FESEM images confirm that the pore size of the membranes decreases with the addition of D-TA in the membrane. FESEM images confirm that the pore size of the membranes decreased with the addition of AAP.
Membrane preparation and characterization 31−46
67 CHAPTER 4 Preparation and characterization of a hydrophilic polysulfone ultrafiltration membrane with added pH copolymer poly(vinyl. pyrrolidone-co-isoatoic anhydride).
Racemic and enantiomeric effect of tartaric acid on the hydrophilicity of polysulfone membrane
Notations
Background
- Classification of membrane
Membranes can be further classified according to (i) nature, (ii) structure and (iii) mechanism of action [1 - 3]. The symmetric membranes can be further subdivided into porous, non-porous or dense and electrically charged membranes.
Membranes
Asymmetric membranes consist of a very dense top layer or skin with a thickness of 0.1 – 0.5 µm supported by a porous substrate with a thickness of around 50 -150 µm.
Solid membranes
Liquid membranes
Classification of membrane separation processes
The portion of the feed solution that passes through the membrane is called permeate, or filtrate. The portion of the feed solution that does not pass through the membrane is called
Retentate
- Materials for ultrafiltration membranes
- Membrane fouling
- Antifouling mechanism by improved hydrophilicity of polymeric membrane surface
- Surface modification methods for polymeric membranes 1. Improvement of membrane preparation process
- Introduction of organic materials
- Introduction of inorganic nanoparticles
- Surface alteration of existing polymeric membranes
- State of the art
- Modification of polymeric membrane by blending hydrophilic polymer
Surface modification of polymeric membranes can be achieved during the preparation process, for example by introducing hydrophilic or antifouling modifiers by mixing. Physical modification of PVDF membranes can be achieved in two ways: (1) Hydrophilic polymers are directly coated or applied to the surface of the membrane (sometimes post-treatment is performed). 2) The polymer membrane is first immersed or coated with a solution of chemically active monomers.
- Racemic and enantiomeric effect of tartaric acid on the hydrophilicity of polysulfone membrane
- Impact of synthesized amino alcohol plasticizer on the morphology and hydrophilicity of polysulfone ultrafiltration membrane
- Objectives of thesis work
- Organization of the thesis
However, investigation of enantiomeric and racemic effect of tartaric acid (TA) on the hydrophilicity of PSF membrane has not yet been reported. This chapter gives a broad knowledge about the enantiomeric and racemic effect of TA on the morphology and hydrophilicity of PSF membrane.
Membrane preparation and characterization
- Materials
- Preparation of membrane
- Membrane characterization
- Liquid-liquid displacement (LLDP) porosimetry method
- Microscopic observation
- Permeation experiments
- Equilibrium water content (EWC) and porosity
- Hydrophilicity
- Ion exchange capacity (IEC) of membranes
- ATR-FTIR of modified membranes
- Ultrafiltration experiment and fouling studies
- Characterization of synthesized additive
- Proton nuclear magnetic resonance ( 1 H NMR) spectroscopy
- Fourier transform infrared (FTIR) spectroscopy
- Photon correlation spectroscopy (PCS)
- Determination of molecular weight cut off (MWCO)
The morphology of the prepared membranes was investigated by liquid-liquid displacement porosimetry (LLDP) method and microscopic observations. The average pore size, number of pores and pore area distribution of the prepared membranes were determined by LLDP [1]. An average value of the thickness of the skin layer corresponding to 0.1 µm was considered in the present work, although it would probably vary along the surface of the membrane.
A number of FESEM images were taken at different magnifications for both the top surface and cross sections of the prepared membranes. The hydrophilic property of the membrane was evaluated by measuring the static contact angle between the deionized water and membrane film at ambient conditions at room temperature using a digital camera (cannon power shot), and a goniometer was used to determine the contact angle. Membrane pieces with an area of approx. 1 cm x 1 cm were prepared and then these samples were held at the sample holder of the instrument using the tape.
Experimental 1. Materials
- Membrane preparation
Effects of PVP-PAA mixture on the morphology, permeation property and on the hydrophilicity of PSF membrane were investigated. Membrane casting solution contains PSF as base polymer, N-Methyl-2-pyrrolidone (NMP) as solvent and PVP-PAA as non-solvent additives.
Membrane characterization 1. Morphological studies
- Characterization by permeation studies
- Pure water flux (PWF) and hydraulic permeability (P m )
- Equilibrium water content (EWC), porosity and hydrophilicity
Results and discussion
- Preparation of PAA-PVP blend
- FTIR spectroscopy analysis of PAA-PVP blend
- Morphological studies
- SEM analysis
- FESEM analysis
- AFM analysis
- Analysis of liquid–liquid displacement porosimetry results
- Permeation studies
- Effect of molecular weight of PVP with PAA on CF
- Effect of molecular weight of PVP on PWF and hydraulic permeability
- Variation in EWC, porosity and hydrophilicity
- Ultrafiltration of BSA
- Effect of molecular weight of PVP on the BSA flux and rejection
This may be due to the fact that the number of pores on the surface increased (i.e., porosity increased) with an increase in the molecular weight of PVP. It was observed that with the increase in molecular weight of PVP, the number of pores increased for all membranes, consequently obtaining more porous membranes. The figure showed that the steady-state PWF decreases with an increase in the molecular weight of PVP.
This increasing trend confirms the presence of an increasing number of pores in the membrane with an increase in the molecular weight of PVP (Table 3.3). The increase in membrane porosity with higher molecular weight of PVP was possibly due to a decrease in the miscibility of the casting solution with water. It can be seen from Table 3.3 that the contact angle decreases and porosity increases with the increase in molecular weight of PVP.
Summary
Experimental 1. Materials
- Membrane preparation
Details of all materials used in this chapter are given in Table 2.1 of Chapter 2. Flat sheet PSF membranes were prepared by the phase inversion method as described in Section 2.2 of Chapter 2 with a thickness of 100 µm.
Membrane characterization 1. Microscopic study
- Permeation experiments
- Pure water flux (PWF) and hydraulic permeability (P m )
- Equilibrium water content (EWC), porosity and hydrophilicity
- Ultrafiltration experiment
Initially all membranes were compressed for 3 hours at 275.8 kPa which was higher than the maximum operating pressure (150 kPa) in this chapter. Pure water flux (PWF) was measured by allowing deionized water to pass through the compressed membrane. Pure water flux values at various transmembrane pressures (from 0-275.8 kPa) were measured at steady state using equation 2.10.
Ultrafiltration experiments were carried out in the stainless steel cell discussed in the previous chapter to study the impact of different concentrations of copolymer on the permeate flux and solute separation behavior of the fabricated membrane. It was dissolved in deionized water at room temperature and the concentration was kept constant at 1000 mg/L for all filtration experiments. Therefore, the pH of the BSA solution was kept at four values: 7 (neutral state), 3 (acidic state), 4.8 (i.e. in isoelectric) and 10 (i.e. basic state) for finding of the pH dependence of flux and repulsion for all membranes.
Result and discussion
- Preparation and characterization of copolymer poly(VP-co-IAH)
- Synthesis of poly (VP-co-IAH) copolymer
- Investigation of FTIR-ATR spectra of copolymer poly(VP-co-IAH)
- FTIR-ATR spectroscopy analysis of plain and copolymer poly(VP-co-IAH) containing membranes
- Morphological study
- FESEM study of cross section
- FESEM study of top surface
- AFM studies
- Effect of weight % of copolymer on hydrophilicity
- Liquid–liquid displacement porosimetry studies
- Permeation studies
- Effect of addition of copolymer poly(VP-co-IAH) on compaction factor
- Effect of copolymer on PWF and Hydraulic Permeability
- Membrane characterization by EWC, porosity and hydrophilicity
- Effect of addition of copolymer on BSA flux at normal pH
- Effect of addition of copolymer on BSA rejection at normal pH
- Effect of pH on the flux and rejection behaviour of BSA solution
It was found that the contact angle decreases with the addition of copolymer for all the membranes. Steady state PWF was found to be increased by addition of copolymer as shown in Figure 4.11. This increasing trend approves the occurrence of increased number of pores in the membrane by the addition of copolymer.
From table 4.4 it is confirmed that the contact angle decreased and the hydrophilicity increased with the addition of copolymer to the membrane. M_4 showed maximum hydrophilicity with the addition of copolymer, this may be due to the fact that 4 wt % of copolymer possesses optimal viscosity for demixing [42, 74]. It can be attributed to the fact that with the addition of the copolymer to the PSF casting solution, the hydrophilic functional groups increased.
Experimental 1. Materials
- Preparation of Flat Sheet Membranes
PVP was used as a pore former and D-TA and DL-TA were used as additives in the membranes. Flat sheet membranes were prepared using different compositions of PSF, D-TA, DL-TA, PVP and DMAc (as shown in Table 5.1). The casting solution was stirred at 350 rpm with the help of a magnetic stirrer for 8 h and further degassed for 12 h at room temperature.
The solution was then cast onto a clean glass plate using a casting knife, maintaining a uniform thickness of 100 µm in room atmosphere.
Membrane characterization
- Surface Characterization of D-TA and DL-TA Blended Membranes
- Water permeation experiment
- Membrane compaction and hydraulic permeability
- Membrane performance characterization by BSA ultrafiltration experiment
- Membrane performance characterization by CVD ultrafiltration experiment
The solute separation and permeate flux behavior of the prepared membranes were studied by BSA ultrafiltration experiments. Each membrane was initially compacted for 1 hour at 414 kPa, then the pressure was reduced to the working pressure of 208 kPa and membrane cell was filled with BSA solution; the flood was recorded. UV-VIS spectrophotometer (Perkin-Elmer Precisel, Lamda-35) was used to find out the BSA concentration, at wavelength of 280 nm.
Solute separation and permeate flow behavior of the prepared membranes were also studied by CVD ultrafiltration experiments (molecular weight 407.9 Da). Apart from that, the description of the flux and rejection of solute through the membranes is mostly evaluated by the morphology of the membrane and the properties of the feed solution, especially its pH. A UV-VIS spectrophotometer (Perkin-Elmer Precisel, Lamda-35) at a wavelength of 582 nm was used to determine the CVD concentration.
Effect of NaCl on SDS and CVD solution
Results and discussion
- FTIR-ATR analysis of different membranes
- Structure of membrane
- SEM image analysis
- FESEM analysis
- AFM analysis
- Determination of molecular weight cut off (MWCO)
- Analysis of liquid–liquid displacement porosimetry results
- Permeation studies
- Compaction behaviour of membranes
- Effect of the addition of D-TA and DL-TA on PWF and hydraulic permeability Figure 5.13 depicts the effect of addition of D-TA and DL-TA or enantiomeric and racemic
- Effect of addition of D-TA and DL-TA on EWC, hydrophilicity and porosity EWC, hydrophilicity and porosity of the membrane are important parameters in membrane
- Effect of concentration of D-TA and DL-TA on BSA rejection
- Effect of pH of BSA solution on the flux and rejection
- Ultrafiltration of CVD
- Effect of addition of D-TA and DL-TA on the performance of PSF membrane for CVD separation
- Effect of the addition of anionic surfactant sodium dodecyl sulphate (SDS) on the flux and rejection of CVD
- Effect of pH on the flux and rejection of CVD
It was confirmed that addition of DL-TA increased the pore size while addition of D-TA decreased the pore size of the membrane. This may be due to the fact that surface porosity increased by the addition of D-TA. Fabricated membranes were checked by permeation behavior to observe the effect of the addition of D-TA and DL-TA.
It was confirmed that the rejection of BSA increased with the addition of D-TA and DL-TA. Effect of addition of D-TA and DL-TA on PSF membrane performance for CVD separation for CVD separation. Hydraulic permeability, EWC, and hydrophilicity increased with the addition of D-TA and decreased with the addition of DL-TA.
Impact of synthesized amino alcohol plasticizer on the morphology, hydrophilicity and fouling of polysulfone
Experimental 1. Materials
- Synthesis and characterization of amino alcohol plasticizer
- Fabrication of blended flat sheet membranes by phase inversion method
Four kinds of amino alcohol plasticizers (AAP) were synthesized by the reaction of PEG of four different molecular weights with IAH. To prepare the amino alcohol plasticizer, 6.52 wt% IAH and 22.4 wt% PEG were taken in a three-neck round bottom flask (heated in an oil bath). Removal of benzene was carried out by applying heat (65°C) and vacuum for 12 hours to obtain the amino alcohol plasticizer.
Flat sheet membranes were prepared by phase inversion method using AAP by different molecular weight of PEG (as shown in Table 6.1). It is expected that the hydrophobic part of plasticizer molecules located at the top interface during the wet phase inversion process will be inclined towards the liquid, providing a more hydrophilic environment. However, as the casting solution was immersed in a solidification bath and once phase inversion was driven, plasticizer molecules rearranged upside down [82].
Membrane characterization
- Surface characterization of AAP blended membranes
- Pore size distribution experiment
- Ultrafiltration performance and fouling behaviour experiment
The pore size distribution of the membranes was determined by the liquid-liquid displacement porosimetry (LLDP) method. This method gives the pore number, average pore size and pore size distribution of the fabricated membranes. Pure water flux (PWF) was determined by allowing deionized water to pass through the compressed membrane.
Ultrafiltration experiment was performed to study the solute separation, permeate flux and fouling behavior of the prepared membranes. Each membrane was initially compacted for 30 min at 275.8 kPa, then the pressure was reduced to 150 kPa and the water flux (Jw1) was measured for 1 hour duration. After the first round of BSA rejection and membrane cleaning, water flux was measured, which is used to calculate first flux recovery ratio (Flux1RR).
Results and discussion
- FTIR and NMR spectroscopy analysis of AAP
- Surface and morphological characterization of modified PSF membranes
- ATR-FTIR analysis of plain and blended membranes
- Pore size distribution study
- Pure water permeation and hydraulic permeability studies
- Effect of addition of AAP on CF
- Membrane characterization by EWC and porosity
Since AAP has hydrophilic property; the addition of these plasticizers affects the rate of diffusion of the non-solvent and the solvent. Image J software was used to measure the size of the pores from FESEM images; The PSD clearly shows that the number of smaller pores increases with the addition of AAP for both membranes m2 and m5. Cumulative permeability and cumulative pore number in terms of pore size (nm) are shown in Figures 6.10 and 6.11, respectively.
This may be due to the fact that the pores become denser, leading to a decrease in pores [1]. These results confirm the findings of compaction studies as shown in figure 6.12, as well as the water contact angle measurements shown in figure 6.14. Flux profiles based on transmembrane pressure were used to determine the hydraulic permeability (Pm) of the membranes (equation 2.11).
Plain
- Ultrafiltration and fouling studies using BSA
- Reversible and irreversible fouling study
- Conclusions
- Summary
- Recommendations on future work
It may be due to the fact that AAP-1 contains a higher number of hydrophilic –OH groups. The hydrophilicity of the modified membranes m2, m3, m4 and m5 was found to be increased by the addition of amphiphilic AAP. Rejection of BSA was found more regardless of the molecular weight of PVP at pH 4.8 (IEP of BSA).
The IEC of the membranes was improved by 20.5% with the addition of both D-TA and DL-TA. The top surface FESEM images and LLDP data revealed that AAP increases the pore formation and therefore the pore density of the modified membranes increases with the addition of AAP (See Figures 6.6, 6.7 and 6.9). 62 ̊, the M2 membrane has a WCA value of 55 ̊ and also has the highest BSA rejection due to the zeta potential of the membrane (See Table 5.4).
