Color Stability Enhancement of Curcumin Bioplastic Films Using Natural Hybrid Fillers of Montmorillonite and Revalorized Cellulose

Abstract

Naturally colored packaging systems with improved color stability are essential as alternatives to mainstay synthetic colored conventional plastics, which typically present high toxicity and environmental pollution challenges. Herein, we report a versatile all green fabrication process for colored bioplastic films. Curcumin (CUR), a model plant-based colorant, was incorporated with newly developed natural hybrid fillers of montmorillonite (MMT) and biomass waste-recovered cellulose (CEL) for improved color stability performance. The CUR-based hybrid fillers were compounded with polylactic acid (PLA) to fabricate sustainable, colored composite films via hot-melt extrusion. Fourier transform infrared (FTIR), X-ray diffraction (XRD), and thermogravimetric analysis (TGA) results indicated good compatibility between the filler counterparts. Macro- and microstructure analysis of the colored films confirmed the good dispersion of the natural hybrid fillers within the PLA matrix. No change was observed in the thermal properties of the colored films, while dynamic mechanical analysis (DMA) results demonstrated a moderate increase in the films’ elastic modulus, from 870 to 970 MPa. The color entrapment efficiency of the hybrid filler-based films was evaluated through a study of CUR release in ethanol. A sustained CUR release profile reaching around 50% after 48 h was observed in the hybrid filler-based films in contrast to 80% in the PLA–CUR film. This was correlated with the significantly improved color stability of the PLA films containing the hybrid fillers under weathering conditions of UV irradiation, high temperature, and humidity. Over a period of 10 days, the CUR-CEL-MMT-based films had relatively consistent color stability, showing a color shift value (ΔE*) of only 1.1 in comparison to 5.1 for the PLA film containing only CUR.