| Polyvinylidene fluoride(PVDF) is a macromolecular organic polymer which owns the feature of both fluorine resin and common resin. PVDF is widely preferred due to its excellent temperature, oxygen, weather, radiation, chemical corrosion resistance property, as well as the approachable film formation characteristic. However, because of the lower free energy on the surface of PVDF, the hydrophobicity of this separation membrane is relatively high and is easy to be contaminated, which would decrease the water flux during its application. Enhance the hydrophilicity of the membrane by modification is an effective way to solve its fouling problem.To improve the contamination resistance of PVDF ultrafiltration by increasing its hydrophilicity and then enhance its water flux, nonionic surfactant OP-10 with extremely high hydrophilicity was mixed with PVDF for the fabrication of PVDF macromolecular plate ultrafiltration membrane by using phase transformation method. By using cup ultrafiltration device, the influence of OP-10 amount on the water flux, retention, porosity and other properties of modified membrane was investigated. The tensile strength and the fracture elongation rate of the film was measured by W-56 strength tester. The hydrophilic change was characterized by testing the contact angle between the film and pure water with contact angle measurement. The impact of OP-10 on PVDF polymorphs was analyzed by Fourier transform infrared spectroscopy(FT-IR) and the pore distribution, film section structure and surface roughness observed by scanning electron microscopy(SEM) and atomic force microscopy(AFM). The results showed that the microscopic structure wasn’t altered by the adding of OP-10 and the pure water flux increased 368.2% maximumly on the base of retaining its original properties. The contact angle descended from 83.52° to 54.67°, which indicated the ascendance of hydrophilic. At the meantime, the porosity increased 9.28% and the toughness of the modified film was improved. The performance of the film, as well as the modification effect was obtained with 1.67% w(OP-10) adding amount of OP-10.The flux and hydrophilic was improved by the adding of OP-10, while also decreased its retention rate and mechanical strengthen slightly. In order to improve these deficiencies, nano-alumina(Al2O3), nano silicon dioxide(SiO2) and titanium dioxide(TiO2) were appended for the modification of PVDF membrane along with surfactant in terms of phase transformation method. The results proved that three kinds of nano particles increased the water flux in different degrees, among which the nano-alumina exhibited the best modification effects combined with OP-10. The pure water flux reached to 1410.96 L·m-2·h-1 and the contact angle decreased into 53.14o. What’s more, the retention rate increased into 97.6% while the mechanical tensile obtained at 20.5123 N, along with 7.18% breaking elongation rate. These results all showed that the drawbacks caused by adding OP-10 in strength tensile and retention rate were improved.In order to investigate the pollution resistance ability of modified membrane, oil contained wastewater from oil filed was ultrafiltrated by tubular modified membrane, and then the contaminated membrane was cleaned. The result revealed that the oil amounts in the water after ultrafiltration were less than 0.6 mg/L, and the removal rate of TOC(Total Organic Carbon) was more than 95%. Furthermore, the removal rate of COD(Chemical Oxygen Demand) and turbidity were more than 90% similarly. The particle size of suspended solids content was less than 0.5 mg/L with its size less than 2μm. The effluent index of modified membrane were all higher than the unmodified membrane, and the water quality of effluents has reached the re-injected water standards of oil field. Several different types of chemicals for membrane cleaning have been used to testify the recovery extent of the contaminated membrane. The results indicated that alkali chemicals shows the best cleaning effects with the most obvious flux recovery. The content of 2% sodium dodecyl benzene sulfonate solution exhibited the best cleaning capability among all those alkali chemicals with 95.7% flux recovery rate. In a word, the hydrophilicity of PVDF, as well as its contamination persistence were improved by the effect of surfactant OP-10 and nano metal particles. |
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