The Extraction Of Silk Fibroin & Preparation, Modification And Application Of Silk Fibroin Membrane

China is a large country in silk production. The output of its silk production accounts 65% output of the world. There are a lot of silk scraps produced during the process of silk production and processing. The reuse of silk scraps is becoming an important research hotspot. Silk fibroin as a kind of natural macromolecule polymer is an important component of natural silk. It has many unique properties, such as soft molecular long chain, excellent forming film characteristic, ease of molecular design(synthesis, blending modification, grafting etc.). The extraction of silk fibroin and study of biological fibroin membrane materials have important theoretical significance and potential application. However, pure fibroin membrane is easy swollen in water, and has low mechanical strength and poor alkaline resistance property. The membrane structure is difficult to control during the preparation process.In the paper, SF and its hydrolysis products were used as raw materials. Water-insoluble fibroin membrane was prepared with silk fibroin and silicon coupling agent as crosslinking agent. SF/MWCNTs hybrid membrane and SFP/PVA blend membrane were prepared with fibroin(peptide) blending with multi-walled carbon nanotubes(MWCNTs) or polyvinyl alcohol and other raw materials, respectively. Schiff base compound and the quaternary ammonium salts with reactive groups were synthesized to modify the different prepared fibroin-based membrane. Then, the structure, performance, the adsorption behavior to heavy metal ions and free radical scavenging properties of the fibroin membrane material before and after modification were investigated.1. The water soluble fibroin peptide was prepared by the hydrolyzed silk fibroin with Alcalase alkaline protease. With the single factor experiment combine with orthogonal experiment optimization method, the optimum peptide preparation process was determined. It was described as following: fibroin concentration 4%, hydrolysis temperature 55 �C, the ratio of enzyme to substrate 2%, p H 8.0, and hydrolysis time of 6 h. Hydrolysis degree of fibroin hydrolysis product was measured with ninhydrin colorimetry and being 18.3% under the optimum preparation process. The relative molecular weight distribution of fibroin hydrolysate was tested by SDS-PAGE gel electrophoresis. The relative molecular weight of fibroin hydrolysate was mainly distributed in the range of 5 KDa to 6.5 KDa. 1,1-Diphenyl-2-picrylhydrazyl radical 2,2-Diphenyl-1-(2,4,6-trinitrophenyl)hydrazyl(DPPH?) free radical scavenging performance of fibroin peptide and standard antioxidants vitamin C was measured. SC50 of fibroin peptide and vitamin C to DPPH? free radical clearance was 1.85 mg/ml and 0.024 mg/ml, respectively.SFP/PVA blend membrane was prepared with fibroin peptide SFP and polyvinyl alcohol. The mechanical property, dissolubility, and DPPH? free radical clearance of the blend membrane were tested. The tensile strength and fracture elongation of SFP/PVA blend membrane under different blending ratio with Silane WD-50 were higher than that without Silane WD-50. In addition, dissolubilities of SFP and SFP/PVA blend membranes were tested in methanol/water system. SFP and PVA in the SFP/PVA blend membrane were mainly interacted with hydrogen bonding and Van der Waals' force. The DPPH? free radical removal performance of SFP/PVA blend membrane was measured. DPPH? radical scavenging rate of SFP/PVA membrane gradually increased with the increase of SFP proportion in blend membrane. It is found that DPPH? free radical clearance rate of the SFP/PVA blend membrane was more than 50% when the SFP/PVA blend ratio was more than 15/85.2. Water-insoluble fibroin membrane was prepared with silicon coupling agent KH560 as crosslinking agent. The weight loss rate of the water-insoluble fibroin membrane in water decreased with the increase dosage of KH560. When the quantity of coupling agent KH560 was 15 %, the water dissolution rate of SF/KH560 membrane was only 2%. By means of peak fitting and quantitative analysis of infrared spectra, relative percentage of each secondary structure in different silk fibroin membrane was calculated. The addition of silicone coupling agent could promote the transition of silk fibroin conformation from ? helix and random coil/extension chain to the ? folding conformation and side chain/assembled chain structure. X-ray diffraction analysis further verified the analysis results of ATR-FTIR. The sorption behavior of SF/KH560 membrane for six metal ions, such as Cu(II), Co(II), Ni(II), Cr(III), Pb(II) and Cd(II), was investigated. SF/KH560 composite membrane showed selective sorption for Pb(II) and Cd(II), and adsorption amount being 11.8 mg/g and 14.7 mg/g, respectively. The adsorption kinetics SF/KH560 composite membrane for Cd(II) was investigated. The adsorption process followed the pseudo-second-order model.3. With 3, 5-di-aminobenzoic acid as raw material, a novel water soluble compound containing azo conjugated system and crosslinking reactive groups, 3,5-bis[(2-hydroxy-4'-sodiumsulphato-ethylsulphonyl)azobenzene-methyneimino]-benzoic acid(ligand Z1), and its metal complexes with Mn2+, Cu2+, Co2+ were synthesized and characterized. UV-Vis absorbance spectra of the ligand Z1 and its metal complexes with Mn2+, Cu2+, Co2+ were measured in water solution. It was found that the absorbance peak of the ligand Z1(?max) occurred at 402 nm while the absorbance peak of the complex moved to 380 nm for Co2Z1, 382 nm for Mn2Z1, 378 nm for Cu2Z1, respectively. The catalytic decomposition of H2O2 was carried out at 40 �C under the alkaline condition. It was found that ligand Z1 had no noticeable catalytic activity for H2O2 decomposition. However, its complexes, Co2Z1, Mn2Z1, Cu2Z1, had strong catalytic activity for H2O2. Manganese complex, Mn2Z1, had the strongest catalytic activity among three complexes. When the concentration of manganese complex was 5 mg/l, the decomposition of H2O2 nearly finished in 40 min at 40 �C. When Co2Z1 was used as catalyst, the H2O2 decomposition reached 80% in 60 min. The decomposition of H2O2 with Cu2Z1 was the slowest among the three metal complexes.Ligand Z1 was used to modify the water insoluble fibroin membrane SF/KH560 Then, the surface morphology and structure of the membrane before and after modification was characterized by SEM-EDS and UV-Vis transmittance curve, respectively. With EDS spectrum data, it could be found that element sulfur was detected on the surface of the M-SF/KH560 membrane. The results of UV-Vis transmittance test shows that the transmittance of SF/KH560 film between 440-800 nm was always above 65%. However, transmittance of M-SF/KH560 film between 440-800 nm was lower than that of SF/KH560 and it began to decrease obviously when the irradiation wavelength was less than 500 nm.4. The water insoluble SF/MWCNTs hybrid membrane was prepared with SF and MWCNTs as raw material. The quaternary ammonium salt was used to modify the SF/MWCNTs hybrid membrane. Peak fitting and quantitative analysis of infrared spectra and X-ray diffraction analysis of SF/MWCNTs hybrid membrane indicated that, compared with pure SF membranes, silk fibroin conformation of SF/MWCNTs hybrid membrane was transformed from the ? helix and random coil/extension chain to the ? folding conformation. The mechanical property of SF/MWCNTs hybrid membrane was measured. SF/MWCNTs hybrid membrane has good mechanical property when the quantity of silk fibroin, coupling agent and carbon nanotubes was 0.05 g/ml, 10% and 1%, respectively. The tensile strength under dry and wet state of SF/MWCNTs hybrid membrane was 48.8 MPa and 21.9 MPa, while breaking elongation rate was 4.62% and 58.8%, respectively. The tensile strength and elongation of modified SF/MWCNTs hybrid membrane with quaternary ammonium salt were 20.8 MPa and 56.4%, respectively.