Porosimetrie gequollener makroretikularer Ionenaustauscher

The relative micro and macro pore volumes and the macro pore size distribution were used to characterize the pore structure of ion exchangers. The evaluation of these from density measurements and mercury penetration measurements was described for a sulphonated macro reticular ion exchange resin in the swollen state with different contents of swelling agent. On taking up water the dry volume of the exchange resin increased (swelling) until a water content of about 33 wt.-% was reached. Additional water filled up the macro pores to a final content of 58 wt.-%. With the specific volume of the exchange resin in the swollen state in addition to the specific volume of the gel phase, the relative macro pore volume of the fully swollen state was evaluated. The results of the mercury penetration method agreed with those of the density measurements taking into account the compressibility of the mercury itself and those of the swelling agent and the matrix. Corresponding correction factors could be evaluated from measurements on micro reticular ion exchange resins. The mercury penetration measurements provided additional information on the macro pore size distribution of the swollen state. For the examined ion exchange resins a logarithmic standard distribution with an arithmetically weighed mean pore radius of about 1 100 Å was evaluated. The relative over-all pore volume of 0,65 was not identical with the value of 0,61 for the partition coefficient of ethylene glycol from dilute aqueous solutions, as only that part of the water, which is bound to the sulphonic groups (hydrated water), could be exchanged by ethylene glycol. Pure ethylene glycol substituted the hydrated water completely. The specific volume of the exchange resin thereby decreased in comparison to that of the water-swollen state.     

Comparison of rigid divinylbenzene with flexible 1,7‐octadiene crosslinks in acrylic acid resins—effects on kinetics of swelling and loading of heavy metal ions from water

Acrylic acid–1,7‐octadiene resin was synthesized in beaded form by a two‐step process: suspension polymerization of ethylacrylate and 1,7‐octadiene monomers, followed by hydrolysis using either 98% H₂SO₄ or 10 M NaOH. Acrylic acid–divinylbenzene resins were also synthesized by the same process for the purpose of comparing a rigid divinylbenzene with a flexible 1,7‐octadiene crosslinkage in the acrylic acid resins. Swelling of the resins in distilled water shows that replacing divinylbenzenes with 1,7‐octadiene makes the resin achieve greater swelling in a significantly shorter time. 1,7‐Octadiene also allowed for an increase in crosslinkage to 20% compared to 4% in the case of divinylbenzene, without compromising the loading rates of toxic heavy metal ions like Pb²⁺, Cu²⁺, and Cr³⁺ from water samples. The acrylic acid–1,7‐octadine resin was found useful for removal of the toxic heavy metal ions from wastewater samples. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41038.     

Synthesis of epoxy resins from alcohol‐liquefied wood and the mechanical properties of the cured resins

New wood‐based epoxy resins were synthesized from alcohol‐liquefied wood. Wood was first liquefied by the reaction with polyethylene glycol and glycerin. The alcohol‐liquefied wood with plenty of hydroxyl groups were precursors for synthesizing the wood‐based epoxy resins. Namely, the alcoholic OH groups of the liquefied wood reacted with epichlorohydrin under alkali condition with a phase transfer catalyst, so that the epoxy groups were put in the liquefied wood. The wood‐based epoxy resins and the alcohol‐based epoxy resins as reference materials were cured with polyamide amine. The glass transition temperature (Tg), the tensile strength, and the modulus of elasticity of the wood‐based epoxy resin were higher than those of the alcohol‐based epoxy resin. Also, the shear adhesive strength of the wood‐based epoxy resin to steel plates was higher than those of the alcohol‐based epoxy resins, which was equivalent to the level of petroleum‐based bisphenol‐A type epoxy resins. The higher Tg of the wood‐based epoxy resin than that of the alcohol‐based epoxy resin is one of the evidences that the wood‐derived molecules were chemically incorporated into the network structures. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Rheometry of aging of colloidal melamine–urea–formaldehyde polycondensates

Aged and whitened melamine–urea–formaldehyde (MUF) resins in a colloidal state were tested with parallel‐plate rheometry to determine the extent of their viscoelastic behavior. Only in advanced colloidal states, and so only when aggregated colloidal clusters occurred, did the resins present clear indications of viscoelastic responses, as illustrated by the crossover of elastic modulus and viscous modulus curves at lower strain percentages. These colloidal clusters were labile microstructures, which, broken by applied shear, justified the known thixotropic behavior of these resins sufficiently advanced by aging or other means. MUF resins already in the colloidal state, but for which colloidal clustering had not yet occurred, behaved exclusively as viscous liquids. Two different cases of physical gelation were observed, reversible physical gelation and irreversible physical gelation, underlying which a true gel situation possibly occurred. Physical gelation due to colloidal superstructures occurred in both, but the difference in the resin average molecular masses revealed if the physical gelation was reversible or irreversible and, therefore, if the liquid/cluster separation was defined as the terminal phase of physical gelation. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 655–659, 2005     

Physicochemical characterization of hydrogels based on polyvinyl alcohol–vinyl acetate blends

Hydrogels made of polyvinyl alcohol–vinyl acetate and its blends with water soluble polymer were studied in terms of swelling behavior, microstructure, and dynamic mechanical properties. Hydrogels prepared by blending polyvinyl alcohol–vinyl acetate with either polyacrylic acid or poly(4‐vinyl pyridine) exhibited a strong pH dependency. When poly(vinyl pyrrolidone) was used for blending, an unusual pH dependency was observed. An increase in the equilibrium water content in all systems resulted in an increase in the freezable water as determined by DSC. Critical point drying led to a striated surface on polyacrylic acid–polyvinyl alcohol–vinyl acetate hydrogels, whereas a porous structure was observed on the freeze‐dried poly(vinyl pyrrolidone)–polyvinyl alcohol–vinyl acetate gels. Hydrogels with elevated storage modulus were obtained when either polyvinyl alcohol–vinyl acetate alone or polyacrylic acid–polyvinyl alcohol–vinyl acetate blends were thermally treated at high temperatures (i.e., 150°C). Low storage modulus was observed for both poly(vinyl pyrrolidone) and poly(4‐vinyl pyridine)‐containing hydrogels. Temperature dependency of storage modulus from 20 to 60°C was observed only for poly(4‐vinyl pyridine)–polyvinyl alcohol–vinyl acetate hydrogels. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 3578–3590, 2001     

Delamination mechanism of high‐voltage coil insulators made from mica flakes and thermosetting epoxy resin

To clarify the delamination mechanism of high‐voltage coil insulators made from mica flakes and epoxy resin due to static mechanical stress, the relationships between the shear strength of the insulator and the physical properties of the component materials were studied. The mechanism of their delamination was thought to be either a lack of epoxy resin between the mica flakes, interface failure between the mica flakes and the epoxy resin, or cleavage of the mica flakes. The first two mechanisms were discounted because the shear strength of the insulator was found to be independent of both the contact angle of the corresponding liquid epoxy resin on the mica flakes and the critical surface tension of the epoxy resin. Furthermore, the shear strength of the model insulator was improved by using an epoxy resin with a higher bending elastic modulus, implying that the delamination mechanism in this system is the cleavage of mica flakes. Therefore, the epoxy resin should have a high elastic modulus to ensure high delamination resistance, that is, the temperature to which the insulators are exposed should be lower than the glass transition temperature of the corresponding epoxy resin. Optical microscope studies also supported these results. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 2164–2169, 2001     

Curing of epoxy resin contaminated with water

Epoxy resins used for reinforcement of bridges and buildings are explored in the light of both curing rates and mechanical properties when resins are contaminated with water in outdoor construction. The developed resin is composed of a conventional resin of bisphenol A diglycidyl ether and a hardener with a polyoxipropyldiamine base. Curing rates were obtained by time variation of the near infrared absorbance of amine groups in the hardener at various water contents. They obeyed the second‐order reaction law with respect to the hardener, of which the activation energy was 70 kJ mol⁻¹. Water increased the reaction rate. Mechanical properties such as ultimate tensile strength, adhesive shear stress, and flexural strength were measured at various water contents for the developed epoxy resin and the commercially available low‐temperature epoxy resin. The developed cured resin shows not only higher mechanical strengths but also much less deterioration by water than the conventional cured resin. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 214–220, 2001     

High strength thermoresponsive semi‐IPN hydrogels reinforced with nanoclays

Two series of nanoclay reinforced, thermoresponsive hydrogels were prepared, one based on poly(N‐isopropylacrylamide) (PNIPA) and the other on semi‐interpenetrating networks containing PNIPA and poly(N‐vinyl pyrrolidone) (PVP), designated as SIPNs. The gels were crosslinked with 1, 3, and 5 wt % inorganic clay (hectorite) and SIPN gels additionally contained 1 wt % of PVP. The hydrogels were tested in the “as‐prepared state,” i.e., at 10 wt % PNIPA concentration in water and at equilibrium (maximum) swelling. Increasing the concentration of nanoclays increases crosslink density, modulus, tensile strength, elongation (except in equilibrium swollen gels), hysteresis and with decreases in the degree of swelling, broadening of the phase transition region, and a decrease in elastic recovery at high deformations. The presence of linear PVP in the networks increases porosity and the pore size, increases swelling, deswelling rates, and hysteresis, but decreases slightly lower critical solution temperature (LCST), tensile strength, elongation, and elastic recovery. The strongest hydrogels were ones with 10 wt % PNIPA and 5 wt % of nanoclays, displaying tensile strengths of 85 kPa and elongation of 955%. All properties of hydrogels at the equilibrium swollen state are lower than in the as‐prepared state, due to the lower concentration of chains per unit volume, but the trends are preserved. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Urea–formaldehyde–propionaldehyde physical gelation resins for improved swelling in water

Urea–formaldehyde (UF) resins' water tolerance and swelling thickness of interior‐grade wood panels bonded with UF resins were improved markedly by introducing small amounts of UFPropanal (UFP) polycondensates into the UF resin. ¹³C NMR of urea–propanal (UP) resins showed that urea and propanal do react up to the formation of dimers. The water repellancy imparted by insertion in the resin of the alkyl chain of propanal limits the proportion of propanal that can be used. Gel permeation chromatography showed that this appears to be so because UP resins and UFP resins exist as an equilibrium between two separate intermingling phases, namely one in solution and the second in a state of physical gelation. This latter is different from the state of physical gelation observed on ageing or advancement of formaldehyde‐only based polycondensation resins. This physical gelation is brought on by the insertion in the resin of the water repellant chain of the propanal reacted with urea and constitutes a new state of physical gelation of polycondensates other than what was already reported in the literature. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 5131–5136, 2006     

Microstructure dependent diffusion of water-ethanol in swollen poly(vinyl alcohol): A molecular dynamics simulation study

Molecular dynamics (MD) simulation was used to study the swelling properties of poly(vinyl alcohol) (PVA) in ethanol solutions containing 15, 30 and 45 wt% water. The characteristics of the swollen PVA, intrinsic relation between the microstructure of the swollen PVA and the diffusion of water and ethanol in the PVA matrix were analyzed. It was found that the free volume of the swollen PVA reduced with reductions in the degree of crystallinity was accompanied by an increase in the mobility of PVA chains. Water located mostly in the hydrophilic region of the hydroxyl groups of PVA chains; and hydrogen bonding formed between water and PVA. It was also noted water clusters form in the swollen PVA, whose size increased with increasing degree of swelling, whereas ethanol molecules disperse almost individually in the PVA matrix. The diffusion coefficients of water and ethanol in the swollen PVA are predicted to increase linearly with increasing swelling.     

Swelling and elasticity of poly (N‐isopropylacrylamide‐co‐4‐vinyl benzene sulfonic acid sodium salt) hydrogels

The mechanical properties and the swelling behavior of hydrogels based on N‐isopropylacrylamide (NIPA) and 4‐vinylbenzenesulfonic acid sodium salt (styrene sulfonate, SSA) monomers were investigated. The mole fraction of SSA in the comonomer feed varied between 0 and 1, whereas the crosslinker ratio was fixed at 1/85. Both the swelling and the elasticity data of the hydrogels swollen in water show that they are in the non‐Gaussian regime. The exponents found for the charge density dependence of the equilibrium swelling ratio as well as for the volume dependence of the gel elastic modulus are in good agreement with the predicted course of the non‐Gaussian elasticity of swollen hydrogels. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 135–141, 2004     

Water‐swellable hydrophobic porous copolymer resins based on divinylbenzene and acrylonitrile. I. Water‐swelling behavior

Hydrophobic porous copolymer resins based on divinylbenzene (DVB) and acrylonitrile (AN) could be prepared as directly swellable in water by using purified DVB (98.8%) and technical DVB (79.3%) in the presence of 1,2‐dichloroethane as porogen. Compared with the resins based on DVB and methyl acrylate (MA/DVB resins), the AN/DVB resins thus obtained are water‐swellable over a wider range of copolymer compositions, and the swelling ability of the AN/DVB resins in water was further confirmed by investigating the water‐swelling behavior of the AN/DVB resins undergoing solvent treatment. The copolymer composition (AN and DVB contents) of the resins and the property of the porogen affect the water‐swellable behavior of the AN/DVB resins profoundly. The results in this paper provide additional evidence to support the hypothesis that the swelling ability of a hydrophobic porous copolymer in water originates from the existence of the inner stresses in the strained polymer network of the resins and the weak interaction between polymer and water that is negligible in the case of a conventional hydrophobic polymer. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 2041–2049, 2004     

Water‐swellable hydrophobic porous copolymer resins based on divinylbenzene and acrylonitrile. II. Pore structure and adsorption behavior

By using purified divinylbenzene (DVB, 98.8%) or technical DVB (79.3%), the hydrophobic, but water‐wettable or swellable porous copolymer resins based on DVB and acrylonitrile (AN) could be prepared with a wide range of pore structures under certain conditions. The specific surface area for the resulting AN/DVB resin, with an AN/DVB ratio of 40/60 (by mole), could reach a value of 704 m²/g, while such a resin is still water wettable or swellable by direct contact with water. The adsorption behavior of the AN/DVB resins was investigated by focusing on the comparison between the resins with and without prewetting, using caffeine and phenol as model adsorbates. Adsorption behavior of the AN/DVB resins, without prewetting, correlates well with the wetting ability of the resins in water, suggesting that a well water‐wettable hydrophobic porous AN/DVB resin could be directly applied, in a dry state, to the adsorption in an aqueous medium, almost without diminishing the ability of the resin to adsorb the solutes. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 2050–2056, 2004     

Comparative study of the recovery of silver(I) from aqueous solutions with different chelating resins derived from glycidyl methacrylate

Glycidyl methacrylate (GMA) was polymerized in the presence of divinylbenzene (DVB). The GMA/DVB resin was immobilized with different chelating moieties containing nitrogen or sulfur donor atoms. The resins obtained [an amino‐bearing resin (RI), an amino/thiocarbamate‐bearing resin (RII), a triazole‐bearing resin (RIII), and an amino/thiol‐bearing resin (RIV)] were tested toward the recovery of Ag(I) from its aqueous solutions. The adsorption behavior of Ag(I) and the resin regeneration were studied. The sulfur‐containing resins showed higher uptake and lower elution efficiency than those containing nitrogen. The maximum uptake values were 1.20, 1.33, 1.40, and 2.86 mmol/g for RI, RII, RIII, and RIV, respectively. The mechanism of interaction between Ag(I) and the resins is also suggested. Regeneration was achieved with a 0.5N thiourea solution, acidified thiourea, or 0.5N H₂SO₄, where the resins were stable over five cycles. Elution efficiencies of 94–96 and 90–93% were achieved for the nitrogen‐ and sulfur‐containing resins, respectively. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 806–812, 2005     

Parametric studies on the synthesis of amidoximated adsorbent resins

The main goal of this study was to obtain acrylonitrile (AN)‐divinylbenzene (DVB) copolymer beads that can serve as the matrix for preparation of amidoxime resins. AN‐DVB amidoxime resin was synthesized via suspension polymerization and the effect of different parameters such as the speed of stirrer, the amounts of suspending agent, hydrophilic agent, diluent agent, and initiator on its properties was investigated by fractional factorial (Taguchi) experimental design method. This method gives much‐reduced variance for the experiments with optimum control parameters setting and provides a set of minimum experiments compared to the conventional methods. The results showed that the most effective parameters on the amidoximation of resins were hydrophilic agent content, speed of stirrer, and the amount of suspending agent, respectively. Furthermore, anion‐exchange capacity of the amidoxime resins was utilized as a criterion for the evaluation of amidoxime adsorbent groups and the adsorption potential of the synthesized resins was determined by cation‐exchange capacity. The amount of methylacrylate as a hydrophilic agent had the most significant effect on the ion‐exchange capacity of the final product. Swelling ratio was also measured to evaluate the adsorption capacity of the synthesized resin. The results showed that the amounts of hydrophilic and diluent agents had significant effects on swelling ratio of resin. Finally, cation‐exchange capacity and swelling ratio of amidoxime resin were changed greatly because of alkaline treatment, but it had no significant effect on the anion‐exchange capacity of the synthesized resin. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Formulation design,optimization, characterization and swelling behaviour of a cationic superabsorbent based on a copolymer of [3‐(methacryloylamino)propyl]trimethylammonium chloride and acrylamide

A series of crosslinked copolymers with cationic nature have been prepared based on acrylamide (AAm) and [3‐(methacryloylamino)propyl]trimethyl ammonium chloride (MAPTAC) using N,N′ methylene‐bis‐acrylamide (MBA) as crosslinking agent. Taguchi's method has been employed for the purpose of formulation design and optimization as well as investigating the effects of various compositional parameters, such as total monomer concentration, cationic monomer and crosslinking agent concentration. The swelling behaviour of the synthesized gels in electrolyte solutions composed of ions with different valency has been studied and compared with an anionic‐based superabsorbent. The swelling capacity and absorbency were found to be enhanced with increase of the MAPTAC moieties of the copolymer chains, and therefore increase of their cationic character. All the cationic hydrogels prepared had greater swelling capacity, with less change in their swelling behaviour, when immersed into aqueous solutions containing multivalent cations. The anionic‐based hydrogels collapsed in similar ionic solutions with moderate‐to‐high ionic strength and did not show any tendency to re‐swell. The complex modulus (G*) of the crosslinked copolymers in the equilibrium swollen state was measured by rheomechanical spectroscopy and was correlated with the chemical composition of the network. Thermogravimetric analysis of the dry cationic superabsorbent showed more bound water but similar thermal behaviour to crosslinked polyacrylamide Copyright © 2003 Society of Chemical Industry     

Production of microporous resins for heavy‐metal removal. II. Functionalized polymers

Ion‐exchange polymers were used successfully in water‐treatment operations. In this study, three ion‐exchange resins based on 4‐vinylpyridine and divinylbenzene functionalized with N‐oxide groups were obtained. Their ion‐adsorption properties were measured in solutions containing chromium at concentrations of 4 and 500 ppm with column and batch equilibrium techniques. The removal efficiency of the chromium ions with HCl was observed to increase after the protonation of the N‐oxide groups. The resins could be reused after 10 cycles with the metal removal efficiency maintained at higher than 95%. These studies evidenced a strong correlation between the morphology and ionic group content in the resin and its chromium ion sorption capability. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

A novel method to prepare magnetic polymer‐based anion exchangers and their application

Magnetic microspheres with ion‐exchange features were prepared by applying a swelling and penetration process using polystyrene–divinylbenzene‐based anion‐exchange resins as starting materials. The polymeric anion‐exchange particles were swollen with an aqueous solution of N‐methyl‐2‐pyrrolidone, followed by incubation with superparamagnetic iron oxide nanoparticles to allow them to penetrate into the swollen particles. The pH value in the solution of magnetic nanoparticles could significantly influence the uptake of magnetic nanoparticles by the swollen anion‐exchange particles. Higher amounts of magnetic nanoparticles entrapped within anion exchangers could be achieved at pH 10–12. An increase in the concentration of magnetic nanoparticles led to a higher density of magnetic nanoparticles entrapped within the interior of anion exchangers and, thus, higher magnetization of the magnetic anion exchangers. Loading of the magnetic nanoparticles onto the exchanger had no effect on anion‐exchange functionality. The utility of the resulting magnetic anion‐exchange resins was demonstrated for the isolation of plasmid pEGFP‐C1 from Escherichia coli cell lysates. The magnetic anion‐exchange microspheres could be easily collected within a few seconds in a magnetic field. Thus, automation of the protocol for DNA isolation using these magnetic anion‐exchange resins has a high potential. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40725.     

Surface modification of polyethylene by radiation-induced grafting for adhesive bonding. IV Improvement in wet peel strength

Adhesive joints of hydrolyzed methyl acrylate grafts, bonded with epoxy adhesives, yield extremely high peel strength (adherend failure) in dry conditions. However, when the joints are exposed to humid environments, the peel strenght rapidly decreases with exposure time and then reaches a constant value (wet peel strength). Since the locus of failure changes from the adherend to the homopolymer layer with decreasing peel strength, the decrease is due to a decrease in mechanical strength of the homopolymer layer itself, which results from its swelling by water absorption. Many attempts to reduce the swelling of the homopolymer layer or to strengthen the swollen homopolymer layer were unsuccessful except (1) priming with epoxy solutions consisting of a base epoxy resin and organic solvents which can dissolve not only epoxy resins but also hydrolyzed poly(methyl acrylate) and (2) partial etching of the homopolymer layer by photo-oxidative degradation. All the results on the improvement in wet peel strength can be explained in terms of the penetration of epoxy resins into the homopolymer layer and subsequent curing of the penetrated epoxy resin.     

pH-responsive swelling behavior,elasticity and molecular characteristics of poly(<Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>-dimethylaminoethyl methacrylate) gels at various initial monomer concentrations

The equilibrium swelling degree and the modulus of elasticity of pH-responsive poly(N,N-dimethylaminoethyl methacrylate) (PDMAEMA) gels prepared at various initial monomer concentrations were investigated both in buffer solutions and in aqueous salt solutions. As pH of the solution is increased, PDMAEMA gels first remain in the swollen state up to pH 7.7, then exhibit pH-sensitive phase transitions at 8.0 in which PDMAEMA gels attain a collapsed state. The swelling kinetic measurements of PDMAEMA gels showed that pH sensitivity of PDMAEMA is quite stable and the swelling process is reproducible in accordance with pH changing. The swelling behavior of PDMAEMA gels was analyzed by Flory-Rehner theory and the results were combined by the results of compression measurements to calculate the molecular characteristics of gels. The resulting pH-responsive PDMAEMA gels were elastic and displayed good swelling behavior both in buffer solutions and in aqueous salt solutions, therefore, they can be used as a kind of carrying material in drug delivery systems.