Continuous High-Content Keratin Fibers with Balanced Properties Derived from Wool Waste

Abstract

The full utilization of discarded wool for the preparation of continuous recycled keratin fibers has been a challenging subject. The key issue lies in how to utilize wool keratin as much as possible without damaging the main chain structure of the protein molecules. Based on small molecule simulation reactions, the authors find out that disulfide bonds, the only cross-linking bonds in keratin, can be effectively broken by starch-derived dithiothreitol, and the resultant keratin can be well separated by the cosmetic ingredient sodium dodecyl sulfate, which forms micelles that stabilize the keratin solution. Accordingly, the traditional strong hydrogen-bond breakers like urea and LiBr can no longer be used, which helps to protect the integrity of keratin. The resultant fully dissolved, highly concentrated keratin solution (keratin content = 18 wt %) is directly applied for wet spinning. To toughen and strengthen the envisaged keratin fibers, a few hydroxypropyl cellulose and glutaraldehyde and 4,4′methylenebis(phenyl isocyanate) are incorporated. Eventually, the regenerated continuous fibers with keratin content as high as 90 wt % offer a combination of properties similar to natural wool.

A review: can waste wool keratin be regenerated as a novel textile fibre via the reduction method?

“…Thiols are often employed, although a variety of different reducing agents can carry out this process and can therefore be chosen depending on availability/accessibility. Different reagents can also have an influence on the keratin chain length range that is extracted and can therefore be chosen accordingly (Cao et al, 2020). For these methods to be economically viable, the reagents used should be inexpensive and abundant.…”

“…Urea disrupts hydrogen bonding and denatures the protein (Liu et al, 2018). However, this could be an issue as some literature suggests that ammonia can damage the keratin backbone and lead to shorter keratin chain extraction (Cao et al, 2020). After careful removal of any undissolved wool via filtration methods, dialysis should be carried out to remove any unreacted reagents to obtain a purer dissolved keratin solution (Liu et al, 2018).…”

“…Figure 13. Regenerated wool keratin fibres from waste wool, blended with highly substituted hydroxypropyl cellulose, wet-spun and then cross-linked with glutaraldehyde and 4,4 0 -methylenebis-(phenyl) (Cao et al, 2020).…”

“…processing can be seen in the variety of materials created (Cao et al, 2020;Puppi & Chiellini, 2017). As this process is already established for man-made synthetic fibres, it could be employed for making keratin fibres for wearable textile products, with additional post-processing such as cross-linking imparting favourable properties to the obtained material (Cao et al, 2020).…”

“…Reduced keratin still contains free thiol groups so it cross-links spontaneously in air to itself (Aluigi et al, 2013) (Equation 3), or it can be reacted with a specific cross-linking agents to increase cross-linking in the structure. This is important because cross-linking between the keratin chains and/or to other materials (Wu et al, 2018;Cao et al, 2020;Poole et al, 2011) can improve the tensile strength of fibres (Poole et al, 2009). As regenerated wool keratin has predominantly b-keratin character, blending and post-processing helps obtain useful fibre qualities (Wang et al, 2020), such as optimised tensile strength and breaking elongation, and cross-linking specifically tackles the problem of wet strength (Poole et al, 2009).…”