To meet the increasing demand for sustainable products, one can look to nature to scout new functional materials. For instance, the most brilliant and striking colours in plants are obtained using cellulose nanofibrils organised in helicoidal architectures. Interestingly, similar helicoidal architectures with analogous optical response can be obtained in vitro by self-assembly of cellulose nanocrystals (CNCs). CNCs are rod-like colloids capable of arranging into a liquid crystalline phase above a critical concentration in suspension. So far, the process that governs the self-assembly of CNCs into photonic structures was studied only at small scale. This neglects the limitations and challenges posed by large-scale and continuous processes which are prevalent in industrial contexts. Here we demonstrate how the self-assembly of CNCs can be precisely controlled to produce meters-long films using a roll-to-roll (R2R) equipment. Starting with commercially available material, the preparation of CNC suspension was optimised for R2R deposition to produce films with vibrant photonic colour across the visible range. Particularly, we show how the suspension properties, the casting parameters and drying time relate to the optical properties of the produced films. To validate the use of such materials for pigment preparation, we developed a protocol to produce a series of coloured microparticles from R2R-cast CNC films. The optical properties of the CNC microparticles were then assessed in various environment and finally benchmarked against other commercial effect pigments and glitters. These microparticles are compatible with a wide range of formulation, making them ideal to replace controversial mineral pigments based on mica and titanium dioxide as well as non-biodegradable glitter which is a known source of microplastic pollution.

Large-scale fabrication of structurally coloured cellulose nanocrystal films and pigments

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.