Coagulation Medium Research Articles

Manufacturing of cellulose-based nano- and submicronparticles via different precipitation methods

Nanoprecipitation is one of the most popular methods for producing polymer nanoparticles. However, the reported results show a large variability. In order to provide a first-hand comparative study, we prepared cellulose-based nanoparticles via different nanoprecipitation methods. Here, the influence of the coagulating solvents acetone, N,N-dimethylacetamide and tetrahydrofuran on the size and shape of the particles via precipitation using dialysis was investigated. The influence of temperature and concentration was determined by dropwise addition of the coagulation medium. Then, via rapid solvent shifting, particles were prepared from cellulose acetates with different molecular masses and the cellulose acetate propionate and cellulose acetate butyrate derivatives in the concentration range of 1–20 mg mL− 1. Thereby, it was possible to prepare spherical particles in the range from 43 to 158 nm. Furthermore, the impact of the molecular weight of these derivatives on the obtained particle size distributions was determined. It is possible to obtain pure regenerated cellulose particles in the nanometer range by a deacetylation of the derivatives. In addition, the findings were used to directly convert cellulose from a DMAc/LiCl solvent system into regenerated cellulose nanoparticles with a size of 10 ± 3 nm.Graphical abstract

Polyvinylidene fluoride membrane formation using carbon dioxide as a non-solvent additive for nuclear wastewater decontamination

Polyvinylidene fluoride (PVDF) membranes were prepared by phase inversion in the most commonly used solvents for membrane manufacture, with CO2 as a non-solvent additive. The effects of changing the polymer concentration (10, 12.5 and 15% by weight), the type of solvent (NMP, DMAc and DMF) and the coagulation bath with three levels of CO2 concentration on the phase inversion process, as well as the phase diagram, morphology and transport properties of the membranes were studied. The best performing membranes were used to desalinate salt aqueous solutions and decontaminated simulated nuclear wastewater by membrane distillation using two configurations (DCMD and AGMD). All selected membranes showed high rejection with acceptable permeate fluxes reaching an infinite decontamination factor. The proposed approach of this novel idea of using CO2 dissolved in water as a coagulation medium in the field of membranes avoids the increase of the harmful effect on the environment caused by the addition of a harsh non-solvent to the coagulation bath. It constitutes a beneficial use of carbon dioxide that reduces the negative environmental impact of membrane manufacturing and represents a decisive step towards its sustainability. Furthermore, this study highlights the potential benefits of using these membranes in DM for desalination and treatment of simulated nuclear wastewater.

Regeneration of Cellulose from a Switchable Ionic Liquid: Toward More Sustainable Cellulose Fibers

AbstractA CO2 switchable solvent system is investigated to find an environmentally friendlier way to produce man‐made cellulose fibers. Cellulose solutions with concentrations from 2 wt% to 8 wt%, based on derivative and non‐derivative dissolution approaches, are investigated. Three different switchable solvent systems are tested. After accessing the stability of the produced cellulose solutions, their regeneration is investigated using different alcoholic coagulation media. In order to find a suitable coagulation medium and stable cellulose solution, a dissolution–regeneration cycle is investigated, while trying to minimize the amount of waste by recovering the employed solvents. The process is optimized and the resulting fibers are characterized by infrared (IR) spectroscopy, optical microscopy, as well as scanning electron microscopy.

Preparation of Highly Hydrophobic PVDF-HFP Membrane with Anti-Wettability Characteristic

Membrane gas-liquid separation technology has gained great interest in membrane desalination, distillation, and gas absorption attributed to its good operation flexibility, small footprint and high specific interfacial area. Membrane acts as the non-selective barrier between gas and liquid solvent by allowing the diffusion of gas molecules via pressure difference. Currently used membrane is susceptible to pore wetting at high operational pressure, transforming its non-wetted condition to partially wetted and wetted mode. Such condition introduces additional mass transfer resistance to gas molecules, leading to the poor removal flux. In order to alleviate the wetting tendency, membrane hydrophobicity needs to be enhanced. In this work, highly hydrophobic PVDF-HFP membrane of improved anti-wettability properties was synthesized via non-solvent induced phase separation. The effect of polymer concentration and coagulation medium on membrane wettability were studied. The results revealed that PVDF-HFP membrane of 10wt% polymer concentration presented high water contact angle of 100.4°. By changing water to ethanol as coagulation medium, membrane exhibited a symmetric nodular structure which enhanced water contact angle by 20.3% to 130.5º. To further improve membrane hydrophobicity, modified silica (MS) nanoparticles were used as surface modifier in coagulation bath. When the nanoparticles content increased from 0g to 2g, the water contact angle of the PVDF-HFP modified membrane increased significantly from 130.5° to 163.1°. As a result, the liquid entry pressure of the membranes increased gradually from 0.58bar to 3.38bar with MS incorporation. This disparity in membrane anti-wettability is due to the increase in surface roughness and reduction in surface energy. Additionally, the modified membrane at MS loading of 2g showed high porosity at 78%, which is adequate to provide increased mass transfer rate between gas and liquid solvent.

Tuning the properties of regenerated cellulose: Effects of polarity and water solubility of the coagulation medium

In this study, the effect of different alcohols and esters as a coagulation medium in the regeneration of cellulose dissolved in an aqueous LiOH-urea-based solvent was thoroughly investigated using various methods such as solid state NMR, X-ray diffraction, water contact angle, oxygen gas permeability, mechanical testing, and scanning electron microscopy. It was observed that several material properties of the regenerated cellulose films follow trends that correlate to the degree of cellulose II crystallinity, which is determined to be set by the miscibility of the coagulant medium (nonsolvent) and the aqueous alkali cellulose solvent rather than the nonsolvents’ polarity. This article provides an insight, thus creating a possibility to carefully tune and control the cellulose material properties when tailor-made for different applications. [Display omitted] [Display omitted]

3D Plotting using Camphene as Pore-regulating Agent to Produce Hierarchical Macro/micro-porous Poly(ε-caprolactone)/calcium phosphate Composite Scaffolds.

This study demonstrates the utility of camphene as the pore-regulating agent for phase separation-based 3D plotting to produce hierarchical macro/micro-porous poly(ε-caprolactone) (PCL)–calcium phosphate (CaP) composite scaffolds, specifically featuring highly microporous surfaces. Unlike conventional particulate porogens, camphene is highly soluble in acetone, the solvent for PCL polymer, but insoluble in coagulation medium (water). In this study, this unique characteristic supported the creation of numerous micropores both within and at the surfaces of PCL and PCL–CaP composite filaments when using high camphene contents (40 and 50 wt%). In addition, the incorporation of the CaP particles into PCL solutions did not deteriorate the formation of microporous structures, and thus hierarchical macro/micro-porous PCL–CaP composite scaffolds could be successfully produced. As the CaP content increased, the in vitro biocompatibility, apatite-forming ability, and mechanical properties (tensile strength, tensile modulus, and compressive modulus) of the PCL–CaP composite scaffolds were substantially improved.

Coalescence of Oil Droplets using Sponge-like Structure of Polyvinylidene Fluoride Membranes

This work reports the effect of the membrane pore size distribution on the oil droplets size distribution in permeate using the polyvinylidene fluoride (PVDF) membranes. The sponge-like structures of the PVDF membranes were fabricated via the phase inversion technique using 30% v/v ethanol aqueous solution as coagulation medium. Water and polyethylene glycol (PEG1000) were used as the pore forming additives in the dope solutions. Microfiltration was employed to coalesce the oil droplets at the transmembrane pressure of 2.5 bar. Simulated alkaline-surfactant-polymer (ASP) produced water was tested as the feed solution. Results revealed that the PVDF membranes with sponge-like structure were formed. The additives in the dope solutions have induced the membranes to become thicker due to more porous, spongy and resilient structure. The membrane pore sizes increased with the presence of the additives in the dope solutions especially when larger molecular weight of the additive, i.e., PEG1000 was used. The mode of the oil droplets radius increased from 61.2 nm in the feed solution to 95.1, 356.2 and 1335 nm in the permeates by the corresponding membranes without additive, with water and PEG1000 as the additives. The membranes with larger pore sizes as well as more open structure were able to trap and coalesce more oil droplets which produced larger size of the oil droplets in the permeates.

Discretized Modeling of Motionless Printing Based on Retarded Bending Motion and Deposition Control of Electrically Driven Jet

This study is on developing a simple motionless printing in which polyacrylonitrile and N,N-dimethylformamide solution is electrically driven from a fixed nozzle head in a coagulation medium of chloroform and mineral oil. The effect of liquid medium on the bending instability of the jet is studied using the discretized model and experiments. Furthermore, for motionless printing, the inhibited bending motion of the jet is used to control the deposition of the jet to form a square pattern on the collector. The resulting fiber collection pattern obtained from the experiments is favorably compared with the simulation results. In addition, the effects of the switching time and distance between the collector plates on the accuracy of the square and circle three-dimensional patterns are studied from the simulation.

Calculation of magnetic devices cleaning coolants in the agro–industrial complex

Traditional ways of cleaning of cooling lubricants in agrarian–industrial complex are considered in the article. Experimental data on the presence of magnetic impurities and its fractional composition as a result of parts machining on machines with the use of cooling lubricants are cited. Combined devices based on the combination of traditional methods for cleaning technical fluids have been used to intensify the cleaning process. The use of such combined cleaning methods is grounded, the forces effecting on the particles in the process of separation – coagulation forces, magnetic deposition, and medium resistance – are considered. The mathematical model of the coagulation process of two particles having similar size in a homogeneous magnetic field is made up. However, it is impossible to solve the obtained system even by a numerical method with unknown initial conditions. In this connection, the inverse problem is proposed. The physical significance of the effect of forces is as follows: a floccule consisting of two particles is destroyed under the effect of coagulation forces; the resistance of the medium prevents it. Its numerical solution allows finding the main dynamic characteristics of particle coagulation: the speed and distance from which they interact.

Investigation of dissolved cellulose in development of buccal discs for oromucosal drug delivery

Mucoadhesive formulations have a wide scope of application for both systemic and local treatment of various diseases. In the case of recurrent aphthous stomatitis, to ensure effective therapy, the concentration of corticosteroids, and/or anesthetics at the mouth ulcer side should be maintained with minimal systemic absorption. Therefore, the aim of the study was to investigate cellulose-based formulations, in achieving suitable hardness, mucoadhesiveness, and sustained release of the active ingredients directed towards the mucosa for an extended period of time (∼4 h). This was examined by creating polymer reinforced cellulose composites which consisted of porous cellulose discs (CD) and different polymer components namely polyethylene glycol 6000 (PEG6000), polyethylene glycol 400 (PEG400), and ethyl cellulose. Empty CDs were formed by dropping dissolved cellulose into coagulation medium. The empty porous CDs were immersed into different drug loading solutions which were prepared by dissolving three different concentrations of triamcinolone acetonide and lidocaine hydrochloride in five different ratios of PEG 6000:PEG 400:ethanol (w:w:w %) solutions. All formulations were investigated regarding drug content, release, hardness, and mucoadhesive properties. The results indicate that the non-dispersing buccal discs had sufficient hardness, drug content and in vitro release properties, but further studies are needed to achieve proper mucoadhesiveness.

Phase separation analysis of Extem/solvent/non-solvent systems and relation with membrane morphology

The phase separation behavior of Extem/water/solvent systems for various solvents and Extem/NMP/non-solvent systems for different types of coagulants was investigated. Ternary phase diagrams of studied systems were constructed based on cloud point data obtained by titration at room temperature. In the first part, N-methyl-2-pyrrolidone (NMP), dimethylacetamide (DMAc), dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) were employed as solvent and water was used as coagulant. The cloud point curves from these systems showed that Extem/NMP/water and Extem/DMSO/water has the smallest and largest demixing gap, respectively. Subsequently, water, methanol, and glycerol were employed as coagulants and NMP was selected as solvent. The obtained results indicated that water and methanol had the strongest and weakest coagulant power, respectively. The linearized cloud point and precipitation value were applied to identify the strength of the non-solvent for casting solution (Extem/NMP) with a certain concentration. The solubility curve of Extem was obtained using the Hansen solubility parameter, calculated by a group contribution method. In order to evaluate the influence of different solvents and non-solvents on the final structure of the resulting membranes, scanning electron microscopy (SEM) was used. The morphology of the membranes prepared from Extem/solvent/water systems (except Extem/DMSO/water) showed a finger like sub-layer, while a sponge-like structure was observed for the Extem/DMSO/water system. Using methanol as coagulation medium resulted in a thick dense layer over a macroporous sub layer, while a fully sponge like structure with microporous skin layer was obtained for the Extem/NMP/glycerol system. In order to find the source of these unexpected observations, thermodynamic and kinematic aspects such as binary interaction parameters, heat of mixing, viscosity and diffusion rate were discussed thoroughly.

Novel PVDF-HFP flat sheet membranes prepared by triethyl phosphate (TEP) solvent for direct contact membrane distillation

Poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP) flat sheet membranes were prepared for aqueous membrane distillation (MD) applications using triethyl phosphate (TEP) as less-toxic solvent via phase inversion. PVDF-HFP concentrations of 10, 12 and 15wt.% were investigated and it was observed that different polymer concentrations led to membranes with different surface structure and performance; the use of different coagulation bath compositions played a key role in the membrane fabrication and affected the performance in membrane distillation. The results showed that the permeation decreased sharply when the polymer concentration increased from 12 to 15wt.%. By adding isopropanol as non-solvent to coagulation medium led to interesting results in terms of permeation. However, the use of lithium chloride to the casting solution had also a positive impact on membrane characteristics in price of retrograde membrane mechanical properties. Particularly interesting was the membrane produced from solution containing the 12wt.% polymer and coagulated in the isopropanol–water mixture, which gave a DCMD permeation of 16.1kgh−1m−2 at feed temperature of 60°C, and a salt rejection of 99.3%.

PREPARATION AND CHARACTERIZATION OF NANO-POROUS POLYACRYLONITRILE (PAN) MEMBRANES WITH HYDROPHILIC SURFACE

Polyacrylonitrile (PAN) membranes with nano-porous surface and high hydrophilicity were fabricated by addition of polyoxyethylene (40) nonylphenyl ether (IGEPAL) as an additive in the casting solution. The membranes were prepared from PAN/IGEPAL/1-Methyl-2pyrrolidone (NMP) via phase inversion induced by immersion precipitation technique. Pure water was used as coagulation medium. The effects of adding IGEPAL and the PAN concentration on the morphology, wettability, and permeability of the prepared membranes were studied. The morphological studies were investigated by scanning electron microscopy (SEM) and atomic force microscopy (AFM). In addition, the wettability and permeability of membranes were examined by contact angel measurements and permeation experiments. The contact angle measurements indicate that the hydrophilicities of membrane enhanced by the addition of IGEPAL surfactant and decreasing the PAN concentration in the casting solution. According to SEM and AFM analysis, it was found that the addition of IGEPAL and change concentration of polymer have a significant influence on structure of the membrane top surface and the sub-layer. In addition, it was found that decreasing the PAN concentration and addition of IGEPAL resulted in the formation of membranes with high permeability.

Control of Membrane Surface Roughness and Pattern Wave Length by Changing the Nonsolvent (Water) Influx Rate

The control of surface roughness of polyvinylidene fluoride (PVDF), polyethersulfone (PES), polysulfone (PS) and cellulose (CE) membranes was attempted by changing the rate of nonsolvent influx in the phase inversion process. PVDF and CE were chosen to represent membranes of high hydrophobicity and hydrophilicity, respectively, while PES and PS were chosen to represent membranes of intermediate hydrophobicity/-philicity. The concentration of sodium chloride (NaCl) in the aqueous coagulation medium was increased from 0 to 1.9 mol/L to decrease the rate of nonsolvent (water) influx in the solvent/nonsolvent exchange process. As well, the effect of polymer concentration and solvent on the surface roughness was investigated with respect to PVDF and PES. It was observed that the membrane surface roughness increased and decreased, respectively, for the hydrophobic PVDF and hydrophilic CE membrane as the rate of nonsolvent influx was decreased. For the PES and PS membranes of intermediate hydrophilic/-philicity, no significant roughness change was observed. The surface roughness tended to increase as the solution viscosity decreased. It was also observed that the pattern wave length of the hydrophobic membrane did not change significantly while that of the hydrophilic membrane increased significantly as the solvent influx rate was reduced. This trend is predictable by considering the shrinking or swelling of the cast polymer solution during the solvent/nonsolvent exchange process.

Influence of the coagulation medium on the performance of poly(ether sulfone) flat‐sheet membranes

ABSTRACTPoly(ether sulfone) flat‐sheet membranes were fabricated via phase inversion with different nonsolvent mixtures. The effect of the nonsolvent water with the addition of various amounts of ethanol, acetone, or isopropyl alcohol on the membrane morphology (as measured with scanning electron microscopy and atomic force microscopy) and the filtration performance were investigated. For the statistical evaluation of the fabrication process, on average, six membranes were produced. The pure water flux (PWF) and macromolecule retention were determined via filtration experiments. The presence of coagulation additives resulted in modified precipitation kinetics and thermodynamics, yielded different membrane structures, and therefore, influenced the performance. The results show that the addition of ethanol, acetone, and isopropyl alcohol in low concentrations (up to 10%) to water led to an increasing PWF. Higher concentrations led to a decrease in PWF. For high concentrations (>30%), a change in the membrane morphology from fingerlike to spongelike structures was expected, and this was experimentally proven for the case of ethanol. One main finding was the similarity of the influence of the used additives on the membrane performance. This was to be expected from Flory–Huggins theory for additives with high water miscibility; hence, under these circumstances, entropic and not energetic reasoning dominated the phase‐inversion process. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41645.

Structural elucidation of morphology and performance of the PVDF/PEG membrane

Poly(vinylidene fluoride) (PVDF) membranes were prepared through a phase inversion method, using N, N-dimethylacetamide (DMAc) as solvent, poly ethylene glycol (PEG) as hydrophilic additive and water as the coagulation medium. The ternary phase diagram of the PVDF/DMAc/water system at two different bath temperatures of 25 °C and 60 °C was derived through cloud-point measurements. Besides, the effect of PEG inclusion into PVDF solution was investigated in a ternary phase diagram. The results showed that both parameters of coagulation bath temperature and the PEG content affect the system thermodynamic stability. The morphology investigation of the prepared membranes was carried out by SEM cross-section images. The most regular structure of the membrane was obtained by incorporation of 5 wt.% PEG at 60 °C bath temperature. The AFM analysis also showed the favorable effect of the PEG on membrane surface roughness. The polymorphism study of the membrane crystal forms was carried out by FTIR analysis. The study showed that the higher bath temperature and PEG inclusion disfavored the formation of β crystal, which may be attributed to lower thermodynamic stability of the β crystal. The water flux measurements were carried out using dead-end filtration procedure. The membrane flux and total membrane porosity were increased as the PEG content increased, mainly due to the pore forming effect of PEG additive.

Novel materials for moist wound management: Alginate-psyllium hybrid fibres

To assess the feasibility of producing high absorbing, high gelling hybrid fibres made from alginate and psyllium. Three methods of psyllium extraction were attempted: the hot, cold and hydrolysed method. The extracted psyllium was sieved before addition to the alginate dope. To assess feasibility, each dope was in turn extruded on a bench-top extruder and then on a pilot-size wet extruder. Calcium chloride solution was used as the coagulation medium for all the extrusions. The produced fibres were subsequently assessed for their linear density, tensile strength, absorption characteristics and swelling behaviour. Optical microscopy was also used to illustrate hybrid fibre swelling behaviour under different conditions This feasibility study has shown that hybrid fibres can be produced when using different methods of psyllium extraction, proving the feasibility of the proposed methodology. However, based on physical and functional assessment of the fibres, it was found that the cold water extraction method leads to better hybrid fibres with superior tensile properties, liquid absorption and swelling, which would render them most suitable for heavily exudating wounds. The cold water route is found to be the most effective way of producing polysaccharide-based hybrid fibres. This method is also the least expensive, both in terms of room temperature preparations and functional effectiveness, using only 0.75% psyllium. This fibre is therefore recommended for wound dressing applications. There were no external sources of funding for this study. The authors have no conflicts of interest to declare.

Antimicrobial m-Aramid/Cellulose Blend Membranes for Water Disinfection

An m-aramid/cellulose blend membrane for nonpressure driven filtration was prepared. The m-aramid/cellulose solution in DMAc/LiCl was thin layered on a glass plate and then dipped into a coagulation medium. Scanning electron microscopy was used to examine the morphology of the m-aramid/cellulose blend membranes. The liquid permeability of the m-aramid/cellulose blend membranes was determined using capillary flow porometry. LiCl in a water/DMAc coagulation medium resulted in an enhancement of the average pore size of the m-aramid/cellulose blend membranes during coagulation. The chlorinated m-aramid/cellulose membrane disinfected bacterial solutions of both Escherichia coli and Staphylococcus aureus to a much higher degree than that observed for the unchlorinated m-aramid/cellulose membrane.

Performance of PSf Ultrafiltration Membrane: Effect of Different Nonsolvent on Coagulation Medium

One of the big challenges in developing a good asymmetric membrane is macrovoid formation that leads to reduction of rejection value. The most common method to reduce or suppress macrovoid formation is by addition of controlled solvent to the coagulation bath. Therefore, the effect of difference coagulants based on dissolved KCl (monovalent) and dissolved Na2SO4(divalent) with different concentration onto asymmetric Polysulfone (PSf) ultrafiltration membrane was investigated in this work. The PSf ultrafiltration membranes were prepared by using phase inversion method using these two immerse aqueous solutions. The performances of membranes were evaluated via pure water flux (distilled water) and solute rejection (humic acid). Results on the cross section revealed that the structure of membrane show a straight pattern of bigger finger-like pore structure from top to bottom layer tend to reduce with at the same time the diameter of finger-like pore structure also increased, as salt medium of coagulant increases. These obviously shown by permeation values for both salt mediums were higher compared to without salt coagulant. This reduction of finger-like structure at bottom layer occurred along together with the formation of sponge shape structure. The growth of thick sponge shape is strongly influence by kinetic phase inversion of salt coagulant that also creates resistance to permeation mechanism. However the intense salt coagulant medium can cause the bigger sponge structure that will slightly reduce rejection and increase the permeation. This was proved by the rejection of KCl medium started to increase at 1-3% but slightly reduced at 4%. Based on the result analysis demonstrated that the ideal membrane with highest rejection and good permeation values was membrane immersed into 1% Na2SO4 coagulation medium.

Influence of water on swelling and dissolution of cellulose in 1-ethyl-3-methylimidazolium acetate

In this study the effect of residual coagulation medium (water) on cellulose dissolution in an ionic liquid is discussed. Solubility of dissolving grade pulp; HWP and SWP, and microcrystalline cellulose in binary solvents, mixtures of 1-ethyl-3-methyl-imidazolium acetate and water, was investigated by turbidity measurements, light microscopy, rheometry, and CP/MAS 13C-NMR spectroscopy. The viscoelastic properties of the cellulose solutions imply that residual water affect the cellulose dissolution. However, it is not obvious that this always necessarily poses serious drawbacks for the solution properties or that the effects are as severe as previously believed. Turbidity measurements, viscosity data and crystallinity of the regenerated cellulose correlated well and an increased conversion to cellulose II was found at low water and cellulose contents with an apparent maximum of conversion at 2–5wt% water. At high water content, above 10wt%, dissolution and conversion was largely inhibited.