Abstract
Adipic acid was evaluated as a novel solvent for wet spinning of chitosan fibers. A solvent with two carboxyl groups could act as a physical crosslinker between the chitosan chains, resulting in improved properties of the fibers. The performance of adipic acid was compared with conventional solvents, i.e., lactic, citric, and acetic acids. Chitosan solutions were injected into a coagulation bath to form monofilaments. Sodium hydroxide (NaOH) and its mixture with ethanol (EtOH) were used as coagulation agents. Scanning electron microscopy confirmed the formation of uniform chitosan monofilaments with an even surface when using adipic acid as solvent. These monofilaments generally showed higher mechanical strength compared to that of monofilaments produced using conventional solvents. The highest Young’s modulus, 4.45 GPa, was recorded for adipic acid monofilaments coagulated in NaOH-EtOH. This monofilament also had a high tensile strength of 147.9 MPa. Furthermore, taking advantage of chitosan insolubility in sulfuric acid (H2SO4) at room temperature, chitosan fibers were successfully formed upon coagulation in H2SO4-EtOH. The dewatering of fibers using EtOH before drying resulted in a larger fiber diameter and lower mechanical strength. Adipic acid fibers made without dehydration illustrated 18% (for NaOH), 46% (for NaOH-EtOH), and 91% (for H2SO4-EtOH) higher tensile strength compared to those made with dehydration.
Highlights
Chitin, the second most abundant polysaccharide in nature, can be found naturally as ordered crystalline microfibrils forming structural components in the exoskeleton of arthropods and the fungal cell wall
To evaluate the effect of different spinning solvents on the fiber properties, chitosan was dissolved in lactic acid (LA), acetic acid (AC), citric acid (CI), or adipic acid (AD)
Chitosan monofilaments are usually created by wet spinning using lactic acid, citric acid, or acetic acid as a solvent
Summary
The second most abundant polysaccharide in nature, can be found naturally as ordered crystalline microfibrils forming structural components in the exoskeleton of arthropods and the fungal cell wall. Chitosan is not soluble in water due to its hydrogen bonds and hydrophobic interactions between the chain segments. It can be dissolved in dilute acidic solutions such as aqueous solutions of acetic acid, citric acid, lactic acid, malic acid, and formic acid, due to the presence of non-bonding pairs of electrons in the amino groups, which become protonated in acidic solutions. Chitosan fibers are biocompatible, biodegradable, and non-toxic. Chitosan can be degraded in vivo by several enzymes, mostly by lysozyme Based on this property, absorbable surgical suture was produced using the wet spinning system, from chitosan incorporated with N-acetyl-DGlucosamine (GlcNAc) [7]. The most common technique used to produce chitosan fibers is wet spinning
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