Macromolecular Composites as Physical Analogues for Biomatter Plastics

Innovative and sustainable technologies intended to prevent the harmful effects of sourcing, manufacturing, and disposing of synthetic plastics are rarely both biobased and biodegradable. Even many biodegradable plastics will not fully decompose in natural settings and despite the best recycling efforts, a significant portion of the plastic produced annually escapes into the biosphere. In an effort to create a fully biobased and backyard-compostable plastic alternative, we recently reported a bioplastic produced directly from spirulina biomass, without the need for chemical extraction or other preprocessing. The application of heated compression molding was found to transform the spirulina biomass into a rigid, compostable biomatter plastic with mechanical performance comparable to polylactic acid and polystyrene. In this work, we investigate the mechanism governing the self-bonding of spirulina during thermomechanical processing by creating a representative analogue for biomatter plastics. Varying ratios of pure carbohydrates, lipids, and proteins are physically combined and subjected to heated compression molding to form materials similar to algal bioplastics. The effect of the varying macromolecular composition, and the contribution of each class of macromolecule to the morphology of the produced bioplastics and their mechanical properties are evaluated through scanning electron microscopy (SEM) and flexural testing. Specifically, the varying ratio of protein to carbohydrates is utilized to compare the mechanical performance of biomatter analogues to several species of algae. The bonding mechanism of the biomatter analogues is first assessed qualitatively during sequential reprocessing to isolate contributions of dynamic bonding. Fourier transform infrared spectroscopy (FTIR) and x-ray photoelectron spectroscopy (XPS) are then utilized to quantitatively measure both secondary and primary bonding interactions between different macromolecular components of the analogue composites. Experimental measurements of bonding and cohesion are complemented by molecular dynamic (MD) simulations of multi-component macromolecular systems and a mechanism is proposed for self-bonding in biomatter plastics.