Design and Characterization of Chitosan-Based Nonwoven Fibrous Materials

Chitosan-based nonwoven fibrous materials have found applications in many fields, especially in wastewater treatment, food packaging, wound dressing, and tissue engineering. Additive polymers, such as other biopolymers and synthetic polymers, are often used to improve the functional utility of chitosan-based fibrous materials. However, the interactions between chitosan and additive polymers are poorly understood since conventional characterization methods for solid-phase materials such as chitosan/biopolymers systems have some limitations, especially when overlapping spectral signatures are convoluted. Hence, the use of complementary methods and spectral deconvolution becomes important for the study of polymer interactions since it governs the structure and properties of such chitosan-based fibrous materials. The overall goal of this thesis research focuses on developing novel chitosan-based nonwoven micro-/nanofibrous materials with good water stability, various adsorption properties, and tunable surface features, along with an investigation of the formation of these materials. The overall goal can be divided into three objectives. In Chapter 4, carboxymethyl chitosan (chi)/alginate/poly(ethylene oxide) (PEO) self-assembled sponges (nonwoven microfibrous materials) were prepared via freeze-drying. Their structurally modified forms were prepared via heat treatment (annealing). Original and thermally treated forms were characterized by a novel characterization method based on Raman spectral imaging. The results highlighted the multi-functional role of PEO and the value of Raman spectral imaging in understanding the interactions occurring for chitosan-based materials. In Chapter 5, various chi/hydroxypropyl-β-cyclodextrin (HP-β-CD) electrospun nanofibers were prepared and characterized by the Raman spectral imaging method (developed in Chapter 4) and other characterization methods. The results highlighted the formation of a supramolecular assembly (chi + HP-β-CD + solvent) and its importance to facilitate the electrospinning of chi/low molecular weight polymers systems. In Chapter 6, the chemically modified chitosan/low molecular weight (LMw) PEO electrospun nanofiber was prepared by forming the chi/LMw PEO assembly. A porous chitosan nanofiber was prepared through physical treatment. The results revealed that tunable porous surface features could be obtained using LMw PEO as a sacrificial template. Moreover, a dye uptake study with Methylene blue was conducted that revealed the porous fiber materials displayed enhanced uptake. The studies reported herein provide a greater understanding of the interactions between chitosan and additive polymers, which contribute to the design of novel chitosan-based materials with tunable surface features and various physicochemical properties.