Dissolution of Different Animal Hair Yarn in 1‑Ethyl-3-methylimidazolium Acetate

The partial dissolution of cashmere and merino wool yarns in the ionic liquid 1-ethyl-3-methylimidazolium acetate was studied both with and without pretreatment of the yarns using sodium bisulfite. The cross sections of both yarn fibers were analyzed using optical microscopy for different dissolution times and temperatures. It was found that the dissolution of cashmere yarn (CY) and merino wool yarn (WY) has two competing processes: one rate limited by disulfide bonds and the other rate limited by hydrogen bonds. The yarn dissolution obeyed the time-temperature superposition. From this, two activation energies for each yarn were obtained, one with respect to low temperature (LT) and one for high temperature (HT), E _CY LT = 110 ± 12 kJ/mol, E _CY HT = 61 ± 6 kJ/mol, E _WY LT = 124 ± 14 kJ/mol, and E _WY HT = 35 ± 1 kJ/mol. The crossover temperature between the low- and high-temperature regimes was found to be 70 °C. The reducing agent (sodium bisulfite) was used to cleave the disulfide bonds in CY and WY. FTIR spectroscopy provided evidence that the disulfide bonds were, in fact, cleaved during this pretreatment. A single linear regime (instead of two) was found on the Arrhenius graphs of the pretreated cashmere (PCY) and the pretreated merino wool yarn (PWY), strongly confirming our hypothesis that at low temperatures, the disulfide bonds determined the rate of dissolution. The subsequent dissolution activation energies were found to be reduced from the low-temperature activation energies for the CY and WY, with their values being E _PCY = 62 ± 4 kJ/mol and E _PWY = 66 ± 3 kJ/mol, respectively. With further analysis, the self-diffusion coefficients of [C2mim]-[OAc] for the CY, PWY, and PCY dissolution systems were quantified and compared to the self-diffusion coefficient of pure [C2mim]-[OAc] measured using NMR.