Improved water barrier and mechanical properties of soy protein isolate films by incorporation of SiO2 nanoparticles

Abstract

SiO₂ nanoparticles with different sizes were prepared under ultrasonic irradiation and incorporated with soy protein isolate (SPI) films. The morphology, size distributions and stability of the obtained SiO₂ nanoparticles were characterized by transmission electron microscopy and zeta potential measurements. The effects of differently sized SiO₂ nanoparticles on the morphological, physical, water barrier, oxygen barrier, mechanical and thermal properties of the SPI-based films were investigated. The results showed that the moisture content and total soluble matter values of the SPI-based films decreased with decreasing SiO₂ nanoparticle size and showed the lowest values of 16.70 ± 0.40% and 30.44 ± 0.06%, respectively, with a minimum particle size of 8.11 nm. Smallest particle sizes not only improved the contact angle and tensile strength by 21.12% and 17.65%, but also reduced the water vapor permeability and oxygen permeability of the SPI films by 11.79% and 9.66%, respectively. Furthermore, the addition of SiO₂ enhanced the thermal stability of the SPI films.