Katherine A. M. Creber

Ionic conductivity of chitosan membranes

AbstractChitosan membranes with various degrees of deacetylation and different molecular weights (MW) were prepared by film casting withaqueous solutions of chitosan and acetic acid. Ultraviolet (UV) spectrometry and infrared (IR) spectrometry were used to determine thedegree of deacetylation (DDA) of chitosan. The viscosity–average MW of chitosan was measured in an aqueous solvent system of 0.25 MCH 3 COOH/0.25 M CH 3 COONa. The intrinsic ionic conductivities of the hydrated chitosan membranes were investigated using impedancespectroscopy. It was found that the intrinsic ionic conductivity was as high as 10 24 Scm 1 after hydration for 1 h. The tensile strength andbreaking elongation of the membranes were evaluated according to standard ASTM methods. The crystallinity and swelling ratio of themembranes were examined. A tentative mechanism for the ionic conductivity of chitosan membranes is also suggested.q 2002 Published by Elsevier Science Ltd. Keywords: Chitosan membrane; Hydration; Ionic conductivity

Improved mechanical properties of chitosan fibers

A highly deacetylated chitosan from shrimp with a degree of deacetylation of 95 ± 3% was prepared and spun into a monofilament fiber using a solution of 5% by weight chitosan in 5% by volume aqueous acetic acid. Samples of the spun fibers were immersed in separate solutions containing phosphate ions and phthalate ions, and subsequently washed and dried. The various solutions ranged in pH from 4.12 to 7.75. The highest dry mechanical properties resulted from solutions containing phthalate ions between 4.5–5.5 pH, and from solutions containing phosphate ions at pH 5.4. Immersion time was varied between 1 and 60 min at 25.8°C, and temperature was varied between 25.8 and 70.0°C, in the phosphate ion solutions at a pH of 5.8. Dry mechanical properties were highest at 25.8°C and after 1 h of treatment. Chitosan films were subjected to similar treatments in phosphate and phthalate ion solutions. Fourier transform infrared data (FTIR) on the films suggest that some interaction is occurring between the phosphate ions and the amine group on the chitosan backbone. An additional experiment was performed whereby the same chitosan was used to prepare a dope of 4% by weight chitosan in 4% by volume aqueous acetic acid with 30% by volume methanol. This solution was spun into fibers, but was subjected to a “final draw” by increasing the speed of the winder. With increasing the final draw, denier and elongation-at-break decreased, while the other mechanical properties showed a marked increase.

Crosslinking of chitosan fibers with dialdehydes: Proposal of a new reaction mechanism

A highly deacetylated chitosan from shrimp with a degree of deacetylation of 95.28 ± 3.03% was prepared and spun into a monofilament fiber using a solution of 4% (w/v) chitosan in 4% (v/v) aqueous acetic acid. Samples of the spun fibers were immersed in aqueous solutions containing glutaraldehyde and glyoxal, and subsequently washed and dried. When the concentration of crosslinking agent was varied at room temperature over a constant time of 1 h, dry mechanical properties improved up to a point after which increasing concentrations resulted in degradation. Immersion time was also varied between 1 and 60 min at 25.8°C, and temperature was varied between 25.8 and 70.0°C, at fixed concentrations of both glyoxal and glutaraldehyde. It was demonstrated that mechanical improvements might be rendered at higher temperatures over lesser times. However, it was also shown that at higher temperatures, fiber mechanical properties would begin to diminish. Chitosan films were subjected to similar treatments in aqueous crosslinking solutions. Fourier transform infrared data (FTIR) on the films suggest that some interaction is occurring between the glutaraldehyde or glyoxal and the amine group on the chitosan backbone.

Coagulation rate studies of spinnable chitosan solutions

The coagulation properties of some mixtures of 5% chitosan in 2% aqueous acetic acid were investigated with the goal of determining the optimal coagulation conditions for the spinning of chitosan fibers. The chitosan was characterized and found to possess a deacetylation value of 84.9 ± 0.2%. Molecular weight of the chitosan was also measured; based on intrinsic viscosity, the Mv value was 7.73 × 105 g mol−1, and based on high-pressure liquid chromatography, the Mw value was 1.14 × 105 g mol−1. Solutions of 5% chitosan/2% acetic acid were prepared, filtered, and extruded through a large-diameter hole syringe into coagulation baths of varying composition that were all strongly basic in nature, at least a pH of 12 or greater. For each coagulant, time was varied from between 22 s and 2 minutes at room temperature. A second set of experiments was conducted where the temperature was varied from 20°C to 70°C at a constant time of 45 s. In a third set of experiments, using a 1M NaOH coagulant, different chitosans were also analyzed. Throughout all of the experiments, a distinct moving boundary between coagulated and uncoagulated polymer was observed within the cylindrical-shaped polymer fibers. Using a series of equations based on Ficks 2nd Law, a straight line relationship has been demonstrated between boundary motion and time and between boundary motion and temperature for each coagulant tested. The activation energy for each coagulant was also determined.

Improvements in the drying process for wet‐spun chitosan fibers

Chitosan fibers were wet spun from a 6% by weight chitosan in 3% by volume acetic acid solution. The fibers were collected as a 20 filament yarn intended for use as a chaff substrate. The yarn had to be sufficiently dry following spinning to allow for winding and subsequent separation of the filaments. Drying of the yarn was attempted using various techniques including direct and radiant heat, forced air, and chemical drying agents. Product yarns were analyzed for ease of separation of the filaments, as well as comparison of mechanical properties. Individual fibers were evaluated on the basis of moisture content, surface morphology and fiber diameter. Results indicate that the particular drying method or agent used has a considerable impact upon all of the characteristics listed above. A methanol dry bath was found to provide optimum drying of the chitosan yarn, producing filaments with low moisture content that separated easily from one another. Methanol drying yielded chitosan fibers with smaller diameter, superior surface smoothness and superior mechanical properties to fibers dried using forced air, heat, or other tested drying agents such as acetone and isopropanol.