Modeling of absorption kinetics of poly(acrylamide) hydrogels crosslinked by EGDMA and PEGDMAs

In this study, acrylamide-based hydrogels are synthesized by free radical solution polymerization in aqueous solution using ethylene glycol dimethacrylate (EGDMA) and its derivative polyethylene glycol dimethacrylate (PEGDMA) with different molecular weights as crosslinkers in the solution medium. The Fourier transform infrared spectroscopy technique is used for the structural characterization of the hydrogels. Dynamic swelling tests are conducted on acrylamide-based hydrogels for the determination of the swelling characteristics with respect to different crosslinking concentrations at room temperature. The parameters of swelling kinetics and diffusion mechanisms of the hydrogels are calculated with the aid of the data obtained. Accordingly, PEGDMA and EGDMA absorption capacity is found to increase with increasing concentrations. The lowest and highest water absorption capacities in PEGDMA₈₁₀ and EGDMA crosslinked hydrogels are 22.73–48.39 and 10.15–16.02 g/g, respectively. Water intake of hydrogels crosslinked by EGDMA and PEGDMAs followed Fickian nature type diffusion except for PEGDM₈₁₀, which has a swelling exponent greater than 0.5 and so does not follow a Fickian type of diffusion. PEGDM₈₁₀ showed the fastest diffusion rate of between 5.87 × 10^?4 and 10.87 × 10^?4 cm² s^?1.     

Preparation of composites and nanocomposites based on bentonite and poly(sodium acrylate). Effect of amount of bentonite on the swelling behaviour

A series of composite and nanocomposite hydrogels were synthesized by copolymerization reaction of partially neutralized acrylic acid (SA) on bentonite micropowder (BT) using N,N′-methylenebisacrylamide (MBA) as a crosslinker and potassium persulfate (I) as an initiator in aqueous solution. The influences of Na⁺-BT, organoBT (O-BT), and the content of the BT in the copolymeric gels on the swelling behaviour in deionized water and saline solution (0.2 wt.% NaCl_(aq)) were investigated. Results showed that the equilibrium swelling (W_∞) was decreased by adding a small amount of the BT, however, at higher BT contents, the W_∞ increased with the increase of the amount of clay. It was found that a concentration of 14 wt.% Na⁺-BT gave the best results absorption (955 g/g). Moreover, the amount of swelling for these absorbents in saline solution was smaller than that in deionized water. These hydrogels were characterized by X-ray diffraction and scanning electron microscopy. Finally, the thermogravimetric analysis indicated that introduction of clay to the polymer network resulted in an increase in thermal stability.     

New Bio-Based Furanic Materials Effectively Absorb Metals from Water and Exert Antimicrobial Activity

Development of sustainable bio-based materials for removal of toxic contaminants from water is a high priority goal. Novel bio-based binary and ternary copolymers with enhanced ion-exchange, adsorption and antibacterial properties were obtained by using plant biomass-derived diallyl esters of furandicarboxylic acid (FDCA) as crosslinking agents and easily available vinyl monomers. The synthesized copolymer materials showed higher sorption capacities for Ni^II, Co^II and Cu^II compared to the commercial ion-exchange resins, and they maintained their high metal adsorption capacities for over 10 cycles of regeneration. The synthesized copolymer gels containing 1–5 wt % of the crosslinker showed excellent water absorption capacities. The synthesized copolymers with 1 % crosslinker content showed swelling ratios high enough to also act as moisture absorbents. Synthesized copolymers with crosslinker content of 10 wt % performed as contact-active antibacterials by inhibiting the growth of Gram-positive (S. aureus) and Gram-negative bacteria (E. coli, K. pneumonia) in suspension tests.     

Gamma irradiation induced photochemical reactions in V-doped borate glasses

Glasses of the composition XNa₂O · 4Al₂O₃ (96-X) B₂O₃ (mole%) where X = 10, 20, 30 to which 0.03 g V₂O₅ per 100 g glass was added, were prepared by normal melting. Their absorption characteristics together with the corresponding V-free base glasses were determined before and after gamma irradiation. The characteristic spectra of the unirradiated glasses show absorption bands at 315, 470, 560–580, 610–650, 700–870, and 860–1000 nm, indicating the presence of vanadium ions in more than one oxidation state, viz, V⁵⁺, V⁴⁺, and V³⁺. Gamma irradation of V-containing glasses causes the formation of color centers in the glass matrices, with absorption bands at 330, 500, and 610 nm, and photoreduced [V³⁺] and [V²⁺] ions with absorption bands at 350–355 and 530–570 and 520 nm, respectively. Photoreduced [V⁴⁺] may also be formed, giving rise to absorptions at 690–700 and 750–800 nm. The induced vanadium ions are found to absorb at shorter wavelengths than the intrinsic ones. An explanation based on the difference in the field energy of the two states is given.     

Superabsorbent materials derived from hydroxyethyl cellulose and bentonite: Preparation,characterization and swelling capacities

Superabsorbent polymers (SAPs) and composites (SAPCs) were prepared entirely by graft copolymerization of polyacrylamide (PAM) onto hydroxyethyl cellulose (HEC), using potassium persulfate (KPS) as an initiator, and N,N′-methylenebisacrylamide (MBA) as a crosslinker, in an aqueous solution. The extent of grafting was evaluated from % grafting efficiency (%GE) for various HEC/AM ratios, and a near optimal ratio was determined. Influences of various preparation parameters, i.e., the ratio of HEC/AM, amount of initiator and crosslinker, reaction temperature and time, and amount of filler on water swelling capacity of SAPs and SAPCs were studied. An FT-IR determination confirmed that the PAM was successfully grafted onto the HEC backbone, by showing absorption bands of the HEC backbone and new absorption bands from the grafted copolymer. The swelling capacity of SAPs and SAPCs depended strongly on different parameters, and the maximum swelling capacity was over 426 g/g and 538 g/g for the SAPs and SAPCs, respectively.     

Synthesis and characterization of a novel copolymer of glyoxal dihydrazone and glyoxal dihydrazone bis(dithiocarbamate) and application in heavy metal ion removal from water

We demonstrate synthesis of water insoluble, novel copolymer P_A1 from condensation of glyoxal dihydrazone and glyoxal dihydrazone bis(dithiocarbamate) monomers having high capacity to remove metal ions from aqueous solution. The presence of a high atomic percentage of nitrogen and sulfur atoms in P_A1 leads to strong ligating ability with metal ions. The monomers and the polymer have been characterized by FTIR, UV–Visible spectroscopy, CHNS elemental analysis, NMR, MALDI-MS, and TG/DTA. As a proof of concept, the P_A1 is tested for its ability to remove heavy metal ions Cu²⁺, Co²⁺, Fe²⁺, Ni²⁺, Mn²⁺, and CrO ₇ ^2? from aqueous solutions. P_A1 efficiently removed metals ions from the metal solutions. The highest absorption ability has been observed toward the iron salts where 0.969 g metal salt is absorbed by 1 g polymer. This study has implication for inexpensive and efficient polymer for purification of water.     

Novel amphiphilic network polymers consisting of nonpolar,short primary polymer chains and polar,long crosslink units: Influence of characteristic dangling chains on swelling behavior of resulting amphiphilic gels

Novel amphiphilic network polymers consisting of nonpolar, short primary polymer chains and polar, long crosslink units were prepared, and the swelling behavior of resulting amphiphilic gels is discussed by focusing on the influence of characteristic dangling chains; that is, benzyl methacrylate (BzMA) was copolymerized with tricosaethylene glycol dimethacrylate [CH₂?C(CH₃)CO(OCH₂CH₂)₂₃OCOC(CH₃)?CH₂, PEGDMA‐23] in the presence of lauryl mercaptan as a chain‐transfer agent because BzMA forms nonpolar, short primary polymer chains and PEGDMA‐23 as a crosslinker contains a polar, long poly(oxyethylene) unit. The enhanced incorporation of dangling chains into the network polymer was brought by shortening the primary polymer chain length, and copolymerization with methoxytricosaethylene glycol methacrylate, a mono‐ene counterpart of PEGDMA‐23, enforced the incorporation of flexible dangling poly(oxyethylene) chains into the network polymer, although the former dangling chains as terminal parts of primary poly(BzMA) chains were rather rigid. Then, the influence of characteristic dangling chains on the swelling behavior of amphiphilic gels was examined in mixed solvents consisting of nonpolar t‐butylbenzene and polar methanol. The profiles of the solvent‐component dependencies of the swelling ratios were characteristic of amphiphilic gels. The introduction of dangling poly(oxyethylene) chains led not only to an increased swelling ratio but also to sharpened swelling behavior of amphiphilic gels. The swelling response of amphiphilic gels was checked by changing the external solvent polarity. The dangling chains with freely mobile end segments influenced the swelling response of gels. The amphiphilic gels with less entangled, collapsed crosslink units exhibited faster swelling response than the ones with more entangled, collapsed primary polymer chains. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2192–2201, 2004     

Polyimide/polyoxometalate copolymer thin films: synthesis,thermal and dielectric properties

A mono‐lancunary keggin‐type decatungstosilicate (SiW₁₁) polyoxometalate (POM) modified by γ‐aminopropyltriethoxysilane (KH550) was incorporated into polyimide (PI) through copolymerization. Nuclear magnetic resonance (NMR), fourier transition infrared spectroscopy (FTIR), and wide angle X‐ray diffraction (WAXD) were used to characterize the structure and composition of the polyoxometalate–organosilane hybrid (SiW₁₁KH550) and PI/SiW₁₁KH550 copolymers. The differential scanning calorimetry (DSC) studies indicate that the glass transition temperature (T_g) of PI/SiW₁₁KH550 copolymers increases from 330°C (for neat PI) to 409°C (for the copolymer sample with 10 wt% of SiW₁₁KH550). Dielectric measurement showed that both the dielectric constant and the dielectric loss for the copolymer thin films decreased with the increase in SiW₁₁KH550 content, and the dielectric constant and dielectric loss values decreased to 2.1 and 3.54 × 10^?3, respectively, for the copolymer sample with 10 wt% of SiW₁₁KH550. The incorporation of SiW₁₁KH550 into polymer matrices is a promising approach to prepare PI films with a low dielectric constant and low dielectric loss. Copyright © 2009 John Wiley & Sons, Ltd.     

Acrylamide–itaconic acid superabsorbent polymers and superabsorbent polymer/mica nanocomposites

Superabsorbent polymer acrylamide (AM)/itaconic acid (IA) and its nanocomposite were synthesized by redox polymerization in an aqueous solution of both monomers with mica used as an inorganic additive. The influences of IA concentration, mica content, and crosslinker concentration on the water absorption and physical properties of the superabsorbent polymer and its nanocomposite were examined. Water absorbency in artificial urine by the synthesized copolymers, and the gel strength of the superabsorbent copolymers and their nanocomposites, were tested with loads of 0.28 or 0.70 psi. Transmission electron micrographs and X‐ray diffraction confirmed that the polymer chains were successfully intercalated into the silicate layers in the mica. The water absorbency and the artificial urine absorbency of the composite with an AM‐to‐IA mole ratio of 95:5, 0.2% mol N‐MBA, and 5% w/w mica were 748 ± 5 and 76 ± 2 g g^?1, respectively, whilst the neat copolymer achieved only 640 ± 7 and 72 ± 2 g g^?1 in water and artificial urine, respectively. The viscoelastic behavior suggested that the swollen gel of the nanocomposites exhibited mechanical stability and elasticity. Copyright © 2009 John Wiley & Sons, Ltd.     

Effect of intercalated reactive mica on water absorbency for poly(sodium acrylate) composite superabsorbents

A series of superabsorbents based on sodium acrylate (NaA), mica (MI), and N,N′-methylene-bis-acrylamide (NMBA) were prepared by inverse suspension polymerization. The influences of the type and content of mica such as pure K⁺-MI and intercalated-MI (IMI) in the composite gels on the water absorbency and the initial absorption rate in deionized water and salt solutions were investigated. Results showed that the water absorbency and initial absorption rate gradually decrease with increasing amounts of pure K⁺-MI and intercalated-MI. In addition, the water absorbency and initial absorption rate for the gels prepared by intercalated-MI were lower than those prepared by pure K⁺-MI.     

Study on superabsorbent composite XVI. Synthesis, characterization and swelling behaviors of poly(sodium acrylate)/vermiculite superabsorbent composites

A series of superabsorbent composites were synthesized by copolymerization reaction of partially neutralized acrylic acid on unexpanded vermiculite (UVMT) micropowder using N,N′-methylenebisacrylamide (MBA) as a crosslinker and ammonium persulfate (APS) as an initiator in aqueous solution. And the samples were further characterized by means of fourier-transform spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and thermogravimetric analysis (TGA). The effects of vermiculite content on water absorbency were studied. Swelling behaviors of the superabsorbent composites in various cationic salt solutions (NaCl, CaCl₂ and FeCl₃), anionic salt solutions (NaCl, Na₂SO₄ and Na₃PO₄) and pH solutions were also systematically investigated. Results obtained showed that the equilibrium water absorbency increased with increasing UVMT content and the concentration of 20 wt.% clay gave the best absorption (1232 g/g in distilled water and 89 g/g in 0.9 wt.% NaCl). Data achieved also suggested that the water absorbency in various saline solutions decreased with an increase in the ionic strengths of these solutions. And it was found that at a higher ionic strength (>1 × 10⁻³ M), the water absorbency in monovalent cationic solutions was higher than those in multivalent cationic solutions. However, at the same ionic strength (>1 × 10⁻³ M), the effect of three anionic salt solutions on the swelling has the following order: NaCl < Na₂SO₄ < Na₃PO₄.     

Features of the Interaction of Alcian Blue with Gels Based on Copolymer of <Emphasis Type="Italic">N</Emphasis>-Vinylcaprolactam and Methacrylic Acid

The interaction of N-vinylcaprolactam–methacrylic acid copolymer hydrogel and N-vinylcaprolactam homopolymer hydrogel with alcian blue in aqueous solutions is studied. It is shown that copolymer gel are thermo- and pH-sensitive. Dye sorption by the copolymer gel and gel swelling degree depends on the pH of the solution. The features of the system behavior resulting from the pH sensitivity of both the gel and the dye are shown. The thermocollapse of gels incubated in aqueous solutions of alcian blue is studied. It is shown that the transition temperature of N-vinylcaprolactam–sodium methacrylate copolymer gel to the collapsed state decreases with the dye absorption. The temperature-induced collapse of homopolymer gels in dye solutions is reversible, while the copolymer gel mass restores incompletely during the return temperature decrease. The dye absorption by the copolymer gel leads to decreased hysteresis.     

Synthesis,characterization and water absorbency properties of poly(acrylic acid)/sodium humate superabsorbent composite

A novel poly(acrylic acid)/sodium humate superabsorbent composite was synthesized by aqueous solution polymerization of acrylic acid using N, N′‐methylenebisacrylamide as a crosslinker and ammonium persulfate as an initiator in the presence of sodium humate. The effects on water absorbency such as initial monomer concentration, degree of neutralization of acrylic acid, amount of crosslinker, initiator and sodium humate, etc. were investigated. The water absorbency of the superabsorbent composite synthesized under optimal synthesis conditions with a sodium humate content of 20% exhibited an absorption of 1268 g H₂O/g sample and 93 g H₂O/g sample in distilled water and in 0.9 wt% NaCl solution, respectively. Swelling rate and water retention tests were also carried out. The results show that sodium humate, as a kind of functional filler, can enhance comprehensive properties of superabsorbent composite and reduce the product cost significantly. Copyright © 2005 John Wiley & Sons, Ltd.     

Influence of crosslinker and ionic comonomer concentration on glass transition and demixing/mixing transition of copolymers poly(N-isopropylacrylamide) and poly(sodium acrylate) hydrogels

Hydrogels based on N-isopropylacrylamide and sodium acrylate as ionic comonomer were synthesized by free radical polymerization in water using N,N′-methylenebisacrylamide as crosslinker and ammonium persulfate as initiator. The glass transition of dried copolymers poly(N-isopropylacrylamide) (PNIPA) and poly(sodium acrylate) (SA) gels and demixing/mixing transition of PNIPA-SA hydrogels swollen with increasing amounts of water were studied using conventional differential scanning calorimetry. In the crosslinked polymers, the glass transition linearly increases, and the transition range becomes broader, with increasing crosslinker content. Increasing content of ionic comonomer also produces an increase of glass transition temperature, which moves to higher temperatures with higher sodium acrylate fraction. The influence of chemical structure of PNIPA-SA hydrogels on the lower critical solution temperature (LCST) of PNIPA-SA/water mixtures during heating and cooling was quantified as function of the content of the crosslinker and the ionic comonomer, as well as water content of the hydrogel in the range from 95 to 70 wt%. At parity of water content, the LCST occurs at higher temperatures for gels containing higher amounts of sodium acrylate. Similarly, the introduction of N,N′-methylenebisacrylamide causes an increase of the LCST, which grows with increasing of crosslinking degree of the hydrogel.     

Aqueous solution properties of amphiphilic triblock copolymer poly(p-dioxanone-co-l-lactide)-block-poly(ethylene glycol)

A poly(ethylene glycol) (PEG)-based new amphiphilic block copolymer bearing the poly(p-dioxanone-co-l-lactide) (PPDO/PLLA) hydrophobic moieties was prepared. Depending on the copolymer composition and molecular weights, solubility of the polymeric samples in water was varied. Its diluted aqueous solution properties were studied by viscometry, dye solubilization, ¹H-NMR and dynamic light scattering. 1,6-Diphenyl-1,3,5-hexatriene solubilization and ¹H-NMR spectra carried out in CDCl₃ and D₂O were used to prove the existence of hydrophobic domains as the core of micelle. Average particle size of 60-165 nm with low polydispersity and lower negative zeta (ξ) potential of −3 to −14 mV were observed on the aqueous copolymer dispersion.     

Superfast Responsive Ionic Hydrogels: Effect of the Monomer Concentration

A series of strong polyelectrolyte gels were prepared in aqueous solution, using the sodium salt of 2‐acrylamido‐2‐methylpropane sulfonic acid (AMPS) as the monomer and N,N'‐methylene(bis)acrylamide (BAAm) as a crosslinker. The gels were both prepared below (?22°C) and above (25°C) the bulk freezing temperature of the water, producing cryogels and hydrogels, respectively. The crosslinker (BAAm) content was set at 17 mol%, while the initial monomer concentration C_o was varied over a wide range. It was found that, at ?22°C, a macroscopic network starts to form at an initial monomer concentration of as low as 0.1 w/v%. In contrast to the conventional hydrogels formed at 25°C, the cryogels have a discontinuous morphology consisting of polyhedral pores of sizes 10⁰–10² μm. The cryogels exhibit superfast swelling properties, as well as reversible swelling–deswelling cycles in water and acetone. An increase in the initial monomer concentration from 2.5 to 10% further increases the response rate of the cryogels due to the simultaneous increase of the porosity of the networks.     

Converting water absorbent polymer to alcohol absorbent polymer

In this paper, a commercial water absorbent polymer based on poly (sodium acrylate) (PAANa) was converted to an alcohol absorbent polymer. PAANa collapses in alcoholic swelling media such as ethanol and methanol. In the present paper, first, a full interpenetrating polymer network (IPN) gel was prepared through immersing PAANa hydrogel in a solution containing 2‐acrylamido2‐methyl propane sulfonic acid (AMPS), polyethylene glycol dimetahcrylate and ammonium persulfate. The second network was formed in hydrated PAANa through heating. It was synthesized in two conditions by chemical crosslinker and crosslinker‐free. The IPN was acid treated to investigate the effect of removing Na⁺ on alcohol absorbency. The synthesized IPN gels have the ability of absorbing up to 21 and 39 g/g ethanol and methanol, respectively. The samples which were synthesized using the chemical crosslinker in the second stage had more alcohol absorbency in comparison with the crosslinker‐free samples. Unexpectedly, acid treatment caused a decrease in alcohol absorbency. The IPN gels were characterized through thermogravimetric analyses (TGA) and dynamic mechanical thermal analysis (DMTA). The DMTA results confirmed the IPN structure of the gels, two distinctive peaks, which can be attributed to PAANa, and poly (AMPS) was observed in tan delta figures. TGA thermograms demonstrated that IPN had lower thermal stability in comparison with the initial PAANa, which can be attributed to higher vulnerability of SO₃H group for degradation that reduced initial decomposition temperature. Copyright © 2012 John Wiley & Sons, Ltd.     

Effective preparation of crack-free silica aerogels via ambient drying

Effective ambient-drying techniques for synthesizing crack-free silica aerogel bulks from the industrial waterglass have been developed. Silica wet gels were obtained from aqueous colloidal silica sols prepared by ion-exchange of waterglass solution (4–10 wt% SiO₂). Crack-free monolithic silica aerogel disks (diameter of 22 mm and thickness of 7 mm) were produced via solvent exchange/surface modification of the wet gels using isopropanol/trimethylchlorosilane/n-Hexane solution, followed by ambient drying. The effects of the silica content in sol and the molar ratio of trimethylchlorosilane/pore water on the morphology and property of final aerogel products were also investigated. The porosity, density, and specific surface area of silica aerogels were in the range of 92–94%, 0.13–0.16 g/cm³, and ∼675 m²/g, respectively. The degree of springback during the ambient drying processing of modified silica gels was 94%.     

Thermal analyses of poly(N-isopropylacrylamide) in aqueous solutions and in nanocomposite gels

The coil-to-globule transition of poly(N-isopropylacrylamide) (PNIPA) prepared by free-radical redox polymerization in aqueous solutions and its nanocomposite (NC) gels were investigated by differential scanning calorimetery. The lower critical solution temperatures (LCST) of aqueous solutions of PNIPA of different molecular weights were not significantly affected by molecular weight (M _w: 0.19?×?10⁶?4.29?×?10⁶?g?×?mol^?1) or polymer concentration (1?10?wt%), although the enthalpy of transition increased with molecular weight, at M _w (<1.2?×?10⁶ g?×?mol^?1). The glass-transition temperature of PNIPA in the dried state also remained constant (138?°C), regardless of molecular weight. On the other hand, the enthalpy of the coil-to-globule transition of PNIPA in NC gels consisting of a PNIPA/clay network decreased with increasing clay concentration (C _clay), while the onset temperature (≡LCST) was almost constant, regardless of C _clay. The PNIPA chains in NC gels could be classified into the following three types: P-1, which exhibits a normal LCST transition, similar to that of linear PNIPA; P-2, exhibiting restricted transition at higher temperatures as a result of interactions with the clay; and P-3, which does not undergo that transition because of stronger restrictions. It was found that the proportion of P-3 increases with increasing C _clay. However, some P-1 and P-2 was still observed, even in NC gels with high C _clay. That the transition to the hydrophobic globular state was restricted by interactions with the clay was confirmed by measurements on PNIPA after removal of the clay from NC gels.     

Swelling behaviors of polyelectrolyte hydrogels containing sulfonate groups

Series of maleate monoester and diester monomers based on poly(ethylene glycol) monomethyl ether (MPEG) were copolymerized using the ionizable 2‐acrylamido‐2–methyl propane sulfonic acid (AMPS) via different dose rate of electron‐beam irradiation (40–150 kGy). The crosslinking of the copolymers were carried out in aqueous acidic solutions at pH 1 or in the presence of 1% N,N‐methylene bisacrylamide (MBA) as crosslinking agent. The final equilibrium water content and swelling capacities for the prepared hydrogels were determined in aqueous solutions at pH 1, 6.8, and 12 and in aqueous salt solutions at 298 K. Swelling equilibria for prepared hydrogels were determined in different molar salt solutions of NaCl, KCl, CaCl₂, Na₂SO₄, K₂SO₄, and CaSO₄. The swelling ratios of gels in pure water and in the salt solutions were found to depend on the counterion species in the increasing sequence of Ca²⁺, Na⁺ and K⁺. Copyright © 2002 John Wiley & Sons, Ltd.