Study On Graft Modification Of Polymer Porous Membranes In Supercritical Carbon Dioxide

In this paper, the surface graft polymerization of porous membrane in supercritical carbon dioxide(SC CO₂) was proposed to improve the hydrophilic and antifouling properties. Different reaction systems in SC CO₂ was studied, especially focusing on polypropylene(PP) hollow fiber membrane with acrylic acid under different experiment conditions.The influences of monomer and initiator concentration, soaking time, soaking temperature, soaking pressure, reaction time, reaction temperature and reaction pressure on modification were experimented. The modification results of different substrate membrane (PP hollow fiber membrane, PP dense film, PP plate membrane, PES plate membrane), grafting monomer (acrylic acid, copolymer of styrene and maleic anhydride) and different initiator system (benzyl peroxide, plasma treatment) were discussed. It was concluded that the effect of substrate membranes on grafting degree was very important. The mechanical properties of membranes modified by plasma treatment could be reduced.The surface microstructures of all membranes were characterized by FTIR-ATR, mercury porosimeter, differential scanning calorimetric analysis(DSC) and scanning electron microscopy(SEM). It was found that the outer and inner surface of modified PP hollow fiber membranes really had PAA chains, and their pore sizes and porosities decreased with the increase of grafting degree. Simultaneously, the roughness was increased via grafting polymerization in SC CO₂. However, the crystallization in PP hollow fiber membrane was changed by the modification reaction in supercritical carbon dioxide, and the toughness of modified PP hollow fiber membrane was increased.The hydrophilicity of modified PP hollow fiber membrane was improved. The degree of absorbed water was increased from 0% for unmodified PP hollow fiber membrane to 75.5% for modified membrane with AA (grafting degree in 33.6wt%) Water flux of ethanol treated PP hollow fiber membrane was 118.8 I7m²h, and for the modified PP hollow fiber membrane with AA(grafting degree in 5.5wt%), the waterflux was increased to 180.2 L/m2h. While increasing the grafting degree, the increase of water flux was restricted due to the decrease of pore size and porosity. Extraordinarily, the contact angle of modified membrane was not changed obviously. Corresponding principle of these results should be studied in detial in the future.