The production of fibres from chitosan

A wet spinning procedure was developed for the production of chitosan fibres. The dope was prepared by dissolving 5% w/w medium grade chitosan in 2% aqueous acetic acid; after filtration and degassing, fibres were produced by extrusion of the dope into an aqueous NaOH bath and further drawing, washing, drying and winding. The effect of changes in the spinning conditions on the properties of chitosan fibres was studied; it was found that spinning variables such as jet stretch ratio, draw ratio and coagulation bath concentration had little effect on the fibre properties, though higher draw ratios would be obtained at lower jet stretch ratios and slightly improved tenacities were obtained using more dilute NaOH solutions as the coagulant. The drying methods, however, had a big effect on the fibre properties; the fibres obtained by air drying had a much higher extensibility than those dried by radiant heating. The addition of i-propanol to the dope gave much whiter fibres while the addition of Na2S04 to the coagulation bath produced the strongest fibres. Overall, the fibres produced in this work had tenacities between 0.61 and 2.48 g/dtex and extensibilities of 5.7 to 19.3%, with individual fibre decitex ranging from 2.5 to 7.5. The fibres had round cross-sections and a smooth surface when dried with heating or a rough surface when dried with acetone. The chelating properties of the chitosan fibres were studied; it was found that upto 8% Cu(II) and 5% Zn(II) can be absorbed into the fibres within 40 minutes. The Cu(II) and Zn(II) ions had strong effects on the fibre tensile properties; both dry and wet strengths were remarkably increased with the absorption of metal ions. In addition, the fibres chelated with ZnS04 had a LOI estimated to be 52%. The chitosan fibres were acetylated using acetic anhydride in methanol. It was found that 88% of the amine groups were acetylated within 30 minutes at 40 °C. The effects of temperature, time, ratio of anhydride to amine groups and the addition of water were studied; it was found that the addition of water to the methanol anhydride mixture greatly accelerated the reaction. Some O-acetylation was noticed in the reaction and this was removed by a treatment using 1 M aqueous NaOH. The changes in fibre properties after acetylation were also studied. It was found that after the acetylation process, the fibre had a better thermal stability and improved dry and wet strength. However, the fibre lost its chelating ability when substantially acetylated.