Effect of cellulose nanocrystals addition on electrospun silk fibroin composites for the valorization of sericulture production waste streams

Abstract

The accelerated development in sciences experienced during the last decades, along with the significant expansion of our knowledge about material synthesis and processing have produced relevant breakthroughs in several key disciplines and industries ultimately intended to improve personal and social welfare. Nevertheless, the continuous demand for sustainable solutions to address different problems has limited the use of traditional materials and has opened the door for the application of alternative approaches. Bombix mori silk, the most commonly used type of silk worldwide, is a naturally occurring polymer primarily based on a fibrillar protein called fibroin (SF), and a globular protein known as sericine. Silk has been used by mankind for thousands of years, predominantly as a staple for textiles, and for wound dressing. With its inherent biological and mechanical properties, silk is a promising candidate for use in biomedical applications such as tissue engineering, drug delivery and cell culture. However, in most cases in order to process and take advantage of these properties, sericine must be removed and fibroin dissolved to produce a solution of regenerated SF, which can be processed into various shapes depending on the final application. Electrospinning or electrostatic spinning, is a processing technique to generate ultra thin polymer fibers, where a strong electrostatic field is generated in the space between a reservoir containing a polymer in solution, and a conductive surface used as collector. In the last few decades, the interest in this technique has increased by virtue of the fascinating set of properties of electrospun materials including high porosities and surface areas, and enhanced thermal resistance and surface energy. Consequently, based on the properties of silk, electrospinning has been proposed as a potential processing technique, such that the production of SF electrospun nonwovens is expected to impact different areas like material science, nanotechnology, textiles, and biomedicine. Such applications have been hindered by reports regarding poor mechanical performance and degradation control for materials produced using regenerated SF. To address this, studies have examined reinforcing SF electrospun mats by blending with other polymers, or adding fillers to regenerated SF solution before electrospinning. It has also been reported that cellulose nanocrystals (CNC), with, high aspect ratios, interfacial adhesion and surface activity can be used to reinforce different polymers, resulting in improved mechanical properties. Additionally, due to its renewability, biocompatibility, biodegradability and availability, CNC may be a replacement for non renewable fillers. Hence, CNC might represent a new opportunity with potential revenues accruing to the forest products industry. This project is concerned with blending regenerated SF with CNC at different ratios, followed by electrospinning to generate SF/CNC composites with enhanced properties. The reinforcing capacity of CNC was assessed through mechanical and thermal testing, whereas morphological, chemical and rheological variations generated by the addition of CNC into SF were observed in each sample.