Modified Superhydrophobic Polypropylene Hollow Fiber Membrane And Its Application In Membrane Distillation

In this paper,polypropylene hollow fiber membrane is used as the substrate,and its surface is coated with a porous superhydrophobic coating,and the hollow fiber membrane is modified into super-hydrophobic hollow fiber membrane.This paper aims to find a cheap,simple and feasible method to prepare super-hydrophobic polypropylene hollow fiber membrane.Different sizes of silica particles were prepared by using different proportions of APS/TEOS.And the particle size was observed by transmission electron microscopy(TEM).Then,the polypropylene particles are added into the xylene solution to dissolve,then silica particles are added to obtain the sol by the sol-gel method,and the non-solvent 2-butanone is added.Under the action of phase separation,the sol is coated with surface of the polypropylene hollow fiber membrane.The silica particles are attached to the surface of the film by using the network structure formed on the surface of the polypropylene solution to increase the surface roughness of the film.The surface free energy of the modified PP hollow fiber membrane was reduced by 1H,1H,2H,2H-perfluorooctyltriethoxysilane(POTS),and then the surface free energy of the modified polypropylene hollow fiber membrane was decreased.The super-hydrophobic polypropylene hollow fiber membrane has a contact angle of 158°.The modified polypropylene hollow fiber membrane was observed by scanning electron microscopy(SEM)and atomic force microscopy(AFM).It was found that the coating on the surface of the membrane was a porous continuous coating.And compared with the original membrane,the modified membrane surface roughness has been greatly improved.By XPS and Fourier transform infrared spectroscopy(FTIR)tests,it was found that POTS and silica were successfully grafted on the surface of the film,effectively increasing the roughness and reducing the surface energy.At the same time,the effects of the amount of silica particles,the amount of polypropylene particles,the times of coating and the amount of MEK on the super-hydrophobic properties of polypropylene hollow fiber membranes were discussed.The results show that the super-hydrophobic modification of polypropylene hollow fiber membranes good condition.The experiment of membrane distillation of modified superhydrophobic polypropylene hollow fiber membrane was carried out.the average pore size and porosity of the modified super-hydrophobic polypropylene hollow fiber membrane were determined by mercury intrusion method.The average pore diameter of the modified membrane decreased,and the porosity was increased compared with the original membrane,indicating that the superhydrophobic coating was porous.The flux and rejection of the modified membranes in 3.5wt%NaCl solution were measured.The results showed that the membrane flux increased compared with the original membrane,and the rejection increased to 99.9%.The change of flux and rejection of modified superhydrophobic polypropylene hollow fiber membrane in membrane distillation was also discussed by changing the conditions of NaCl solution temperature,NaCl solution concentration and vacuum degree.