Abstract
Keratin from a variety of sources is one of the most abundant biopolymers. In livestock and textile industries, a large amount of rabbit hair waste is produced every year, and therefore it is of great significance to extract keratin from waste rabbit hair in terms of the treatment and utilization of wastes. In this study, a novel, eco-friendly and benign choline chloride/oxalic acid deep eutectic solvent at a molar ratio of 1:2 was applied to dissolve waste rabbit hair, and after dissolution keratin was separated by dialysis, filtration, and freeze-drying. The dissolution temperature effect was discussed, and the resulting keratin powder was characterized by X-ray diffraction, scanning electron microscope, Fourier transform infrared spectroscopy, protein electrophoresis, thermogravimetry and differential scanning calorimetry, and amino acid analysis. During the dissolution process, the α-helix structure of rabbit hair was deconstructed, and the disulfide bond linkages were broken. The solubility of rabbit hair was significantly enhanced by increasing dissolution temperature, and reached 88% at 120 °C. The keratin produced by dissolving at 120 °C displayed flaky powders after freeze-drying, and had a molecular weight ranging from 3.8 to 5.8 kDa with a high proportion of serine, glutamic acid, cysteine, leucine, and arginine. Such features of molecular weight and amino acid distribution provide more choices for the diverse applications of keratin materials.
Highlights
Keratin is one of the most abundant biopolymers, and is widely distributed in animal hairs and feathers [1]
The solubility of rabbit hair in deep eutectic solvent (DES) at various temperatures was observed from the quantity of residual3.1
DES, and number the of rabbit hairsofwere dispersed in DES, and most of the scales rabbitinhair surface were the shape of rabbit hairand wasscales clearlywere visibledamaged, with the clean scales onthe its low surface
Summary
Keratin is one of the most abundant biopolymers, and is widely distributed in animal hairs and feathers [1]. The different dissolution and extraction approaches of animal hairs and feathers produce different molecular weight keratins which can provide more choices for the diverse applications of keratin materials. The breakage of peptide bonds by strong acids and alkalis, the disruption of disulfide bonds by oxidizing and reducing agents, and the deconstruction of physical structures by hydrogen bond disrupters as well as their combinations must be used to dissolve the keratin fiber [14]. Of these approaches, some are limited because of the use of long time, high temperature, and harsh reaction conditions, whereas others have the shortcomings of the use of toxic and harmful reagents. The resulting keratin powders were characterized by Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), thermogravimetry (TG)/differential scanning calorimetry (DSC), protein electrophoresis, scanning electron microscope (SEM), and amino acid analysis
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