Effect Of Coagulation Bath Temperature Research Articles

Effects of coagulation bath temperature and polyvinylpyrrolidone content on flat sheet asymmetric polyethersulfone membranes

AbstractIn this study, effects of coagulation bath temperature (CBT) and polyvinylpyrrolidone (PVP K15) concentration as a pore former hydrophilic additive on morphology and performance of asymmetric polyethersulfone (PES) membranes were investigated. The membranes were prepared from a PES/ethanol/NMP system via phase inversion induced by immersion precipitation in a water coagulation bath. The morphology of prepared membranes was studied by scanning electron microscopy (SEM), contact angle measurements, and mechanical property measurements. Permeation performance of the prepared membranes was studied by separation experiments using pure water and bovine serum albumin (BSA) solution as feed. The obtained results indicate that addition of PVP in the casting solution enhances pure water permeation flux and BSA solution permeation flux while reducing protein rejection. Increasing CBT results in macrovoid formation in the membrane structure and increases the membrane permeability and decreases the protein rejection. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers

Formation mechanism and crystallization of poly(vinylidene fluoride) membrane via immersion precipitation method

Poly(vinylidene fluoride) (PVDF) membranes were prepared by immersion precipitation method at different coagulation bath temperatures. Effects of coagulation bath temperature on the morphology and crystal structure of PVDF membranes were studied. The phase diagram of PVDF/DMAc/H 2O ternary system was divided into three regions: one phase region, liquid–liquid two phase region and gelation region. Binodal line and spinodal line of phase inversion were calculated based on the thermodynamics equations of membrane formation, and the gel phase boundaries of the systems at 25 and 60°C were determined via cloud point measurement. Based on the phase diagram analysis and experiment results, it was found that gelation is the dominate membrane formation mechanism at low temperature, but the bicontinuous structure of the formed membrane at 60°C is attribute to spinodal decomposition. Moreover, the thermal behavior and crystal structure of membranes prepared using different coagulation bath temperatures were examined by differential scanning calorimetry (DSC) and wide angle X-ray diffusion (WAXD). The results shows that the PVDF membrane precipitated at 60°C had a typical ‘‘α’’ form crystal structure. While at 15°C, the PVDF crystallites are a mixture of ‘‘α’’ and ‘‘ β’’ form crystal structure. The crystallization degree of the prepared membrane has not increased with the coagulation bath temperature decreasing.

Effect of coagulation bath temperature on formation mechanism of poly(vinylidene fluoride) membrane

AbstractEffects of coagulation bath temperature on the membrane formation mechanism and the morphologies of the formed membranes were studied. The binodal and spinodal lines in the phase diagrams of water/DMAc/Poly(vinylidene fluoride) (PVDF) were calculated based on the thermodynamics equations of membrane formation, and the gel phase boundaries of the systems at 25°C and 60°C were determined via cloud point measurement. The obtained ternary phase diagrams of water/DMAc/PVDF contain three regions: the one‐phase region, the liquid–liquid two‐phase region, and the gel region. In the phase diagrams, the liquid–liquid demixing line (binodal) is located inside the gelation line. At low temperature, there exists a wide region between gelation line and binodal line. Gelation could occur in the absence of liquid–liquid demixing, and becomes the dominant membrane formation mechanism. At high temperatures (60°C), however, the gelation line approaches the binodal line, which results in a much smaller gelation zone. The kinetics of the solvent out‐flux and water influx were enhanced, liquid–liquid demixing is the dominant mechanism. The membrane formation mechanisms at different temperature were confirmed by the light transmission measurements during membrane forming process and the morphologies of the membranes examined by SEM imaging. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008.

Preparation of porous PVDF hollow fibre membrane via a phase inversion method using lithium perchlorate (LiClO 4) as an additive

Polyvinylidene fluoride (PVDF) hollow fibre membranes were prepared via a phase inversion method, using N, N-dimethylacetamide (DMAc) as solvent, lithium perchlorate (LiClO 4) as inorganic salt additive and water as the coagulation medium. The phase diagram of the LiClO 4/PVDF/DMAc/water quaternary systems was constructed using cloud-point experimental data. With the addition of the LiClO 4, the effect of coagulation bath temperature on the structure of membranes was investigated. The gas permeation method was used to estimate the pore size and pore size distribution of the PVDF hollow fibre membrane prepared. Also, the effect of the composition of internal coagulant on the membrane structure was investigated using different ratio of 1-methyl-2-pyrrolidone (NMP)/water mixtures.