange color changes under ultraviolet light. The fluorescence intensity ratio corresponds to the color change of the film, which can be used for fluorescence coding design. By fine-tuning the addition ratio of the two types of QDs, the fluorescence intensity ratio and the color of the film can be precisely controlled, enhancing the anti-counterfeiting performance of the film. PVA is employed as a carrier to maintain high transmittance (>80%). The strength of the film was elevated up to 90 MPa due to the reinforcing effect of CNF, and the hydrophobic property was significantly improved with a contact angle higher than 113° through modification with diphenyl diisocyanate (MDI). This type of fluorescent PVA/CNF composite film, with its high mechanical strength and transparency, holds great potential in the field of anti-counterfeiting.