Fabrication of homogeneous and enhanced soybean protein isolate-based composite films via incorporating TEMPO oxidized nanofibrillated cellulose stablized nano-ZnO hybrid

Abstract

Soybean protein isolate (SPI) is well-suited to the preparation of composite films due to its abundance, renewability, biodegradability, and favorable film-forming capacity. In this study, different SPI-based composite films were prepared by incorporating nano-ZnO and 2,2,6,6-Tetramethylpiperidine 1-oxyl (TEMPO) oxidized nanofibrillated cellulose (TNFC) separately or together. Nano-ZnO was introduced to endow the films with multifunction capability, while TNFC was introduced to stabilize the nanoparticles. Both the macro optical characterization and micro scanning electron microscope with energy dispersive X-ray (SEM–EDX) analysis indicated that TNFC could significantly decrease nano-ZnO aggregation and improve its dispersibility in the SPI matrix due to the mechanical restriction and physical adsorption effect of TNFC to the nano-ZnO. In addition to the improved dispersibility, incorporating nano-ZnO and TNFC benefitted the mechanical properties and thermo stability of the SPI-based composite films. The tensile strength and Young’s modulus increased by 73 and 57%, respectively, and the maximum degradation temperature increased by 10 °C, compared to that of the unmodified SPI film. These results can be attributed to the hydrogen bonds formed among SPI components, TNFC, and nano-ZnO, which were further examined by attenuated total reflectance-fourier transform infrared spectroscopy and X-ray diffraction analysis. After the incorporation of nano-ZnO, the SPI-based composite films also possessed excellent UV-shielding capacity and superior antimicrobial ability. To this effect, this work provides a valuable reference for nanoparticles dispersion and application in regards to polymer enhancement and multi-functionalization.