| As a major leather-producing country,China has concentrated a quarter of the world’s leather output.However,a large amount of chrome-containing waste will be produced in the leather production process.China produces 300,000 tons of chrome-containing waste every year,which is mainly chrome shavings.At present,a large number of incineration and landfill are used for this waste,resulting in a great waste of biomass resources and environmental pollution.Therefore,it is urgent to properly handle this part of biomass waste for resource utilization and high-value utilization.In this paper,starting from the essential structure of chrome shavings,related functional composite materials including chrome shavings/polyurethane composite materials,electromagnetic shielding materials and flexible hydrogel pressure sensors were prepared from their different hierarchical structures,namely collagen fiber bundles,collagen fibers,collagen fibrils and collagen molecules.It provides some new ideas for the construction of high-value functional materials of chrome shavings.Mainly as follows:Chrome shavings are mainly leather collagen fiber bundles after tanning,which have good mechanics and hydrophilicity.A specific size of chrome shaving filler was proposed as the support material for the polyurethane foam layer of synthetic leather to solve the problem of flattening the foam coating during the drying process.In addition,in the composite coating,chrome shaving will also play the role of water vapor channel and mechanical enhancement.In the preparation process of the composite foam layer,the chrome shaving filler with a similar size to the initial thickness of the foam layer is selected so that it can be supported on the upper and lower sides of the foam layer.After drying,the thickness retention rate of the composite foamed coating reaches 96%,which is 17%higher than that of the pure PU foamed layer.At the same time,the addition of chrome shavings greatly reduces the cell diameter and wall thickness of the coating,reaching 57μm and 20μm respectively,which are only43%and 24%of the pure PU foam layer.When m（chrome shavings）:m（PU）=1:8,the water vapor permeability and tensile strength of the finished leather reach 368 mg/10cm2·24h and 11.45 MPa,respectively,which is 232%and 85%higher than that of pure foamed PU synthetic leather.Collagen fiber of chrome shavings has stable fiber structures and abundant amino acid residues,which is a potential electromagnetic shielding material matrix.In this paper,a ternary electromagnetic shielding material is proposed to use leathery collagen fibers as the matrix,through reasonable structural design,the material has three high-efficiency electromagnetic shielding structures of the conductive skeleton,heterostructure and combined functional layer structure at the same time.In this material,a dense and continuous polypyrrole（PPy）conductive coating is first coated on the surface of collagen fibers to provide a solid conductive network with a conductivity of 222 S/m,which also acts as a bottom electromagnetic wave.reflective layer.The multiwall carbon nanotube（MWCNT）conductive network is then coated on top of this PPy coating as a diffuse reflection layer and an absorber layer.Moreover,a rich heterogeneous interface will also be formed between the MWCNT network with the PPy layer and collagen fibers.The composite material has excellent electrical conductivity（354 S/m）and excellent electromagnetic shielding performance,achieving a shielding effectiveness of more than 30 d B in the X-band with a thickness of 0.48mm.Collagen itself is a common raw material for natural hydrogels.In order to solve the problems of the low sensitivity of current ionic hydrogel pressure sensors and the difficult processing of hydrogel microstructures.A simple,low-cost preparation method for high-sensitivity chrome shavings-based hydrogel pressure sensor is proposed.The method includes three steps:construction of leather fiber matrix membrane,low-temperature alkali urea impregnation and acetic acid regeneration,thermal gelation transition and re-swelling.A hydrogel with collagen fibril-gelatin hybrid synapses on the surface and fiber-gel composite gel walls inside was successfully prepared.Due to these two characteristics,the hydrogel based on chrome shavings has excellent sensitivity,reaching 5.32 k Pa-1（0-0.8 k Pa）,3.43 k Pa-1（0.8-2 k Pa）,2.68 k Pa-1（2-7.5 k Pa）in the sensing range（0-7.5 k Pa）.This is the highest reported sensitivity value of the ionic hydrogel pressure sensor.However,the gel has poor mechanical properties,and the elastic modulus is only 2.0 k Pa.Thereafter,in order to further improve the mechanical properties and durability of the hydrogel,PVA was selected as the reinforcement matrix.The final hydrogel has PVA-collagen fibril hybrid synapses on the surface,and the internal fiber skeleton nests the PVA gel wall structure,which makes the material have excellent sensitivity and mechanical properties at the same time.Its sensitivity reaches 4.20 k Pa-1（0-3 k Pa）,1.09 k Pa-1（3-9 k Pa）,0.28 k Pa-1（9-54 k Pa）.The gel has an elastic modulus of 10.7 k Pa,its sensing ranges up to 0-54 k Pa,and exhibits excellent durability. |
