Preparation And Characterization Of Hydroxypropylcellulose/Polyacrylonitrile Blend Membranes

Thermo-sensitive macromolecular membrane was defined as a membrane,of which water flux,retention ratio and porosity discontinuously vaned with environmental temperature.They were widely used in isolation purification,artificial organs,drug delivery system and bionics,and so on.Hydroxypropylcellulose(HPC)is an alkyl-substituted hydrophilic cellulose derivative that not only shows particular phase transition behavior in aqueous solution or some organic solvents,but also has a lot of advantages such as excellent film-forming property,degradability,biocompatibility,and so on.It could be dissolved in water when water temperature was lower than its low critical solution temperature(LCST).In recent years,considerable research attention has been focused on its film forming from aqueous solution and modification by blending with proton donor polymers.But there were no reports on the modification of HPC by blending with proton acceptor,rheological behavior of HPC solution,and ternary phase diagram of film forming process for HPC.In this paper,with HPC and PAN as raw materials,the properties of blend solutions and the permeability of thermo-sensitive membranes were investigated in order to develop a new blend membrane.Based on the exsistance of LCST on HPC, the temperature-sensitivity of HPC/PAN blend membranes was investigated by swelling-deswelling.The membrane properties were characterized by water flux, retention ratio and porosity through permeation.In addition,both theory analysis and computer simulation of the film-forming process of HPC were presented,and the ternary phase diagram was drawn,thus,a mass transfer process was elucidated in the end.In consideration of compatibility which is a key factor in design and development of a new blending material.Firstly,a new blending solution of hydrogen-bonding-group-containing polymers HPC/PAN was studied.The compatibilitiy of the two polymers were investigated by means of FTIR,POM,SEM,△H_m,viscosimetry and TGA over the composition range.The three Hansen solution parameters of HPC were remarkably different from those of PAN though the total solubility parameters of the two polymers were approaching.It was concluded that this binary blend system was incompatible by theoretical calculation of the solubility parameters,but was found compatible by the experimental results.Because the viscosimetry more sensitively,simply and accurately reflected the changes of compatibility in polyblends,interaction parameters,Huggins constants and association constants that were calculated based on the viscosimetry were very creditable.The same results were also obtained from SEM,POM,TGA and FTIR analyses.The nature of compatibility of HPC/PAN was attributed to the hydrogen-bonding interaction between hydroxyl group and nitrile group when blending.In view of rheological behavior of polymer solution being an important factor of polymer processability,in the second part,the rheological behavior was investigated in detail at different concentrations,blend ratios and temperatures.The results showed that the non-newtonian index of HPC/PAN blend solutions was less thanl,and decreased with the increase of concentration below 30℃.The apparent viscosity increased with the increase of concentration at the same shear rate.The structural viscosity index also increased with the increase of concentration.Formability and workability of blend solution became worse when concentration was 16%.With the increase of temperature Non-newtonian index increased greatly,and structural viscosity index decreased in the range of 30-40℃.However,the results were on the contrary when temperature was higher than 40℃.The viscous flow activation energy of the blends in which temperature was less than 40℃was higher than that in which temperature was higher than 40℃.It was because that the phase transition in HPC occurred when temperature was higher than LCST,and then,the phase separation appeared,thus,phase domains increased.So,the suitable temperature of molding process was less than 40℃.Based on that,permeability,porosity and temperature-sensitivity of HPC/PAN blend film were studied in detail.The results were as follows:the water flux decreased and retention increased with the increase of solid content;the water flux increased and retention decreased with the increase of HPC content in HPC/PAN blends.It was indicated that the hydrophilicity of the blend membrane was improved by the addition of HPC.The water flux decreased and retention increased with the increase of prevaporation time.Adjusting coagulation bath composition and temperature could control structure and properties of blend films.The phase transition temperature of blending solutions decreased with the increase of PAN,and the phase transition temperature was influenced by warming-up rate.Swelling rate increased with the increase of HPC,and the polymer chain relaxation process became a controlling process during membrane swelling at pH=1.4 and temperature lower than LCST.Up to now,there was no detailed report about the process of film-forming from HPC aqueous solution.In this paper,computer simulation of solidification process in HPC/water/glycerol ternary system was studied.Solvent-nonsolvent interaction parameter was measured by freezing point depression.The results showed that the interaction parameter increased with the increase of glycerol mass fraction,and the value of solvent-nonsolvent interaction parameter was between 1.4 and 2.0.In addition,polymer-nonsolvent interaction parameter was determined by equilibrium swelling.The binodal and spinodal of HPC/water/glycerol ternary system were calculated,and the ternary phase diagram was drawn.A mass transfer dynamics model was established based on Reuvers mass transfer model.Effects of the casting solution concentration and coagulation composition on mass transfer process were investigated based on polymer concentration distribution during coagulation.The conclusion of this research was that the volume fraction of polymers was gradually decreased with the increase of the distance from membrane surface.