The Investigation of Thermodynamic and Kinetic Effects in TiO2/Al2O3/ PVDF Composite Membrane Forming Process

Abstract

Background: The addition of inorganic nano dioxide (TiO2) and alumina (Al2O3) particles into the organic polymer material Polyvinylidene Fluoride (PVDF) can enhance the composite membranes’ hydrophilicity and anti-pollution capacity in the water treatment process. Objective: The study aimed to investigate thermodynamic and kinetic effects of the inorganic nanoparticles on composite membrane in the membrane forming process. Method: The turbid point titration method was adopted to determine casting solution phase separation point of the system and draw ternary phase diagrams. Ternary system phase diagrams were used to investigate the thermodynamic effects of nanoparticles on the membrane forming process. UV spectrophotometer transmittance decline curves of the casting solution system added different amounts of nanoparticles were measured in order to investigate the kinetic effects of nanoparticles in the membrane forming process. Results: The results show that nanoparticles have a very high specific surface area, which can make strong adsorption of PVDF polymer chain and reduce the cohesive energy of the polymer in the casting solution. The membrane forming system is more prone to phase separation, thereby reducing the sedimentation values of the phase separation point. The casting solution system becomes unstable thermodynamically. The decreasing trend casting solution system and precipitation values is obvious in the range of 1% to 3% nanoparticles content and this trend weakens when nanoparticles content is 4%. Nanoparticles can decrease the ability of non-solvent to accommodate in the casting solution and make membrane form in smaller non-solvent concentration. The hydrophilic nanoparticles in the casting solution can affect mass transfer resistance of the solvent and non-solvent and augment mass transfer driving force for mutual diffusion of the solvent and non-solvent thus shortening the membrane forming time from the casting solution being immersed in the gelation bath for membrane formation. In the system with PVP as pore-forming agent, the process takes about 800s without nanoparticles addition and about 600s to complete the process after adding the nanoparticles. Conclusion: The addition of nanoparticles reduces the cohesive energy of the polymer in the casting solution, the casting solution becomes unstable in thermodynamics; The addition of nanoparticles increases the mass transfer force by bidirectional diffusion of solvent and non-solvent in the casting solution.