Lignin nanoparticles enable and improve multiple functions of photonic films derived from cellulose nanocrystals.

Flexible photonic materials derived from cellulose nanocrystals (CNCs) have attracted significant attention, particularly in multifunctional sensors, intelligent detection, and anti-counterfeiting applications. However, the major bottleneck with traditional CNC photonic materials is the provision of flexibility and multifunctional properties which often comes with compromises in optical properties. To address these challenges, we incorporated organosolv lignin nanoparticles (LNPs) and polyethylene glycol (PEG) into CNC films. LNPs were produced from sugarcane bagasse using various solvents, resulting in nanoparticles with distinct structural and chemical properties, such as different sizes and surface chemistries. The addition of LNPs and PEG to CNC films led to enhanced flexibility, strong iridescence, improved thermal stability and superior UV-blocking performance. Interestingly, the intercalation of LNPs significantly improved the strain at break by 89.6 % with slight increase of 7.7 % and 23.1 % in tensile strength and young's modulus respectively. Additionally, distinguished UV-blockage performance of up to 99.9 % in the UVB region and 94 % in the UVA region was also achieved in CNC-LNP-PEG films. The films exhibited varying responses to several organic solvents and HCl gas with reversible color changes. These responses were attributed to the distinct surface chemistries of the LNPs, which influenced their interactions with the CNC matrix through mechanisms such as hydrogen bonding and hydrophobic interactions. This study highlights the potential of CNC-LNP-PEG composite films for advanced applications in chemical safety and anti-counterfeiting measures, demonstrating the importance of composite formulation and processing conditions in achieving desirable properties.