Corn straw cellulose nanocrystals: Preparation, structural coloration, and high-level anti-counterfeiting

Cellulose nanocrystals (CNCs) are drawing increasing attention for offering versatile and sustainable building blocks that can self-organize into lyotropic cholesteric liquid crystal phases in solid materials. However, their preparation has been limited to raw material sources holding significant economic and ecological value in agriculture and industry. Considering the high-value utilization of agricultural waste straws as well as the sustainable development of optical cellulosic materials, here, we demonstrate the extraction and preparation of CNCs capable of self-assembling into structural color arrays from waste corn straws. Notably, through a series of chemical treatments and controlled acid hydrolysis, straw CNCs with moderate dimension and surface charge density are obtained. In this case, the requirements of particle size, surface charge, and rheological properties are clarified for the self-assembly into helicoidal orders, and the kinetic arrest mechanism for generating structural colors is discussed. Furthermore, by utilizing wide structural color regulation and the left-handed cholesteric nature, and combining this with the “Coloring Klotski Puzzle” for the first time, a multi-color array having significant storage information capacity is fabricated, realizing advanced multi-level encryption. These findings pave the way for high-value utilization of agricultural wastes and sustainable development of photonic cellulosic materials. • CNCs prepared from waste corn straws can self-assemble for structural coloration. • kinetic mechanism of the formation of structural colors is clarified. • High anti-counterfeiting performance is achieved with the Coloring Klotski Puzzle.