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Scheme of the experimental set‐up of the precipitation experiment, performed using a light microscope.
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In this study, we focus on membranes of polyethersulfone and poly(N‐vinyl pyrrolidone) and elucidate the influence of composition on the rheological, diffusion and precipitation properties of solutions which are used for membrane preparation via a non‐solvent‐induced phase separation process. The low‐molar‐mass component of the solution is a mixtur...
Citations
... In this study, using an annular slit nozzle on a single screw meltextruder, extruded hollow fibers of a polymeric blend were produced. This blend was developed based on polyethersulfone (PESU), a commercially available polymer, widely used for developing ultrafiltration membranes given its excellent chemical, thermal and structural stability [4][5][6]8,19,25,[83][84][85][86][87][88][89][90][91][92][93][94][95][96][97]. The other components of this blend are water-soluble polymers, such that, the extruded hollow fibers can be treated using inorganic aqueous solutions for their removal. ...
... 5 kDa) and two outer poly(alkylene oxide)-blocks (Mn of each outer block approx. 3.75 kDa, determination of averaged molecular weights see Ref [21,23]) were synthesized as described in the next section. The chemical structure of PESU, PVP, and the triblock copolymer poly(alkylene oxide)-PESU-poly(alkylene oxide) is presented in Figure 1. ...
... The solution AS 0 does not contain any additive and is associated with two clearly pronounced relaxation processes. In a previous work [23] it was shown that the second, slower process only appears in the presence of glycerol. An increasing additive concentration (solutions AS 3 to AS 9) leads to a slower decay of the function . ...
... The components of the solutions (see Table 1) affect the properties and the structure formation process as follows: PESU favors precipitation at a low water content, PVP in pure form is soluble in water and raises the viscosity as well as glycerol which acts as non-solvent and therefore decreases the solubility of the polymers in solution [23,33,34]. The PESU-PEO additive decreases the viscosity of the solutions due to its lower molecular weight, decreases the precipitation speed due to its amphiphilic nature and the solubility of the PEO, and of course makes the membrane hydrophilic. ...
In this study, a triblock copolymer was used as additive to fabricate new dual layer hollow fiber membranes with a hydrophilic active inner surface in order to improve their fouling resistance. The polymeric components of the solutions for membrane fabrication were poly(ether sulfone), poly(N-vinyl pyrrolidone), and the triblock copolymer. The additive consists of three blocks: a middle hydrophobic poly(ether sulfone) block and two outer hydrophilic alkyl poly(ethylene glycol) blocks. By varying the additive concentration in the solutions, it was possible to fabricate dual layer hollow fiber membranes that are characterized by a hydrophilic inner layer, a pure water permeance of over 1800 L/(m2 bar h) and a molecular weight cut-off of 100 kDa similar to commercial membranes. Contact angle and composition determination by XPS measurements revealed the hydrophilic character of the membranes, which improved with increasing additive concentration. Rheological, dynamic light scattering, transmission, and cloud point experiments elucidated the molecular interaction, precipitation, and spinning behavior of the solutions. The low-molecular weight additive reduces the solution viscosity and thus the average relaxation time. On the contrary, slow processes appear with increasing additive concentration in the scattering data. Furthermore, phase separation occurred at a lower non-solvent concentration and the precipitation time increased with increasing additive content. These effects revealed a coupling mechanism of the triblock copolymer with poly(N-vinyl pyrrolidone) in solution. The chosen process parameters as well as the additive solutions provide an easy and inexpensive way to create an antifouling protection layer in situ with established recipes of poly(ether sulfone) hollow fiber membranes. Therefore, the membranes are promising candidates for fast integration in the membrane industry.
Porous polymer and copolymer membranes are useful for ultrafiltration of functional macromolecules, colloids, and water purification. In particular, block copolymer membranes offer a bottom-up approach to form isoporous membranes. To optimize permeability, selectivity, longevity, and cost, and to rationally design fabrication processes, direct insights into the spatiotemporal structure evolution are necessary. Because of a multitude of nonequilibrium processes in polymer membrane formation, theoretical predictions via continuum models and particle simulations remain a challenge. We compiled experimental observations and theoretical approaches for homo- and block copolymer membranes prepared by nonsolvent-induced phase separation and highlight the interplay of multiple nonequilibrium processes-evaporation, solvent-nonsolvent exchange, diffusion, hydrodynamic flow, viscoelasticity, macro- and microphase separation, and dynamic arrest-that dictates the complex structure of the membrane on different scales.
Most of literature reporting on performance of ultrafiltration membranes was performed in bench-scale experiments employing flat-sheets at operating conditions irrelevant to full-scale application. Subsequently, there is a critical need for an appropriate lab-scale testing protocol employing reliable fouling surrogates. Common individual foulants, e.g., humic acid, bovine serum albumin and sodium alginate, were extensively reported; however, their ability to resemble organic fouling by real surface waters remains questionable. In this study, potting soil extracts were investigated as reliable and inexpensive model foulants for testing the performance of new modified polyphenylene sulfone (PPSU) hollow fiber membrane modules. Assessment experiments were performed in comparison with corresponding polyethersulfone (PESU) membranes modules using mini-plant testing unit operated at full-scale conditions. At comparable total organic carbon content, aqueous extracts of four different potting soil types had different dissolved organic carbon compositions and turbidity. Humic substances were the main constituents; however, hydrophobic organic carbon (HOC) and biopolymers varied significantly. An application-oriented testing protocol comprising 24 filtration-cycles was developed. Potting soil extract feeds were emphasized to imitate chemical composition and characteristics of moderately organic-loaded surface waters, at high reproducibility, and induce typical organic fouling within experiment time. Feeds exhibiting high biopolymer content (or modest portions of biopolymer and HOC) were able to distinguish explicitly between fouling propensity of different modified membrane materials. Besides regular performance measures, fouling propensity was quantified as hydraulic irreversible fouling index (HIFI) that was related to turbidity removal; however, no consistent correlation was found with humics and low molecular weight organic fractions. Furthermore, impact of feed solution type on the interplay between membranes’ characteristics and HIFI values was investigated. Good correlation between PPSU-based membranes’ characteristics and HIFI values was noticed upon using feeds containing considerable biopolymers and HOC portions. Nevertheless, in case of PESU-based membranes, impact of improvement of pure water permeability (due to modification) was dominating.
