Ductile, High-Lignin-Content Thermoset Films and Coatings

In the context of transitioning toward a more sustainable use of natural resources, the application of lignin to substitute commonly utilized petroleum-based plastics can play a key role. Although lignin is highly available at low cost and presents interesting properties, such as antioxidant and UV barrier activities, its application is limited by its low reactivity, which is a consequence of harsh conditions normally used to extract lignin from biomass. In this work, the use of glyoxylic acid lignin (GA lignin), rich in carboxylic acid groups and hence highly reactive toward epoxy cross-linkers, is presented. GA lignin, which is directly extracted from biomass via a one-step aldehyde-assisted fractionation process, allowed the preparation of thermoset films and coatings via a simple reaction with sustainable poly(ethylene glycol) diglycidyl ether and glycerol diglycidyl ether cross-linkers. This allows one to prepare freestanding films containing up to 70 wt % lignin with tunable mechanical properties and covalently surface-attached coatings containing up to 90 wt % lignin with high solvent resistance. Both films and coatings display antioxidant properties and combine excellent UV barrier activity with high visible transparency, which is attractive for applications in sustainable food packaging.

Enhancing the UV-Light Barrier, Thermal Stability, Tensile Strength, and Antimicrobial Properties of Rice Starch-Gelatin Composite Films through the Incorporation of Zinc Oxide Nanoparticles

The effects of zinc oxide nanoparticles (ZnONPs) on the properties of rice starch−gelatin (RS−G) films were investigated. ZnONPs were synthesized by a green method utilizing Asiatic pennywort (Centella asiatica L.) extract. The ZnONPs were rod-shaped, with sizes ranging from 100−300 nm. An increase in the concentration of ZnONPs significantly (p < 0.05) increased the thickness (0.050−0.070 mm), tensile strength (3.49−4.63 MPa), water vapor permeability (5.52−7.45 × 10−11 g m/m2 s Pa), and thermal stability of the RS−G−ZnONPs nanocomposite films. On the other hand, elongation at break (92.20−37.68%) and film solubility (67.84−30.36%) were significantly lower (p < 0.05) than that of the control RS−G film (0% ZnONPs). Moreover, the addition of ZnONPs strongly affected the film appearance, color, transmission, and transparency. The ZnONPs had a profound effect on the UV-light barrier improvement of the RS−G film. The crystalline structure of the ZnONPs was observed in the fabricated nanocomposite films using X-ray diffraction analysis. Furthermore, the RS−G−ZnONPs nanocomposite films exhibited strong antimicrobial activity against all tested bacterial strains (Staphylococcus aureus TISTR 746, Bacillus cereus TISTR 687, Escherichia coli TISTR 527, Salmonella Typhimurium TISTR 1470) and antifungal activity toward Aspergillus niger. According to these findings, RS−G−ZnONPs nanocomposite film possesses a potential application as an active packaging: antimicrobial or UV protective.