Sterically-encumbered ionenes as hydroxide ion-conducting polymer membranes

Hydrogen/oxygen-based electrochemical energy conversion cells that operate under highly alkaline conditions deploy inexpensive electrocatalysts compared to their acidic counterparts. Solid polymer electrolyte (SPE) cells offer a reduced system footprint, and an additional reduction in capital cost. Alkaline membrane, SPE systems are attractive because they offer a synergistic combination of the two cost savings. Durable, hydroxide-conducting SPEs operating in highly caustic media are lacking because organic molecules and polymers, particularly their cationic derivatives, are inherently unstable to caustic conditions. This review focuses on an emerging class of alkaline SPE's, Ionenes: polymers that incorporate cations directly into the polymer backbone. The purpose of this opinion piece is to highlight the fact that fixed cationic charges may be incorporated into the polymeric backbone to provide membranes with high conductivity, mechanical strength, and stability, and to dispel the widely-held view that distancing a cationic group from the polymer backbone is a necessary requirement.     

Bacterial cellulose based flexible multifunctional nanocomposite sheets

Bacterial cellulose is an ideal material that is sustainable, biodegradable and inherently capable of functionalization. Hence this has been functionalized with a single component, Ni to exhibit multiple functionalities such as electrical conductivity, magnetic sensitivity as well as catalytic activity in both dried and hydrogel forms. A novel, simple ‘inverse chemical reduction’ technique has been developed to incorporate this component and make bacterial cellulose multifunctional. This technique mercerizes and opens the interfibrillar spaces which results in the formation of nanoparticles that lead to percolating paths for conduction. The flexible sheet becomes electrically conducting with just 20 vol% of nanoparticles in the composite as determined by thermogravimetry. The room temperature electrical conductance increases by about 7 orders of magnitude, 10^?6–10 S on changing the Ni-precursor solution concentration from 0.015 to 0.02 M, indicating this to be the critical concentration for conduction percolation. The composites are highly magnetic at room temperature with a maximum energy product of 140 J m^?3, comparable to some of the commercially available bonded oxide magnets. The hydrogel form of the nanocomposite is found to be catalytically active. The catalytic activity is retained even after leaving the nanocomposite hydrogel in water for 12 h in water.     

Rheology and rheokinetics of triethanolamine modified carboxymethyl hydroxyethyl cellulose

To meet requirements of fracturing fluid thickener, triethanolamine was used to modify carboxymethyl hydroxyethyl cellulose (CMHEC) to obtain product called T-CMHEC of high viscosity. Rheological properties of CMHEC and T-CMHEC solutions were investigated to compare its structure and rheological performance, including viscosity, flow curve, thixotropy, and viscoelasticity. Viscosities of CMHEC and T-CMHEC solutions are, respectively, 19.0 and 63.2?mPa?·?s for the same concentration of 0.3%. Viscosity of T-CMHEC solutions is 3.3 times of CMHEC ones. Besides, the thixotropy and viscoelasticity of T-CMHEC system are both getting stronger than before. In summary, the T-CMHEC system shows better rheological performance after modification. Crosslinking process of T-CMHEC system is investigated under steady shear under different conditions, containing shear rates, concentrations of crosslinking agent, concentrations of pH adjuster, and temperature. Viscosity curves changing with time are obtained during crosslinking process. Four-parameter crosslinking rheokinetics equation is suitable to fit the viscosity curves under different conditions. Study on crosslinking process of T-CMHEC solutions is helpful to deepen the understanding on gel formation, and provides a theoretical basis for its application.     

Blend membranes from cellulose/konjac glucomannan cuprammonium solution

The blend membranes were prepared from cellulose/konjac glucomannan (KGM) cuprammonium solution by coagulating with aqueous 10 wt% NaOH solution, 20°C and 40°C water, respectively. Miscibility, pore morphology, structure, water permeability and mechanical properties of the blend membranes were investigated. The complex forms of cellulose/KGM in the mixed solutions, the effect of various coagulants and the percent content of KGM (w_KGM) on the structure and properties of the blend membrane are discussed. SEM and mechanical relaxation analysis indicate that the blend membranes are miscible in the range of 0–30 wt% of w_KGM. When w_KGM was smaller than 20 wt%, the tensil strength of the blend membrane coagulated by alkali aqueous solution was enhanced, corresponding to homogeneous structure and small pore size. However, blend membranes having a larger pore size (366 nm by SEM) and water permeability (560 ml/m² h mmHg) were obtained by coagulating the cellulose/KGM (70:30) cuprammonium solution with 40°C water, where ca. 20% of KGM as pore former were removed from the membrane.     

Morphology and permeability of cellulose/chitin blend membranes

A series of biodegradable cellulose/chitin blend membranes were successfully prepared from blend solution of cellulose and chitin in 9.5 wt% NaOH/4.5 wt% thiourea aqueous solution coagulating with 5.0 wt% (NH₄)₂SO₄. The influence of chitin content on the morphology and structure of the membranes was studied by scanning electron microscopy, environmental scanning electron microscopy and wide-angle X-ray diffractometry, as well as Fourier transform infrared spectroscopy. Using double-cell method and solution depletion method, the permeability and partition coefficients of three model drugs (ceftazidine, cefazolin sodium, and thiourea) were determined in phosphate buffer solution to clarify the diffusion mechanism governing transport of solutes in these membranes. Diffusion coefficients were calculated from the permeability and partition coefficients in terms of Fick's law. The effects of the chitin content, pH, ionic strength, molecular size and temperature on the drug diffusion were also studied. Our results revealed that all of the membranes had a porous-like structure. The introduction of chitin exhibited great influence on the morphology and crystal structure of the blend membranes, resulting in a significant different permeability. For the first time, a dual diffusion mechanism with some hindrance of molecular diffusion via polymer obstruction was employed to explain the transport of drugs in the membranes.     

Characterization of magnetic membranes based on bacterial and man-made cellulose

Ferrites were synthetized in situ in two different neutral cellulose gels: a never-dried bacterial cellulose membrane and a never-dried cast film using N-methylmorpholine-N-oxide as solvent. X-ray diffraction, transmission electron microscope (TEM), vibrating sample magnetometry (VSM) and Mossbauer spectroscopy were used to characterize the resulting magnetic nanocomposites. TEM micrographs showed the presence of ferrites in two different shapes, acicular and equiaxial, respectively hydrated ferric oxides (FeOOH) and the spinel oxides: maghemite (gamma-Fe2O3) or magnetite (Fe3O4). Thin sections of bacterial cellulose showed these particles to be located along the cellulose microfibrils, which are assumed to provide a site for their nucleation. Room temperature magnetization curves showed all samples to be superparamagnetic     

Potentiometric ion- and bio-selective electrodes based on asymmetric cellulose acetate membranes

The potentiometric response properties of ammonium-, carbonate-, and proton-selective electrodes prepared by incorporating appropriate neutral carriers within novel asymmetric cellulose acetate membranes are reported. The membranes are formed by first casting a thin layer of cellulose triacetate without carrier, hydrolyzing one side of this film with base, and then on the other side casting a second layer of cellulose triacetate containing the membrane active components. The resulting asymmetric ion-selective membranes function equivalently, in terms of selectivity and response slopes, to non-asymmetric cellulose triacetate membranes and conventional poly(vinyl chloride)-based membranes. The hydrolyzed surface of the asymmetric membranes can be activated in aqueous solution with carbonyldiimidazole for the direct immobilization of proteins on the surface of the membranes, without loss in potentiometric ion-response. As an example, the immobilization of urease on the surfaces of ammonium- and carbonate-selective membranes yields potentiometric bio-selective urea-probes with desirable dynamic response properties.     

High-flux,porous and homogeneous PVDF/cellulose microfiltration membranes

Low hydrophilicity of membranes is probably the biggest concern in membrane filtration since it increases the costs for water treatment. Conversely, application of hydrophilic biopolymers (such as cellulose) is limited because of its complex and crystalline structure. Enabling the wide use of the most common biopolymer in nature is crucial to improve the performance of water treatment, especially in terms of membrane sustainability. Here, we study the effect of cellulose dissolution in the synthesis of homogeneous PVDF/cellulose membranes. Although only partial dissolution was achieved for studied samples, adding cellulose to the membranes greatly improved their water flux. Besides, the porous structure obtained after partial solvent removal indicates the water flux (and consequently the pore size) may be tailored according to the membrane production method. Therefore, the homogeneous cellulose microfiltration membranes studied here may have potential for water treatment considering their high-water flux and low complexity to produce.

     

Ultrafine fibrous cellulose membranes from electrospinning of cellulose acetate

Three solvents, that is, acetone, acetic acid, and dimethylacetamide (DMAc), with a range of solubility parameter δ, surface tension γ, viscosity η and boiling temperature were used to generate mixtures for electrospinning cellulose acetate (CA) (degree of substitution, DS = 2.45). Although none of these solvents alone enables continuous formation of fibers, mixing DMAc with either acetone or acetic acid produced suitable solvent systems. The 2:1 acetone:DMAc mixture is the most versatile mixture because it allows CA in the 12.5–20% concentration range to be continuously electrospun into fibrous membranes. These CA solutions have η between 1.2 and 10.2 poise and γ around 26 dyne/cm and produce smooth fibers with diameters from 100 nm to ～1 μm. Fiber sizes generally decrease with decreasing CA concentrations. The nature of the collectors affects the morphology as well as packing of fibers. Fibers collected on paper have more uniform sizes, smooth surfaces, and fewer defects, whereas fibers collected on water are more varied in size. Electrically conductive solid collectors, such as Al foil and water, favor more tightly packed and less porous membranes. Porous collectors, like paper and copper mesh, produce highly porous membranes. The pores in membranes collected on the Al foil and paper are much better interconnected in the planar directions than those in membranes collected on water. There is evidence that electrospinning induces order in the fibers. Deacetylation of CA membranes is more efficient and complete in NaOH/ethanol than in aqueous NaOH, producing DS values between 0.15 and 2.33 without altering fiber surfaces, packing, or organization. The fully regenerated cellulose membranes are similarly hydrophilic as commodity cellulose fibrous matrices but absorb nearly 10 times as much water. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2119–2129, 2002     

Antibacterial membranes based on chitosan and quaternary ammonium salts modified nanocrystalline cellulose

Etherification of nanocrystalline cellulose (NCC) with three kinds of quaternary ammonium salts epoxypropyltrimethylammonium chloride, N,N‐dimethyl‐N‐dodecyl‐N‐(1,2‐epoxypropyl) ammonium chloride (DMDEPAC), and N,N‐dimethyl‐N‐octadecyl‐N‐(1,2‐epoxypropyl) ammonium chloride (DMOEPAC) was successfully performed via a nucleophilic addition reaction. The synthesized DMDEPAC and DMOEPAC were characterized by nuclear magnetic resonance. The modified NCC particles, NCC epoxypropyltrimethylammonium chloride, NCC‐DMDEPAC, and NCC‐DMOEPAC, were characterized by energy dispersive spectrometer. Nanocomposite films based on chitosan (CS) containing quaternary ammonium salts modified NCC were prepared with nanoparticle loadings of 5.0, 7.5, and 10.0%, respectively. The effect of nanoparticle content on the tensile strength of composite films was studied. The results indicated that the films with 5.0% nanoparticle loading exhibited the biggest increase in tensile strength. Surface morphology, smoothness, and antibacterial properties of composite films containing 5% modified NCC were also studied. CS/NCC‐DMDEPAC‐5.0 and CS/NCC‐DMOEPAC‐5.0 displayed excellent biocidal abilities against both Gram‐positive Staphylococcus aureus (ATCC 6538) and Gram‐negative Escherichia coli O157:H7 (ATCC 43895). The bio‐based nanocomposite films with increased mechanical strength and excellent antibacterial properties show great potential as food packaging materials. Copyright © 2017 John Wiley & Sons, Ltd.     

New biologically active arylchalcogenylacetates based on triethanolamine N-oxide

Russian Chemical Bulletin - New potentially pharmacologically active tris(2-hydroxyethyl)hydroxyammonium salts were synthesized by the reaction of triethanolamine N-oxide with biologically active...     

Cellulosic nanocomposite membranes from hydroxypropyl cellulose reinforced by cellulose nanocrystals

Cellulosic nanocomposite membranes were prepared by incorporation of cellulose nanocrystals (CNCs) into a hydroxypropyl cellulose (HPC) matrix using a mixing/evaporation technique. CNCs were obtained from filter paper using the sulfuric acid hydrolysis method with the aid of ultrasonication. The relationship between the microstructure and mechanical properties of the CNCs/HPC nanocomposite membranes was studied. Scanning electron microscopy showed that the CNCs were well dispersed in the HPC matrix, and the fracture surface demonstrated a fibrous characteristic. With increasing CNCs content, the tensile strength and Young’s modulus of the CNCs/HPC nanocomposite membranes gradually increased. At 5 wt% content of CNCs, the strength was increased by 525 % and the Young’s modulus by 124 % compared with pure HPC membrane. Moreover, the effect of the phase change of HPC on the mechanical properties of the CNCs_5wt%/HPC nanocomposite membranes and the corresponding mechanism were also studied.     

Bacterial cellulose/gelatin composites: in situ preparation and glutaraldehyde treatment

Bacterial cellulose (BC)/GEL composites were prepared in situ by adding gelatin into BC-producing culture medium. The addition of gelatin interfered with the formation of the BC pellicle structure and thus made the BC yield and growth rate quite different from that of pure BC. Scanning electron microscope images showed that the width of cellulose ribbons became narrower than that of pure BC and the gelatin filled in the pores of BC to form a dense structure. The addition level of gelatin significantly influences the yield of BC/GEL composites. An optimum value of 0.5 wt/v% gelatin was attained, with which the highest yield of 0.0541 g/100 mL was achieved. Under this condition, the weight percentage of gelatin in BC/GEL composite was 65 wt%. BC/GEL composites were treated with glutaraldehyde to crosslink BC fibrils and gelatin. The crosslinking degree, determined by the concentration of glutaraldehyde and crosslinking time, could affect the swelling behavior, thermal stability and mechanical properties of composites. With increasing of the crosslinking degree, the crystallinity index and swelling behavior of the composites decreased. The increase in the crosslinking degree also descreased the composite’s strain at break in elongation but increased the compressive and tensile strength. Covalent bonding between BC and gelatin provides good strength retention to the glutaraldehyde-treated composites with a high crosslinking degree. Considering the cytocompatibility and properties of composites, the most appropriate concentration of glutaraldehyde and crosslinking time were 1.0 wt/v% and 24 h, respectively.     

Flexible ion-conducting membranes with 3D continuous nanohybrid networks for high-performance solid-state metallic lithium batteries

Polyethylene oxide(PEO)-based electrolytes are considered as one of the most promising solid-state electrolytes for next-generation lithium batteries with high safety and energy density; however, the drawbacks such as insufficient ion conductance, mechanical strength and electrochemical stability hinder their applications in metallic lithium batteries. To enhance their overall properties, flexible and thin composite polymer electrolyte(CPE) membranes with 3D continuous aramid nanofiber(ANF)–Li     

Structure and properties of the regenerated cellulose membranes prepared from cellulose carbamate in NaOH/ZnO aqueous solution

Regenerated cellulose (RC) membranes were prepared from cellulose carbamate—NaOH/ZnO aqueous solutions by coagulating with H₂SO₄ solution. Structure, morphology and properties of the membranes were investigated by using scanning electron micrograph (SEM), X-ray diffraction, Fourier transform infrared spectroscopy, flow rate method, and tensile testing. The results from SEM and water permeability revealed that the pore size and water permeability of the membranes in wet state changed drastically as a function of the concentration of H₂SO₄ and coagulation temperature, whereas they hardly changed with the coagulation time. RC membranes coagulated with the relatively dilute H₂SO₄ solution at relatively low temperature exhibited better mechanical properties. This work provided a promising way to prepare cellulose membranes with different pore sizes and good physical properties.     

Modified cellulose acetate flat membranes for desalination

In this article, the radiation grafting of acrylamide on to cellulose acetate flat membranes using UV-irradiation on the initiator is described. The modified membranes thus obtained have been characterized by IR, DSC, and TGA. Their transport properties have been studied. The modified membranes exhibit higher salt rejection with slightly reduced water flux as compared with cellulose acetate membrane. The work is further extended to study the thermal stability of these modified membranes in a dry state. These modified membranes up to 330°C are stable.