Calcium chloride (CaCl2) has been widely used to maintain the quality of fresh-cut fruits and vegetables because it stabilizes and strengthens the membrane system against fungal attacks. It is mainly applied via spray coating and dip coating techniques. This study explored a method of incorporating calcium chloride extracted from eggshells in a packaging material, thermoplastic starch (TPS), via a hot-melt extrusion process. The composites were characterized by FTIR, DSC, SEM-EDX and tensile testing. FTIR confirmed the chemical reactions between CaCl2 and TPS. DSC results showed a significant decrease in the heat of fusion by adding 20 wt% of CaCl2 content in TPS, indicating a drop in the degree of crystallinity. The Young’s modulus of TPS was not significantly affected by the incorporation of 10 wt% CaCl2 (P = 0.968), but reduced notably with the addition of 20 wt% CaCl2 (P = 0.05), indicating the plasticizer effect of the CaCl2. Physiochemical analysis of fresh-cut apple slices was assessed. Samples placed on the surface of the TPS/CaCl2 composites displayed less pH reduction, reduced antioxidant activity, more weight loss and increased reducing sugar compared to the samples placed on the surface of virgin TPS films. CaCl2 released from the TPS/CaCl2 films was measured and their antimicrobial activity was confirmed by bacterial inhibitory growth assessment. Fungal growth was observed on apple slices placed on virgin TPS film by day 21 while apple slices placed on TPS/CaCl2 20 wt% composites did not support any fungal growth for 28 days. In summary, TPS and eggshell-extracted CaCl2 showed the ability to maintain the quality of fresh-cut apples, and TPS/CaCl2 10 wt% composite could be a good option as a packaging material for fresh-cut fruits due to active antimicrobial activity and maintained Young’s modulus.
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.
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