Research Of Modified Polyethersulfone Membrane Based On Lignin-cellulose Nanofibrils/Dopamine

In this research,lignin-cellulose nanofibrils(LCNF)were prepared based on the material of unbleach pulp.LCNF were blended with polyethersulfone(PES)to prepare LCNF/PES membrane through Loeb-Sourirajan phase inversion process to improve the antifouling property,hydrophilic property,permeability and mechanical property of PES membrane.Then dopamine(DPM)as modification agent were used to surface coat LCNF/PES membrane to prepare LCNF/PDPM/PES membrane.The properties of LCNF/PES membrane and LCNF/PDPM/PES membrane were investigated.The rheological performances of LCNF/PES casting solutions were characterized by rotational rheometer.Through comparison,the LCNF/PDPM/PES membrane with the best performance was chosen to applied in the ultrafiltration process of walnut protein solution,the suitable process conditions of ultrafiltration process and several membrane cleaning methods were investigated.LCNF presents a nano-size rod-like fibrous structure.The diameter of LCNF ranges from 30nm to 50 nm and its length ranges from 150nm to 600 nm.The LCNF was blended with PES to prepare LCNF/PES.The suitable preparation conditions are:PES content is 16wt%,LCNF content is 0.8wt%,pore-forming agent PVP content is lwt%,DMAc is the solvent and the deionized water is coagulation bath.Compared to pure PES membrane,the performances of membrane prepared under the best preparation conditions were improved.The pure water flux of LCNF/PES membrane enhanced 118%,the tensile strength of LCNF/PES membrane enhanced 55.88%,the elongation at break of LCNF/PES membrane increased 23.32%,the hydrophilic angle of LCNF/PES membrane decreased from 63.5°to 37.80 and attenuation coefficient of LCNF/PES membrane decreased from 47.2%to 36.3%.The non-newtonian fluid index of LCNF/PES casting solution and PES casting solution were both less than 1.As a result,both LCNF/PES casting solution and PES casting solution were all belonged to pseudoplastic fluid.When the LCNF additive amountenhanced,the non-newtonian fluid index of LCNF/PES casting solution decreased,modulus of LCNF/PES casting solution increased.DPM is used to surface coat LCNF/PES membrane to prepare LCNF/PDPM/PES membrane.The optimal surface coat modification conditions(value of pH was 8.7?concentration of DPM was 4g/L?coating time was 6h)of membranes were investigated in this study:Compared with LCNF/PES membrane,the performances of LCNF/PDPM/PES membrane prepared under the best modification conditions were enhanced.The pure water flux of LCNF/PDPM/PES membrane was 733.7L/m2·h,the tensile strength of membrane enhanced 24.9%,the elongation at breakof membrane increased 36.1%,the hydrophilic angle of membrane decreased from37.80 to 34.2°and attenuation coefficient of membrane decreased from 36.3%to 28.3%.LCNF/PDPM/PES membrane as the optimal comprehensive performance membrane was used to investigate suitable technological conditions in the ultrafiltration process of walnut protein solution.The suitable preparation conditions are:walnut protein concentration is 1.2 g/L,operating pressure is 0.2 MPa,the temperature of solution is 40?,the pH value of walnut protein solution is 9.2.The sodium dodecyl sulfate(SDS)solution showed the optimal effect in the cleaning process of the polluted LCNF/PDPM/PES membranes and the water flux recovery rate reached above 90%.