Kemijska modifikacija in karakterizacija površine polisulfonskih membran

Abstract

Asymmetric porous membranes were prepared from polysulfone by a wet-phase separation procedure. Different chemical modifications were applied to the upper membrane surface, i.e. the surface which was exposed to interaction with nonsolvent (water) in the coagulation bath during the membrane formation. The membrane surface was modified by the series of Friedel-Crafts electrophilic substitutions of aromatic rings in the polysulfone molecules. As a reagent 1-chlorodecane or propylene oxide dissolved in hexane and $AlCl_3$ as a catalyst were used. In the former case a hydrophobic and in the latter one a hydrophilic coating was achieved, respectively. The membrane surface was also modified by sulfonization with sulfuric (VI) acid water solutionin this way negative charges were introduced at the membrane surface. The membranes, unmodified and chemically modified, were characterized by measuring the membrane thickness, the deionized water flux through the membrane, the zeta potential and contact angle. The specific chemical modifications of the membrane surface affect the water flux, the zeta potential and contact angle values whereas the membrane thickness remains unchanged. These effects are interpreted in terms of hydrophilicity and hydrophobicity, changes of the membrane surface charge and the thickness of shear layer at the membrane surface, all with respect to the particular modification applied. Reaction with 1-chlorodecane gave a hydrophobic surface by nonpolar $–(CH_2)_9-CH_3$ groups and reaction with propylene oxide gave a hydrophilic surface with polar group $-CH(CH_3)-CH_2-OH$. The surface of sulfonized polysulfone membranes contained ionizable ($-SO_3H$) functional groups.Površino asimetričnih poroznih membran iz polisulfona, pripravljenih po postopku mokre fazne separacije, smo kemijsko modificirali s Friedel-Crafts-ovo elektrofilno substitucijo aromatskih delov molekule polisulfona, kjer smo kot reagent uporabili 1-klorodekan in propilen oksid ob prisotnosti $AlCl_3$ kot katalizatorja. Na površino smo vezali nepolarne in polarne skupine, ki tvorijo hidrofobno oziroma hidrofilno oblogo. Površino membrane smo kemijsko modificirali tudi s sulfoniranjem z žveplovo(VI) kislino in s tem vezali na površino negativni naboj. Nemodificirane in kemijsko modificirane membrane smo karakterizirali z merjenjem debelin, pretokov za deionizirano vodo, potenciala zeta in omočitvenega kota. Kemijske modifikacije površine membrane so vplivale na pretok za deionizirano vodo, na potencial zeta in omočitveni kot, debelina pa je ostala nespremenjena. Te spremembe smo kvalitativno pojasnili s spremembami hidrofilnosti in hidrofobnosti ter spremembami naboja na površini in debeline mejnega sloja ob površini membrane. Pri reakciji z 1-klorodekanom tvorijo nepolarne $–(CH_2)_9-CH_3$ skupine hidrofobno površino, pri reakciji s propilen oksidom pa tvorijo polarne $–CH(CH_3)-CH_2-OH$ skupine hidrofilno površino. Površina membrane, modificirana z žveplovo(VI) kislino, pa vsebuje ionizabilne $–SO_3H$ funkcionalne skupine