Controlled mechanical and swelling properties of poly(vinyl alcohol)/sodium alginate blend hydrogels prepared by freeze–thaw followed by Ca2+ crosslinking

Poly(vinyl alcohol) (PVA)/sodium alginate (SA) blend hydrogels have immense potential for use as functional biomaterials. Understanding of influences of processing parameters and compositions on mechanical and swelling properties of PVA/SA blend hydrogels is very important. In this work, PVA/SA blend hydrogels with different SA contents were prepared by applying freeze–thaw method first to induce physical crosslinking of PVA chains and then followed by Ca²⁺ crosslinking SA chains to form interpenetrating networks of PVA and SA. The effects of number of freeze–thaw cycles, SA content and Ca²⁺ concentration on mechanical properties, swelling kinetics, and pH‐sensitivity of the blend hydrogels were investigated. The results showed that the blend hydrogels have porous sponge structure. Gel fraction, which is related to crosslink density of the blend hydrogels, increased with the increase of freeze–thaw cycles and strongly depended on SA content. The SA content exerts a significant effect on mechanical properties, swelling kinetics, and pH‐sensitivity of the blend hydrogels. The number of freeze–thaw cycles has marked impact on mechanical properties, but no obvious effect on the pH‐sensitivity of the PVA/SA blend hydrogels. Concentration of CaCl₂ aqueous solution also influences mechanical properties and pH‐sensitivity of the blend hydrogel. By altering composition and processing parameters such as freeze–thaw cycles and concentration of CaCl₂ aqueous solution, the mechanical properties and pH‐sensitivity of PVA/SA blend hydrogels can be tightly controlled. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

State of water in chitosan–PVA hydrogel

The bound water fraction (X_BW) of a newly‐ developed pH‐sensitive, biodegradable chitosan‐polyvinyl alcohol (PVA) hydrogel crosslinked with glutaraldehyde (GA) was investigated as a function of the chitosan/PVA molar ratio, GA concentration (C_GA), and ionization state. Differential scanning calorimetry (DSC) was used to determine the X_BW of the initial hydrogel, and of the hydrogel equilibrated in pH 3 and pH 7 buffers. Changes in X_BW during swelling and shrinking of hydrogel were also investigated. In the initial state of hydrogel, X_BW increased with increasing PVA concentration (C_PVA), without being significantly affected by C_GA. In the buffer‐equilibrated hydrogels, X_BW decreased with increasing C_PVA and decreasing C_GA. The amount of bound water based on dry mass (C_BW) was substantially higher when the hydrogel was in the ionized (swollen) state compared to its unionized counterpart. This may be due to the association of a large quantity of water molecules with ? NH₃⁺ groups of chitosan when the gel swelled in the acidic environment. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3227–3232, 2006     

Preparation and characterization of biocompatible spongy cryogels of poly(vinyl alcohol)–gelatin and study of water sorption behaviour

Porous biocompatible spongy hydrogels of poly(vinyl alcohol) (PVA)–gelatin were prepared by the freezing–thawing method and characterized by infrared and differential scanning calorimetry. The prepared so‐called ‘cryogels’ were evaluated for their water‐uptake potential and the influence of various factors, such as the chemical architecture of the spongy hydrogels, pH and the temperature of the swelling bath, on the degree of water sorption by the cryogels was investigated. It was found that the water sorption capacity constantly decreased with increasing concentration of PVA while initially an increase and thereafter a decrease in swelling was obtained with increasing amounts of gelatin in the cryogel. The water sorption capacity decreased with an increase in the number of freeze–thaw cycles. The hydrogels were also swollen in salt solutions and various simulated biological fluids and a fall in swelling ratio was noticed. The effect of the drying temperature of the cryogel on its water sorption capacity was also investigated, and a decrease in swelling was obtained with increasing temperature of drying. The biocompatibility of the prepared materials was assessed by in vitro methods of blood‐clot formation, platelet adhesion, and per cent haemolysis. It was noticed that with increasing concentration of PVA and gelatin the biocompatibility increased, while a reduced biocompatibility was noted with an increasing number of freeze–thaw cycles. Copyright © 2005 Society of Chemical Industry     

Swelling behavior of semi‐interpenetrating polymer network hydrogels composed of poly(vinyl alcohol) and poly(acrylamide‐co‐sodium methacrylate)

Interpenetrating polymer network (IPN) hydrogels based on poly(vinyl alcohol) (PVA) and poly(acrylamide‐co‐sodium methacrylate) poly(AAm‐co‐SMA) were prepared by the semi IPN method. These IPN hydrogels were prepared by polymerizing aqueous solution of acrylamide and sodium methacrylate, using ammonium persulphate/N,N,N¹,N¹‐tetramethylethylenediamine (APS/TMEDA) initiating system and N,N¹‐methylene‐bisacrylamide (MBA) as a crosslinker in the presence of a host polymer, poly(vinyl alcohol). The influence of reaction conditions, such as the concentration of PVA, sodium methacrylate, crosslinker, initiator, and reaction temperature, on the swelling behavior of these IPNs was investigated in detail. The results showed that the IPN hydrogels exhibited different swelling behavior as the reaction conditions varied. To verify the structural difference in the IPN hydrogels, scanning electron microscopy (SEM) was used to identify the morphological changes in the IPN as the concentration of crosslinker varied. In addition to MBA, two other crosslinkers were also employed in the preparation of IPNs to illustrate the difference in their swelling phenomena. The swelling kinetics, equilibrium water content, and water transport mechanism of all the IPN hydrogels were investigated. IPN hydrogels being ionic in nature, the swelling behavior was significantly affected by environmental conditions, such as temperature, ionic strength, and pH of the swelling medium. Further, their swelling behavior was also examined in different physiological bio‐fluids. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 302–314, 2005     

Swelling behavior and cell viability of dehydrothermally crosslinked poly(vinyl alcohol) hydrogel grafted with N‐vinyl pyrrolidone or acrylic acid using γ‐radiation

To improve equilibrium water content, dehydrothermally crosslinked poly(vinyl alcohol) (PVA) hydrogel was grafted with N‐vinyl pyrrolidone (NVP) or acrylic acid (AA) monomer using γ‐radiation. Swelling behavior of the grafted hydrogels was studied in phosphate‐buffered saline, and cell viability was evaluated using fibroblast cells from mouse connective tissue. Equilibrium water content of AA‐ and NVP‐grafted PVA hydrogel ranged between 40–60% and 60–80%, respectively, depending on radiation dose and monomer concentration. For maximum degree of swelling, the optimum monomer concentration and radiation dose were 20% by weight and 20 kGy, respectively. Fibroblast cells seeded on NVP‐grafted hydrogel had an extended oval morphology while those seeded on AA‐grafted PVA had a rounded spherical morphology. These results support the use of NVP for grafting PVA to increase swelling and improve cell viability. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2862–2868, 2004     

Synthesis of an alginate–poly(sodium acrylate‐co‐acrylamide) superabsorbent hydrogel with low salt sensitivity and high pH sensitivity

This article describes the synthesis and swelling behavior of a superabsorbing hydrogel based on sodium alginate (NaAlg) and polyacrylonitrile (PAN). The physical mixture of NaAlg and PAN was hydrolyzed with a solution of NaOH to yield an alginate–poly(sodium acrylate‐co‐acrylamide) [Alg–poly(NaAA‐co‐AAm)] superabsorbent hydrogel. A proposed mechanism for hydrogel formation was suggested, and the structure of the product was established with Fourier transform infrared spectroscopy. The effects of reaction variables were systematically optimized to achieve a hydrogel with a swelling capacity as high as possible. Under the optimized conditions concluded, the maximum capacity of swelling in distilled water was 610 g/g. The absorbency of the synthesized hydrogels was also measured in various salt solutions. The swelling ratios decreased with an increase in the ionic strength of the salt solutions. In addition, the swelling capacity was determined in solutions with pHs ranging from 1 to 13. The Alg–poly(NaAA‐co‐AAm) hydrogel exhibited pH responsiveness, so a swelling–deswelling pulsatile behavior was recorded at pHs 2 and 8. This on–off switching behavior made the hydrogel as a good candidate for the controlled delivery of bioactive agents. Finally, the swelling kinetics of the hydrogels with various particle sizes were preliminarily investigated as well. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2927–2937, 2006     

Network parameters and volume phase transition behavior of poly(N‐isopropylacrylamide) hydrogels

Thermosensitive hydrogels were prepared by free radical polymerization in aqueous solution from N‐isopropylacrylamide (NIPA) monomer and N,N‐methylenebis(acrylamide) (MBAAm) crosslinker. The swelling equilibrium of the hydrogels in deionized water was investigated as a function of temperature and MBAAm content. The results indicated that the swelling behavior and temperature sensitivity of the hydrogels were affected by the amount of MBAAm content. The average molecular mass between crosslinks and polymer–solvent interaction parameter (χ) of the hydrogels were determined from equilibrium swelling values. The swelling variations were explained according to swelling theory based on the hydrogel chemical structure. The swelling equilibrium of the hydrogels was also investigated as a function of temperature in aqueous solutions of the anionic surfactant sodium dodecyl sulfate (SDS) and the cationic surfactant dodecyltrimethylammonium bromide (DTAB). In deionized water, the hydrogels showed a discontinuous volume phase transition at 32°C. In SDS and DTAB solutions, the equilibrium swelling ratio and the volume phase transition temperature (lower critical solution temperature) of the hydrogels increased, which is ascribed to the conversion of nonionic PNIPA hydrogel into polyelectrolyte hydrogels because of binding of surfactant molecules through the hydrophobic interaction. Additionally, the amount of free SDS and DTAB ions was measured at different temperatures by a conductometric method; it was found that the electric conductivity of the PNIPA–surfactant systems depended strongly on both the type and concentration of surfactant solutions. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1756–1762, 2006     

Synthesis and characterization of an interpenetrating polymer network composed of poly(methacrylic acid) and poly(vinyl alcohol)

Temperature and pH‐responsive interpenetrating polymer network (IPN) hydrogels, constructed with poly(methacrylic acid) (PMAA) and poly(vinyl alcohol) (PVA), by a sequential IPN method, were studied. The characterization of IPN hydrogels was investigated by Fourier‐transform infrared spectroscopy, differential scanning calorimetry (DSC) and swelling under various conditions. The IPN hydrogels exhibited relatively high swelling ratios, in the range 230–380 %, at 25 °C. The swelling ratios of the PMAA/PVA IPN hydrogels were pH and temperature dependent. DSC was used for the quantitative determination of the amounts of freezing and non‐freezing water. The amount of free water increased with increasing PMAA content in the IPN hydrogels. Copyright © 2004 Society of Chemical Industry     

Synthesis and network parameters of hydrophobic poly(N‐[3‐(dimethylaminopropyl)]methacrylamide‐co‐lauryl acrylate) hydrogels

Hydrophobic poly(N‐[3‐(dimethylaminopropyl)]methacrylamide‐co‐lauryl acrylate) [P(DMAPMA‐co‐LA)] hydrogels with different LA content were synthesized by free‐radical crosslinking copolymerization of corresponding monomers in water by using N,N‐methylenebis(acrylamide) as the crosslinker, ammonium persulfate as the initiator, and N,N,N′,N′‐tetramethylethylenediamine as the activator. The swelling equilibrium of the hydrogels was investigated as a function of temperature and hydrophobic comonomer content in pure water. An interesting feature of the swelling behavior of the P(DMAPMA‐co‐LA) hydrogels with low LA content was the reshrinking phase transition where the hydrogels swell once and collapse as temperature was varied in the range of 30–40°C. The average molecular mass between crosslinks (M?_c) and polymer–solvent interaction parameter (χ) of the hydrogels were calculated from equilibrium swelling values. The enthalpy (ΔH) and entropy (ΔS) changes appearing in the χ parameter for the hydrogels were determined by using the Flory–Rehner theory based on the phantom network model of swelling equilibrium. The positive values for ΔH and ΔS indicated that the hydrogels had a positive temperature‐sensitive property in water, that is, swelling at a higher temperature and shrinking at a lower temperature. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 4159–4166, 2006     

Properties of hydrogels of atactic poly(vinyl alcohol)/NaCl/H2O system and their application to drug release

In order to prepare cost‐effective physically cross‐linked hydrogels including food salt sodium chloride, samples, were prepared with various concentrations of NaCl and respective atactic poly(vinyl alcohol) (a‐PVA), and were evaluated. It had been observed that hydrogels containing NaCl concentration (9–11 wt%) along with a‐PVA concentration 9–5% respectively exhibited higher melting points (91.5–95.1 °C). A higher melting point characterizes the hydrogel composition of a system like a‐PVA(7%)/NaCl(11%)/H₂O. The swelling degree of this hydrogel was found to be comparatively better at 37 °C than at any other temperature studied here. However, irregular Fickian swelling was found at this temperature. The UV light absorption maximum at 362–364 nm and minimum at 351 nm for this hydrogel had been found as evidence of physical cross‐linking. A drug, theophylline was loaded by solvent‐sorption and feed‐mixture dissolving methods. The feed‐mixture dissolving method is better than solvent sorption because of high drug loading, comparatively low fraction release rate and more sustained‐release of drug than that of solvent‐sorption. Theophylline was released twice as fast from the hydrogel after solvent‐sorption drug loading (3 h) than from that which used the feed‐mixture dissolving method (6.5 h). Theophylline‐loaded hydrogels of this system (feed‐mixture dissolving) were then prepared at high temperature (60 °C) thawing for 6 h followed by chilling at 0.4 °C for 3 h as one cycle. And the drug release behaviour and mass transfer were found almost the same as for chilling (24 h at 0.4 °C)–thawing (48 h at room temperature). Drug release behaviour was studied as apparently irregular Fickian diffusion (Higuchi Matrix Dissolution Model). © 2002 Society of Chemical Industry     

Thermally crosslinked anionic hydrogels composed of poly(vinyl alcohol) and poly(γ‐glutamic acid): Preparation,characterization, and drug permeation behavior

pH‐sensitive anionic hydrogels composed of poly(vinyl alcohol) (PVA) and poly(γ‐glutamic acid) (γ‐PGA) were prepared by the freeze drying method and thermally crosslinked to suppress hydrogel deformation in water. The physical properties, swelling, and drug‐diffusion behaviors were characterized for the hydrogels. In the equilibrium swelling study, PVA/γ‐PGA hydrogels shrunk in pH regions below the pK_a (2.27) of γ‐PGA, whereas they swelled above the pK_a. In the drug‐diffusion study, the drug permeation rates of the PVA/γ‐PGA hydrogels were directly proportional to their swelling behaviors. The cytocompatibility test showed no cytotoxicity of the PVA/γ‐PGA hydrogels for the 3T3 fibroblast cell lines. The results of these studies suggest that hydrogels prepared from PVA and γ‐PGA could be used as orally administrable drug‐delivery systems. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Preparation and characterization of polyacrylic acid‐poly(vinyl alcohol)‐based interpenetrating hydrogels

Some structural features of hydrogels from poly(acrylic acid) (PAAc) of various crosslinking degrees have been investigated through mechanical and swelling measurements. Interpenetrating polymer hydrogels (IPHs) of poly(vinyl alcohol) (PVA) and PAAc have been prepared by a sequential method: crosslinked PAAc chains were formed in aqueous solution by crosslinking copolymerization of acrylic acid and N,N‐methylenebisacrylamide in the presence of PVA. The application of freeze–thaw (F–T) cycles leads to the formation of a PVA hydrogel within the synthesized PAAc hydrogel. The swelling and viscoelastic properties of the IPHs were evaluated as a function of the content of crosslinker and the application of one F–T cycle. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 5789–5794, 2006     

Synthesis and characterization of cetirizine‐containing,pH‐sensitive acrylic acid/poly(vinyl alcohol) hydrogels

In this study, interpenetrated acrylic acid (AA)/poly(vinyl alcohol) (PVA) hydrogels were prepared by free‐radical polymerization with N,N‐methylene bisacrylamide (MBAAm) as a crosslinker. The basic structural parameters, such as the molecular weight between crosslinks, volume interaction parameter, number of crosslinks, Flory–Huggins solvent interaction parameter, and diffusion coefficient, were calculated. Cetirizine dihydrochloride was loaded as a model drug in selected samples. The prepared hydrogels were evaluated for swelling, sol–gel fraction, and porosity. The swelling of the AA/PVA hydrogels was found to be directly proportional to the pH, that is, 1.2–7.5, depending on composition. The percentage of cetirizine hydrochloride was found to be directly proportional to the buffer pH and was at its maximum at pH 7.5, that is, 90–95%, and its lowest at pH 1.2, that is, 20–30%. The gel fraction increased with increasing concentration of AA and MBAAm, whereas the porosity showed the same response with AA, but an inverse relationship was observed with MBAAm. The drug‐release data were fitted into various kinetics models, including the zero‐order, first‐order, Higuchi, and Peppas models, which showed non‐Fickian diffusion. The prepared hydrogels were characterized by Fourier transform infrared spectroscopy and scanning electron microscopy, and no interaction was found among the polymer ratio and the drug. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43407.     

Partially hydrolyzed kappa carrageenan—polyacrylonitrile as a novel biopolymer‐based superabsorbent hydrogel: Synthesis,characterization, and swelling behaviors

In this paper, synthesis and swelling behavior of a novel superabsorbent hydrogel based on kappa carrageenan (κC) and polyacrylonitrile (PAN) was investigated. To achieve partially hydrolyzed κC‐PAN hydrogel, physical mixture of κC and PAN was hydrolyzed by NaOH solution. During alkaline hydrolysis, the nitrile groups of PAN are converted to a mixture of hydrophilic carboxamide and carboxylate groups follow by in situ crosslinking of the grafted PAN chains. The reaction variables affecting on the swelling capacity of the hydrogel were systematically optimized to achieve a hydrogel with swelling capacity as high as possible. Under the optimized conditions concluded, super swelling hydrogel with the ability of water absorption up to 3260 g/g (water/dry hydrogel powder) has been prepared. Swelling measurements of the synthesized hydrogels was carried out in various salt solutions and solutions with different pH. The results indicate that the hydrogels have good pH sensitivity and pH‐reversible property between pH 2 and pH 8. POLYM. ENG. SCI. 46:1778–1786, 2006. © 2006 Society of Plastics Engineers.     

Preparation and swelling behavior of macroporous poly(acrylamide‐co‐sodium methacrylate) superabsorbent hydrogels

Macroporous superabsorbent hydrogels (SAHs) composed of acrylamide (AAm) and sodium methacrylate (NMA) were prepared by aqueous solution polymerization in the presence of a glucose solution. Their swelling capacity was investigated as a function of the concentrations of the glucose solution, sodium methacrylate, crosslinker, initiator, and activator. The porosity of the poly(acrylamide‐co‐sodium methacrylate) superabsorbent hydrogels was confirmed using scanning electron microscopy. The SAHs were characterized by IR spectroscopy. To estimate the effect on the swelling behavior, three types of crosslinkers were employed: N,N′‐methylenebisacrylamide, 1,4‐butanediol diacrylate, and diallyl phthalate. Network structural parameters such as initial swelling rate, swelling rate constant, and maximum equilibrium swelling were evaluated by water absorption measurement. The equilibrium water content (EWC%) of the AAm–NMA macroporous SAHs was found to be in the range of 93.31–99.68, indicating that these SAHs may have applications as biomaterials in the medicinal, pharmaceutical, and veterinary fields. Most of the SAHs prepared in this investigation followed non‐Fickian‐type diffusion, and few followed a case II– or super–case II‐type diffusion. The diffusion coefficients of these macroporous SAHs were investigated. Further, the swelling behavior of these SAHs also was investigated at different pHs and in different salt solutions and simulated biological fluids. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3202–3214, 2006     

Synthesis of copolymeric hydrogels using gamma radiation and their utilization in the removal of some dyes in wastwater

Copolymer hydrogels were prepared by γ‐radiation copolymerization of maleic acid (MA) and 2‐hydroxyethylacrylate (HEA) or acrylamide (AAm). The effect of AAm/MA and HEA/MA composition and irradiation dose on the gel fraction yield in the prepared hydrogels was determined. It was found that as the content of MA increased, the gel fraction yield decreased. The increase of irradiation dose resulted in increasing the crosslinked network structure and consequently the gel percent. The parameters of equilibrium swelling, maximum swelling, initial swelling rate, diffusion exponent, and diffusion coefficient of the hydrogels were calculated and evaluated, and it was found that water diffusion to the hydrogels generally was a non‐Fickian diffusion type. Characterization of the prepared hydrogels was studied and accordingly the possibility of its practical use in the treatment of waste dyes from aqueous solution was studied. The effect of treatment time, the pH of the feed solution, initial feed concentration, and temperature on the dye uptake was also investigated. The maximum uptake of the investigated dyes was higher for HEA/MA hydrogel than that for AAm/MA hydrogel. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102:3720–3731, 2006     

Temperature and pH‐response swelling behavior of poly(2‐ethyl‐2‐oxazoline)/chitosan interpenetrating polymer network hydrogels

Interpenetrating polymer network (IPN) hydrogels composed of poly(2‐ethyl‐2‐oxazoline) (PEtOz) and chitosan (CS) were prepared with radical polymerization and were characterized for their swelling properties. Sample OC11 (hydrogel weight ratio PEtOz/CS = 1/1) swelled more than samples OC21 (PEtOz/CS = 2/1) and OC31 (PEtOz/CS =3/1), exhibiting a swelling ratio of about 2000 wt % in deionized water; the swelling ratios of the other samples were about 1000 and 700 wt %. The swelling behavior of the IPN hydrogels was observed under various pH and temperature conditions. The swelling ratios of the samples ranged from about 2000 to 6500 wt % at lower pHs, with a maximum swelling ratio of about 6500 wt % in a pH 2 aqueous solution. They exhibited low critical solution temperature behavior, with sample OC31 more sensitive to temperature and sample OC11 more sensitive to pH. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1100–1103, 2006     

Synthesis and characterization of superabsorbent hydrogels composites based on polysuccinimide

A kind of novel superabsorbent hydrogel with high swelling ratio property that could be used for the development of water absorbing resin, soil water retention agent, and chemical sand‐fixing material was synthesized in this study. The hydrogels were prepared by the crosslinking reaction of polysuccinimide (PSI). The relationships between swelling ratio and volume of solvent as well as the concentration of crosslinking agent were investigated in detail. Several composites, such as starch, carrageenan, and polyacrylamide, were added into hydrogels to enhance the swelling ratio. It was found that the swelling ratio was significantly increased, which the maximum water absorbency was enhanced 2.46 times when the composite polyacrylamide (PAM) was added compared to the control. The effects of ionic strength and sensitivity of pH on hydrogels were also studied. The modified hydrogels products with swelling ratio less sensitivity to the salinity as well as relative high swelling ration in salinity system were also obtained by adding PAM. Through the Fourier transform infrared spectroscopy (FTIR) characterizations, the crosslinking reaction mechanism and the structure of composite were proposed. In addition, the transmission electron microscopy (TEM) examinations showed that some composite materials elevated the physical crosslinked and connected channels density substantially. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 550–557, 2006     

Radiation synthesis and characterization of 2‐hydroxyethyl‐methacrylate‐based hydrogels containing di‐ and tri‐protic acid and its application on wastewater treatment

Radiation‐crosslinked 2‐hydroxyethylmethacrylate/citric acid (HEMA/CAc), 2‐hydroxyethylmethacrylate/tartaric acid (HEMA/TA), and 2‐hydroxyethylmethacrylate/succinic acid (HEMA/Sc) copolymers were prepared by using ⁶⁰Co γ‐rays. The gel fraction yield and the swelling behavior of the prepared hydrogels were studied. It was shown that increasing irradiation doses was accompanied by an increase in yield of gel fraction and a decrease in swelling degree. The parameters of equilibrium swelling, maximum swelling, initial swelling rate, swelling exponent, and diffusion coefficient of the hydrogels were determined by studying the swelling behavior of the hydrogels prepared. It was seen that the equilibrium swelling degree increases as the content of acid increases, as a result of introducing more hydrophilic groups. When the hydrophilic polymer (acids) varies in the content range of 40–80 mg, swelling exponents (n) decreases, thereby indicating a shift in the water‐transport mechanism from the anomalous (non‐Fickian)‐type to the Fickian‐type. Characterization and some selected properties of the prepared hydrogels were studied, and accordingly the possibility of its practical use in the treatment of industrial wastes such as dyes and heavy metals (Fe, Ni, Co, and Cu) were also studied. The effect of treatment time, pH of feed solution, initial feed concentration, and temperature on the dye and heavy metals uptake was determined. The uptake order for a given metal was HEMA/TA hydrogel > HEMA/CAc > HEMA/Sc hydrogel. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Thermosensitive and ampholytic hydrogels for salt solution

A series of N‐isopropylacrylamide/[[3‐(methacryloylamino)propyl]dimethy(3‐sulfopropyl)ammonium hydroxide] (NIPAAm/MPSA) copolymer hydrogels were prepared with various compositions. Swelling of the hydrogels in water, aqueous NaCl, KCl, CaCl₂, and MgCl₂ solutions was studied. NIPAAm/MPSA hydrogels have a higher degree of swelling in water and salt solutions than that of poly(N‐isopropylacrylamide) (PNIPAAm). Also, NIPAAm/MPSA hydrogels are more salt resistant when deswelling in salt solutions. For <7 mol % MPSA, the formed hydrogels retain both temperature reversibility and high swelling. A higher content of MPSA (>11 mol %) leads to better salt resistance but a decrease in thermosensitivity. The swelling of NIPAAm/MPSA hydrogel in 0.05M NaCl is non‐Fickian. In NaCl and KCl aqueous solutions, the zwitterionic hydrogels do not show obvious antipolyelectrolyte swelling behavior, whereas in divalent salt CaCl₂ and MgCl₂ solutions, the swelling ability of NIPAAm/MPSA hydrogels is enhanced at low salt concentration, then decreases with further increase in salt concentration. The lower critical solution temperatures of NIPAAm/MPSA hydrogels are also affected by concentrated salt solution. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2032–2037, 2003