Research progress in regeneration process and high-value applications of waste wool keratin
Significance Excesive consumption of petroleum-based synthetic fibers limits the sustainability of textile industry.It is urgent to find low-cost renewable biomass resources to replace convenitional petroleum resources.Due to the quick expansion of fast fashion,the amount of waste wool grows every year.In addition,waste wool is normally disposed through incineration or landfill,which is not conducive to economic development and causes severe secondary pollution to the environment.Keratin is the major component of wool,which has excellent mechanical stability,shape memory properties,piezoelectric properties,biological activity,biodegradability,biocompatibility,and adsorption properties.Thus,keratinous material extracted from waste wool can be applied to produce high-value applications such as functional finishing agents,thermal and sound insulation materials,flexible electronic devices,biomedical applications,or adsorption materials.The regeneration technology of keratin effectively contributes to the sustainable development of wool resources,which triggered dramatically interest in recent years.Progress This review mainly reports the regeneration techniques of keratin,which includes the methods of extraction and recent high-value applications in the form of fibers,membranes,gels,and scaffolds.The common methods of keratin extraction primarily include physical,chemical,and biological methods.Owing to precisely destroying disulfide bonds and hydrogen bonds,chemical methods,such as reduction,oxidation,ionic liquid,and deep eutectic solvent methods,are widely applied.The reduction methods effectively preserve the secondary structure of keratin,and the free sulfhydryl groups generated after extraction can be reconstructed in the subsequent process to cross-link keratin chains,thus perfectly restoring the hierarchical structure in fibers.However,keratinous materials are normally brittle due to poor mechanical properties.In previous work,researchers had demonstrated that 1,4-dithiothreitol can effectively modulate the viscoelastic spinning dope and act as a bridge in the keratin chains.After the drafting in wet spinning,fibers were induced to rearrange to the secondary structure.The regenerated keratin materials with excellent mechanical properties have extensive application prospects,which mainly include flexible electronic devices(such as humidity sensors,conductive composites,gel electrolytes,and so on),biomedical productions(such as wound healing,hemostasis,drug release carriers,tissue engineering,and so on)as well as adsorption applications.Conclusion and Prospect The regenerated techniques of waste wool keratin and its high-value applications receive a lot of attention,promoting the transformation of biomass resources into the valuable materials.However,there are still some challenges that prevent its further practical and commercial production,such as poor mechanical properties,toxicity of chemical reagents,higher cost,and non-environmentally friendly disposal techniques.In-depth investigations on keratin extraction techniques not only can ensure high extraction rate,but also guarantee integral secondary structure of keratin chains.For the extraction techniques,ionic liquids,and green reducing agents such as cysteine,glutathione,and lower toxic 1,4-dithiothreitol gain widespread attention.In addition,chemical methods to enhance the extraction rate of keratin can be assisted by ultrasonic or microwave treatment.A dearth of information regarding the improvement of mechanical property has far limited the process of industrialization.It is also suggested that further investigations are required to gain high molecular weight keratin,find eco-friendly cross-linking agents,increase the orientation and crystallinity of the prepared fibers.In order to reduce purification cost in the biomedical applications,researches should use green and environmentally friendly reagents in the extraction process.The rapid development of keratin regeneration techniques can greatly promote the recycling of biomass resources,and sustainable economic development.
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