Silk Fibroin-based Hybrid Fiber Materials:Preparation And Oil/water Separation

In recent years,with the frequent occurrence of offshore oil spills and the increase of industrial oily sewage discharge,the new technologies and materials for oil/water separation has become a research hotspot.Aerogel is a new type of materials with porous network structure,featuring low density and high porosity,while electrospinning nanofiber membranes have the advantages of small fiber diameter,adjustable pore size,large specific surface area and high porosity,so both of them have received great attention in the field of oil/water separation.In this paper,the rich in resources and low-cost silkworm cocoons are used as raw materials,silk fibroin(SF)aerogels with high oil absorption rates were prepared by exfoliating degummed silk using NaOH/CO(NH2)2/H2O system,a spinning solution containing silk nanofibrils was obtained by dissolving silk with the CaCl2/FA system,and a hydrophilic SF nanofiber membrane was prepared using the electrospinning technique.In addition,the electrospun poly(vinylidene fluoride-co-hexa-fluoropropylene)(PVDF-HFP)nanofiber membrane was prepared by using PVDF-HFP with high mechanical strength as the raw material,and the hydrophobicity of the PVDF-HFP membrane was improved by adding SiO2 nanoparticles,and finally combined with the prepared SF nanofibre membrane,an amphiphilic PVDF-HFP/SiO2//SF double-layer oil/water separation membrane was obtained.The main results of this paper are as follows:(1)NaOH/CO(NH2)2/H2O system could be used to exfoliating degummed silk in micro-nanoscale fibers,and the SF aerogels with densities of 5.206×10-2 g·cm-3 and 7.429×10-2 g·cm-3 were prepared by freeze-drying methods when sorbic alcohol and glycerol were as cross-linking agents.After hydrophobic treatment of the SF aerogels with organosilane(OTS),the water contact angle of the SF aerogels was increased from 0° to 113.2° or 119.4°,respectively.The oil absorption tests showed that the oil absorption rates of the SF aerogels were all high,up to 843.62%.At the same time,the results also show that the oil absorption effect of the sorbitol treated aerogel was better than that of glycerol treated aerogel.(2)SF solutions containing SF nanofibrils could be prepared by dissolving degummed silk with CaCl2/FA system,and it was found that the viscosity of the SF solution was increased from 0.45 Pa·S to 0.78 Pa·S when the CaCl2 concentration in the CaCl2/FA solution increased from 3(w/v)%to 8(w/v)%,and when the SF concentration increased from 15(w/v)%to 25(w/v)%,the viscosity of the SF solution was increased from 0.55 Pa·S to 2.0 Pa·S.Meanwhile,it was also found that the fiber diameters of electrospun SF nanofibers was increased from 98±30 nm,105±31 nm to 124±66 nm when the SF concentration increased from 20(w/v)%,23(w/v)%to 26(w/v)%.(3)PVDF-HFP was used as raw materials for electrospinning.When the concentration of PVDF-HFP increased from 18(w/v)%to 24(w/v)%,the average fiber diameter of electrospun PVDF-HFP fibers increased from 210±79 nm to 574± 178 nm.The contact angle test showed that the contact angle of the fiber membrane increased with the increase of PVDF-HFP concentration.By adding SiO2 nanoparticles into PVDF-HFP spinning solution,the roughness and hydrophobicity of PVDF-HFP fiber membranes were improved.On the contrary,SF nanofiber membrane showed superhydrophilicity.(4)By combining hydrophobic PVDF-HTP/SiO2 monolayer membrane with hydrophilic SF monolayer membrane,PVDF-HFP/SiO2//SF double-layers membrane could be obtained.Mechanical tests show that the tensile strength and breaking elongation were 0.17 MPa and 11%respectively,which were lower than the tensile strength of SF monolayer membrane and PVDF-HFP/SiO2 monolayer membrane.The oil absorption tests showed that when the concentration of PVDF-HFP increased from 18(w/v)%to 24(w/v)%,the oil absorption rates decreased from 41.0%to 33.3%.When the concentration of SiO2 in the PVDF-HFP/SiO2 membrane increased from 0.25(w/v)%to 5(w/v)%,the oil absorption rates increased from 90.0%to 262.0%.The oil/water separation results showed that both of the PVDF-HFP/SiO2 monolayer membrane and SF monolayer membrane had no oil/water separation effect,but the double-layer PVDF-HFP/SiO2//SF membranes had oil/water separation effect,the separation flux is 811.84 L·m-2·h-1,and the oil/water separation efficiency is 99.65%.In summary,this study provides a low-cost method for the preparation of a biocompatible and high oil absorption rates aerogels containing SF microfibrils.An amphiphilic PVDF-HFP/SiO2//SF bilayer oil/water separation membrane with adjustable hydrophobicity of top-layer was prepared by electrospinning technique.