The Preparation Of Polyvinylidene Fluoride Ultrafiltration Membrane And Its Application Inseparation Of Soybean Proteins

Poly vinylidene fluoride(PVDF)with the excellent thermostability,chemical stability and good mechanical ability,and so on,has been widely used as a membrane material.It has great significance to study the preparation and application of the PVDF membranes.In this study,the PVDF membranes were prepared by the immersion phase inversion process.The effect of coagulation bath on PVDF membranes performance was investigated,then the anti-pollution ability of PVDF membrane has improved after blending and surface modified of those membrane.The optimal separation conditions of soybean proteins by PVDF membranes were determined by single factor experiment and orthogonal experiment.PVDF membranes were prepared on different thickness of non-woven fabric,and the thickness of 0.205 mm of non-woven fabric was selected at last.Then PVDF membrane were prepared in the coagulation bath of acid system and octyl alcohol,the effect of different coagulation bath,concentration and immersion time of membrane on their performance were investigated.In the acid system,the membrane performance was best when the coagulation bath was formic acid.When the concentration of formic was 50%,the water flux was 751.63L/m~2·h,porosity was 80.80%,and the retention still at a high level of 85.42%.In the coagulation bath of octyl alcohol,the PVDF membrane tend to form macroporous structure,and its retention is very low,therefore,it is not suitable for the preparation of membrane to separation soybean protein.In order to further improve the performance of PVDF membrane,the polymers poly methyl methacrylate(PMMA)and polyethersulfone(PES)were used as blending agents for preparation of a PVDF:PMMA:PES blend ultrafiltration membrane.At the same time,the effect of the melt temperature and the content of additive LiCl were studied.The blend ultrafiltration membranes with the good hydrophilicity were obtained,when the ratio of PVDF,PMMA and PES was 85:10:5,80:15:5,75:15:10 and 70:20:10,The water flux and porosity of the blend ultrafiltration membrane were increased and its retention was decline with the increase of melt temperature,In order to ensure the retention of the blend membrane at a high level,the melt temperature was selected at 100?.The number of membrane hole and porosity were increased with the increase of the content of LiCl,and the 5%LiCl was selected as an optimal condition for the better performance of the blend ultrafiltration membrane.In order to improve the hydrophilicity and the ability of antipollution of PVDF membranes,the chitosan was used as a surface coating agent to modified PVDF membranes,and the effect of different concentrations of chitosan was investigated.The hydrophilicity of PVDF membrane was improved when its surface was coated with chitosan.The number of hole on membrane surface was decrease and its aperture became smaller with the increase of the concentration of chitosan,as result,the water flux and porosity of PVDF membrane were declined.At last,the optimal concentration of chitosan to modified membrane was selected as 5~10 g/L.In addition,the self-made ultrafiltration membrane has a better antipollution ability than the commercial membranes.The separation conditions of soybean proteins by PVDF membranes were optimized by single factor experiment and orthogonal experiment.When temperature was 50?,pH=9,operating pressure was 0.5 MPa,and the concentration of aqueous extract was 240?g/mL,the soy protein aqueous extract flux of PVDF membrane reached 96.32 L/m~2·h,and the retention of soy protein reached 96.25%.When the blend membrane was used at the above optimal conditions,the fulx can reach 450.32 L/m~2·h,and the retention of soy protein was 94.87%.