Physical and thermal improvement of bioplastics based on potato starch/agar composite functionalized with biogenic ZnO nanoparticles

This study investigated potato starch/agar-based bioplastics' structure, properties, and biodegradability by adding ZnO nanoparticles (NPs) biogenically synthesized using Coriandrum sativum extract. ZnO NPs presented crystalline structure, good optical properties, and a size of 6.75 ± 1.4 nm, which were added at various concentrations (419.66–104.23 ppm) in bioplastics and their presence was confirmed via EDS elemental analysis and X-ray fluorescence. The highest NPs concentration contributed to a smoother surface, while FTIR and Raman analyses suggested interactions between the NPs and functional groups of the biopolymeric matrix. ZnO NPs addition slightly reduced bioplastic transparency but significantly improved UV-A and UV-B blocking capacities. It also increased hydrophobicity, evidenced by a 22 % reduction in water absorption and a 55 % increase in contact angle. Thermogravimetric analysis (TGA) indicated that NPs raised the bioplastic's thermal stability. Mechanical property tests showed that ZnO NPs concentrations had negligible or negative effects probably due to the heterogeneous distribution of NPs, or the non-isotropic characteristic of the bioplastic. Finally, biodegradability assays in seawater and soil revealed over 43.5 % and 66 % degradation after 15 and 28 days, respectively. Therefore, biosynthesized ZnO NPs mainly enhanced the bioplastic's UV-blocking capacity, hydrophobicity, and thermal properties, offering an eco-friendly option for future studies/applications.