Understanding the Effects of Secondary Structure on Mechanical Properties of Protein-Based Copolymers through Protein Screening

One of the most significant environmental issues today is plastic pollution, as plastic takes up to 450 years to degrade with more than 6 billion tonnes of it discarded in the environment since the 1950s. With up to 99% of plastics derived from non-renewable fossil fuels, it is time for an alternative. Protein-based copolymers are a strong candidate as plastic feedstock replacements since proteins are renewable and have functional groups that can facilitate cross-linking. Through understanding how secondary structures of protein-based copolymers affect mechanical properties, this will allow for the design of a plastic’s replacement with biodegradable material that can compare to plastic’s mechanical qualities. Three proteins with vastly different secondary structures (whey, zein, and gelatin) were copolymerized with comonomers forming rubbery segments and the influence of secondary structures was analyzed with tensile testing and FTIR spectroscopy. It can be concluded that copolymerization can be utilized in various proteins due to the presence of primary amines as copolymers with zein and gelatin were successfully prepared. A combination of proteins result in weaker mechanical properties compared to their pure counterparts. Gelatin was observed to have an increase β-sheet to ɑ-helix ratio in heated samples, but there was no indication of an improvement in mechanical properties. Although β-sheet to ɑ-helix ratio cannot be used to predict mechanical properties across proteins, this ratio correlates with specific properties in gelatin, where it has the potential to be utilized within the same protein type. Future work includes further microstructural characterization through electron microscopy or small angle x-ray scattering.