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theses

Structural proteins and polysaccharides form hydrophobic and electrostatic interactions when mixed, and the resulting matrices can exhibit novel and useful properties. This study investigates the morphology, and physicochemical properties, especially ionic conductivity, of a mixture of silk and cellulose biomacromolecules as a function of composition, ionic liquid type, coagulation agent, and ionic liquid concentration. The structural, morphological, thermal, mechanical, and conductive 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 scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC), X-ray scattering, atomic force microscopy (AFM) based nanoindentation, and dielectric relaxation spectroscopy (DRS). The results demonstrate that the thermal, electrical, 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 cellulose semicrystallinity varied with coagulation agent, composition, and ionic liquid concentration. Specifically, samples containing a higher percentage of cellulose and coagulated with hydrogen peroxide showed an increase in cellulose semicrystallinity, ultimately impacting properties such as elastic modulus, hardness, and ionic conductivity of the biocomposites. Also, the results revealed a strong correlation between β-sheet content and cellulose semicrystallinity and ionic conductivity. Specifically, it was seen that when the composition of silk and cellulose is equal, or the composition of silk is higher, the ionic conductivity is dependent on protein β-sheet content, with increasing β-sheet content leading to higher ionic conductivity. When the cellulose composition was higher than the silk, cellulose morphology and physicochemical properties became an essential factor in determining the ionic conductivity of the biocomposites. Furthermore, a change in the ionic liquid concentration in the biomaterial resulted in strong morphological and ionic conductivity changes. For these reasons, it is possible to suggest that ionic conductivity is dominated by molecular composition, ionic concentration, and morphology, as stated by the Vogel-Fulcher-Tammann model.

ETD_10966

M.S.

Includes bibliographical references

doi:10.7282/t3-vxef-n219

ETD graduate

The author owns the copyright to this work.