What Happens during Natural Protein Fibre Dissolution in Ionic Liquids

Abstract

Here, we monitor the dissolution of several natural protein fibres such as wool, human hair and silk, in various ionic liquids (ILs). The dissolution of protein-based materials using ILs is an emerging area exploring the production of new materials from waste products. Wool is a keratin fibre, which is extensively used in the textiles industry and as a result has considerable amounts of waste produced each year. Wool, along with human hair, has a unique morphology whereby the outer layer, the cuticle, is heavily cross linked with disulphide bonds, whereas silk does not have this outer layer. Here we show how ILs dissolve natural protein fibres and how the mechanism of dissolution is directly related to the structure and morphology of the wool fibre.

Rapid and effective cuticle removal from wool fibers using ionic liquid

“…In our previous study we found that the dissolution of a wool fiber, started with significant swelling of the cuticle [18]. Based on this, we designed the experiment of cuticle removal by accurately controlling the heating temperature and the time, whereby only the cuticle is selectively swollen whilst cortex dissolution is avoided.…”

“…In Figure 3 it can be seen that even when the cuticle had been fully swollen at 80 o C, no trace of fluorescent dye was detected in the cortex, indicating the IL did diffuse into the cortex during the time taken to remove the cuticle. Exposure of the wool fiber to the IL for longer amounts of time does result in complete dissolution [18].…”

“…[bmim]OAc was chosen as it showed the highest efficiency in wool fiber dissolution among all the ILs we had tested previously [18]. To optimize the treatment temperature, we studied the swelling behaviour of the fibers in [bmim]OAc at room temperature, 60 o C, 70 o C, and 80 o C respectively, under a polarizing optical microscope, as shown in Figure 2.…”

“…The dissolution process of a single fiber was recorded with the Nikon 80i Eclipse polarizing optical microscope (POM) equipped with a camera and a hot stage, as reported in a paper previously published by our group [18]. The wool fibers were carefully stretched to straighten and fixed on a glass slide with tapes.…”

“…In comparison to traditional solvents, ILs have many advantages, such as negligible vapour pressure, excellent efficiencies in the dissolution of many compounds and are highly tuneable with the numerous anion and cation combinations [12]. In general, wool fibers are difficult to dissolve in traditional solvents, while they can be readily dissolved in ILs [13][14][15][16][17][18].…”