The significance of protein aggregation has been extensively studied in biomedical and food research. While biomaterials derived from plant proteins, such as soy protein, as green material alternatives, have gained enormous attentions in various industrial and engineering fields including food packaging and adhesives, etc., the roles of protein aggregation in material properties and functionalities are still insufficiently understood, which will be the main focus of this study.
In this study, soy protein isolate (SPI) with different aggregated structures, was investigated as a functional modifier to tune the microstructures, ferroelectric properties and dielectric properties of two polymers: hydrophobic poly(vinylidene fluoride) (PVDF) and hydrophilic poly(ethylene oxide) (PEO). The aggregated structures of SPIs were obtained via various controlled denaturation and modification processes, including heat treatment, high-energy sonication, tuning pH values, and usage of denaturation agents. Denatured SPIs were then applied to polymer matrices. It was found that SPI aggregation and SPI-polymer interactions were strongly subjected to the denaturation conditions, as well as properties of polymer matrix, which led to distinctive morphologies and structures of the resulting polymer/SPI films, investigated via scanning electron microscope, confocal laser scanning microscopy, X-ray diffraction spectrum and Fourier transform infrared spectroscopy. The changes in microstructures consequently caused the variation of ferroelectric and dielectric properties of the films, leading to different dielectric polarization and energy storage properties. The energy storage performances of the polymer/SPI films in this study were sensitive to the denaturation conditions of SPI, due to altered SPI aggregation and distinctive SPI-polymer interactions. Regardless of polymer matrices, it was found that high temperature heat denaturation of SPI accounted for the most desirable dielectric energy storage performances with high released energy density and high energy storage efficiency. Meanwhile, the polymer matrix also plays an important role. While the highest polarization was achieved in PVDF/SPI films via high energy sonication denaturation of SPI, the SPI denatured by sonication was responsible for the lowest dielectric polarization in PEO/SPI films, suggesting the importance of polymer matrix in SPI aggregation and SPI-polymer interactions.