Investigating the structure and water permeation of membranes modified with natural and synthetic additives using tensile, porosity, and glass transition temperature studies (original) (raw)
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Polymer Testing, 2014
This paper reports on the effects of lignin, polyvinyl pyrrolidone and polyethylene glycol as additives to polysulfone ultrafiltration membranes prepared by nonsolvent induced phase separation. The focus is on the mechanical and thermal properties of the resultant membranes. Differential scanning calorimetry (DSC) and thermogravimetric analysis were used to probe the thermal properties, while an Instron tensile tester was used to characterise the mechanical properties. Morphological studies indicate that the porosity of the bottom sub-layer increased with the use of each additive, suggesting that coagulation in the sub-layer differed from that of the top layer. Membranes fabricated using lignin were thermally stable as the residue at 800 C increased from 13% to 44%, suggesting interaction of lignin with the polymer. The increase in free fractional volume was confirmed by DSC thermograms as the glass transition temperature decreased considerably after incorporating the additives. Generally, the modulus and tensile strength decreased after the introduction of the additives. These results offer new insight into the use of an emerging, cheap and readily available natural additive (lignin) compared to traditional synthetic additives in membrane formation.
Investigating the Usability of Alkali Lignin as an Additive in Polysulfone Ultrafiltration Membranes
Bioresources, 2015
The effects of natural and synthetic polymer additives on the properties of ultrafiltration membranes were studied. The use of NaOH to remove the residual additive remaining in the membranes during coagulation was also investigated, as was the effect of NaOH post-treatment relative to membrane performance. To evaluate the residual additives present, ATR-FTIR was used. Contact-angle analysis and water-absorption experiments were used to examine the hydrophilic properties of the prepared membranes. Membranes modified with lignin (Lig) were found to absorb more water (94% water uptake) than other membranes. In general, the contact angles were found to be low for membranes treated with NaOH. Membrane permeability was greatest in lignin_polysulfone (Lig_PSf), followed by polyvinylpyrrolidone_polysulfone (PVP_PSf), and with polyethylene glycol_polysulfone (PEG_PSf) the least permeable, similar to the trend observed in water uptake. A 'Robeson plot' analogue showed that Lig_PSf membranes had high separation factors regardless of the size of the solute being rejected. This study indicates the feasibility of using cheap, readily available additives to increase the performance of membranes.
Journal of Applied Polymer Science, 2002
The determination of the pore size, porosity, number of pores, molecular weight cutoff (MWCO), and morphology of an ultrafiltration membrane is necessary for predicting the performance of a membrane for a specific application. For ultrafiltration membranes prepared from cellulose acetate and sulfonated polysulfone in the presence and absence of various concentrations of the additive poly(ethylene glycol) 600, pore statistics and MWCOs were determined in studies with dextrans of different molecular weights. Surface and cross-sectional morphologies of the membranes were analyzed with scanning electron microscopy at different magnifications. The pore size increased with increasing concentrations of sulfonated polysulfone and additive in the casting solution. Similarly, the MWCOs of the membranes ranged from 19 to 150 kDa, depending on the various polymer blend compositions and additive concentrations. Results from scanning electron microscopy provided qualitative evidence for the trends observed for the pore statistics and MWCO results.
Industrial & Engineering Chemistry Research, 2001
The determination of the pore size, porosity, number of pores, molecular weight cutoff (MWCO), and morphology of an ultrafiltration membrane is necessary for predicting the performance of a membrane for a specific application. For ultrafiltration membranes prepared from cellulose acetate and sulfonated polysulfone in the presence and absence of various concentrations of the additive poly(ethylene glycol) 600, pore statistics and MWCOs were determined in studies with dextrans of different molecular weights. Surface and cross-sectional morphologies of the membranes were analyzed with scanning electron microscopy at different magnifications. The pore size increased with increasing concentrations of sulfonated polysulfone and additive in the casting solution. Similarly, the MWCOs of the membranes ranged from 19 to 150 kDa, depending on the various polymer blend compositions and additive concentrations. Results from scanning electron microscopy provided qualitative evidence for the trends observed for the pore statistics and MWCO results.
Journal of Membrane Science, 2014
In this study, three nonwoven fabrics were used as supports to form thin film composite membranes for forward osmosis (FO) applications. Lignin additive was added to the polysulfone layer in two different concentrations to increase the porosity of the substructure. The fabrics were characterized in terms of their Frazier permeability, tortuosity, porosity, thickness, structural parameter and capillary pressure. It was found that the fabric tortuosity and thickness had strong negative correlations with FO water flux, while fabric porosity had a strong positive correlation. The fabric capillary pressure was found to be indicative of how well the polysulfone layer adhered to the fabric layer. The membrane structural parameter of the fabric, unsupported and supported polysulfone layers were measured and compared using a "resistance-in-series" model. Although seepage of the casting solution into the fabric layer was physically observed, the addition of the individual structural parameters of the layers offered a good approximation of the composite membrane structural parameter. Membrane structural parameters calculated for fabric supported composite membranes using reverse osmosis (RO) permeability parameters and FO/RO established transport equations were much larger than structural parameters obtained from physical measurements. The difference may be due to compaction of composite membranes in reverse osmosis experiments, casting solution seepage partially plugging the upper layers of the support fabric and other non-idealities not captured in the established FO/RO transport equations.
Preparation and performance of polysulfone-cellulose acetate blend Ultrafiltration membranes
Journal of Macromolecular Science Part a Pure and Applied Chemistry, 2006
In the development of high performance polymeric membranes, it is essential to design the molecular and morphological characteristics for specific applications. Polysulfone and cellulose acetate of blend membranes with various concentration of polymer pore former, PEG600 were prepared by phase inversion technique and used for ultrafiltration. Polymer blend composition, additive concentration, and casting conditions were optimized. The blend membranes were characterized in terms of compaction, pure water flux, water content, hydraulic resistance and separation of dextran studies. Surface morphology of the embranes was analyzed using scanning electron microscopy at different magnifications. Further, the characterized membranes were attempted for treatment of distillery effluents after secondary treatment and the results are discussed in detail.
DESALINATION AND WATER TREATMENT, 2017
The influence of macromolecular additives on the mechanical properties of polyethersulfone (PES) and polysulfone (PS) is investigated. Ultrafiltration membrane sheets are prepared from PES and PSF based polymers via liquid non-solvent induced phase separation (NIPS), and employing polyvinylpyrrolidone (PVP), polyethylene glycol (PEG) and Pluronic ® (PLU) co-polymers as macromolecular additives. The impact of additives on the main membranes' characteristics are studied; i.e., pure water permeability, membrane porosity, morphology and surface chemistry. The main mechanical properties are examined for all membranes and are correlated to the chemical composition of the membranes. Overall, the membranes prepared using PLU showed a superior tensile strength compared to other membrane samples, while PVP was found to enhance the membrane formation by suppressing microvoids formation. This study provides a better understanding of the main mechanical and other characteristics of membrane materials with regards to using additives.
Results in Materials , 2019
Membrane morphology is a key parameter that affects membrane characterization and performance. The objective of the current study is to control the morphology of the Polysulfone Membranes (PSF) for further flux improvement using heat treatment. The study investigated relaxed heating and tension heating as to how both of these approaches influenced membrane porosity and membrane fiber diameter. Furthermore, the influence of changed morphology parameters on the membrane's performance, membrane fouling, and increase in trans-membrane pressure were examined. PSF flat sheet membrane was selected for this study. PSF membranes were treated with relaxed heating and tension heating, from 180 to 195 C for the duration of 1-5 h. In addition, computational density functional theory (DFT) with Lee-Yang-Parr (B3LYP) was used to study the behavior of molecular fragments of the PSF at the treating temperatures. The experimental results showed that tension heating contributed to stretching and rearranging the membrane fibers along the direction of the external force under the effects of both heat and tension. This resulted in an improved structural density of the internal fibers and a decrease in the fiber diameter. The optimum treatment of tension heating was determined to be 1 h at 185 C, and had the optimum membrane porosity for an enhanced membrane flux and lower fouling. The computational behavior of molecular fragments of PSF showed atom vibrations, increase in bond lengths and a rise in the kinetic energy at 185 C.
Hollow fiber ultrafiltration membranes prepared from blends of poly (vinyl chloride) and polystyrene
Desalination, 2012
Polymeric blend ultrafiltration membranes based on poly(vinyl chloride) (PVC) and polystyrene (PSR) were prepared by phase inversion method. The PSR concentration in dope solution varied from 1 to 6 wt.%. DMAC was used as a solvent, while water was used as internal and external coagulant. Scanning electron microscope (SEM) was utilized to characterize cross-section, outer, and inner surfaces of the hollow fiber structure. Differential scanning calorimetry (DSC) was used for the determination of the glass transition temperature (Tg) of the blends. From the experimental results it was found that, the structural morphology of the polymeric blend varied with the PSR concentration. There is no significant decrease in pure water permeation flux by using 1 and 2 wt.% PSR concentration in dope solution. The PVP K-90 rejection highly improved from 76.2% to 98.53% with the addition of 1 wt.% PSR concentration. The PVC/PSR blends show incompatibility by the results of SEM and DSC. Also it was found that the mechanical properties of PVC/PSR blend membranes were improved randomly compared with that of PVC membrane.
Preparation and Performance of Polysulfone‐Cellulose Acetate Blend Ultrafiltration Membrane
Journal of Macromolecular Science, Part A, 2006
In the development of high performance polymeric membranes, it is essential to design the molecular and morphological characteristics for specific applications. Polysulfone and cellulose acetate of blend membranes with various concentration of polymer pore former, PEG600 were prepared by phase inversion technique and used for ultrafiltration. Polymer blend composition, additive concentration, and casting conditions were optimized. The blend membranes were characterized in terms of compaction, pure water flux, water content, hydraulic resistance and separation of dextran studies. Surface morphology of the embranes was analyzed using scanning electron microscopy at different magnifications. Further, the characterized membranes were attempted for treatment of distillery effluents after secondary treatment and the results are discussed in detail.