Chiral nematic cellulose nanocrystal films: Sucrose modulation for structural color and dynamic behavior

This study explores the effect of sucrose addition on the properties of chiral nematic cellulose nanocrystal (CNC) films for potential food industry applications, including biodegradable packaging and food coloring. The addition of sucrose altered the films' structural color, shifting from blue in pure CNC films to aqua blue, green, yellow-green, and red with increasing sucrose concentrations (up to 21 %). Surface analysis revealed a reduction in contact angle from 96° to 48° due to sucrose's hydrophilic nature and smoother film surfaces. XRD results indicated a decrease in crystallinity from 84.5 % to 15.6 %, linked to the disruption of CNC alignment by sucrose. Mechanical testing showed reduced tensile strength (138 MPa to 35 MPa) and Young's modulus (1.634 GPa to 70 MPa) with higher sucrose content. Notably, over the storage time, films with 21 % sucrose exhibited dynamic structural coloration caused by localized sucrose recrystallization, leading to pitch shifts and color transitions. These findings demonstrate the tunable optical and mechanical properties of CNC-sucrose films, positioning them as promising materials for sustainable food packaging and responsive coatings.