Preparation And Properties Of Ultrahigh Molecular Weight Polyethylene Hollow Fiber Membranes

Ultrahigh molecular weight polyethylene(UHMWPE)has a planar zigzag structure,long molecular chain and without any side groups.Compared with other membrane materials,UHMWPE hollow fiber membrane materials have high strength,raw materials easily available,inexpensive and some other advantages.Due to its excellent characteristics,UHMWPE hollow fiber membranes can be widely used in sewage treatment,medical used hollow fiber membrane separation,hollow fiber membrane reactor and many other areas.In this thesis,UHMWPE hollow fiber membrane was prepared,the structure and properties of hollow fibers got under different conditions were measured and investigated.Firstly,UHMWPE hollow fiber membranes were prepared by thermally induced phase separation(TIPS)method,using mineral oil as diluent and xylene as extractant.It is found that only solid-liquid separation occurred under the low cooling rate to the strong interaction between UHMWPE and mineral oil,and it is induced by the crystallizing of UHMWPE in solution during cooling process.The phase separation temperature increases with increasing UHMWPE concentration or with decreasing of cooling rate.As the molecular weight of UHMWPE or UHMWPE concentration increases,the pore size decreases,water flux and porosity are decreased,while the BSA retention rate and fracture strength of fiber membranes are increased.With the increasing of draw ratio,UHMWPE network orientated along fiber axis,fiber porosity decreases,fiber fracture strength increases,the crystallinity and orientation of hollow fiber membranes increases.Then inorganic particles of calcium carbonate(CaCO3)was used as an additive and UHMWPE/CaCO3 hollow fiber membranes were prepared with the mixture.It is found that the water flux of fiber membranes is increased after adding CaCO3,while the porosity and BSA retention are reduced because of the carbonate particles.After treated with hydrochloric acid,the water flux is further improved.During the drawing process,some interfacial microporous are formed between the inorganic particles and the polymer.With the increasing of draw ratio,the interfacial microporous connect together to form larger pores and others become narrower and elongated.On the other hand,the micropores formed by thermally induced phase separation become more tiny or clogging due to the increase of the draw ratio.Due to a combination of two aspects,water flux and porosity of the UHMWPE/CaCO3 hollow fiber membrane reach maximum at draw ratio of 2 times,and they both decrease at draw ratio of 3,while the changing trend of BSA retention with draw ratio is contrary to membrane porosity.With the increasing of the draw ratio,fiber fracture strength increases,and the melting point of fibers,the crystallinity,crystal size and orientation are all increased to some extent.At last,UHMWPE hydrophilic hollow fiber membranes were prepared by using PEG20000 as a modifier.UHMWPE hollow fiber membranes were also treated with Ar plasma to improve their hydrophilic property.It is found that the pore size and porosity of modified membrane are increased,while the BSA retention is reduced.With the increasing of added PEG20000 content,the hydrophilic properties of the hollow fiber membrane is gradually improved.However,the influence of PEG20000 content on the pore diameter,porosity and BSA retention is not obvious.The mechanical properties of PEG modified UHMWPE fiber membranes is decreased slightly.The attenuation of hydrophilicity would occur due to the loss of PEG20000 with prolonging of soaking time in water.Pure UHMWPE hollow fiber membranes are vulnerable to protein pollution,which makes the BSA solution flux decrease,the water flux recovery is relatively low even after cleaned by pure water.Compared with unmodified UHMWPE hollow fiber membrane,the notable rise in water flux or its recovery rate of PEG modified hollow fibers are observed,as well as the significant decline in attenuation of protein flux.After treated with Ar plasma,the surface of hollow fiber membrane becomes rough,some cracks are formed on membrane surface.The hydrophilicity of hollow fiber membranes is improvised with the prolonging of plasma treating time.