Preparation And Application Of Wool Microkeratin And Nanokeratin Particles

Wool is a kind of natural protein fiber consisting of a 10%scale layer and 90%cortex layer.The cortical layer has a complex multi-layered microstructure composed of cortical cells,macorfibrils,microfibrils,and a series of microstructures with gradually decreasing size.The inherent microstructure of wool makes it an ideal raw material for the preparation of microkeratin and nanokeratin.In this study,microkeratin and nanokeratin particles were prepared from wool fiber by ultrasonic-assisted enzymatic hydrolysis.In this study,Esperase was used to destroy peptide bond,L-cysteine was used as a reducing agent to destroy disulfide bond,and finally,wool was decomposed with the aid of ultrasound.The effects of p H,ultrasonic time,and ultrasonic power on the yield of microkeratin and nanokeratin particles were investigated.The reaction conditions were optimized,making the yield of microkeratin and nanokeratin particles reached 25.5%and 10.6%,respectively.The appearance of the products was observed by SEM and a polarizing microscope.The molecular structure,crystal structure,and thermal properties were analyzed by FTIR,XRD,DSC,and TG.The fluorescence properties were investigated by fluorescence microscope.The results show that the microkeratin and nanokeratin particles are spindle-shaped and retain wool keratin’s chemical characteristics during the preparation process.The microkeratin has moreα-helix crystal structure and higher crystallinity than wool fiber,while the main crystal structure of nanokeratin isβ-fold design.The fluorescence microscopy results showed that the microkeratin and nanokeratin had fluorescence properties.With the reduction of scale,the fluorescence intensity of the samples became stronger.A new idea for the preparation of regenerated materials is proposed based on the inherent microstructure of natural polymer materials.The regenerated keratin membrane with good flexibility and mechanical properties was prepared using wool microkeratin particles,which have the inherent microstructure of wool.It overcomes the problems of brittleness,hardness,and difficulty in forming keratin membrane prepared by the traditional macromolecular regenerated method.The regenerated keratin membrane based on microkeratin particles can be bent and folded like paper.The breaking stress is 18.48±0.51MPa,and the breaking strain is 7.58±0.62%.The formation mechanism,molecular structure,and fluorescence properties were studied by SEM,FTIR,XRD,laser confocal microscope,and fluorescence spectrophotometer.The results show that the membrane is an irregular stack of micronkeratin particles,which is tightly connected by hydrogen bonding between the amorphous protein matrix at the junction and retains micronkeratin particles’chemical molecular structure.Due to the increase of specific surface area,wool fiber’s fluorescent property is better than that of wool fiber.On this basis,silver nanowires were used to functionalize the regenerated keratin membranes.Silver nanowires were used as conductive materials,and keratin/silver nanowires composite flexible conductive fmembranes were prepared by first filtering microkeratin particles and then filtering silver nanowires.The flexible conductive membrane retained the flexibility and mechanical properties of the protein-membrane,the fracture stress was 18.52±0.62MPa,and the fracture strain was 7.58±0.66%.The conductivity and mechanical properties of the composite were studied.The results show that the composite has excellent conductivity(1.82×10~4S/m)and conductivity stability(the resistance has no noticeable change after 300 bending cycles).SEM,EDS,FTIR,XRD,and DSC were used to analyze the morphology,molecular structure,and thermal properties.The results show that the flexible conductive membrane is a bilayer membrane with a silver nanowire layer on the upper layer and a keratin layer on the lower layer.A 3-D entangled network structure is formed between the microkeratin particles and the silver nanowires at the junction,making the microkeratin and the silver nanowire firmly combine and endows the composite membrane with a stable physical structure.The application environment of the flexible conductive membrane should be below 200℃.