Fabrication of Cellulose Nanofiber-Reinforced Polylactic Acid Nanocomposite Containing Anthocyanidin-Based Red Cabbage Extract For Anti-counterfeiting Thermochromic Ink

Hydrogel inks that alter color in reaction to temperature change were developed for self-healing anti-counterfeiting printing applications. A self-healing ink of cellulose nanofibers (CNF)-reinforced polylactic acid (PLA) hydrogel immobilized with anthocyanidin (ACD) chromophore that was isolated from a red cabbage plant was prepared for security encoding. The current self-healable ink (CNF@PLA) showed efficient thermochromism with high reversibility. Using various concentrations of ACD-based red cabbage extract, different thermochromic inks were developed. Homogeneous films were applied to a paper surface to display a purplish shade (614 nm) at room temperature, demonstrating a color change to reddish (449 nm) when increasing the room temperature to 60 °C as proved by absorbance spectral analysis and CIE (International Commission on Illumination) Lab coordinates. CNF were employed as dispersive nanofiller to avoid the agglomeration of IACD particles. Transmission electron microscopy (TEM) showed that the diameters of IACD nanoparticles ranged between 12–19 nm, and CNF showed diameters of 50–80 nm. Energy dispersive X-ray (EDX), scanning electron microscopy (SEM), and infrared spectroscopy (FTIR) were used to examine the morphological properties and elemental analysis of thermochromic samples. Both rheological and mechanical features were determined for hydrogel and printed papers, respectively. The cytotoxicity study and antimicrobial activity of ink (CNF@PLA) were also reported.