Superabsorbent polymeric materials. IV. Swelling behavior of crosslinked poly [sodium acrylate-co-N,N-dimethyl (acrylamidopropyl) ammonium propane sulfonate] in aqueous salt solution

A series of xerogels based on sodium acrylate (SA), N,N-dimethyl(acrylamidopropyl)ammonium propane sulfonate (DMAAPS), and N,N′-methylene bisacrylamide (NMBA) were prepared by inverse suspension polymerization. The water absorbency or swelling behavior for these xerogels in water or various saline solutions was investigated. Results obtained from this study revealed a water absorbency of 721 g H₂O/g sample in deionized water and 83 g H₂O/g sample in 0.9 wt % NaCl solution for a gel containing a 1.50 × 10 ⁻² molar fraction of DMAAPS. The absorbency in the chloride salt solutions decreased with an increase in the ionic strength of the salt. For the same ionic strength of various salt solutions, the swelling amount had the following tendency: Co ²⁺ > Ni ²⁺ > Cu ²⁺ for the higher ionic strength of 2.44 × 10 ⁻⁵–1.8 × 10 ⁻² M. The Co ²⁺, Ni²⁺, and Cu ²⁺ solutions induce approximately the same degree of swelling at the lower ionic strength of <2.44 × 10 ^minus;5 M. The pH effect on the water absorbency for these xerogels was also investigated. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66:499–507, 1997     

Superabsorbent polymeric materials. II. Swelling behavior of crosslinked poly[sodium acrylate-co-3-dimethyl(methacryloyloxyethyl) ammonium propane sulfonate] in aqueous salt solution

A series of xerogels based on sodium acrylate (SA), 3-dimethyl (methacryloyloxyethyl) ammonium propane sulfonate (DMAPS), and N,N′-methylene-bis-acrylamide (NMBA) are prepared by inverse suspension polymerization. The water absorbencies or swelling behaviors for these xerogels in water or various saline solutions respectively exhibit a value of 1435 g H₂O/g sample and 96 g H₂O/g sample of deionized water and 0.9 wt % NaCl solution at a gel containing 1.88 × 10⁻³ molar ratio of DMAPS while the extent of 1.53 × 10⁻³ molar ratio (0.25 wt % based on total monomer) of NMBA was used in the polymerization. The absorbency in the chloride salt solutions decreases with an increase in the ionic strength of salt. For the same ionic strength of various salt solutions, the swelling amount has the following tendency: Na⁺ > Fe³⁺ > A1³⁺ > Ca²⁺ for the higher ionic strength of 5 × 10⁻³ −2 × 10⁻²M and Na⁺ > Fe³⁺ > Ca²⁺ > A1³⁺ for the lower ionic strength of < 2 × 10⁻⁴M. The bound water found by DSC investigation is approximately equal to 2 g H₂O/g sample. The pH effect and thermal effect on the water absorbency for these xerogels are also investigated. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 1701–1712, 1997     

Superabsorbent polymeric materials VIII: Swelling behavior of crosslinked poly[sodium acrylate‐co‐trimethyl methacryloyloxyethyl ammonium iodide] in aqueous salt solutions

A series of xerogels based on sodium acrylate (SA), cationic comonomer, trimethyl methacryloyloxyethyl ammonium iodide (TMMAI), and N,N‐methylene‐bis‐acrylamide (NMBA) were prepared by inverse suspension polymerization. The water absorbency and the swelling behavior for these high absorbent polymers in deionized water and various saline solutions were investigated. Results indicated that the water absorbency for the present copolymer gel increased when a small amount of TMMAI monomer was introduced into the SA gel, then decreased with increase in TMMAI content. The water absorbency was 583 g H₂O/g for a gel sample in deionized water containing 2.5 × 10⁻³ molar fraction TMMAI. But a contrary result was observed for initial absorption rate, that is, the initial absorption rates increased with an increase of TMMAI in deionized water and 0.9 wt % NaCl solution. The absorbency in the chloride salt solution decreased with an increase in the ionic strength of the salt solution. Finally, the adsorption of copper ion by these gels was also investigated. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1665–1674, 2001     

Superabsorbent polymeric materials. I. Swelling behaviors of crosslinked poly(sodium acrylate-co-hydroxyethyl methacrylate) in aqueous salt solution

A series of crosslinked poly(sodium acrylate-co-hydroxyethyl methacrylate) based on sodium acrylate (SA), 2-hydroxyethyl methacrylate (HEMA), and N,N′-methylene-bis-acrylamide (NMBA) are prepared by inverse suspension polymerization. The resultant crosslinking polymers are xerogellants. This work investigates not only the absorbency or swelling behavior for these xerogellants composed of different ratios of HEMA/SA in water, but also the effects of various salts and pH values on the swelling properties. Experimental results indicate that the absorbency in deionized water decreases with an increase in the HEMA in copolymeric gel, which is related to the degree of expansion of the network and the strength of the hydrophilic group. The absorbency in the chloride salt solutions decreases with an increase in the salt concentration (swelling is 50 times for the IA group chloride salt solutions, but is less than 5 times for the IIA group salt solution), owing to the osmosis of water and ions between the polymeric gel and the external solution. A decrease in the extent of swelling occurs for divalent and trivalent chloride salt solutions. For the salt solutions of the same ionic strength, the swelling amount has the following tendency: LiCl(aq) = NaCl(aq) = KCl(aq), CaCl₂(aq) < SrCl₂(aq) < BaCl₂(aq), and Fe³⁺ > Ca²⁺ > Zn²⁺ > Cu²⁺. These orders are related to the complexing ability between metallic cations and the carboxylate group in the polymeric chains. Finally, the adsorption of ferric ion by these gels is also investigated. © 1996 John Wiley & Sons, Inc.     

Superabsorbent polymeric material. V. Synthesis and swelling behavior of sodium acrylate and sodium 2-acrylamido-2-methylpropanesulfonate copolymeric gels

A series of xerogels based on sodium acrylate (SA), sodium 2-acrylamido-2-methyl propanesulfonate (NaAMPS), and N,N-methylene-bis-acrylamide (NMBA) are prepared by inverse suspension polymerization. The water absorbency and swelling behavior for these high absorbent polymers in deionized water and transition salt solutions are investigated. Experimental results indicated that the absorbency in deionized water increases with an increase of the NaAMPS content in the copolymeric gels, which is related to the degree of charge density of the network and the strength of hydrophilic group. The extent of crosslinking agent also influenced the swelling capacity because of elastic chain force of the polymer chain. The absorbency in chloride salt solutions decreases with an increase in the ionic strength of salt. But the decrease of absorbency is different in monovalent and multivalent salt solution. This behavior can be accounted for in terms of counterion condensation or screening effect for monovalent cations, as well as complexation for multivalent cations. The swelling rates in various salt solutions for these xerogels are also investigated. At last, SA-NaAMPS copolymeric gels were used for ion adsorption. But the result showed that the adsorptive amount of transition metal ions for SA-NaAMPS copolymeric gels was lower than that for pure poly(SA) gel. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 229–237, 1998     

Superabsorbent polymeric materials. VI. Effect of sulfobetaine structure on swelling behavior of crosslinked poly(sodium acrylate‐co‐sulfobetaines) in aqueous salt solutions

A series of xerogels based on sodium acrylate (SA), N,N‐dimethyl(acrylamidopropyl) ammonium propane sulfonate (DMAAPS) or dimethyl(methacryloyloxy ethyl) ammonium propane sulfonate (DMAPS), and N,N′‐methylene bisacrylamide (NMBA) was prepared by inverse suspension polymerization. The water absorbencies or swelling kinetic behaviors for these xerogels in water or various saline solutions were investigated. The swelling behaviors of these absorbents were related to their chemical structures, their compositions, and the nature of external salt solutions. The water absorbencies of these two copolymeric gel series in deionized water or in various salt solutions would be improved effectively by copolymerizing SA with a small amount of zwitterionic monomer (DMAAPS or DMAPS). The water absorbency of the gel containing DMAPS is larger than that of the gel containing DMAAPS when the amount of zwitterionic monomer in the copolymeric gel is <0.8 mol %, but a contrary result is observed when the zwitterionic monomer content is >0.8 mol %. The tendency of the absorbency for these gels in dilute solution is in the order Cu²⁺ > Zn²⁺ > Co²⁺ > Ni²⁺ for CuCl₂, ZnCl₂, CoCl₂, and NiCl₂ aqueous solution, respectively. The absorbency and initial absorption rate for those gels are related with gel compositions and salt concentrations. Finally, the adsorption of cupric ion by these gels is also investigated. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 1221–1232, 1999     

Studies on poly(acrylic acid)/attapulgite superabsorbent composites. II. Swelling behaviors of superabsorbent composites in saline solutions and hydrophilic solvent–water mixtures

The effect of the attapulgite content on the swelling for a series of poly(acrylic acid)/attapulgite superabsorbent composites in water was studied. The effects of the temperature and pH values on the water absorbency of the superabsorbent composites were investigated. The swelling behavior of the superabsorbent composites in various saline solutions was also investigated. The water absorbency in various salt solutions decreased with an increase in the ionic strength of the solutions. At a high ionic strength (>1 × 10^?3M), the water absorbency in monovalent cationic solutions was higher than that in multivalent cation solutions. This dramatic reduction of the water absorbency in multivalent cationic solutions of high ionic strength may have been due to the complexing ability of the carboxylate groups inducing the formation of intramolecular and intermolecular complexes, which resulted in an increased crosslink density of the network. The swelling behavior of the superabsorbent composites in mixtures of water and hydrophilic solvents, including methanol, acetone, ethanol, and dimethyl sulfoxide (DMSO), was also investigated. The water absorbency decreased with an increase in the concentration of any of the four organic solvents, and two transitions were observed in the superabsorbent composite/hydrophilic solvent–water mixture systems. The main transition for the four hydrophilic solvent–water mixtures was a collapse of the swollen gel (at 50–80% methanol, 30–80% acetone, 50–80% ethanol, and 50–80% DMSO). For the methanol–water system, the magnitudes of the first and second transitions for the poly(acrylic acid)/attapulgite superabsorbent composites containing lower proportions of attapulgite were larger than those for the superabsorbent composites with higher attapulgite contents. The effect of the mixture temperature on the water absorbency of the superabsorbent composites in 10 min was also reported. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1869–1876, 2004     

Superabsorbent polymeric materials IX: Effect of cationic structure on swelling behavior of crosslinked poly(sodium acrylate‐co‐cationic monomers) in aqueous salt solutions

Two series of xerogels based on sodium acrylate (SA), trimethyl methacrylamidopropyl ammonium iodide (TMMAAI), trimethyl methacryloyloxyethyl ammonium iodide (TMMAI), and N,N′‐methylene‐bis‐acrylamide (NMBA) as a crosslinker were prepared by inverse suspension polymerization. The water absorbency and swelling kinetic behavior for these xerogels in water or various saline solutions were investigated. The results showed that the swelling behaviors of these absorbents are related to their chemical structures, their compositions, and the type of external salt solutions. There would be effective improvement in the water absorbency of these two gel series by copolymerizing SA with a small amount of cationic monomer (TMMAAI or TMMAI). The initial absorption rates in deionized water were found to be faster for TM series gels than for TA series gels. The two series of superabsorbents had a tendency to absorb water in dilute nitrate aqueous solutions in the order: Fe³⁺, Ni²⁺, Ca²⁺, Cu²⁺, and Na⁺ for Fe(NO₃)₃, Ni(NO₃)₂, Ca(NO₃)₂, Cu(NO₃)₂, and NaNO₃ aqueous solution, respectively. The absorbency and initial absorption rate for these gels were related to the gel compositions and salt concentrations. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 1827–1837, 2001     

Synthesis,characterization, and swelling behavior evaluation of hydrogels based on Gum ghatti and acrylamide for selective absorption of saline from different petroleum fraction–saline emulsions

In this research article, the synthesis of Gum ghatti and acrylamide based superabsorbents under pressure with N,N′‐methylene bisacrylamide as a crosslinker and an ascorbic acid–potassium persulfate redox pair as an initiator is reported. To study the impact of the different reaction variables on the water absorbance of the candidate polymer, different reaction parameters, including the reaction time, amount of solvent, pH of the medium, initiator ratio, pressure, and monomer and crosslinker concentrations, were optimized. The candidate polymer was characterized with different techniques, including Fourier transform infrared spectroscopy, scanning electron microscopy, thermogravimetric analysis, differential thermal analysis, differential thermogravimetry, and X‐ray diffraction. The crosslinked product was found to be thermally more stable than the initial backbone. The swelling capacity of the synthesized polymer was investigated in deionized water as a function of time, temperature, and pH of the swelling medium. Moreover, the effects of the ionic strengths of different cations on the swelling capacity of the candidate polymer were studied with different salt solutions. The tendency of absorbency for these hydrogels in salt solutions was found to be in the following order: Na⁺ > Ba²⁺ > Fe³⁺ > Sn⁴⁺ for NaCl, BaCl₂, FeCl₃, and SnCl₄ salt solutions. Further, the candidate polymer was used for the selective absorption of saline water from different petroleum fraction–saline emulsions. The results showed that the saline absorption capacities of the hydrogels were 667, 610, 646, and 680% in kerosene–saline, diesel–saline, petrol–saline, and petroleum ether–saline emulsions, respectively. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Immobilization of strontium by crystalline zirconium phosphate

Mixtures of HZr₂(PO₄)₃ with varying amounts of Sr(NO₃)₂ were thermally treated at 600–1200 °C in order to investigate the immobilization of radioactive Sr. When the Sr(NO₃)₂ / HZr₂(PO₄)₃=0.2 mixture was thermally treated at 700 °C, the main product was postulated to be SrZr₄(PO₄)₆ from the XRD results. The Sr(NO₃)₂/HZr₂(PO₄)₃=0.2 immobilized product thermally treated at 700 °C containing the maximum amount of immobilized Sr (a 0.2 molar ratio of Sr(NO₃)₂/HZr₂(PO₄)₃ equates to approximately 4 wt.% of Sr) had minimal Sr leaching rates in several solvents at 160 °C in an autoclave. The leaching rate of Sr ion from that product was <10⁻⁶, 1.3×10⁻⁴, 1.4×10⁻⁴, 1.1×10⁻³, 2.0×10⁻³, 8.8×10⁻³ and <10⁻⁶ g m⁻² day⁻¹ in deionized water, sea water, 0.1 mol l⁻¹- HCl, 0.5 mol l⁻¹- HCl, 1 mol l⁻¹- HCl, 1.5 mol l⁻¹- HCl and 1 mol l⁻¹- NH₃ in an autoclave at 160 °C, respectively, indicating that HZr₂(PO₄)₃ reacts with Sr(NO₃)₂ to give a stable Sr-immobilized product.     

Solidification of glass-ceramics of simulated fission products RE3+, Sr2+, Ba2+ in chlorine-containing waste molten salt

Embedding nuclear waste in glass-ceramic and immobilizing nuclides in ceramic lattice is an effective way for the disposal of high-level radioactive waste. In this paper, a method of solidification of simulated various nuclides was proposed, i.e., RE³⁺(RE = La, Sm, Nd, Dy), Sr²⁺ and Ba²⁺ precipitated from waste molten salt in the form of REPO₄, SrCO₃ and BaCO₃ were solidified in glass-ceramics. To avoid the decomposition of SrCO₃ and BaCO₃ at high temperature, SrCO₃/BaCO₃ containing Cl⁻ salt was further sintered with NH₄H₂PO₄ to form Sr₅(PO₄)₃Cl/Ba₅(PO₄)₃Cl ceramics. It was found that the prepared REPO₄ belonged to monoclinic or tetragonal crystal system, while Sr₅(PO₄)₃Cl and Ba₅(PO₄)₃Cl belonged to hexagonal crystal system. REPO₄, Sr₅(PO₄)₃Cl and Ba₅(PO₄)₃Cl ceramics were co-solidified in iron phosphate glass. BET results showed that the ceramics had a dense structure without any pore inside. XRD, TEM and HRTEM results showed all ceramics had high crystallinity, and nuclides could enter the lattice structure of ceramics through isomorphic replacement, which made the nuclides stable in the crystal structure. The effects of embedding rate on the volume density, Vickers hardness and wettability of glass-ceramics were explored. It was found that the density of the glass-ceramics gradually increased with the increase of ceramic embedding rate, however, the Vickers hardness firstly increased and then decreased. When the embedding rate reached 20 wt%, the Vickers hardness of the glass-ceramics could reach 583.90 GPa. The water contact angles of glass-ceramics with an embedding rate 0–40 wt% were measured to be 70.45°–84.05°, indicating glass-ceramics having a good water leaching resistance. Furthermore, the normalized leaching rate NR_i of La³⁺, Sm³⁺, Nd³⁺, Dy³⁺, Sr²⁺, Ba²⁺, Cl⁻ on the 28th day were estimated to be 7.53 × 10⁻⁷, 5.02 × 10⁻⁷, 5.12 × 10⁻⁷, 4.04 × 10⁻⁷, 1.22 × 10⁻³, 1.59 × 10⁻⁴, 1.07 × 10⁻⁴ g‧m⁻²‧d⁻¹, which indicating that all elements remained good leaching resistance.     

Improved structural stability and ionic conductivity of Na3Zr2Si2PO12 solid electrolyte by rare earth metal substitutions

Sodium zirconium silicon phosphorus with the composition of Na₃Zr₂Si₂PO₁₂ (NZSP) was prepared by a facile solid state reaction method. The effects of the calcination temperature and rare earth element substitution on the structure and ionic conductivity of the NZSP material were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and AC impedance measurement. The results show that the microstructure and ionic inductivity of the NZSP was strongly affected by the aliovalent substitution of Zr⁴⁺ ions in NZSP with rare earth metal of La³⁺, Nd³⁺ and Y³⁺. At room temperature, the optimum bulk and total ionic conductivity of the pure NZSP solid electrolyte sintered under different conditions were 6.77×10⁻⁴ and 4.56×10⁻⁴ S cm⁻¹, respectively. Substitution of La³⁺, Nd³⁺ and Y³⁺ in place of Zr⁴⁺ exhibited higher bulk conductivity compared with that of pure NZSP. Maximum bulk and ionic conductivity value of 1.43×10⁻³ and 1.10×10⁻³ S cm⁻¹ at room temperature were obtained by Na_3+xZr_1.9La_0.1Si₂PO₁₂ sample. The charge imbalance created by aliovalent substitution improves the mobility of Na⁺ ions in the lattice, which leads to increase in the conductivity. AC impedance results indicated that the total ionic conductivity strongly depends on the substitution element and the feature of the grain boundary.     

Study on superabsorbent composite. XX. Effects of cation‐exchanged montmorillonite on swelling properties of superabsorbent composite containing sodium humate

In this work, the effects of different cation‐exchanged montmorillonite on water absorbency of poly(acrylic acid‐co‐acrylamide)/montmorillonite/sodium humate (PAA‐AM/MMT/SH) superabsorbent composite were systematically investigated under the same preparation conditions. The superabsorbents doped with different cation‐exchanged montmorillonite were characterized by Fourier‐transform infrared spectroscopy, X‐ray diffraction, and scanning electron microscopy technologies. Swelling behaviors of developing superabsorbent composite in various cationic saline solutions (NaCl, CaCl₂, and FeCl₃) were also investigated. The water absorbencies of superabsorbent composite with 20 wt% MMT and 30 wt% SH are 638, 723, 682, and 363 g g⁻¹ in distilled water for incorporating natural Na⁺‐MMT, Li⁺‐exchanged MMT, Ca²⁺‐exchanged MMT, and Al³⁺‐exchanged MMT, respectively. The results showed that the cation‐exchange process had some obvious influences on final water absorbency of superabsorbent composite. NaCl, CaCl₂, and FeCl₃ solutions did not alter the swelling characteristics of the superabsorbent materials at a concentration of less than 0.01 mM, however, a concentration of greater than 0.1 mM caused a collapse in the swelling curves. The excellent swelling‐reswelling‐swelling behavior and lower swelling rate testified that Al³⁺‐exchanged MMT can act as an assistant crosslinker in the polymeric network. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

An amphoteric hydrogel: Synthesis and application as an internal curing agent of concrete

A new crosslinked amphoteric hydrogel (PAC) was synthesized and evaluated as an internal curing agent of concrete. PAC was prepared from acrylamide (AM) and 4‐(2‐((carboxylatomethyl)dimethylammonio)ethoxy)?4‐oxobut‐2‐enoate (CMD) through free‐radical polymerization by using ammonium persulfate (APS) as an initiator and methylene‐bisacrylamide (MBA) as a crosslinker. The structure of the prepared polymer was verified by the IR spectra. The effects of the polymerization variables on the swelling capacity of PAC were investigated. The water absorbency of PAC was found to increase with increasing CMD/AM ratio, reach a maximum value, and decrease afterword. Increase of either APS or MBA content decreased the water absorbency. The highest water absorbency of PAC hydrogel (P7) achieved in deionized water, 0.1M NaCl solutions and 0.1M CaCl₂ solutions, was 306 g/g, 32 g/g, and 22 g/g, respectively. Compared with a commercial acrylate‐based hydrogel 283HA, P7 was less sensitive to the existence of Ca²⁺ ions in cement pore solutions, and more effective in reducing the cracking tendency of cement pastes. Finally, mortars incorporated with proper amounts of P7 showed smaller drying shrinkage and higher compressive strength than that without hydrogel present. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42175.     

Synthesis and swelling behaviour of poly (sodium acrylate)/sepiolite superabsorbent composites and nanocomposites

A series of novel composites and nanocomposites xerogels based on acrylic acid, sepiolite and N,N′‐methylenebisacrylamide were prepared using a solution polymerization technique at 70 °C. The quality of dispersion of the micronized sepiolite in the monomer is the crucial point for obtaining nanocomposites. A good dispersion explains the improvement of the absorbent properties of the nanocomposites with respect to the composites. This work investigates not only the influence of the mixing procedure on the swelling behaviour, but also the effect of the amount of clay on the absorbency of these hydrogels in deionized water and saline solution (0.2 wt% NaCl_(aq)). A crosslinker concentration of 5 wt% sepiolite nanocomposite superabsorbent was shown to give the best results (1419 g g^?1). Moreover, experimental results indicate that the absorbency in saline solution is smaller than that in deionized water. Rates of swelling for these absorbents were found to fit the Voigt expression. Finally, the model approximates Case II sorption in the early stages of the swelling process and Case I in the later stages. Copyright © 2006 Society of Chemical Industry     

Synthesis and characterization of pH‐ and salt‐responsive hydrogels based on etherificated sodium alginate

Hydrogels composed of etherificated sodium alginate (ESA), sodium acrylic acid (NaAA), and poly (vinyl alcohol) (PVA) were synthesized by aqueous solution polymerization. The effects of reaction variables such as terminal pH, ions, and ionic strength on hydrogel swelling ratio (SR) were determined and compared. SR was influenced strongly by pH and ionic strength. SR increased with increasing pH but tended to decrease with PVA content. At a given ionic strength, SR of ESA/NaAA/PVA hydrogel was dependent on the valence of anion; SR was higher in multivalent anion salt solution than in monovalent anion salt solution, i.e., SR_K2SO4 > SR_KCl and SR_Na2SO4 > SR_NaCl. The swelling kinetic of the hydrogels showed Fickian kinetic diffusion in acidic media and non‐Fickian behavior in alkaline media. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Superabsorbent composite. XIII. Effects of Al3+‐attapulgite on hydrogel strength and swelling behaviors of poly(acrylic acid)/Al3+‐attapulgite superabsorbent composites

Al³⁺‐attapulgite (Al³⁺‐APT) was prepared by treating attapulgite (APT) with AlCl₃ aqueous solution of various concentrations. The poly(acrylic acid)/Al³⁺‐attapulgite (PAA/Al³⁺‐APT) superabsorbent composite was prepared by reaction of partly neutralized acrylic acid, and Al³⁺‐APT in aqueous solution using N, N′‐methylenebisacrylamide as a crosslinker and ammonium persulfate as an initiator. The surface morphology of the composite was investigated by SEM, and the Al³⁺‐APT composite generated a relatively planar surface comparing the nature APT. The effects of Al³⁺‐APT on hydrogel strength and swelling behaviors, such as equilibrium water absorbency, swelling rate, and reswelling capability, of the superabsorbent composites were also studied. The hydrogel strength and reswelling capability were improved, however, the equilibrium water absorbency and swelling rate decreased with increasing AlCl₃ solution concentration. The equilibrium water absorbency firstly increased, and then decreased with increasing Al³⁺‐APT content. The results indicate that Al³⁺‐APT acts as an assistant crosslinker in the polymeric network, which has great influences on hydrogel strength and swelling behaviors of the PAA/Al³⁺‐APT superabsorbent composites. POLYM. ENG. SCI., 47:619–624, 2007. © 2007 Society of Plastics Engineers.     

Preparation and properties of a salt‐resistant superabsorbent polymer

Crosslinked sodium polyacrylate was prepared by solution polymerization with N,N‐methylene‐bisacrylamide (bisAM) as crosslinking agent; it was subsequently surface‐crosslinked by ethylene glycol diglycidyl ether (EGDE) and then was modified with inorganic salt to obtain a superabsorbent with water absorbency in 0.9 wt % NaCl aqueous solution at atmosphere and applied pressure (P ≈ 2 × 10³ Pa) of 55 and 20 g.g^?1, respectively. Moreover, it also had excellent hydrogel strength. The effects of reaction temperature, reaction time, neutralization degree (ND) of acrylic acid, amount of initiator, crosslinking agent, and surface‐crosslinking agent, mass ratio of inorganic salt to initial superabsorbent, molar ratio of sodium aluminate (NaAlO₂) to potassium dihydrogen hyphosphate (KH₂PO₄) on water absorbency (WA) in 0.9 wt % NaCl aqueous, and the hydrogel modulus were investigated and optimized. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2532–2541, 2004     

Effect of various environmental conditions on the swelling property of PAAm/PAAcK superabsorbent hydrogel prepared by ionizing radiation

Polyacrylamide/potassium polyacrylate (PAAm/PAAcK) superabsorbent hydrogels were prepared by using ionizing radiation for possible use in agricultural purposes. The influence of environmental conditions such as water quality, fertilizer salts, soil pH, and surrounding temperature on PAAm/PAAcK water absorbency and retention was investigated. The water absorbency apparently decreased with an increase in the valence and ionic strength of the salt solutions. The swelling of PAAm/PAAcK immersed in the solutions containing fertilizer of different nitrogen sources followed the order: Urea > NH₄NO₃ > (NH₄)₂SO₄. The PAAm/PAAcK water absorbency in solutions containing different types of phosphate sources was in the order: H₃PO₄ > KH₂PO₄ > K₂HPO₄. However, the water absorbency of PAAm/PAAcK in the solution of different types of potassium salts followed the order: KCl > K₂SO₄ > K₂HPO₄. PAAm/PAAcK hydrogel is fully swollen at pH 6. The relation between the ability of PAAm/PAAcK to retain water against time at different temperatures was studied. As the environmental temperature increases, the water retention of PAAm/PAAcK decreases. Potential application of PAAm/PAAcK in agriculture was evaluated. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3955–3962, 2006     

Radiation initiated synthesis of 2‐acrylamidoglycolic acid grafted carboxymethyl cellulose as pH‐sensitive hydrogel

This article exploits a new approach for synthesis of carboxymethyl cellulose/poly 2‐acrylamidoglycolic acid by graft and crosslinked copolymerization in aqueous solution by a simple one‐step using γ‐radiation. The reaction parameters affecting the equilibrium swelling, i.e., mass ratio of AG to CMC and irradiation dose were systematically optimized to achieve a superabsorbent hydrogel with a maximum swelling capacity. The structure, crystallinity, thermal stability, and surface morphology were characterized by Fourier transform infrared spectroscopy (FT‐IR) and elemental analysis, X‐ray diffraction (XRD), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM), respectively. FTIR proved that the grafting reaction occurred between the hydroxyl group of CMC and PAG chain. The thermal analysis data show that the prepared hydrogel is more thermally stable than pure CMC. The swelling behaviors in distilled water in various pH solutions, temperature and various ionic salt solutions (NaCl as monovalent, CaCl₂ as divalent and FeCl₃ as trivalent) were investigated in detail. The effect of cationic salt solutions on the swelling had the following order: Na⁺ > Ca²⁺ > Fe³⁺. In addition, the pH‐reversibility was preliminarily investigated with alternating pH between 12 and 2. The equilibrium swelling of CMC/PAG was achieved in 70 min. The hydrogel was responsive to the pH and salts; it also has reversible swelling and deswelling character. POLYM. ENG. SCI., 54:2753–2761, 2014. © 2013 Society of Plastics Engineers