Effect of polyethylene glycol (PEG) as an additive on the fabrication of polyvinylidene fluoride-co-hexafluropropylene (PVDF-HFP) asymmetric microporous hollow fiber membranes (original) (raw)
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Desalination, 2009
Poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF–HFP) hollow fiber membranes were prepared by the dry/wet spinning technique at different copolymer concentrations from 17 to 24 wt%. All the spinning parameters were kept constant except the copolymer concentration. The temperature of both the internal and external coagulants was maintained at 40ºC. The effects of the copolymer concentration on the morphological properties of the hollow fibers were studied in terms of external and internal diameter and scanning electron microscopy (SEM). It was found that the thickness of all tested hollow fibers did not change significantly. An evolution of the cross-section structure with the increase of the copolymer concentration was detected. The cross-section of the hollow fiber prepared with the lowest copolymer concentration exhibited a finger-like structure in both the external and internal layers disappearing in the internal layer as the copolymer concentration increases. Finally, a sponge-like structure is formed through all cross-section of the hollow fiber prepared with the highest concentration. This may be explained based on the decrease of the coagulation rate with the increase of the copolymer concentration in the dope solution.
Chinese Journal of Chemical Engineering, 2012
Poly(vinylidene fluoride) (PVDF) has become one of the most popular materials for membrane preparation via nonsolvent induced phase separation (NIPS) process. In this study, an amphiphilic block copolymer, Pluronic F127, has been used as both a pore-former and a surface-modifier in the fabrication of PVDF hollow fiber membranes to enhance the membrane permeability and hydrophilicity. The effects of 2nd additive and coagulant temperature on the formation of PVDF/Pluronic F127 membranes have also been investigated. The as-spun hollow fibers were characterized in terms of cross-sectional morphology, pure water permeation (PWP), relative molecular mass cutoff (MWCO), membrane chemistry, and hydrophilicity. It was observed that the addition of Pluronic F127 significantly increased the PWP of as-spun fibers, while the membrane contact angle was reduced. However, the size of macrovoids in the membranes was undesirably large. The addition of a 2nd additive, including lithium chloride (LiCl) and water, or an increase in coagulant temperature was found to effectively suppress the macrovoid formation in the Pluronic-containing membranes. In addition, the use of LiCl as a 2nd additive also further enhanced the PWP and hydrophilicity of the membranes, while the surface pore size became smaller. PVDF hollow fiber with a PWP as high as 2530 L•m −2 •h −1 •MPa −1 , a MWCO of 53000 and a contact angle of 71° was successfully fabricated with 3% (by mass) of Pluronic F127 and 3% (by mass) of LiCl at a coagulant temperature of 25 °C, which shows better performance as compared with most of PVDF hollow fiber membranes made by NIPS method.
Background: Diclofenac sodium (DS), being a potent anti-inflammatory drug and having a short half life of 1-2 hour, is a good candidate for sustained release microsphere formulation. Method: Microspheres were prepared by water-in-oil (W/O) emulsification solvent evaporation technique using Kollidon® SR (KSR) as the core polymer where drug: polymer was maintained at 1:1 ratio. Two preparative techniques were adapted: firstly, DS and KSR were dissolved in methanol and this solution was emulsified in Light liquid paraffin (LLP) containing 1% (wt/wt of the continuum) of span 60 (Method 1) and secondly, DS was dispersed in LLP containing same amount of emulsifier and previously prepared KSR solution was emulsified in it (Method 2). Results: Microspheres of method 1 were comparatively larger in size. DS loading was also high in these microspheres. Surface morphology was examined by a scanning electron microscope (SEM) and characteristic differences between the microspheres of two methods were found. Microspheres of the method 2 showed smooth and less porous surface whereas a high porous surface containing embedded DS crystals was observed in case of method 1. DS release was at a slower rate from the microspheres of method 2.
Membranes
Existing toxic solvents in the manufacturing of polymeric membranes have been raising concerns due to the risks of exposure to health and the environment. Furthermore, the lower tensile strength of the membrane renders these membranes unable to endure greater pressure during water treatment. To sustain a healthier ecosystem, fabrication of polyvinylidene fluoride (PVDF) hollow fiber membrane using a less toxic solvent, triethyl phosphate (TEP), with a lower molecular weight polyethylene glycol (PEG 400) (0–3 wt.%) additive were experimentally demonstrated via a phase inversion-based spinning technique at various air gap (10, 20 and 30 cm). Membrane with 2 wt.% of PEG 400 exhibited the desired ultrafiltration asymmetric morphology, while 3 wt.% PEG 400 resulting microfiltration. The surface roughness, porosity, and water flux performance increased as the loading of PEG 400 increased. The mechanical properties and contact angle of the fabricated membrane were influenced by the air gap...
Journal of Membrane Science, 2009
Highly porous and macrovoid-free PVDF hollow fiber membranes are of great interest for membrane contactor applications such as sea water desalination by membrane distillation in order to enhance the flux and long term stability of the process. For the first time in this paper, porous PVDF hollow fiber membranes with high outer surface porosity were fabricated by applying a two-phase flow consisting of a solvent and a dope solution in the air-gap region of spinning through a non-solvent induced phase separation process (NIPS). In this approach, the dope solution and the N-methylpyrrolidone (NMP) solvent were co-discharged from the middle and outer channels of a triple orifice spinneret, respectively. Then, the two-phase flow went through an air-gap region and finally entered the coagulation bath. It was observed that the introduction of the two-phase flow greatly increased the outer surface porosity of the PVDF fibers and eliminated the formation of macrovoids in the cross-section of the fibers as well. It was also found that the energy efficiency and the flux of the fibers spun through the solvent-dope solution co-exterusion were two to three times higher than the standard dry jet wet-spun fibers. A water vapor flux as high as 67 kg/(m 2 h) at 80 • C was obtained through the newly spun fibers.
Polymer, 2003
The effect of a salt additive, lithium perchlorate, on the morphology and crystal structure of PVDF membranes prepared by wet phase inversion process was studied. The gelation phase boundaries of the quaternary system, LiClO4/water/DMF/PVDF, were determined at 25 8C. It was found that the gelation lines shifted up progressively with increasing salt contents in this system. For a salt-free casting dope, the formed membrane exhibited a typical asymmetric structure characterized by the skin, parallel columnar macrovoids, and cellular pores. WAXD analysis indicated that PVDF crystallized into 'a' (type II) structure in this membrane. By contrast, when PVDF was precipitated from high salt-content dopes (e.g. $5 wt%), the macrovoids bent and extended towards the bottom region while the original cellular pores evolved into very large voids. The PVDF crystallites became 'b' form (type I) in these membranes. Thermal analysis (DSC) of all membranes showed dual melting peaks at low heating rates (# 5 8C/min), suggesting that the crystallites formed in the immersionprecipitation process were imperfect and they underwent re-crystallization during the heating process. Using low voltage SEM at high magnifications (e.g. 100 KX at 0.55 KV) on uncoated samples, the fine structures (10-20 nm) of the PVDF crystallites were observed. And at very high magnifications (225 KX at 0.59 KV), it was observed that the skin region of the membrane prepared from high salt-content dopes actually contained many nano-pores (e.g. 20 nm). This contributes to the high permeation rate and low solute rejection as revealed from the water-flux measurements.
Macromolecular Research, 2015
Poly(vinylidene fluoride) (PVDF) dual-layer hollow fiber membranes with porous layers were successfully prepared by simultaneous spinning of thermally induced phase separation (TIPS) and non-solvent induced phase separation (NIPS) through a triple orifice spinneret (TOS). The support layer was produced using a TIPS system from PVDF, with γ-butyrolactone (GBL) as the diluent. The prepared membranes were evaluated by analysis of their morphology, water flux, and tensile strength. The NIPS dope solution plays an important role in suppressing the formation of the dense top layer and forms a porous coating layer on the TIPS support layer. In addition, the effect of various non-solvent additives (polyvinylpyrrolidone (PVP), lithium chloride (LiCl), ethylene glycol (EG), and glycerol (Gly)) employed in the TIPS process was investigated. A specific morphology, namely, micro-sized holes in the spherulite structure, was observed on addition of specific mixtures of the non-solvent additives PVP, LiCl, and glycerol. Controlling the amount of added glycerol can help tune the dimensions of the holes. Because of this structure, the water flux of the membrane significantly increased, while a slight decrease in the tensile strength was observed. The specific morphology (hole structure) was very effective in controlling the porosity of the support layer on PVDF dual-layer hollow fiber membranes.
Novel porous membranes from chemically modified poly(vinylidene fluoride)
Journal of Membrane Science, 2006
Porous membranes were prepared by immersion in pure water or in water-NaOH baths of poly(vinylidene fluoride) solutions in different types of solvent (N,N-dimethylformamide or 1-methyl-2-pyrrolidone or triethylphosphate). Membranes were characterized through ultrafiltration tests, scanning electron microscope observations and vibrational spectroscopy (FT-Raman and FT-IR) measurements. The presence of NaOH in the immersion bath caused not only chemical dehydrofluorination of the polymer but also affected the membrane formation thus leading to membranes with different structures, permeability and retention properties. Membrane prepared by coagulation in NaOH rich bath were treated with NaOCl and H 2 O 2 to attack the double bonds and to obtain membrane with improved hydrophilicity.
Indian Journal of Science and Technology, 2017
Objectives: Investigation the influence of PVP added into the dope solution with (0, 5, 7 and 9) wt. % on membrane characteristics, structure and performance for DCMD system. Determine the impact of process operating parameters on the performance of the (PVDF-co-HFP) hollow fibre membrane in DCMD applications such as hot feed temperature. Methods/ Statistical analysis Prepared and fabrication a PVDF-co-HFP hollow fibre membrane using a various parentage of PVP (0, 5, 7 and 9 wt. %) as a pore former into the dope solution. Characterisation the structure and morphology of the (PVDF-co-HFP) membrane via FESEM technique. Investigating the performance of the PVDF-co-HFP hollow fiber membrane through a DCMD system. Improvement of PVDF-co-HFP hollow fibers through the adding of PVP molecules into the dope solution was studied. Finding The addition of 5, 7, and 9 wt. % PVP into the dope solution resulted in repressed the sponge-like shapes and promoted the forming of two finger-like shapes. Modified the pore area per unit surface area (porosity) and the pore structure of the synthesized hollow fibres. The pore size of the hollow fibre was enhanced with the addition of 9 wt. % PVP into the dope solution. The PVDF-co-HFP fibres permeate flux with PVP additives was superior to that neat PVDFco-HFP by about 75% at feed temperature (T f) of 70 °C. The rejected salt factor for all PVDF-co-HFP hollow fibres was over 99.98%. The increase of hot feed temperature led to increased permeation flux for the DCMD process. Application/ Improvements: Outcomes give a good indication for the improvement of PVDF-co-HFP hollow fiber via adding the PVP particles onto the dope solution. It can be concluded that the PVDF-co-HFP hollow fiber appropriate for use in DCMD application for seawater desalination.
Journal of Membrane Science, 2017
Membranes with outstanding anti-wetting property are essential for membrane distillation (MD) applications. In this work, a hydrophobization treatment for porous polyvinylidene fluoride (PVDF) hollow fiber membranes using an etching method combined with an ultrafiltration coating process was developed to achieve this desired property. PVDF particle was subjected to an etching process to coarsen its surface. Etched PVDF particles were subsequently dispersed in a dispersant with a specific PVDF-dissolving capacity and then coated onto the PVDF hollow fiber membrane surface via ultrafiltration to construct a super-hydrophobic surface with a micro/nanostructure. After this process, the super-hydrophobic PVDF hollow fiber membrane with the surface contact angle of 163.8˚was obtained, and the coating layer on the membrane surface was exceedingly stable. Moreover, the membrane pores were not blocked by the coating layer. The optimal etching conditions for the PVDF particles were as follows: solubility parameter of the etchant, 25.6 (J/cm 3) 1/2 ; etching time, 60 min at 25 °C. A super-hydrophobic surface with a stable particles coated layer is achieved in an optimal coating condition (solubility parameter of the dispersant, 25.87 (J/cm 3) 1/2 ; PVDF particles coated, 18.0 g/m 2). The direct contact membrane distillation (DCMD) experiments showed that after the surface modification process, the hydrophobicity of the membrane was significantly enhanced. In addition, the anti-wetting property of the membrane improved, the time for membrane to be wetted through the channel increased from 40 to 180 min, the pure water DCMD flux increased from 26.0 to 29.9 kg•m-2 •h-1 , and the critical wetting depth increased from 19.5 to 35.7 μm.