Morphology and ionic conductivity relationship in silk/cellulose bio-composites

In this paper, the relationship between morphology and ionic conductivity of polysaccharide-protein bio-electrolyte membranes is revealed. Structural proteins and polysaccharides form hydrophobic and electrostatic interactions, and the resulting matrices from the mixture can exhibit novel and useful properties. However, transforming these natural biomacromolecules from their native state to a more usable form is non-trivial. This paper focuses on studying morphological and physicochemical properties of biomaterials composed of microcrystalline cellulose and Bombyx Mori Silk when regenerated together using ionic liquids and various coagulation agents. Various techniques were implemented to investigate the structural, morphological, thermal, mechanical, and electrical properties, including Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC), X-ray scattering, atomic force microscopy (AFM), and dielectric relaxation spectroscopy (DRS). The surface topography of the films reveals morphological changes with varying coagulation agent and ionic liquids. It was found that the thermal and mechanical properties were dependent on intermolecular interactions dictated by the type of ionic liquid during the coagulation process. X-ray scattering provided information on how cellulose crystallinity varied with coagulation agent. Specifically, samples coagulated with hydrogen peroxide showed an increase in cellulose crystallinity impacting properties such as elasticity, hardness and ionic conductivity of the biocomposites. In addition, the results revealed a strong correlation between the beta-sheet content and ionic conductivity and cellulose crystallinity. The results provided evidence to suggest that the ionic conductivity is dependent on protein beta-sheet content and cellulose crystallinity.