Surface Modifying Macromolecules Research Articles

Pharmaceutical and personal care products removal from drinking water by modified cellulose acetate membrane: Field testing

To maximize the removal of charged pharmaceutical and personal care products (PPCPs), modified cellulose acetate (CA) nanofiltration (NF) membranes were developed by incorporating charged surface modifying macromolecules (CSMM) to increase their surface charge. The objective of this study was to evaluate their removal of trace levels of PPCPs at two water treatment plants. This new membrane and a commercial thin-film composite (TFC) NF membrane (Filmtec NF-270) were tested simultaneously in the field using two SEPA cells. The testing was conducted at the Britannia Water Treatment Plant (Ottawa, ON) and the Walkerton Clean Water Centre (Walkerton, ON). The challenge waters were filter effluents spiked with ppt and ppb levels of carbamazepine (CBZP), ibuprofen (IBUP) and sulfamethazine (SFMZ). The new experimental modified CA membrane achieved very good IBUP removals, good SFMZ removals and poor CBZP removals. The commercial TFC NF membrane (NF-270) had better removals and significantly higher fluxes than the modified CA membrane. The larger removals are not surprising given that the commercial membrane is the result of extensive development and optimization, while the modified CA membrane has undergone very limited optimization. The larger flux of the NF-270 membrane is also expected given that this is a TFC membrane, while the experimental modified membrane was prepared via a single casting step via the phase inversion technique which produces a thicker skin layer.

Treatment of radioactive wastewater solutions by direct contact membrane distillation using surface modified membranes

Direct contact membrane distillation (DCMD) is proposed for processing low and intermediate level radioactive liquid wastes by means of surface modified flat sheet membranes to produce distilled water and to reduce the volume of the radioactive wastes for further safe storage and disposal. Different membranes were prepared by the phase inversion method using different fluorinated surface modifying macromolecules (SMMs). The host polymers are polysulfone and polyethersulfone. The structural characteristics of the membranes were studied. During membrane formation, SMMs migrate to the top membrane surface changing its characteristics. The DCMD experiments were performed with non-active and radioactive model solutions containing the most common radioisotopes present in liquid radioactive wastes, cobalt-60, 60Co, caesium-137, 137Cs and strontium-85, 85Sr. The surface modified membranes removed completely radioactive species in one stage. The obtained permeate has activity on the level of natural background. The performance of the surface modified membranes was compared to that of the commercial membrane TF200 (Gelman). Higher values of the liquid entry pressure of water, lower permeate fluxes, higher rejection factors and lower radioactive adsorption to the membrane surface were observed for the surface modified membranes. The obtained results indicate that fluorinated surface modifying macromolecules have potential for application in nuclear technology.

Effect of operating temperature on the behavior of promising SPEEK/cSMM electrolyte membrane for DMFCs

The behavior of sulfonated poly (ether ether ketone) (SPEEK) with different degrees of sulfonation (DS) (60–76%) blended with charged surface modifying macromolecule (cSMM) at different operating temperatures as an electrolyte membrane for direct methanol fuel cell (DMFC) application has been studied. A good DMFC electrolyte membrane should possess high proton conductivity and low methanol permeability. In this work, the fabricated SPEEK/cSMM membranes were compared with pure SPEEK and commercial Nafion 112 membranes in terms of water uptake, proton conductivity, and methanol permeability at temperature range of room to 80°C. The water uptake of SPEEK/cSMM membranes increased with the temperature and it was higher than that of SPEEK and Nafion 112 membranes; however newly fabricated membranes with 68% and 76% DS were dissolved at high temperatures although showed the same trend at lower temperatures. In agreement with the result of water uptake, proton conductivity of SPEEK/cSMM membranes also increased with temperature and was higher as compared to the corresponding SPEEK membranes; however it was still lower than that of Nafion 112. The methanol permeability values of the SPEEK/cSMM membranes were lower at different temperatures as compared to corresponding SPEEK and Nafion 112 at the same condition. Owing to considerable proton conductivity and lower methanol permeability values, SPEEK60/cSMM exhibited the highest overall performance than other tested membranes at 60°C. These results indicated that SPEEK60/cSMM membrane is promising to be used as a polymer electrolyte membrane in direct methanol fuel cell.

Performance of surface‐modified poly(etherimide) hollow‐fiber membranes in a membrane gasLiquid contacting process with response surface methodology

AbstractA surface‐modifying macromolecule (SMM) was used to enhance the surface hydrophobicity of poly(ether imide) (PEI) hollow‐fiber membranes. The membranes were used for a membrane contactor to absorb CO2 with water. The effects of three hollow‐fiber fabrication parameters, that is, the PEI concentration in the casting dope, the SMM concentration in the casting dope, and the air gap, on the liquid entry pressure of water (LEPw) and the absorption rate (AR) of CO2 were investigated with response surface methodology. The model developed for LEPw satisfied the criterion for regression but had a low goodness of fit. The model predicted that LEPw would increase with PEI (weight percentage) but decrease with air gap. Furthermore, it showed a minimum value with a change in SMM (weight percentage). The model developed for the AR of CO2 had meaningful statistical parameters and was accurate; this indicated that interactions existed between the fabrication parameters on the AR of CO2. The performance of one of the fabricated membranes was compared with in‐house and commercially made hydrophobic membranes in terms of the AR of CO2 with distilled water as an absorbent on the lumen side and pure CO2 on the shell side. The comparison showed a superior CO2 flux in the surface‐modified membrane; for example, at a liquid velocity of 0.4 m/s, the surface‐modified membrane exhibited a 416% higher AR than the commercial membrane contactor (Celgard MiniModule 0.75X5) made of polypropylene. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Carbon dioxide stripping from diethanolamine solution through porous surface modified PVDF hollow fiber membrane contactor

Porous asymmetric polyvinylidene fluoride (PVDF) hollow fiber membrane were fabricated via a phase-inversion method using surface modifying macromolecules (SMM) (1wt%) as the additive in the spinning dope. Distilled water and tap water were used as internal and external coagulation bath, respectively. The membranes were characterized in terms of gas permeation, wetting resistance, overall porosity, contact angle and collapsing pressure. CO2 stripping from diethanolamine (DEA) solutions was conducted through the gas–liquid membrane contactor. The effect of some operating conditions such as gas and liquid velocities, DEA concentration and rich solution temperature on the CO2 stripping flux and efficiency were investigated. By increasing liquid flow rate to 200ml.min−1, the maximum CO2 stripping efficiency of almost 82% was achieved. In addition, an increase in the liquid flow rate resulted in a significant increase of CO2 stripping flux. By increasing the liquid flow rate from 50 to 200mlmin−1, the CO2 flux increased by 900%. By increasing the gas velocity the CO2 desorption flux increased but this changing was negligible. The effect of rich solution temperature was investigated and the results showed that the CO2 desorption flux increased with increasing the solution temperature from 80 to 90°C. The results of DEA concentration enhancement on the CO2 desorption flux showed that the CO2 stripping flux increased drastically with enrichment of the DEA concentration from 1.0 to 3.0 (moll−1). Therefore, the higher stripping efficiency can be achieved by applying the higher liquid flow rate, temperature and DEA concentration in the absorbent liquid in the membrane contactor module.

Effect of novel surface modifying macromolecules on morphology and performance of Polysulfone hollow fiber membrane contactor for CO2 absorption

A novel surface modified Polysulfone (PSf) hollow fiber membrane was fabricated via dry–wet phased inversion process. surface modifying macromolecule (SMM) was used as additive in the spinning dope. The surface modified membrane showed large pore size, higher effective surface porosity, contact angle and porosity but lower critical water entry pressure (CEPw) compared to Polysulfone hollow fiber membrane without SMM. The performance of surface modified membrane in contactor application for CO2 absorption via distilled water as absorbent was studied. The results show that surface modified membrane has higher performance compared to plain Polysulfone membranes. With the membrane prepared from SMM in the spinning dope a maximum CO2 flux of 5.8×10−4mol/m2s was achieved at 300ml/min of absorbent flow rate, which was almost 76% more than the other membrane. In a long-term stability study, the initial flux reduction was found to be about 18% within the 50h of operation for surface modified membrane.

Surface segregation of fluorinated modifying macromolecule for hydrophobic/hydrophilic membrane preparation and application in air gap and direct contact membrane distillation

A fluorinated surface modifying macromolecule (SMM) was synthesized and blended into the casting solution of polyetherimide used as host polymer. A composite porous hydrophobic/hydrophilic membrane was prepared by the phase inversion technique in a single casting step. The membrane was characterized by different techniques. During membrane formation, SMM migrates to the top membrane surface increasing its hydrophobicity and decreasing its pore size, nodule size and roughness parameters. The thickness of the porous hydrophobic top layer was found to be around 4 mu m. The membrane was used for desalination by air gap membrane distillation and direct contact membrane distillation. The experiments were performed for different sodium chloride aqueous solutions and various operating conditions. The water production rate was found to be high for direct contact membrane distillation because of the low resistance to mass transport achieved by the diminution of the water vapour transport path length through the hydrophobic thin top-layer of the membrane.

Development of high performance surface modified polyetherimide hollow fiber membrane for gas–liquid contacting processes

Low wettability is a vital characteristic for the membrane used in membrane contactor. Blending surface modifying macromolecule (SMM) in spinning dope is an interesting method to enhance the hydrophobicity of membrane and in this research, the effect of SMM on the properties and structure of polyetherimide (PEI) hollow fiber membrane in terms of mean pore size, liquid entry pressure of water (LEPw), membrane porosity and contact angle was investigated and compared with the properties of the PEI membrane without SMM.Furthermore the performance of PEI surface modified membrane in contactor applications in terms of CO2 absorption with distilled water was evaluated and compared with the absorption flux of PEI membrane without SMM and also, with the absorption flux of commercial and in-house made hydrophobic membranes which shows superior performance of surface modified PEI membrane e.g. in case of water in lumen side and pure CO2 in shell side of contactor and at Vliquid=0.5ms−1, the absorption flux of PEI surface modified membrane is 2.94×10−3molm−2s−1 which is 114% higher than PEI without SMM and 73% higher than commercial membrane contactor, Celgard MiniModule® 0.75X5.

Study on synthesis and physical properties of charged surface modifying macromolecules with different end-capping materials for membrane applications

Polyol and end-capping agent were changed systematically when charged surface modifying macromolecules (cSMMs) were synthesized and characterized. Fourier transform infrared spectroscopy detected different degrees of hydrogen bonding interactions for different polyols and end-capping agents via shifting of absorption bands characteristic to the urethane group. Polyol of the lower molecular weight showed the stronger interaction and thus increased the cSMM's structural rigidity. The cSMM's rigidity increased from hydroxyl benzene sulfonate to hydroxyl propane sulfonate when poly(propylene glycol) was used as polyol. The effects of polyol and end-capping agent on the contact angle and water uptake were studied.

A novel surface modified polyvinylidene fluoride hollow fiber membrane contactor for CO2 absorption

A novel surface modified polyvinylidene fluoride (PVDF) hollow fiber membrane was fabricated via a dry–wet phased inversion process. A surface modifying macromolecule (SMM) was used as an additive in the spinning dope. During phase inversion SMM migrates to the membrane surface and functions as both a pore former and surface modifier. The surface modified PVDF membrane showed large pore size, higher effective surface porosity, contact angle and porosity but lower critical water entry pressure compared to the PVDF hollow fiber membrane without SMM. The performance of the surface modified membrane in contactor application for CO2 absorption via distilled water as absorbent was studied. The results show that the surface modified PVDF membrane has higher performance compared to control PVDF membranes. With the membrane prepared from SMM in the spinning dope a maximum CO2 flux of 7.7×10−4 mol/m2 s was achieved at 300 ml/min of absorbent flow rate, which was almost 93% more than the other membrane. In a long-term stability study, CO2 flux was decreased only about 7.7% by using surface modified PVDF membrane during 150 h operation.

Comparison of cellulose acetate (CA) membrane and novel CA membranes containing surface modifying macromolecules to remove pharmaceutical and personal care product micropollutants from drinking water

Abstract Pharmaceutical and personal care products (PPCPs) enter the environment mainly through municipal wastewater effluents, agricultural run-off, pharmaceutical and related chemical industry discharges. The present study was conducted to remove PPCPs through nano-filtration (NF) membranes prepared with two different tailor-made polymeric additives. The first is a novel charged surface modifying macromolecule (CSMM) additive synthesized by reactive diisocyanate and dihydroxy naphthalene disulfonate. The second additive was a tailor made hydrophi l ic SMM (LSMM), which was manufactured incorporating poly(ethylene glycol) as end groups. Cellulose acetate (CA) membranes with and without 3 wt% CSMM or LSMM were prepared by the phase inversion technique. The membranes were characterized by static contact angle, X-ray photoelectron spectroscopy, scanning electron microscopy with energy dispersive spectrometer, and atomic force microscopy. The NF filtration studies were conducted at two different operating pressures (150 and 400 psig). They consisted of pure water flux tests, sodium chloride separation tests, and individual PPCP (ppm level carbamazepine, ibuprofen, and sulfamethazine) separation tests. The long term NF performance for the removal of ibuprofen was also conducted. Significant effect of CSMM blending on the separation performance of ibuprofen for long hours operation was observed.

A novel surface modified polyetherimide hollow fiber membrane for gas–liquid contacting processes

A novel surface modified polyetherimide (PEI) hollow fiber membrane was fabricated via dry–wet phased inversion process where the spinning dope contains Surface Modifying Macromolecule (SMM). The surface modified membrane exhibited large pore size, higher effective surface porosity, contact angle and porosity but lower Liquid Entry Pressure of water compared to polyetherimide hollow fiber membrane without SMM.The performance of surface modified membrane in contactor application for gas separation process was evaluated based on CO2 absorption process using water as absorbent and pure CO2 and 20:80 CO2/CH4 gas mixture. The results show that surface modified membranes have superior performance compared to commercial and in-house made hydrophobic membranes such as polypropylene and polytetrafluoroethylene, e.g., in the case of pure CO2 in the shell side and distilled water in the lumen side, the surface modified PEI membrane shows 72% higher absorption flux than commercial membrane contactor, Celgard MiniModule® 0.75X5 which is made of polypropylene membranes, when the liquid velocity is 0.4ms−1.

Towards antibiofouling ultrafiltration membranes by blending silver containing surface modifying macromolecules

The innovative design and synthesis of membranes with silver incorporated surfaces open up new avenues for applied basic functions.

Preparation and characterization of surface modified electrospun membranes for higher filtration flux

Popular polymers such as polysulfone and poly(vinylidene fluoride) (PVDF) when electrospun into a membrane, have a much higher contact angle and hence are more hydrophobic when compared to the virgin polymeric material. In direct liquid penetration it is more beneficial if the membrane is hydrophilic so that the flux is not compromised and has less tendency to foul. Hence, this research is focused on generating a highly hydrophilic electrospun membrane (EM) based on PVDF material by blending this polymer with several different types of surface modifying macromolecules (SMMs) prepared from urethane pre-polymer with poly(ethylene glycol)s (PEGs) of various average molecular weights (400, 600, and 1000 Da) and poly(propylene glycol) of average molecular weights 3500 and 425 Da. One of the SMMs, with PEG 1000 Da, had a significant impact on the hydrophilic nature (0° SCA with water) of the EM as compared to the blend casted membrane. This could possibly be due to the orientation of the SMMs hydrophilic groups adopted during electrospinning on the surface, whereas they are either encapsulated or submerged in other SMMs. The water flux at a given pressure of blended EM was higher than the non-blended electrospun PVDF membrane. This study highlights the potential benefits of this new hydrophilic polymeric material in the membrane field, which can achieve high-flux rates at low pressure.

Influence of novel surface modifying macromolecules and coagulation media on the gas permeation properties of different polymeric gas separation membranes

AbstractIntegrally skinned asymmetric membranes for the separation of O2 and N2 were fabricated by the phase inversion technique from polysulfone, polyetherimide, and polyimide. Two types of surface modifying macromolecules (SMMs) including hydrophilic SMM (LSMM) and charged SMM (cSMM) were synthesized and blended with the casting solution to modify the membrane surface. The cast film was then immersed in the first coagulant alcohol (methanol, ethanol, or isopropanol) for a predetermined period, before being immersed in the second coagulant (water). The SMMs used in these experiments were laboratory synthesized by the two‐step process of polyurethane prepolymer synthesis and end capping, before being characterized by differential scanning calorimetry. Their molecular structure was determined from the molecular weight obtained by gel permeation chromatography. The membranes were characterized by contact angle measurement and O2 and N2 gas permeation performance. Attempts were made to interpret the gas permeation data by delayed demixing affected by solubility parameters of polymer, solvent, and nonsolvent. Furthermore, the permeation performance of cSMM membranes was interpreted by the solvation of the charged sulfonate groups present in cSMM. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Novel surface modifying macromolecules (SMMs) blended polysulfone gas separation membranes by phase inversion technique

AbstractIn this article an attempt was made to fabricate defect‐free asymmetric polysulfone (PSf) membranes for the separation of oxygen and nitrogen. The approach is based on the enhanced delayed demixing by blending surface modifying macromolecules (SMMs) in the casting solution and by immersing the cast film in isopropanol for a certain period before it is immersed in water. Different SMMs, including hydrophobic and charged SMMs, were synthesized, characterized, and blended to the host PSf. It was found that the charged SMM could indeed contribute to the removal of defective pores from the skin layer and enhancement of oxygen/nitrogen selectivity. The experimental results were further interpreted based on the shift of the phase boundary line on the polymer/solvent/nonsolvent triangular diagram, which occurred when SMMs were blended to PSf, due to the change in the polymer/nonsolvent interaction. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Development of antifouling thin-film-composite membranes for seawater desalination

The present contribution provides detailed information about the development of antifouling novel thin-film-composite (TFC) membranes for mostly water purification with special emphasis on seawater desalination in particular. The novel membranes were prepared by incorporating in-situ hydrophi lic surface modifying macromolecules (iLSMM) into the TFC membranes, rendering the surface of the TFC membranes significantly more hydrophilic. The prepared membranes were then subjected to long term fouling studies using model foulants, including sodium humate (SH), silica particles (SPs), and chloroform (CF) spiked in the feed NaCl solution. The biofouling effect of silver salts was also studied by incorporating some silver salts (silver citrate hydrate, SCH; silver lactate, SL; and silver nitrate, SN) simultaneously with iLSMM into the TFC membranes. Halo test was conducted with Escherichia coli to examine the antibiofouling performance of the silver incorporated TFC membranes. It can be concluded by this work that iLSMM incorporated TFC membranes have performed excellently for the desalination of salty water (3.5 wt% NaCl), especially when the solution was spiked with typical foulants such as SH, SPs, and CF. The flux reduction was reduced significantly when iLSMM was incorporated in the TFC membranes by a newly developed technique. The antimicrobial fouling intensity of the studied membrane was in the order of: SN (ring width 0.55 mm) > SL (0.27 mm) > SCH (0.19 mm).

Development of novel surface modified phase inversion membranes having hydrophobic surface-modifying macromolecule (nSMM) for vacuum membrane distillation

Eleven PES membranes, into which newly synthesized surface-modifying macromolecule (nSMM) was incorporated, were prepared by using the ‘phase inversion technique’ with different preparation conditions to find the effects of membrane casting parameters on the characteristics and performances of the surface modified PES membranes. The membranes so prepared were characterized by solute separation data from ultrafiltration experiments. The results showed that the mean pore size as well as the surface hydrophobicity increased with an increase in evaporation time for the casting solution blended with nSMM (without PVP). When PVP was added into the casting solution, the mean pore size as well as the contact angle decreased while the pure water permeation flux increased. The surface hydrophobicity decreased with an increase in gelation bath temperature. Four membranes were further prepared and subjected to vacuum membrane distillation (VMD). They were characterized by different analytical instruments and pure water permeation test before being used to VMD. The results showed that a distinctive surface layer was formed in nSMM blended PES membranes. It was also found that nSMM blended PES membranes were sufficiently hydrophobic and porous to be used for the separation of an ethanol/water mixture.

Key factors affecting the manufacture of hydrophobic ultrafiltration membranes for surface water treatment

AbstractAs part of the development of poly(ether sulfone) (PES) membranes whose surface is modified by the incorporation of a newly synthesized hydrophobic surface modifying macromolecule (nSMM) additive, this study investigates the impact of four key membrane preparation factors. They are concentration of PES, concentration of nSMM, casting thickness, and casting speed. The synthesis and characterizations of nSMM by nuclear magnetic resonance, gel permeation chromatography, differential scanning calorimeter, and elemental analysis have been presented. The changes in characteristics and performance of the membranes have been evaluated via Fourier transform infrared spectroscopy, contact angle analysis, scanning electron microscopy, and solute transport tests. The addition of 0.5 wt % of nSMM increased the contact angle of PES membranes by 20°; however, higher nSMM concentrations did not increase the hydrophobicity any further. Only the additive concentration had a statistically significant impact on flux reduction and dissolved organic carbon rejection. Even though other factors such as membrane thickness may alter the pore characteristics, their effect on membrane performance was marginal. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Relationship between surface structure and separation performance of poly(ether sulfone) ultra-filtration membranes blended with surface modifying macromolecules

The poly(ether sulfone) (PES) membranes were prepared by blending of two types of surface modifying macromolecules (SMMs)-charged (cSMM) and fluorinated (fSMM). Also, membranes were fabricated in three different conditions: (1) at room temperature (RT) without air-exposure period (the period between film casting and immersion into coagulation bath), (2) at RT with 3 min air-exposure period and (3) at 90 °C with 3 min air-exposure period. The performances and physico-chemical characteristics of the membranes were evaluated. Membrane surface became more hydrophilic when cSMM was blended while more hydrophobic when fSMM was blended. Detailed analysis of the surface free energy demonstrated that the hydrophilic surface was resulted form strong Lewis base (solid)–acid (liquid) interaction while hydrophobic surface was resulted from the weak Lifshitz–van der Waals interaction. Atomic force microscopy (AFM) results could be interpreted by considering the orientation of nodule aggregates at the membrane surface under the casting bar and its relaxation during the air-exposure period between the film casting and immersion to the gelation bath. The pore size of the membranes measured by AFM was much larger than the pore size obtained by filtration experiment.