Preparation Of EVOH Hollow Fiber

Ethylene vinyl alcohol copolymer(EVOH)is one of the most important novel thermoplastic base resin,which is mainly used in the field of packaging.It has many excellent properties,such as good biocompatibility,gas barrier property,oil resistivity,solvent tolerance,hygroscopicity,antistatic,mechanical processing properties and safety.EVOH is ideal material which can be used to produce artificial blood vessel.EVOH(VA= 38mol%)was used as raw material in this paper and Dimethyl sulfoxide(DMSO)was chosen as solvent.The effect of dissolution time and temperature on EVOH was investigated to find out the best dissolution conditions.EVOH micropore membranes were prepared and the properties were characterized.The rheological behavior of the solution was analyzed.The EVOH hollow fibers were produced and the properties were measured.FTIR and DSC were used to analyze and characterize the raw EVOH and EVOH membranes.The results show that the chemical construction of EVOH has been well protected during the process of dissolving.EVOH/DMSO solution should be stored closed as DMSO will absorb water in the air.The increase of temperature was helpful to reduce the dissolving time.TGA analysis indicates that compared with high dissolving temperature,dissolving time is more damaged to the structure of EVOH.The ideal dissolving condition is 70? for 3 hours.XRD analysis show that EVOH's degree of crystallinity is lower than the raw EVOH's.SEM photographs and data of water flux indicate that PEG6000 can be used as pore-causing agent.With the concentration of PEG6000 raised,the porosity of the membrane increased.EVOH has good biocompatibility which is proved by MTT test.The steady flow behavior of EVOH/DMSO solution was also discussed.It appears as a typical pseudoplastic non-newtonian fluid and non-newtonian index n<1.The result indicates that the apparent viscosity of the solution increases with the increasing concentration of EVOH or PEG6000 but it decreases with the increasing of shear rate and temperature.There is no obvious relation between the concentration of solution and the value of viscous flow activation energy.The value of viscous flow activation energy shows that the apparent viscosity of solution is sensitive to temperature which should be controlled strictly when preparing EVOH membranes.Structural viscosity index decreases with increasing temperature and lowering concentration and mechanical processing properties of EVOH solution is improved.When preparing EVOII membranes,concentration of EVOH should not be too high and temperature should be raised properly.EVOH hollow fibers were prepared by wet spinning and DMSO/H2O solution was used as coagulation bath.With the concentration of coagulation bath increases,the double diffusion rate decreases.EVOH hollow fibers,which 10%DMSO/H2O solution is used as coagulation bath,show better mechanical property than other samples.The result from XRD show that the sample which used de-ionized water as coagulation bath has a higher degree of crystallinity than the sample which used 30%DMSO/H2O solution as coagulation bath.The mechanical property of the hollow fibers becomes poorer as the concentration of the increases.SEM photographs show the internal structure of hollow fibers can be changed by adjusting the concentration of PEG6000.From the study of Contact angles,the hydrophilicity of EVOH hollow fiber can be influenced by the concentration of PEG6000.On the other hand,cold plasma modification can improve the hydrophilicity of EVOH.What's more,EVOH is acid and alkalis-resistant.