Morphology and ionic conductivity relationship in silk/cellulose biocomposites

Abstract

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 β‐sheet content and ionic conductivity and cellulose crystallinity. The results provided evidence that the ionic conductivity is dependent on protein β‐sheet content and cellulose crystallinity. © 2019 Society of Chemical Industry

Protein and Polysaccharide-Based Fiber Materials Generated from Ionic Liquids: A Review

“…It was also observed that most of the morphology changes occurred as a function of anion type in ionic liquids. In one study [25], a 10:90 ratio of B. Mori silk-cellulose films was investigated as a function of ionic liquid type. Six types of ionic liquids were used in this study, including AMIMCl, BMIMCl, EMIMCl, EMIMAc, 1-Butyl-3-methylimidazolium bromide (BMIMBr) and 1-Butyl-3methylimidazolium methane sulfonate (BMIMMeSO3).…”

“…This is because the biopolymers are separated due to their electrostatic interactions with the anions in the ionic liquid. The removal of the solvent allows for the biopolymers to interact with each other using hydrogen bonding and causes them to aggregate into a fiber [25]. In addition to ionic liquid extraction, water also helps to modify the diameter and structure of the nanofibers.…”

“…They have an advantage over organic solvents as they do not lead to unwanted side products and are considered as a green alternative as they encompass the ability to be reusable [21]. The composition of an ionic liquid is very important as it combines a bulky asymmetric cation with a weakly coordinated anion, which can cause changes in the intra-and inter-molecular interactions [22][23][24][25]. When biopolymers are dissolved in ionic liquids, the anion forms hydrogen bonds with hydroxyl groups in the biopolymer, disrupting the naturally occurring hydrogen bonding network while the cation associates with the ether oxygen atoms and CH groups [26], thus causing a change in the molecular conformation.…”

In Focus: Poly(ionic liquid)s in Polymer Science and Engineering at the Fall 2018 American Chemical Society National Meeting

“…Salas-de la Cruz and coworkers have investigated the morphological and conductive changes that occur as a result of using ionic liquids (EMIMCl and EMIMOAc) in the dissolution of cellulose/silk biocomposites. 5 Correlations between ionic conductivity, cellulose crystallinity and -sheet content are discussed. X-ray scattering studies showed that coagulation with hydrogen peroxide lead to a high degree of crystallinity and -sheet content which, in turn, resulted in higher ionic conductivity.…”

“…Ionic liquids have become increasingly important in the extraction and dissolution of biomacromolecules. Salas‐de la Cruz and coworkers have investigated the morphological and conductive changes that occur as a result of using ionic liquids (EMIMCl and EMIMOAc) in the dissolution of cellulose/silk biocomposites . Correlations between ionic conductivity, cellulose crystallinity and β ‐sheet content are discussed.…”