In the present study, a more potential and economical method is described to reutilize a waste adsorbent as the waste Cu2+-loaded poly(AAc/AM/SH) SAHs were not undergone any regeneration process and directly applied to adsorb phosphate ion from another waste solution. The SAHs poly(AAc-AM-SH) was anionic in nature, thus show higher affinity toward Cu2+ ions, but it hardly adsorb anions due to its characteristics of negative charge existing on the polymeric surface. The adsorption of Cu2+ makes it positively charged moiety and so it is being capable of anions/anionic dye adsorption. The various factors affecting the phosphate adsorption including pH, contact time, initial concentration of the phosphate were systematically investigated. The maximum phosphate adsorption was obtained 87.62 mg/g. The adsorption data fitted the Langmuir adsorption isotherm. The desorption studies showed that the regeneration of the poly(AAc/AM/SH)–Cu SAHs adsorbent can be easily achieved. The results confirmed that poly (AAc/AM/SH) superabsorbent hydrogels loaded with Cu2+ ion can be applied as effective solid adsorbent for the removal of phosphate ions from waste water and aqueous effluents.

A series of (AAc/SH/NaAlg) superabsorbent hydrogels based on poly Acrylic acid (AAc), sodium humate (SH) and sodium alginate (NaAlg) were prepared by free radical solution copolymerization. The effect of sodium alginate was studied in a range of 20–66 wt%. Synthesized superabsorbent hydrogels (SAHs) were characterized by swelling behavior. Synthesized SAHs were tested as an adsorbent for MB and CV dyes. The binding capacity for MB and CV molecules were 367 mg/g/L and 359 mg/g/L at 380 mg/L respectively, for initial molecules concentration per gram of (AAc/SH/NaAlg) SAHs containing 50 wt% of NaAlg. The adsorption values obeyed Langmuir sorption Isotherm.

A novel superabsorbent hydrogel (SAHs) composed of (acrylic acid, sodium alginate and sodium humate) (AAc/NaAlg/SH) SAHs were tested as adsorbent for metal ions Cu 2+ , Pb 2+ , and Fe 2+ ions as well as MB and CV dyes. The influence of SH concentration varies from 6.97, 8.04, 9.09, 10.11% and 11 wt% were designated as S 1 , S 2 , S 3 , S 4 , S 5 , respectively. The synthesized superabsorbent hydrogel were used for the adsorption of Cu 2+ , Pb 2+ , Fe 2+ and MB and CV dyes from their aqueous solutions. The binding capacity for Cu 2+ , Pb 2+ , Fe 2+ ions were 311 mg/gm/L at 850 mg/L, 209 mg/gm/L at 850 mg/L and 197 mg/gm/L at 850 mg/L for initial ion concentration respectively and MB and CV dyes molecules were 323 mg/gm/L at 360 mg/L, 289 mg/gm/L at 360 mg/L for initial molecule concentration per gram of AAc/NaAlg/SH containing 9.09 wt% SH content. The adsorption data obeyed Langmuir sorption isotherms.

A series of superabsorbent hydrogel (SAHs) based on poly Acrylic Acid (AAc), Sodium Alginate (NaAlg) and Sodium Humate (SH) (AAc/NaAlg/SH) was prepared by free radical solution copolymerization. Hydrogel having sodium humate 9.09 wt% showed maximum water absorbency of 906 g of water per gram of superabsorbent hydrogel. The application of the synthesized superabsorbent hydrogel was investigated in agriculture as soil conditioner for water retention in sandy soil. The study revealed that the synthesized superabsorbent hydrogels could act as an effective water saving material for agricultural applications. Swelling behavior (such as swelling ratio, initial swelling rate constant, swelling exponent, diffusion coefficient and penetration velocity etc.) for all the synthesized superabsorbent hydrogels having various (6.9 to 11 wt %) concentration of SH was studied. Swelling exponent was found in range of (0.712 to 0.802); thus suggesting non fickian diffusion mechanism. The effect of synthesized SAHS on growth of seeds of corn and white gourd are reported.

A series of multi-component poly (acrylamide-co-2-hydroxyethyl actylate-co-acrylic acid) [AM-co-HEA-co-AA] hydrogels were synthesized by varying the hydroxyl ethyl acrylate (HEA) content from 0% - 50% approximately. The hydrogels were characterized by SEM analysis, elemental analysis, residual acrylic acid analysis, network parameters and swelling kinetic parameters. The influence of non-ionic HEA content on the water diffusion rate in three stages (i.e. initial, middle and latter) of swelling process were studied along with the mathematical models fitted on preliminary swelling data. The model fitting exhibited that as HEA content increased in feed, water diffusion rate in the initial stage of swelling process was increased. But However, applicability range of the early-time model for the initial stage of water diffusion decreased. Interestingly, when HEA content exceeded above the 24.39%, the early-time model did not work.

In the last three decades a large number of hydrogels have been developed to suit a wide variety of biomedical applications. In order to tailor a hydrogel structure according to a specifi c medicinal requirement, it is often required to synthesize it by using a combination of three monomers. Out of three, one monomer may be ionic (cationic/anionic) other hydrophobic, and the third application-specifi c. This entry discusses the various types of monomers used in hydrogel synthesis with special focus anionic monomers. The important synthesis parameter such as effect of monomer composition and type, cross-linker type, cross-link density on hydrogel structure, and properties have been discussed in detail with examples. Other synthesis parameters such as nature of reaction medium on swelling also has been discussed. The effect of swelling and chain structure of glass transition temperature has also been discussed. Afterward hydrogels based on polyacrylic acid and recent researches in anionic hydrogels based on acrylic acid and other monomers are discussed. This entry also presents two case studies on terpolymeric hydrogels based on acrylamide, acrylic acid, and butylmethacrylate or hydroxyethylacrylate in order to illustrate the wide variation in swelling that can be achieved by simply altering the monomer ratios of hydrogels. Another very important observation made is the nonlinear variation of swelling with increasing concentration of one monomer (keeping other two constant). It is also important to point out that the monomer concentrations in feed did not necessarily get incorporated in the synthesized hydrogen l. As the monomer composition signifi cantly affects the cross-link density and mesh size of hydrogel, the controlled release properties of hydrogels also get altered signifi cantly.

A novel superabsorbent hydrogel (SAH) composed of poly(acrylic acid-sodium acrylate-acrylamide)/sodium humate poly(AAc-SA-AM)/SH was synthesized and applied as adsorbent to adsorb crystal violet (CV) and methylene blue (MB) dye in its dry as well as swollen condition from the aqueous solutions. The swelling ratios of the synthesized SAHs were determined. The factors affecting adsorption capacity of the poly(AAc-SA-AM)/SH hydrogel, such as contact time, temperature, SH content (wt.%), and initial concentration of both dyes, were systematically investigated. The experimental data suggested that an appropriate addition of SH (2.40 wt.%) increases the swelling ratio as well as adsorption capacity of poly(AAc-SA-AM) hydrogel. The adsorption capacity was approximately equal for the dry (231mg/g for CV and 270mg/g for MB) and equilibrium SAHs (240mg/g for CV and 278mg/g for MB). The results also revealed that the swollen SAHs exhibited higher adsorption rate than the dry SAHs due to presence of functional anionic groups in its elongated state. The adsorption equilibrium data fitted very well to the Langmuir isotherm than the Freundlich isotherm. Thermodynamic parameters of adsorption were also calculated, and the negative change in Delta G degrees and Delta H degrees confirmed that the dye adsorption process was spontaneous and exothermic in nature. The kinetic studies showed that the adsorption phenomenon followed the pseudo-second-order kinetic model.

In the present investigation, a series of hydrogels based on poly (AM-co-AA-co-HEA) from the constant weight ratio (1/1/1) of acrylamide (AM), acrylic acid (AA), and hydroxy ethyl acrylate (HEA) monomers were synthesized by solution polymerization to optimize the reaction conditions. The reaction conditions were optimized by varying the reaction temperature, reaction time, crosslinker and initiator concentration, and amount of solvent. At optimized reaction conditions, two different sets of hydrogels were synthesized by varying the concentrations of cross-linker (glycidyl methacrylate, GMA) from 1 to 4 % and initiator (ammonium per sulphate, APS) from 1 to 4 %, to study the effects of crosslinker variation as well as initiator variation on swelling ratio by Flory’s equations. The three mathematical models (early time, late time and etters model) were fitted on experimental swelling data to investigate the entire swelling profile of all the hydrogels prepared with various amounts of GMA and APS content. Values of swelling transport exponents showed that the swelling mechanism was shifted from diffusion to relaxation controlled in case of increasing APS content, while only diffusion mechanism was followed for increasing GMA content. The proportionality constant (k) was calculated by two different models (1) power law and (2) Baker and Lonsdale to confirm the validity of early-time model fitting on experimental swelling data.

Hydrogels are being prepared for use in a wide variety of applications ranging from medicines, tissue engineering, superalpsorbents, controlled release of drugs & fertilizers, and oil absorbers etc. This review highlights hydrogel structure and their different classifications under various heads. It also discusses various routes to obtain tailormade hydrogels by polymerizing a combination of two or more monomers with proper type of crosslinks in order to obtain desired properties in the resulting hydrogel. Novel hydrogel configurations like microgels and nanogels, slide ring gels, double network hydrogels and nanocomposite gels have also been reviewed.

The traditional method for the treatment of used adsorbents is usually recovery for recycling or direct discarding them. In the present study, a more potential and economical method is described to reutilize a waste adsorbent. Poly(AAc/AM/SH) SAHs have proved to be a good adsorbent for cationic MB dye, and after adsorption, the SAHs were recovered for recycling. In this work, the waste MB dye loaded poly(AAc/AM/SH) SAHs were not recovered but directly applied to adsorb an anionic MO dye from another waste solution. The poly(AAc/AM/SH) SAHs after the MB dye adsorption were stable and suitable for MO dye adsorption for altered surface structures within a wide pH range. The various factors affecting the MO dye adsorption, including pH, contact time, ionic strength, initial concentration of the MO dye, and temperature, were systematically investigated. The equilibrium adsorption data fitted very well to the Langmuir adsorption isotherm and the maximum MO dye adsorption capacity reached to a high of 134mg/g at 30 degrees C. The thermodynamic parameters such as Delta H-0, Delta G(0), and Delta S-0 for the MO dye adsorption processes onto the SAHs were also evaluated, and the obtained negative Delta G(0) and Delta H-0 values confirmed that the MO adsorption process was spontaneous as well as exothermic. The kinetic studies indicate that the MO dye adsorption process was well consistent with the pseudo-second-order kinetic model. The desorption studies showed that the regeneration of the poly(AAc/AM/SH)-MB SAHs adsorbent can be easily achieved.

A novel superabsorbent hydrogel based on poly(acrylic acid-sodium acrylate-acrylamide)/sodium humate poly(AAc-SA-AM)/SH was applied as adsorbent to adsorb metal ions (Pb2+, Fe2+) from the aqueous solutions. The factors affecting adsorption capacity of the poly(AAc-SA-AM)/SH hydrogel such as contact time, pH, temperature, SH content (wt.%), initial concentration of the metal ion, and ionic strength were systematically investigated. Results from the experimental data revealed that an appropriate addition of SH (2.44 wt.%) not only increases the metal ion adsorption of poly(AAc-SA-AM) hydrogel but also improves its regeneration ability. The results showed that the adsorption equilibrium data fitted the Langmuir isotherm better than the Freundlich isotherm. The maximum binding capacity for Pb2+ ion was 198 and 164 mg/g/l for Fe2+ ion for per g of poly(AAc-SA-AM)/SH (SH4) hydrogel (high as compared to many other adsorbents). The changes in thermodynamic parameters were also calculated, and the negative Delta G degrees and Delta H degrees confirmed that the adsorption process was spontaneous and exothermic. The kinetic studies revealed that the adsorption process can be well described by the pseudo-second-order kinetic model.

The most commonly applied methods for the treatment of used adsorbents is to recover them in acid/alkaline medium or direct enflame them. This work dealt with a new potential and economic method to utilize a waste adsorbent. Poly(AAc/AM/SH) superabsorbent hydrogels have proved to be a good adsorbent for Cu2+ ions and after adsorption the hydrogels were recovered in acid medium. In this report, the Cu2+ ion adsorbed hydrogel has not undergone any regeneration process and applied directly to phosphate ion adsorption. The Cu2+ ions-loaded poly(AAc/AM/SH) hydrogels, were stable within a wide pH range and suitable for phosphate ion adsorption. The factors affecting the phosphate adsorption, such as pH, ionic strength, contact time, temperature, initial concentration of the phosphate ion, and coexisting ions were systematically investigated. The phosphate adsorption was highly pH dependent; and the maximum adsorption of 87.62 mg/g was achieved at pH 6.1. The adsorption data fitted the Langmuir adsorption isotherm better than the Freundlich isotherm. The concomitant anions show profounder adverse influence on phosphate ion adsorption of poly(AAc/AM/SH)-Cu hydrogel and the effect follows the order citrate > sulfate > bicarbonate > chloride > nitrate. The thermodynamic parameters including H degrees, G degrees, and S degrees for the adsorption processes of phosphate ions on the gel were also evaluated, and the negative G degrees and H degrees confirmed that the adsorption process was spontaneous and exothermic. The adsorption kinetic results suggest that the adsorption process was well described by the pseudo second-order kinetic model. (c) 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

A series of novel superabsorbent hydrogels based on acrylic acid (AAc), acrylamide (AM), and sodium humate (SH) were prepared by free-radical solution copolymerization for removal of dye and metal ion from waste water. Ammonium per sulfate was used as initiator and N,N' methylene bisacrylamide as crosslinker. The hydrogels were characterized with the help of FTIR and SEM. In this study the concentration of SH was varied in the range of 0.504.76 wt % based on total monomer content and the resulting hydrogels were investigated for the effect of SH on swelling and diffusion kinetic parameters such as equilibrium swelling ratio, initial swelling rate, swelling rate constant, maximum swelling at equilibrium, and type of diffusion, etc. Hydrogel having 2.43 wt % SH content showed the maximum water absorbency of 724 g of water per gram of hydrogel. Swelling exponent found in the range 0.680.79 thus suggesting Non-Fickian diffusion mechanism. The swelling behavior was also studied in different concentrations of salt solutions [sodium chloride (NaCl), magnesium chloride (MgCl2), and ferric chloride (FeCl3)]. The synthesized superabsorbent hydrogels were used for the adsorption of Cu2+ ions and methylene blue (MB) dye from their aqueous solutions. The influence of SH concentration on the Cu2+ ions and MB molecules binding capacity of hydrogels was tested. The chelation behavior was modeled using Langmuir isotherm. The maximum binding capacity for Cu2+ ion was 299 mg/L at 1000 mg/L, initial Cu2+ ion concentration and 269 mg/L at 320 mg/L, initial MB dye molecules concentration per gm of AAc/AM/SH containing 2.43 wt % SH content. (c) 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

A series of poly (AM-co-HEA-co-AA) hydrogels have been synthesized and characterized by varying 2-hydroxy ethyl acrylate (HEA) content in the range of 0-16.22% in feed. The swelling ratio of resulting hydrogels was drastically decreased 10 times, i.e., from 101.12 to 9.23 in an almost linear fashion; but the dimensional stability of these hydrogels was increased significantly from 5 to 46 days with increasing HEA content. The hydrogels exhibited Smart nature in varying pH (2-10), temperature (15-65 degrees C), ionic strength of NaCl solution (0.1M-1.5M), and different cation chloride salt solution having same ionic strength (0.1M). The swelling mechanism was shifted from non-Fickian to Fickian (at pH 2-7), super case to non-Fickian (at pH 10) with increasing HEA content. The controlled release of model drug (salicylic acid) from these hydrogels was investigated using early-time, late-time and Etters diffusion models and compared with the experimental data. It was observed that early model doesn't fit, but Etter and late-time model fitted excluding the initial phase. However, it was also observed that with increasing HEA content, the applicability of Etter's model improved, and for 16.22% HEA containing hydrogel Etters model was fitted in the full range, indicating that by varying hydrogel composition, the diffusion characteristics can be altered.

In this study, a series of poly(acrylamide-co-acrylic acid-co-2-hydroxy ethyl actylate) [AM-co-AA-co-HEA] hydrogels have been synthesized by varying the acrylic acid (AA)content over eightfold in feed in the range of 33.3493.76% by keeping other monomer constant. These hydrogels were characterized by FTIR, SEM analysis, elemental analysis, residual acrylic acid analysis, network parameters, and dynamic swelling behavior. The swelling study showed that equilibrium swelling ratio was nonlinearly increased with increasing AA content. Interestingly, the equilibrium swelling ratio decreased from 53.42 to 48.52 for 7580% AA content hydrogel. The swelling data were found to satisfactorily fit Fick's second law, demonstrating that diffusion rate of water uptake was primarily Fickian. From model fitting, it was observed that early model was applicable for first 30% water absorption, and late model was applicable for latter 70% water absorption for increasing AA content from 33.3490.90%. For 93.76% AA, early-time model was extended up to first 50% of water absorption and late model was contracted for latter 50% water absorption, indicating that excessive AA content affects the applicability range of early-time and late-time diffusion models for water absorption. Etters model was best applicable to all type of hydrogels and followed over all swelling range. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

In the present study, acetaminophen solubility and its interaction with poly(AM-co-HEA-co-AA) hydrogels containing acetaminophen (AMP) from 15% to 35% was determined by DSC thermogram; and confirmed by SEM and FTIR analysis. Results obtained by DSC indicated that acetaminophen dissolved up to 16.33% loading, while acetaminophen above the concentration 16.33% existed in crystalline form in matrices, and was responsible for the melting corresponding to the melting of acetaminophen crystals. The heat required to melt the crystalline portion of acetaminophen was theoretically calculated by using an equation, and its validity was confirmed through melting enthalpies observed experimentally. The effect of increasing amount crystalline acetaminophen on the matrix swelling, and simultaneous controlled release of acetaminophen was investigated. The drug diffusion kinetic was analyzed by fitting early-time, late-time and etters diffusion models to the drug release data observed experimentally. By increasing drug loading, values of all drug diffusional coefficients (i.e., early-time, late-time and etters) were decreased, and rank of diffusion coefficients for each hydrogel matrix was followed in the order of etters> late-time >early-time. From model fitting, it was observed that with increasing AMP content in hydrogels matrix, the applicability of early time and late time model were improved; and for 35% AMP containing hydrogel, early time was applicable for first 60% drug diffusion; late-time model was applicable for latter 50% drug diffusion; indicating that diffusion characteristics can be altered by increasing crystalline acetaminophen depending on the% acetaminophen loading in hydrogel. Etters model was best applicable to all type of hydrogel matrices, and followed over entire range of drug diffusion process.

In the present study five blends of Diglycidyl ether of bisphenol-A and thiol terminated liquid polysulfide with varying amount of polysulfide (i.e. 10 to 50 phr) were synthesized by physical mixing at 90 o C and synthesized blends were cured with phthalic anhydride. Interaction among epoxide group of DGEBA, -SH group of polysulfide and anhydride group of curing agent discussed through FT-IR analysis. The TGA studies revealed a decrease in thermal stability and activation energy (114.35 - 73.04 kJ/mole) with increase in polysulfide content. Volume resistivity decreases from 5.34 × 10 15 to 3.83 × 10 11 ohm-cm with increase in polysulfide content in the blends. The study of chemical resistance for various acids, alkalies to distilled water, sea water, xylene, ethanol, methyl ethyl ketone and acetone indicated that chemical resistance of blends decreased with increase in polysulfide content. Scanning electron microscopy (SEM) indicated the presence of two-phase morphology in the blends.

The blends of diglycidyl ether of bisphenol-A (DGEBA) and poly (hydroxyl ether of bisphenol-A) or phenoxy were synthesized by melt blending at 120 °C. These blends were cured by an aromatic amine hardener, 4,4′- diaminodiphenyl sulphone (DDS). The experiments were performed to study the different amount of phenoxy (10 to 40 parts per hundred resins) on mechanical and electrical properties of the DGEBA/phenoxy blends, such as tensile properties, flexural properties, impact strength, Rockwell hardness, and volume resistivity. The oxirane group of DGEBA epoxy resin reacts with hydroxyl group of phenoxy which provides good toughness to the epoxy resin. The tensile strength, tensile modulus, flexural strength, flexural modulus, heat deflection temperature and volume resistivity of DGEBA/phenoxy blends decreased with increasing the amount of phenoxy from 10 to 40 parts per hundred resins (phr). The opposite trend was observed in impact strength and Rockwell hardness of all DGEBA/phenoxy blends which were increased with increasing the phenoxy content from 10 to 20 phr, but then decreased upto 40 phr. The SEM studies revealed that the DGEBA/phenoxy blends show a multiphase system with an increase in the phenoxy content from 10 to 40 phr. due to inconvenience of mixing of two phases.