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

## TL;DR

This study examines how cashmere and merino wool yarns dissolve in a specific ionic liquid, revealing two competing processes affecting dissolution rates.

## Contribution

The study identifies two distinct activation energies for dissolution processes in animal hair yarns, influenced by disulfide and hydrogen bonds.

## Key findings

- Dissolution of cashmere and merino wool yarns involves competing processes limited by disulfide and hydrogen bonds.
- Pretreatment with sodium bisulfite cleaves disulfide bonds, simplifying dissolution kinetics to a single regime.
- Self-diffusion coefficients of the ionic liquid were measured and compared across different dissolution systems.

## Abstract

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.