Milk Water Permeation Research Articles

Preparation and modification of nano-porous polyimide (PI) membranes by UV photo-grafting process: Ultrafiltration and nanofiltration performance

Polyimide (PI) membranes were prepared via non-solvent induced phase separation. The prepared PI mem- branes were modified by ultraviolet light (UV) and graft polymerization of hydrophilic acrylic and amino monomers in the absence and presence of benzophenone (BP) onto the membrane surface to introduce more hydrophilic and lower fouling membranes. Acrylic acid (AA) and 2-hydroxyethylmethacrylate (HEMA) as acrylic monomers, 1,3-phenylene- diamine (mPDA) as amino monomer and BP as photo-initiator were used. The unmodified and modified PI membranes were characterized by degree of grafting (DG) and contact angle measurements. They were also characterized by their ultrafiltration performance with pure water and non-skim milk and nanofiltration performance with 500 ppm NaCl and MgSO4 single solutions. The DG was increased with increasing monomer concentration, especially at presence of BP. The contact angle measurements indicated that hydrophilicity of PI membrane was improved after UV photo- grafting of hydrophilic monomers onto the membrane surface in all cases. The ultrafiltration results showed that the pure water fluxes and milk water permeation of PI membrane declined after monomer photo-grafting while the protein rejection was extremely increased. The decrease in permeability was remarkable in the presence of BP. The mean pore size of base and modified PI membranes ranged from 8.3 to 0.55 nm when calculated from the solute transport data. Moreover, the irreversible flux loss and flux recovery of PI membrane were modified by UV photo-grafting of hy- drophilic monomers. All modified membranes showed considerable NaCl and MgSO4 rejections. In addition, the mem- brane modified with mPDA at presence of BP showed highest NaCl and MgSO4 rejections.

Nano-porous polyethersulfone (PES) membranes modified by acrylic acid (AA) and 2-hydroxyethylmethacrylate (HEMA) as additives in the gelation media

In this study, the effects of addition of acrylic acid (AA) and 2-hydroxyethylmethacrylate (HEMA) in the gelation media on structure and permeation properties of polyethersulfone (PES) membranes were investigated. The membranes were prepared by phase inversion method using PES and polyvinylpyrrolidone (PVP) in dimethylacetamide (DMAC) as solvent. The surface and sub-layer morphologies of the obtained membranes were analyzed by scanning electron microscope (SEM) and atomic force microscope (AFM). The membrane performance was evaluated in terms of pure water permeation, non-skim milk water permeation, milk protein rejection, fouling analysis and solute separation of polyethylene glycol (PEG) solution of various molecular weights. The morphological studies showed that the average pore sizes of the surface and sub-layer were reduced at the presence of AA and HEMA in the gelation media. Meanwhile, the surface porosity was increased. The mean pore size ranged from 5.2 to 11.3 nm when calculated from the solute transport data. The pure water flux, milk water permeation and protein rejection of the membranes were improved by increasing the AA and HEMA contents in the gelation media. The fouling analysis indicated that the membrane resistance against filtration was decreased. In conclusion the antifouling properties of PES membranes were improved by addition of AA and HEMA in the gelation media.

UV photo-grafting of hydrophilic monomers onto the surface of nano-porous PES membranes for improving surface properties

Polyethersulfone (PES) membrane was prepared via immersion precipitation technique and modified by UV photo-grafting of hydrophilic monomers on the top surface of the membrane. Acrylic acid (AA) and 2-hydroxyethylmethacrylate (HEMA) as acrylic monomers and 1,3-phenylenediamine (mPDA) and ethylene diamine (EDA) as amino monomers were used at different concentrations to improve the surface properties of the membrane. The unmodified and modified PES membranes were characterized by contact angle, ATR-FTIR, scanning electron microscopy (SEM), atomic force microscopy (AFM), cross flow filtration and fouling analysis. The contact angle measurements indicated that the hydrophilicities of the membranes were significantly increased by UV photo-grafting of hydrophilic monomers onto the membrane surface. The ATR-FTIR spectra, SEM and AFM images confirmed that the modification on the PES membrane surface was carried out by UV photo-grafting of hydrophilic monomers. The solute transport data showed that the surface mean pore size of the unmodified membrane declined from 15.8 nm to 6.1, 3.9, 5.5 and 5.7 nm for 6 wt.% of AA, HEMA, mPDA and 5 wt.% of the EDA modified membranes, respectively. The pure water flux and milk water permeation of the membranes were declined by UV photo-grafting but the protein rejection was improved. Moreover, the antifouling properties and flux recovery of the PES membrane were modified by UV photo-grafting of hydrophilic monomers.

Improvement of performance and surface properties of nano-porous polyethersulfone (PES) membrane using hydrophilic monomers as additives in the casting solution

The effects of hydrophilic monomers e.g. acrylic acid (AA) and 2-hydroxyethylmethacrylate (HEMA) on the morphology and performance of polyethersulfone (PES) membrane were investigated. The membranes were fabricated from a casting solution of PES, dimethylacetamide (DMAC), polyvinylpyrrolidone (PVP) and AA or HEMA via phase inversion induced by immersion precipitation. The mixture of water (80 vol.%) and 2-propanole (IPA, 20 vol.%) was employed as gelation media. The prepared membranes were characterized using ATR-FTIR, SEM, AFM, contact angle, viscosity measurements, ultrafiltration performance and fouling analysis. The hydrophilicity of PES membrane was improved after addition of AA and HEMA in the casting solution. The morphological studies (SEM and AFM) showed that the average sizes of membrane pores in surface and sub-layer were reduced with addition of AA and HEMA in the casting solution. Meanwhile the surface porosity was increased. The surface pore size of the untreated PES membrane was decreased from 138 nm to 45.1 and 40.6 nm with introducing 15 wt.% AA and HEMA, respectively. The experimental results showed that the pure water fluxes of membranes were declined at the presence of AA and HEMA. Moreover, the milk water permeation and protein rejection were improved at these conditions. Finally, the fouling analysis demonstrated that the membranes show fewer tendencies for fouling.

Fabrication of polyethersulfone (PES) membranes with nano-porous surface using potassium perchlorate (KClO 4) as an additive in the casting solution

Polyethersulfone (PES) membranes with nano-porous surface were fabricated by addition of potassium perchlorate (KClO 4) as an additive in the casting solution. The membranes were prepared from PES/polyvinylpyrrolidone (PVP)/KClO 4/dimethylacetamide (DMAc) via phase inversion induced by immersion precipitation technique. Mixture of water and isopropyl alcohol (IPA) was used as coagulation medium. The viscosity of PES casting solution increased with addition of KClO 4. The contact angle measurements demonstrated that the hydrophilicities of membrane enhanced by increasing the KClO 4 concentration in the casting solution. According to SEM analysis, it was found that the addition of KClO 4 had a significant influence on structure of the membrane skin layer and the sub-layer. Membranes with dense surface and sub-layer were formed at this condition. The surface AFM images indicated that the addition of KClO 4 in the casting solution resulted in nano-structure membranes with surface small pore size. The effect of KClO 4 on the membrane performance was investigated using cross-flow filtration of pure water and non-skim milk as feeds. The pure water flux through the prepared membranes declined by adding 1, 3 and 5 wt.% of KClO 4 in the casting solution. On the other hand, milk water permeation and protein rejection of prepared membranes were improved.

The influence of sulfonated polyethersulfone (SPES) on surface nano-morphology and performance of polyethersulfone (PES) membrane

In this research, firstly sulfonation of polyethersulfone (PES) was carried out and then polyethersulfone (PES)/sulfonated polyethersulfone (SPES) blend membranes were prepared with phase inversion induced by immersion precipitation technique. polyvinylpyrrolidone (PVP, 2 wt% concentration) was added in the casting solution as pore former. SPES was characterized by FT-IR and UV–visible spectra, ion exchange capacity and swelling ratio. The characterization of SPES polymer indicates that the sulfonic acid groups were produced on PES polymer. Also, the prepared PES/SPES blend membranes were characterized by contact angle, AFM, SEM and cross-flow filtration for milk concentration. The contact angle measurements indicate that the hydrophilicity of PES membrane is enhanced by increasing the SPES content in the casting solution. The SEM and AFM images show that the addition of SPES in the casting solution results in a membrane with larger surface pore size and higher sub-layer porosity. The mean pore size of the membrane increased from 98 nm for PES membrane to 240 and 910 nm for 50/50 and 0/100 PES/SPES blend membranes, respectively. The pure water flux and milk water permeation through the prepared membranes are increased by blending PES with SPES. Moreover, the protein rejection of PES/SPES blend membranes was lower than PES membrane.

Development of high performance nano-porous polyethersulfone ultrafiltration membranes with hydrophilic surface and superior antifouling properties

Hydrophilic nano-porous polyethersulfone ultrafiltration membranes were developed for milk concentration. The membranes were prepared from new dope solution containing polyethersulfone (PES)/polyvinylpirrolidone (PVP)/polyethyleneglycole (PEG)/cellulose acetate phthalate (CAP)/acrylic acid/Triton X-100 using phase inversion induced by immersion precipitation technique. This casting solution leads to formation of new hydrophilic membranes. The morphological studies were investigated by scanning electron microscopy (SEM) and atomic force microscopy (AFM). In addition, the hydrophilicity and performance of membranes were examined by contact angel measurements and cross-flow filtration (pure water flux, milk water permeation, protein rejection and antifouling measurements). The contact angle measurements indicate that a surface with superior hydrophilicity was obtained for PES membranes. Two concentrations of PES (16 and 14.4 wt.%) and two different non-solvents (pure water and mixtures of water and IPA) were used for preparation of membranes. The morphological studies showed that the higher concentration of PES and the presence of IPA in the gelation media results in formation of a membrane with a dense top and sub-layer with small pores on the surface. The pure water flux of membranes was decreased when higher polymer concentration and mixtures of water and IPA were employed for membrane formation. On the other hand, the milk water permeation and protein rejection were increased using mixtures of water and IPA as non-solvent. Furthermore, the fouling analysis of the membranes demonstrated that the membrane surface with fewer tendencies for fouling was obtained.

Preparation and characterization of modified nano-porous PVDF membrane with high antifouling property using UV photo-grafting

In this study, the poly(vinylidene fluoride) (PVDF) membrane was prepared via immersion precipitation technique and modified by UV photo-grafting of hydrophilic monomers on the top membrane surface. Acrylic acid (AA) and 2-hydroxyethylmethacrylate (HEMA) as acrylic monomers and 2,4-phenylenediamine (PDA) and ethylene diamine (EDA) as amino monomers were used at different concentrations to modify the membrane and improve the hydrophilicity with less fouling tendency. Moreover the presence of benzophenon as photo-initiator for grafting the hydrophilic monomers onto PVDF membrane surface was elucidated. The virgin and modified PVDF membranes were characterized by contact angle, ATR–FTIR, SEM and cross-flow filtration. The contact angle measurements demonstrated that the hydrophilicities of the membranes were significantly enhanced by UV photo-grafting of hydrophilic monomers onto the membrane surface. The ATR–FTIR confirmed the occurrence of modification on PVDF membrane by UV photo-grafting. The pure water flux of membranes was declined by UV photo-grafting but the milk water permeation and protein rejection were slightly improved. Moreover the antifouling properties and flux recovery of PVDF membrane were improved by UV photo-grafting of hydrophilic monomers.

Preparation and characterization of hydrophile nano-porous polyethersulfone membranes using synthesized poly(sulfoxide-amide) as additive in the casting solution

In this research, poly(sulfoxide-amide) (PSA) containing hydrophile groups was synthesized via phosphorylation polycondensation. The synthesized polymer was added to polyethersulfone (PES) casting solution at various concentrations for improving membrane properties. Polyvinylpyrrolidone (PVP, 2 wt%) was added in the casting solution as the pore former. The phase inversion induced by immersion precipitation was employed for preparation of asymmetric membranes. The prepared membranes were characterized by contact angle measurement, scanning electron microscopy (SEM), atomic force microscopy (AFM), mechanical strength evaluation and cross-flow filtration. The contact angle measurements demonstrate that the hydrophilicities of PES membrane are strongly enhanced by increasing the PSA concentration in the casting solution. The surface SEM and AFM images show that addition of synthesized PSA in the casting solution results in nano-structure membranes with small surface pore size. The pure water fluxes through the prepared membranes were increased by adding 5, 10 and 15 wt% of PSA in the casting solution. Moreover, milk water permeation and protein rejection were improved. Furthermore it was found that the addition of PSA in the PES casting solution results in membranes with higher mechanical strength.

Coupling TiO 2 nanoparticles with UV irradiation for modification of polyethersulfone ultrafiltration membranes

Polyethersulfone ultrafiltration membranes prepared via immersion precipitation were modified by TiO 2 nanoparticles and UV irradiation. Three sets of membranes, i.e. TiO 2-entrapped membranes, UV-irradiated TiO 2-entrapped membranes and UV-irradiated TiO 2-deposited membranes were prepared. The membranes were characterized by contact angle, SEM, FTIR, cross-flow filtration (pure water flux and milk water permeation) and antifouling measurements. The initial flux of TiO 2-entrapped membrane was lower than the initial flux of neat PES membrane. However, the former membrane showed lower flux decline compared to the neat PES membrane. UV-irradiated TiO 2-entrapped membranes represented higher flux and higher antifouling properties compared to TiO 2-entrapped membranes. Contact angle measurement, FTIR and surface SEM image indicate that the TiO 2 nanoparticles uniformly settled on the membrane surface by dipping the membrane into the TiO 2 colloidal suspension. Flux behavior of 0.03 wt.% UV-irradiated TiO 2-deposited membrane indicated higher performance and antifouling properties. TiO 2 colloidal suspension with 0.03 wt.%, 15 min immersion and 15 min UV irradiation with 160 W lamp were determined as the optimum conditions for modification of PES membrane. Finally, a comparison between UV-irradiated TiO 2-entrapped and deposited membranes proved that coating TiO 2 on membrane surface is a superior technique for the modification of PES membranes to minimize membrane fouling.

Synthesis of a novel poly(amide-imide) (PAI) and preparation and characterization of PAI blended polyethersulfone (PES) membranes

In this study, firstly poly(amide-imide) (PAI) containing flexible groups was synthesized through polycondensation reactions of diimide-diacid with p-phenylene diamine (PPDA) via direct Yamazaki method. PES/PAI blend membranes were prepared with phase inversion induced by immersion precipitation technique. Polyvinylpirrolidone (PVP, 2 wt% concentration) was added in the casting solution as pore former. The PES/PAI blend membranes were characterized by contact angle, AFM, SEM, TGA, mechanical measurements and cross-flow filtration for milk concentration. The contact angle measurements indicate that the hydrophilicities of PES membrane are enhanced by increasing the PAI in the casting solution. The AFM and SEM images show that addition of synthesized PAI in the casting solution or blending with PES results in a membrane with high surface and sublayer porosity. The pure water flux and milk water permeation through the prepared membranes are increased by blending PES with PAI. Moreover, the protein rejection and anti-fouling properties of PES/PAI blend membranes are improved. TGA reveals that thermal stability of PES/PAI blend membranes is slightly decreased compared with PES membrane. Furthermore it was found that blending PES and PAI polymers results in membranes with higher mechanical strength.

Polyethersulfone (PES)/cellulose acetate phthalate (CAP) blend ultrafiltration membranes: Preparation, morphology, performance and antifouling properties

Polyethersulfone (PES)/cellulose acetate phthalate (CAP) blend ultrafiltration (UF) membranes were prepared with phase inversion induced by immersion precipitation method. CAP was employed to improve the hydrophilicity of PES membranes. Polyvinylpyrrolidone (PVP) was selected as pore former. Dimethylacetamide (DMAc) and water + isopropyl alcohol (IPA) (80/20 vol%) were used as solvent and coagulant respectively. The contact angle measurements indicate that the hydrophilicities of PES/CAP membranes are enhanced by increasing the CAP concentration in the casting solution. However this increment does not improve the membrane performance in all cases. The AFM and SEM images reveal that addition of low concentration of CAP in the casting solution results in a membrane with high surface and sub-layer porosity and thin top layer. The pure water flux and milk water permeation for the prepared membranes are increased by introducing 20% CAP in the casting solution. However further addition of CAP sharply decreases the membrane performance. The protein rejection is slightly increased to 99% for 80/20 blend of PES/CAP. This falls to 50% at 60/40 of PES/CAP composition. Furthermore, it was found that the low concentration (2 wt.%) of PVP in 80/20 percent of PES/CAP in the casting solution results in a membrane with higher mechanical strength and better performance. CAP may play a role as an as antifouling agent.

The effect of anionic, non-ionic and cationic surfactants on morphology and performance of polyethersulfone ultrafiltration membranes for milk concentration

In this study, the effects of three surfactants, sodium dodecyl sulphate (SDS) as anionic surfactant, cetyle three methyl ammonium bromide (CTAB) as cationic surfactant and Triton X-100 as non-ionic surfactant on structure and performance of polyethersulfone membranes prepared from PES/PVP/DMAC system via immersion precipitation have been investigated. The mixture of water and isopropyl alcohol (IPA) (30/70 vol.%) was used as gelation media. The morphology and performance of the prepared membranes were studied by scanning electron microscopy (SEM), atomic force microscopy (AFM) and separation experiments using pure water and milk as feed. The obtained results indicate that the small addition of surfactants in the casting solution increases the porosity of the membrane support layer, enhances pure water flux and milk water permeation.