Additive printing of recyclable anti-counterfeiting patterns with sol-gel cellulose nanocrystal inks

The assembly of cellulose nanocrystals (CNCs) that produce attractive structural color shows great potential in anti-counterfeiting application, but their processability and recyclability remain unsatisfactory due to the strong hydrogen bonds between CNCs. For the first time, optical anti-counterfeiting patterns are obtained by additive printing of surface-functionalized CNC inks (CNC-DC5700-NPES). The surface-functionalized CNC inks are prepared by sequential modification of CNCs with organosilane (DC5700) and polyoxyethylene ether (NPES), which show good flowability under shearing force and transform into a gel-like phase rapidly after printing, making possible ink-jet printing without additives. The printed patterns are transparent under natural light but show vivid interference color, showing anti-counterfeiting features between crossed polarizers. The texture and optical properties of the printed patterns can be facilely controlled by tuning the printing parameters, such as nozzle diameter, writing angle, and filling width. Moreover, the CNC-DC5700-NPES patterns with a core-shell structure could be collected in various solvents and reprinted after removing solvents. This work provided a new pathway for the preparation of optical anti-counterfeiting patterns from biomass resources.