Numerical study on mechanisms of soy protein as a functional modifier for polymer materials

Abstract

In the past decades, to meet the increasing demands for protecting the environments, taking bio-degradable green materials as alternatives to traditional petroleum-based polymer materials has become a global interest. From the previous studies, it is demonstrated that soy protein-based biomaterial is one of the promising candidates to be used as functional modifier for polymers, due to the complex structures of protein and diverse interactions with polymers. However, the underlying mechanisms remain unclear. Molecular dynamic (MD) simulation is a power tool and can provide insights in understanding the conformational changes of protein molecules, as well as the interactions between proteins and polymers. In this study, 11S molecule of soy protein is chosen as a representative, and three different denaturation processes are applied via MD simulation, including heat denaturation at two temperatures and the breaking of disulfide bonds. It is observed that by controlling the denaturation conditions, the structures and properties of the protein molecules can be manipulated. Low temperature condition has limited impacts on the structures and properties of 11S molecules; high temperature process, on the other hand, is found to lead to an intensive secondary phase transition of the molecules; moreover, by breaking the disulfide bonds, the hydrophobic residues of the molecules can be largely exposed, potentially forming strong interactions with the hydrophobic poly(vinylidene fluoride) (PVDF) polymer. Besides, different protein-polymer interactions could result in various property-modification effects on PVDF polymer. For instance, due to the strong interaction between PVDF and the protein molecule denatured without disulfide bonds, the dipole moment of PVDF at the interface is largely enhanced, and the polarizability under external electric fields is also improved, which is in agreement with experimental result.