Morphology and ionic conductivity relationship in silk/cellulose biocomposites

The relationship between morphology and the ionic conductivity of polysaccharide-protein bio-electrolyte membranes is explored in this study. Structural proteins and polysaccharides form hydrophobic and electrostatic interactions, and the resulting matrices can exhibit novel and useful properties. However, transforming these natural biomacromolecules from their native state to a more usable form is challenging. The structural, morphological, thermal, mechanical and electrical properties of biomaterials composed of microcrystalline cellulose and Bombyx mori silk when regenerated together using ionic liquids and various coagulation agents were investigated using a diverse set of techniques including Fourier transform infrared spectroscopy, SEM, TGA, DSC, X-ray scattering, AFM-based nanoindentation and dielectric relaxation spectroscopy. The surface topography of the films reveals morphological changes with varying coagulation agents and ionic liquids. It was found that the thermal and mechanical properties were dependent on intermolecular interactions dictated by the type of ionic liquid used during the coagulation process. X-ray scattering provided information on how the 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 beta-sheet content and ionic conductivity and cellulose crystallinity. The results provided evidence that the ionic conductivity is dependent on protein beta-sheet content and cellulose crystallinity. (c) 2019 Society of Chemical Industry