This thesis investigates the partial dissolution of various natural animal-hair yarns (merino wool, cashmere, camel hair, yak and mohair) in the ionic liquid 1-ethyl-3-methylimidazolium acetate ([C2mim][OAc]) for a range of processing times and temperatures. Following partial dissolution, the processed yarns were coagulated in water and then dried at room temperature. Optical microscopy of the partially dissolved yarns showed that the cross-sectional area of the yarns decreased as dissolution time and temperature increased across all investigated animal hair yarns. This, we propose, is due to the dissolved fraction being washed away during coagulation. Optical microscopy was then used quantitatively to track dissolution using the cross-sectional area, which changes with time and temperature, to construct a master curve using time-temperature superposition (TTS).
The dissolution of these animal-hair yarns showed two temperature-dependent regimes with increasing dissolution temperature: one rate-limited by disulphide bonds (which we term the low temperature regime (LT)) and the other rate-limited by hydrogen bonds (the high temperature regime (HT)). The transition between these two regimes was marked by a crossover temperature that varied depending on the type of animal hair yarn. Each regime was fitted with a linear relation consistent with Arrhenius behaviour (that is a single activation energy) in the system. As a result, two dissolution activation energies were calculated for each animal hair yarn, where the LT regime had a higher activation energy than the HT regime.
Further analysis was conducted on some of the yarn/[C2mim][OAc] dissolution systems, where the effective diffusion coefficients were quantified by modelling the dissolution system as a diffusion process. These results were then compared with diffusion data for pure [C2mim][OAc] measured using NMR.
A sodium bisulphite pretreatment was applied to both merino wool and cashmere yarns which was proposed to cleave the disulphide bonds and hence modify the low temperature regime. FTIR evidence is consistent with disulphide-bond cleavage, where a clear increase in the intensity was observed in the spectrum at 1023 cm^-1, which relates to the presence of the cysteine-S-sulfonate groups. These pretreated yarns were partially dissolved using [C2mim][OAc] and analysed using the same methods as those used for untreated yarns. A notable change in the Arrhenius behaviour was observed upon pretreatment, where both yarns now showed only a single linear regime rather than two, with a dissolution activation energy close to that of the HT regime (rate-limited by hydrogen bonds). This result supports our hypothesis that at low temperatures, the dissolution rate is controlled by a disulphide-related barrier.
