Coagulation Bath Research Articles

A tight polyethersulfone ultrafiltration membrane fabricated via polyion complex assisted phase inversion for dye desalination

In this work, a tight polyethersulfone (PES) -based ultrafiltration (UF) membrane was fabricated to separate dye and salt of textile wastewater via a novel polyion complex assisted phase inversion method in one step. Thereinto, sulfonated polysulfone (SPSF) and poly-(diallyl dimethylammonium chloride) (PDADMAC) were added into the PES dope and coagulation bath, respectively. During the phase inversion process of the precast PES/SPSF film, polycation PDADMAC could assemble with anionic SPSF and facilitate SPSF enrichment on membrane surface, forming a dense barrier layer via the electrostatic interaction between quaternary ammonium and sulfonate groups. Morphology, chemical composition, surface charges and pore size analysis characterized via SEM, FTIR, XPS, Zeta potential and Dextran filtration experiment, respectively, testified that a nonporous skin layer comprising of polyion complex and enriched SPSF was successfully constructed on the top of the PES matrix with an effective pore radius of 1.44 nm, which is smaller than that of the reference membrane prepared without using polyion complex assisted phase inversion (2.74 nm). This resultant membrane exhibited a high pure water permeance of 94 LMH/bar. When it was utilized to separate a dye/salt mixture of 100 ppm Congo red (CR) and 2 g/L Na2SO4 at 1 bar, the rejection of CR could reach 99.7%, alongside a very low Na2SO4 rejection of 8.4%, while the water permeance of dye solution maintained 61 LMH/bar. In addition, the membrane also possessed excellent stability in the pH range of 1–13 due to the strong electrostatic interaction between SPSF and PDADMAC and long-term operation stability, demonstrating its application potential in textile wastewater treatment.

Regenerated Fibers from Rennet-Treated Casein Micelles during Acidification.

Micellar casein fibers of defined size and internal structure can be produced by the extrusion of cold-renneted casein micelles into a warm, calcium-rich coagulation bath. Calcium phosphate contacts within the casein matrix are important for fiber stability and production but become less important under acidic pH conditions. We demonstrate this with swelling experiments in media with pH < 2, which we adjust with citric acid of different molarities. In contrast to the simple swelling of dried casein fibers in water, a two-phase process takes place in citric acid similar to swelling in 1 N HCl. However, instead of a second deswelling step, we observe in citric acid that the fiber swells further. The observation is explained by a pH-dependent transition from a rennet casein gel to an acidified rennet gel. This can be simulated with a kinetic model that couples two second-order rate equations via a time-varying ratio. The final swelling values decrease with increasing proton concentration via a scaling relation, which is also confirmed by swelling in other acids (HCl or acetic acid) in this pH range. We attribute this to a decrease in the molecular weights of the aggregated casein structures within the strands of the gel network.

Improvement of persistent hydrophilicity and pore uniformity of polyvinyl chloride ultrafiltration membranes by in-situ crosslinking reaction assisted phase separation

A novel in-situ crosslinking reaction assisted phase separation strategy was proposed for persistent hydrophilization and pore size regulation of polyvinyl chloride (PVC) membranes. In-situ cross-linking between PVC molecular chains was achieved through grafting of 3-aminopropyltrimethoxysilane (APTMS) during the dissolution process and cross-linking reactions between siloxanes in APTMS molecules initiated by the coagulation bath (water). The effect of in-situ crosslinking reaction on the structure, separation and anti-fouling performance of the PVC membranes was studied. Through in-situ crosslinking reaction induced phase separation, the migration and curing of polymer molecular chains in the phase separation process were regulated, which endowed the modified membrane with improved hydrophilicity, higher porosity and narrow pore size distribution. The pure water flux of the obtained membrane increased 3.5 times as much as that of the pure PVC membrane. In addition, the flux recovery rate (FRR) of the obtained membrane was increased by 15.9% and the strength was also increased slightly at the same time. The stability of the membranes was also improved, without chemical agents leaching during filtration, avoiding secondary pollution to our environment.

Characterization of Polysulfone Membrane with Variation of Ethanol Concentrations in Coagulation Bath for Ultrafiltration Membrane

The aim of this research is to study influence of ethanol concentrations in coagulation bath to charecteristic of physical properties and polysulfone membrane performance. Ethanol concentrations that used is 0; 40; 50; 60 ; 70; 80; 90 %. Process of making for polysulfone ultrafiltration membrane is prepared with phase inversion technique. Polysulfone membrane is made from polysulfone solved in N,N- dimetilacetamida (DMAc) and additive poly(ethylene glikol) (PEG) 600 in proportion 18 %: 77 %: 5 %. The result showed that increasing ethanol concentrations causes the increasing of density and increase concentrations from 0 - 50 % causes increasing swelling degree, but decreasing swelling degree from concentrations 60 - 90 %. However influence of ethanol concentration in coagulation bath to membrane performance is increasing of water flux, permeability coefficient, and rejection coefficient to dextran. It based on of result that polysulfone membrane with ethanol concentrations 80 dan 90 % included membrane classification ultrafiltration by rejection coefficient value above 90 %.

Preparation and Application of a Natural Microspheric Soil Conditioner Based on Gelatin, Sodium Alginate, and Zeolite

In this work, a type of natural microspheric soil conditioner, PZ(Fe)/GL-SA-Urea, was prepared by emulsion cross-linking and sharp-hole coagulation bath methods. Gelatin (GL) and sodium alginate (SA) were selected as the outermost shell, and the prepared FeOOH was loaded on pickling zeolite (PZ) to improve the loading ratio of urea. The embedding performance and sustained release behavior of the microspheres showed that when the concentration of urea was 1.5%, the embedding rate reached 37.63%, and the cumulative release rate reached 68% within 100 h, indicating that the microsphere had good encapsulation and sustained release abilities. In addition, the water retention and swelling behaviors of the microspheres can be obtained by controlling the content of added GL. Furthermore, antibacterial and planting experiments revealed that the microspheres had excellent antibacterial effects and can effectively improve soil quality and promote crop growth. Therefore, the PZ(Fe)/GL-SA-Urea microsphere soil conditioners possess good application properties and provide fresh solutions to improve soil quality and raise crop yields.

Wood microchannels with multi-carboxyl groups for selective adsorption of Fe3+ from ionic liquids aqueous solution: Experimental and DFT study

Heavy metal contamination is widely present in the spinning field. Some heavy metal ions such as Fe3+ may accumulate in the coagulation bath using ionic liquids (ILs) as green solvents to prepare regenerated cellulose fibers (RCFs), which seriously affect the performance of RCFs and the subsequent regeneration of ILs. This study proposed a new strategy to selectively adsorb Fe3+ from ILs aqueous solution using carboxyl-functionalized wood microchannel (CW). The CW was optimized by citric acid concentration, reaction time, and temperature using carboxyl group contents as an indicator. The physic-chemical properties of CW were characterized, and its adsorption performance for Fe3+ was also evaluated in a water system. Furthermore, the adsorption selectivity of CW for Fe3+ and ILs was investigated. The results demonstrate that the CW had a high adsorption ratio for Fe3+ (94.73%), while that for ILs was 4.20%. The selective adsorption mechanism, in which the Fe3+ is mainly separated from ILs aqueous solution by complexation with carboxyl group, was confirmed by FTIR, XPS, MIP, and DFT calculation. Accordingly, this paper may provide a new strategy to selectively adsorb Fe3+ from ILs aqueous solution, thus offering an economical and efficient method for ILs recovery and water purification.

Fabrication of Hydrophobic Poly(vinylidene fluoride) Membranes with Manipulated Micromorphology and Enhanced Strength

In this work, an ethanol/water/glycerol ternary coagulation bath system was used to fabricate a hydrophobic PVDF membrane, which will have a considerable impact on the micromorphology. This change will further affect the performance of the membrane. After introducing glycerol into the coagulation bath, the precipitation process was finely regulated. The obtained results implied that glycerol could inhibit solid-liquid separation and promoted liquid-liquid separation. A pleasant discovery was that the mechanical properties of the membrane were improved because of the more fibrous polymers formed by liquid-liquid separation. Besides, a more uniform pore size can be achieved. A fascinating symmetrical interconnected fibrous and spherulitic structure was depicted by membranes fabricated with a coagulation bath consisting of 6% water, 34% ethanol, and 60% glycerol. This membrane had a high water contact angle of 146.6° and a small mean pore size of 0.46 μm. Enhanced tensile strength and elongation at break evidenced that the membrane enjoyed good robustness and flexibility. This facile approach provided the possibility to prepare membranes with tailored pore size and the required strength.

Role of natural deep eutectic solvents (NADESs) in coagulation bath for PVDF-based membranes on enhanced permeation and separation of rare earth ions

Efficient separation of single rare earth element such as neodymium (Nd) has become an important research topic due to the supply crisis which seriously restricts the application and promotion of rare earth permanent magnets. PVDF-based separation membranes prepared by non-solvent induced phase separation (NIPS) method usually exhibited hydrophobic surface properties resulting in performance attenuation and operation cost increase. This article applied an easily available NADES from betaine and lactic acid to regulate and control the coagulation bath of a polymer inclusion membrane (PIM) for the separation of Nd, Sm and Dy ions. Evidences for the formation of DES were characterized via 1H NMR and FT-IR, and betaine showed more obvious changes than lactic acid during the formation of DES via hydrogen bonds. With the help of DES, pores on the surface were much larger and richer, and the migration of PO and P–O groups to the lower epidermal layer of the membrane made the surface layer become more hydrophilic. DES accelerated the liquid-liquid demixing process and led to faster membrane-forming speed and typical finger-like macrovoids and short vertical penetration channels, which could be observed at high DES contents, and a DES content of 5 wt% was found the most optimal considering the overall permeability and separation performances. As an effective means to improve membrane's performances, adding hydrophilic NADESs at a proper ratio in the coagulation bath would be conducive to form more porous structures, higher surface hydrophilicity, optimized permeability and separation performances.

Design, manufacture, and control motion of cartesian robot prototype with 5-DOF robot arm for possible spinning applications at laboratory-level

This document presents the development of a prototype of a Cartesian robot with a 5 degrees-of-freedom articulated robot arm for possible applications in a wet spinning process at the laboratory-level. The mechatronic system was developed using various modular electronics elements compatible with an ArduinoTM Mega 2560 microcontroller. The control algorithm recognizes the position of the servomotors and the speed of the motors so that the prototype performs a complete cycle of displacement in 67 s, which includes the transport of a polymeric filament immersed in a coagulation bath for 10 s. A structural analysis indicates that there will be no tension failures because the maximum and axial stress of the Cartesian robot was 2.89 MPa while the von Mises tension of the robotic arm was 468 MPa, both tensions below their upper limits. The pulse signals, in the order of 4000 +25 ms, of the servomotors were consistent in 96-98% repeatability and 3-19% reproducibility. Forty percent of the extrusion tests performed were satisfactory, since the transport of a polymeric filament within a coagulant solution was achieved.

Robust and knittable wet-spun PEDOT: PSS fibers via water

Since achieving green and sustainable development has become a global goal, a unique coagulation bath system without organic solvents has been developed for wet-spinning poly(3,4-ethylenedioxythiophene): poly (styrene sulfonate) (PEDOT: PSS) conductive fibers. A small amount of metal ions was added to water to promote fiber solidification. Especially, with Fe3+ and thermal drawing aid, the resultant fiber reveals a maximum tensile breaking strength of 1263.1 ± 58.3 MPa, the highest reported value for pure PEDOT: PSS fibers to the best of our knowledge. The knitted fabrics woven from robust PEDOT: PSS fibers show superior flexibility and thermal insulation, demonstrating their excellent application potential in flexible electronic fabrics.

Effect of the Preparation Conditions on Polyvinyl Chloride/Aliquat-336 Microspheres’ Efficiency: Optimization Using Surface Response Methodology

Polyvinyl chloride (PVC)/Aliquat-336 microspheres were prepared with the phase inversion method and optimized for red Cibacron dye adsorption. Response surface methodology (RSM) was used to maximize the adsorption capacity. The optimized parameters were the PVC fraction in the dimethylformamide (DMF) solvent, the Aliquat-336/polymer ratio, and the volume fraction of ethanol in the water coagulation bath. The model significant parameters found were the Aliquat-336/polymer ratio and the ethanol volume fraction. The maximum adsorption of 73.7425 mg g−1 was obtained by optimization with an Aliquat-336/PVC mass ratio of 1.5 and an ethanol volume fraction of 0.0934. This theoretical maximum adsorption capacity was confirmed with the experimental one, which had a close value of about 70.25 mg g−1. Both intraparticle and interparticle diffusion mechanisms controlled the adsorption kinetics, and the equilibrium adsorption time was established as 180 min.

Fabrication of halogen-free and phosphorus-free flame retardant and antistatic PAN fibers based on tea polyphenol phenolic resin chelated with iron (Ⅲ) ions

Polyacrylonitrile (PAN) fibers are one of the three major synthetic fibers in the world, but the drawbacks of flammable and static charge accumulation limit their application. To address the issue, tea polyphenol phenolic resin (TPPR) was firstly prepared from biomass tea polyphenol in this paper. Next, TPPR was blended with PAN spinning solution and wet-spun with Fe3+ solution as coagulation bath to construct phosphorus-free and halogen-free flame retardant PAN fibers (TPPR@Fe/PAN). The results indicated that the limiting oxygen index (LOI) value increased from (17.3 ± 0.51)% of PAN fibers to (31.6 ± 0.51)% of TPPR@Fe/PAN. Even after 30 laundering cycles (LCs), the LOI value of TPPR@Fe/PAN was still up to (27.7 ± 0.51)%, indicating good washing durability. Additionally, the heat release capacity (HRC) and total heat release (THR) of TPPR@Fe/PAN had 35.0% and 48.6% reduction, respectively. Furthermore, TPPR@Fe/PAN obtained excellent antistatic ability. Besides, the TG-IR results demonstrated that both the release of flammable and toxic gases were significantly suppressed. In the work, a simple and feasible flame retardant and antistatic strategy was established which was convenient for fabrication of functional PAN fibers on a large scale.

Preparation of flexible and ultralow dielectric polyimide porous films by a low-cost and environmentally friendly non-solvent phase separation

Polyimide (PI) porous films were prepared by non-solvent induced phase separation with low-cost and simple method. A low-cost and environmentally friendly solution of water and ethanol was selected as non-solvent coagulation bath and effects of water and ethanol content on microstructure and properties was studied. The prepared films showed high mechanical property at high temperature, excellent dielectric property and thermal stability. Thus there are excellent application prospects in fields of flexible electronics and microelectronics industry.

Mixed-matrix ZIF-loaded membranes for effective separation of bio-butanol from fermentation broth

Mixed matrix composite membranes offer superior performance for separation of alcohols from fermentation broth. In this study bio-butanol (Butanol) is recovered from Acetone: Butanol: Ethanol (ABE) fermentation broth using ZIF-71 -PDMS-PVDF membranes. The significance of this work is the supported PVDF layer that was prepared using a dual coagulation bath to increase the surface roughness and contact angle. The addition of hydrophobic ZIF-71 particles into the matrix increases their thermal stability, hydrophobicity, and strength of the membrane. The synthesized membranes exhibited higher hydrophobic characteristic with a contact angle of around 120°. The Pervaporation efficiency of these membranes was analyzed by various experimental parameters such as ZIF loading, permeate pressure, feed temperature, and stirring speed. The membrane interaction parameters were calculated using Flory Huggins and Flory-Rehner equations. The membrane performance was also assessed by Maxwell-Stefan model fitting along with the evaluation of the friction coefficient. The butanol flux (50 g/m2h) was estimated using mathematical modeling and compared with the experimental results (120 g/m2h). The studies inferred that the models are well-fitted for butanol extraction which implies the penetrant-penetrant interaction is lower than penetrant-membrane interactions. A comparison of the present study with literature is well-defined to scale-up the process at an industrial level.

All-solid-state Ti3C2Tx neutral symmetric fiber supercapacitors with high energy density and wide temperature range

All-solid-state Ti3C2Tx neutral symmetric fiber supercapacitors (PVA EGHG Ti3C2Tx FSCs) with high energy density and wide temperature range are constructed by using polyvinyl alcohol (PVA)-ethylene glycol hydrogel (EGHG)-sodium perchlorate (NaClO4) as electrolyte and separator, and Ti3C2Tx fiber as electrodes. Ti3C2Tx fiber is prepared using 130 mg mL−1 Ti3C2Tx nanosheet ink as an assembly unit in a coagulation bath of isopropyl alcohol (IPA) and distilled water with 5 wt% CaCl2 by a wet spinning method. The prepared Ti3C2Tx fiber exhibits a specific capacity of 385 F cm−3 and a capacitance retention of 94 % after 10,000 cycles in 1 M NaClO4 electrolyte. The assembled PVA EGHG Ti3C2Tx FSCs deliver a specific capacitance of 41 F cm−3, a volumetric energy density of 5 mWh cm−3, and a capacitance retention of 92 % after 500 times continuous bending. Furthermore, it shows good flexibility and excellent capacitance over a wide temperature range of −40 to 40 °C and maintains its electrochemical performance under varying degrees of bending. This study provides a viable strategy for designing and assembling all-solid-state neutral symmetric fiber supercapacitors with high energy density and wide temperature range.

Assessing the recyclability of superbase-derived ionic liquids in cellulose processing: An insight from degradation mechanisms

The recyclability of superbase-derived ionic liquids (SILs) as a green and efficient solvent is considered to be an urgent and crucial issue to increase the economic viability of regenerated cellulose (RC) processing. Herein, two novel 1,8-diazabicyclo[5.4.0]undec-7-enium carboxylates ([DBUH][CH3OCH2COO] and [DBUH][CH3CH2OCH2COO]) were first recovered from the coagulation bath in the cellulose regeneration, as compared to traditional 1-allyl-3-methylimidazaolium chloride (AmimCl). The degradation mechanism of ionic liquids (ILs) in the recovery process and the properties of RC prepared from recycled ILs were analyzed to investigate the solvent availability. The results indicated that the average recovery yields of the three ILs were achieved up to 95–97 % without any further process optimisation. The highest recycle times of [DBUH][CH3OCH2COO] (10 times) with the outstandingly thermochemical stability was obtained in the recovery process, which was twice of AmimCl (5 cycles). It can be explained that [DBUH][CH3OCH2COO] exhibited the highest energy gap, the lowest electrophilicity index, and the weakest tendency to nucleophilic reaction with water. Conversely, [DBUH][CH3CH2OCH2COO] was only recovered for 4 cycles because of the active conjugation state between [DBUH]+ and [CH3CH2OCH2COO]−, in especial the strong electron-donating capacity of –OCH2CH3. The CN in [DBUH][CH3CH2OCH2COO] was prone to nucleophilic attack by water to increase the degradation degree. Furthermore, the RC obtained from recycled [DBUH][CH3OCH2COO] possessed higher crystallinity and thermal stability in comparison with that from recycled AmimCl, which was corresponding to the recyclability of ILs. These findings favor [DBUH][CH3OCH2COO] as a promising solvent in the scaling up of the cellulose processing and utilization.

Preparation and Characterization of Novel Membrane from Waste Polyethylene terephthalate and Bio-based Polymer

A large amount of post-consumer Polyethylene terephthalate (PET) bottle waste could be recycled for downstream products. In this work, used PET bottles were utilized as a raw material to develop environmentally-friendly ultrafiltration membranes by phase inversion technique. Poly(ethylene-2,5-furandicarboxylate) (PEF), prepared from a sustainable bio-based monomer, 2,5-furandicarboxylic acid (FDCA), was blended into rPET matrix to improve the mechanical properties of the membrane. Ethanol was also used as a non-solvent in a coagulation bath and polyethylene glycol (PEG) with a molecular weight of 400 Da was added as a hydrophilic additive. The effects of PEF and PEG incorporation to waste PET-based membranes have been thoroughly studied. The morphology of obtained membrane was investigated using Scanning Electron Microscopy (SEM). The membrane’s permeation and resistance were tested using a pressure-driven dead-end membrane module. The result revealed that adding PEF increased the roughness of the membrane surface, which lowered the flux recovery ratio and rejection performance. However, the filtration performance and the membrane resistance could be improved by adjusting the content of the PEG additive.

Influence of structure of porous polyketone microfiltration membranes on separation of water‐in‐oil emulsions

AbstractPressure‐driven filtration is a suitable alternative to conventional methods for separation of surfactant‐stabilized water‐in‐oil (W/O) emulsions. In this work, porous polyketone (PK) membranes for W/O emulsion separation with outstanding organic solvent resistance were prepared by non‐solvent‐induced phase separation (NIPS). The porous PK membrane structures were controlled by changing the non‐solvent concentration in the coagulation bath. The water contact angle in oil increased as the methanol concentration in the coagulation bath increased because of the formation of a rougher membrane surface, implying higher under‐oil hydrophobicity. The PK membranes were able to separate several surfactant‐stabilized W/O emulsions consisting of various organic solvents, with high oil purity value (99.9%). Permeance increased with increasing methanol concentration in coagulation bath due to the increase in membrane pore size and porosity. The best performing membrane, prepared with 45 wt% methanol coagulation bath, showed over 4000 LMH/bar permeance using emulsions of different particle sizes. Furthermore, the relationship between permeance and the ratio of the PK membrane pore size to the W/O emulsion particle size suggested that the initial permeance was dependent on pore size. The PK membranes demonstrated huge potential for W/O emulsion separation because of their easily‐controlled structures, high under‐oil hydrophobicity, and high separation performance.

Effect of the Addition of Polyacrylic Acid of Different Molecular Weights to Coagulation Bath on the Structure and Performance of Polysulfone Ultrafiltration Membranes

Membrane fouling is a serious issue in membrane technology which cannot be completely avoided but can be diminished. The perspective technique of membrane modification is the introduction of hydrophilic polymers or polyelectrolytes into the coagulation bath during membrane preparation via non-solvent-induced phase separation. The influence of polyacrylic acid (PAA) molecular weight (100,000, 250,000 and 450,000 g·mol-1) added to the aqueous coagulation bath (0.4-2.0 wt.%) on the polysulfone membrane structure, surface roughness, water contact angle and zeta potential of the selective layer, as well as the separation and antifouling performance, was systematically studied. It was found that membranes obtained via the addition of PAA with higher molecular weight feature smaller pore size and porosity, extremely high hydrophilicity and higher values of negative charge of membrane surface. It was shown that the increase in PAA concentration from 0.4 wt.% to 2.0 wt.% for all studied PAA molecular weights yielded a substantial decrease in water contact angle compared with the reference membrane (65 ± 2°) (from 27 ± 2° to 17 ± 2° for PAA with Mn = 100,000 g·mol-1; from 25 ± 2° to 16 ± 2° for PAA with Mn = 250,000 g·mol-1; and from 19 ± 2° to 10 ± 2° for PAA with Mn = 450,000 g·mol-1). An increase in PAA molecular weight from 100,000 to 450,000 g·mol-1 led to a decrease in membrane permeability, an increase in rejection and tailoring excellent antifouling performance in the ultrafiltration of humic acid solutions. The fouling recovery ratio increased from 73% for the reference membrane up to 91%, 100% and 136% for membranes modified with the addition to the coagulation bath of 1.5 wt.% of PAA with molecular weights of 100,000 g·mol-1, 250,000 g·mol-1 and 450,000 g·mol-1, respectively. Overall, the addition of PAA of different molecular weights to the coagulation bath is an efficient tool to adjust membrane separation and antifouling properties for different separation tasks.

Wet-spun PEDOT: PSS/ionic liquid composite fibers for wearable e-textiles

Wet-spinning technology plays an essential role in the development of wearable electronics. Poly(3,4-ethylene dioxythiophene): poly(styrene sulfonate) (PEDOT: PSS) fibers have been widely investigated in this field due to their advantages of being environment-friendly and low-cost. They are mainly wet-spun from a coagulation bath containing ethanol and water with additional metal salts. However, the conductivity of PEDOT: PSS fibers spun by this method is low. Here, we propose a novel coagulation bath made of ionic liquid (IL), ethanol, and water, and the resultant PEDOT: PSS fibers could achieve a conductivity of 118.3 S·cm−1. Furthermore, the fiber-shaped supercapacitor prepared by such PEDOT: PSS/IL fibers reveals an optimal capacitance retention rate of 97 % even after 10,000 cycles, and the capacitance loss of the supercapacitor is only 7 % at −20 ℃. The sensor derived from the PEDOT: PSS/IL fibers has superb sensing capability, indicating their promising applications for wearable electronics.