Iridescent Patterns Production from Solid Film Cellulose Nanocrystals Prepared from Coffee Husks

Abstract

The dire need for environmental conservation has spurred the exploration of novel approaches for developing biodegradable and sustainable materials sourced from natural origins, particularly for engineering applications and these include cellulose. Utilizing coffee husks, a waste product from coffee production, offers a sustainable source of cellulose, effectively diverting waste from the environment and turning it into a valuable and profitable resource. The cellulose content within coffee husks were extracted through alkaline treatment, after which, acid hydrolysis was done, yielding cellulose nanocrystals (CNCs) that were utilised to create iridescent films. The process involved treating the coffee husks with sodium hydroxide to obtain cellulose, followed by bleaching with sodium hypochlorite. Acid hydrolysis using gaseous HCl was then employed yielding cellulose nanocrystals. The application of HCl improved the iridescent film quality for secure sheets by preventing the whiskers that are usually seen when sulfuric acid is used. This raises the overall quality and security of the finished product. To avoid contamination, the CNC suspension was carefully transferred into Petri dishes made of polystyrene, and the suspension evaporated at controlled temperature in an oven, resulting in a solid CNC film. To introduce patterns on the film, the Petri dish containing the CNC suspension was placed on a mold engraved with a specific pattern. Heating of the mold imparted different colors onto the film. The outcome of heating the CNC Suspension involved the self-assembly of CNCs into a multitude of colorful and iridescent films possessing unique optical properties. Additionally, these films exhibited water resistance, luminous color variations based on viewing angles, fluorescence, and reflection of left-handed circularly. The value addition of coffee husk waste, which makes it a cleaner environmental product while producing security sheets, is the significance of this work particularly the inclusion of cyclic redundancy, which guarantees improved security features.