New smart carrageenan‐based superabsorbent hydrogel hybrid: Investigation of swelling rate and environmental responsiveness

Synthesis of novel natural‐based superabsorbents with improved properties is of prime importance in many applications. In this article we report an efficient synthesis of new polysaccharide‐based superabsorbent hybrid composing carrageenan, acrylic acid, sodium acrylate, and 2‐hydroxyethyl acrylate through homogenous solution polymerization process. Infrared spectroscopy and thermogravimetric analysis (TGA) were carried out to confirm the chemical structure of the hydrogel. Moreover, morphology of the samples was examined by scanning electron microscopy (SEM). To deeper studies on the structure‐property relation in SAP hydrogels, three hydrogels with different acrylic acid/2‐hydroxyethyl acrylate (AA/HEA) weight ratios were synthesized and swelling capacity in various media was assessed. The hydrogel hybrid was also tested to be swollen and deswollen alternatively in 0.01 and 0.1 M sodium chloride solution. Moreover, the swelling‐deswelling capability of the hydrogel in alternatively changed methanol‐water mixtures was studied. Additionally, the swelling kinetics of the synthesized hydrogels were examined. The absorbency under load (AUL) of hydrogel was also investigated by using an AUL tester at various applied pressures. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Preparation of superabsorbent polymers by crosslinking acrylic acid and acrylamide copolymers

High water-absorbent copolymers comprising acrylic acid (AA) and acrylamide (AM) were prepared in the presence of a crosslinking agent, monofunctional aldehyde, by a solution polymerization technique using a redox initiation system. Such copolymers have very high water absorbency and absorbing kinetics to the distilled water. The copolymer formed which absorbed about 900 g water/g dry copolymer was used to study the influence of sodium chloride on the absorption capacity at 24°C. The swelling of this copolymer was studied in alcohol/water mixtures of increasing alcohol content at 294, 304, and 314 K. The main transition for ethanol/water and methanol/water mixtures is a rapid decrease of the retention capacity of the copolymer at 50–60 vol % ethanol and 55–65 vol % methanol, respectively. Swelling in distilled water at different temperatures (T) and the effect of solvent composition were also studied. Among the variables examined were initiator concentration, polymerization temperature, and amount of AM in the copolymer. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 1345–1353, 1997     

A convenient one‐step preparation of chitosan‐poly(sodium acrylate‐co‐acrylamide) hydrogel hybrids with super‐swelling properties

Hydrogel hybrids were conveniently prepared from alkaline hydrolysis of chitosan–poly(acrylonitrile) mixture under highly practical conditions. The reaction of chitosan alkoxide anions with nitrile groups of poly(acrylonitrile) (PAN) forms crosslinking points and results in a three‐dimensional network with superswelling ability in aqueous media. The hydrogel hybrid was identified using FTIR spectroscopy. The PAN content of the hydrolyzing feed affects proportionally the swelling capacity of the hydrogel hybrid. The swelling properties (capacity and rate) of the ampholytic hydrogel were investigated preliminarily. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1615–1619, 2006     

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     

Preparation and swelling properties of a starch-g-poly(acrylic acid)/organo-mordenite hydrogel composite

A novel hydrogel composite was prepared via inverse suspension polymerization using starch, acrylic acid and organo-mordenite micropowder with the crosslinker, N,N′-methylenebisacrylamide and the initiator, potassium persulfate. Fourier transform infrared spectroscopy, X-ray diffraction spectroscopy, scanning electron microscopy, and energy dispersive spectroscopy confirmed that the acrylic acid was grafted onto the backbone of the corn starch, that the organo-mordenite participated in the polymerization, and that the addition of organo-mordenite improved the surface morphology of the hydrogel composite. The swelling capacity of the hydrogel composite was evaluated in distilled water, and solutions with different pH values, and various salt solutions. It was found that the incorporation of 10 wt-% organo-mordenite enhanced the water absorbency by 144% (from 268 to 655 g·g⁻¹) and swelling was extremely sensitive to the pH values, the concentration of the salt solution and cation type. Swelling kinetics and water diffusion mechanism of the hydrogel composite in distilled water were also discussed. Moreover, the hydrogel composite showed excellent reversibility of water absorption even after five repetitive cycles and the hydrogel composite exhibited significant environmental-responsiveness by changing the swelling medium from distilled water to 0.1 mol·L⁻¹ NaCl solution. In addition, the loading and release of urea by the hydrogel composite were tested and the nutrient-slow-release capability of this material was found to be suitable for many potential applications.     

Solvent-, ion- and pH-specific swelling of poly(2-acrylamido-2-methylpropane sulfonic acid) superabsorbing gels

Homopolymer hydrogel of 2-acrylamido-2-methylpropane sulfonic acid (AMPS) and its nanocomposite counterpart were prepared to study their swelling properties. The hydrogels showed ability to absorb and retain electrolytes as well as binary mixtures of water and organic solvents (i.e., methanol, ethanol, acetone, ethylene glycol (EG), polyethylene glycol, N-methyl-2-pyrrolidone (NMP), and dimethylsulfoxide (DMSO). The nanocomposite gel exhibited lower swelling in all solvent compositions in comparison with non-composite gel. Unlike conventional acrylic acid-based hydrogels, the poly(AMPS) gels showed superabsorbing capacity in pure ethanol, methanol, EG, DMSO and NMP. Meanwhile, swelling capacity of poly(AMPS) hydrogel in DMSO-water mixtures was surprisingly found to be even higher than that in water. This extraordinary superswelling behavior was explained based on the interactions involved in solvation as well as the solubility parameters. The gels showed pH-independent superabsorbency in a wide range of pH (3–11). Saline-induced swelling transitions were also investigated and the ionic interactions were confirmed by FTIR spectroscopy.     

Effect of the anionic‐group/cationic‐group ratio on the swelling behavior and controlled release of agrochemicals of the amphoteric,superabsorbent polymer poly(acrylic acid‐co‐diallyldimethylammonium chloride)

A series of amphoteric, superabsorbent polymers [poly(acrylic acid‐co‐diallyldimethylammonium chloride)] with different molar ratios of anionic groups to cationic groups were prepared by solution polymerization to investigate their swelling behaviors and the controlled release of agrochemicals. Various factors, including the solution pH, the concentrations of different salt solutions, and the temperature, were studied. The dynamic parameters of hydrogels at different temperatures suggested that diffusion was Fickian at lower temperatures, whereas non‐Fickian diffusion prevailed at higher temperatures. A copolymer hydrogel with a low anionic‐group/cationic‐group ratio showed a higher swelling capacity in water and higher salt tolerance. Also, the anionic‐group/cationic‐group ratio was not the dominant factor in determining the water retention. A poly(acrylic acid‐co‐diallyldimethylammonium chloride) hydrogel could control the release of agrochemicals effectively. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 986–991, 2006     

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     

Enhancing the crystallization and orientation of electrospinning poly (lactic acid) (PLLA) by combining with additives

Novel hydrogel films composed of hydroxyethylacryl chitosan (HC) and sodium alginate (SA) were prepared for biomedical application by using calcium chloride (CaCl₂) as a nontoxic ionic crosslinker to form a semi-interpenetrating polymer network (semi-IPN). HC was successfully prepared by following a Michael addition reaction of chitosan (CS) and hydroxyethylacrylate completely dissolved in distilled water at 70 °C. The distribution pattern of Ca²⁺ ions were well-dispersed within the hydrogel films examined by scanning electron microscope-energy dispersive spectrometry (SEM-EDS), implying uniformity of crosslinking. The swelling behavior of the hydrogel films in distilled water, simulated gastric fluid (SGF, pH?=?1.2) and phosphate buffer solution (PBS, pH?=?7.4) were investigated. The equilibrium swelling degree of the hydrogel films in distilled water increased with a decreas of either the SA content or the concentration of CaCl₂. The hydrogel films showed pH-dependent behavior in that the shapes of the hydrogel films were stable in SGF while they degraded in PBS. The tensile strength and elongation of the hydrogel films reached 12.1 MPa and 162%, respectively, which presented reasonable mechanical properties during use and enough flexibility to follow skin movement. Cell viability of the hydrogels was measured using a methylthiazol tetrazolium (MTT) assay. The results indicated that the hydrogel films are not cytotoxic.     

Hybrid hydrogel based on pre-gelatinized starch modified with glycidyl-crosslinked microgel

Hybrid hydrogels based on pre-gelatinized starch were synthesized by inverse emulsion polymerization through modifying the starch with a glycidyl-crosslinked microgel. Glycidyl-crosslinked microgel is a special latex with high ability to impart hydrophilic characteristics to various substrates. Glycidyl-crosslinked microgel latexes with various structures were synthesized, and the effect of latex type on swelling capacity of the hybrid hydrogels based on pre-gelatinized starch was investigated. The highest swelling capacity was achieved for a pre-gelatinized starch modified with a glycidyl-crosslinked microgel latex based on poly(acrylic acid, sodium acrylate, acrylamide, 2-acrylamide-2 methyl propane sulfonic acid) (AA–SA–AM–AMPS). The swelling values of this hybrid hydrogel in distilled water and saline solution were 52.4 and 28.8 g/g, respectively. A key advantage of these hybrid hydrogels is that starch constitutes 64% of their structure. Given the fact that such hybrid hydrogels display low absorbency under load (AUL), they were surface crosslinked using microwave heating instead of conventional heating. Ethylene glycol diglycidyl ether was used as surface crosslinker. The AUL of the surface crosslinked hybrid hydrogels was increased by 85%. The hydrogels were characterized using FTIR, thermogravimetric analysis, scanning electron microscopy, and rheological measurements.     

Swelling of Anion Exchangers in Mixed Solvents. III. A Calorimetric Study

The integral heat evolved on swelling of the anion exchange resin Dowex-1 in chloride and perchlorate forms in water, methanol, ethanol, n-propanol, acetone and formamide, and in aqueous mixtures of these solvents, was measured calorimetrically as a function of the cross-linking of the resin (4,8 and 16% DVB) and the solvent composition. Heats of swelling (wetting) of the resin skeleton were also measured. These were found to be negligible compared with the heats of swelling of the exchangers which were in the range of 4–8 kcal/equiv. resin for the chloride form with water, methanol, ethanol and formamide, or their aqueous mixtures, but considerably smaller for the chloride form and solvents rich in propanol or acetone as well as for the perchlorate form. The heats of solution of the monomer analog, benzyltrimethylammonium chloride were found to be endothermic. Their relevance to the heat of swelling, and that of the heat of mixing of the solvents, was examined.     

Swelling behavior of poly(sodium acrylate)/kaoline superabsorbent composite

Using partly neutralized acrylic acid as monomer, kaoline ultrafine powder as filler and N,N′‐(dimethyl)acrylamide as crosslink agent, poly(sodium acrylate)/kaoline superabsorbent composite was synthesized by aqueous solution polymerization method. Using the superabsorbent composite as collagen, a hydrogel was prepared. The influence of the neutralization degree of superabsorbent collagen, the compositions, the concentration, and the pH value of exterior solution on the swelling behavior of the hydrogel was investigated. It was found that the swelling capability of the hydrogel depended on the groups on the collagen. The swelling capability of the hydrogel relied on the ionic intensity, molecular polarity, molecular volume, as well as the concentration of exterior solution. When the pH value of exterior solution was equal to seven, the hydrogel has a maximum swelling value of 800 times. POLYM. ENG. SCI. 46:324–328, 2006. © 2006 Society of Plastics Engineers     

聚乙烯醇-壳聚糖复合水凝胶的溶胀性能

以聚乙烯醇(PVA)和壳聚糖为原料、以戊二醛为交联剂,在醋酸溶液中合成了聚乙烯醇-壳聚糖复合水凝胶,研究了影响水凝胶溶胀性能的多种因素,实验结果表明,该凝胶对pH、离子、温度敏感,且在pH=3.13盐酸溶液、常温下的蒸馏水及8℃蒸馏水中溶胀度较大,分别为1 112.2%、974.2%、1 036.8%,凝胶溶胀度随着干燥温度及干燥时间的增加而减小,聚乙烯醇种类对水凝胶溶胀性能有显著影响,PVA-1788与壳聚糖形成的水凝胶溶胀度最大为2 074.1%。聚乙烯醇-壳聚糖复合水凝胶因具有优良的机械强度、生物相容性及生物降解性,同时又具有pH/离子/温度敏感性,因此日益显示其在生物医学材料等领域的重要性。     

Effect of solvent interactions on swelling and microstructure of amphiphilic polyurethane networks

Amphiphilic polyurethane (PU) ionomer networks were synthesized by urethane acrylate anionomer (UAA) precursor chains. These networks were prepared with water, dioxane (DO), and dimethyl sulfoxide (DMSO) and exhibited very different swelling behaviors in water/DO (UAADG) and water/DMSO (UAASG) solvent mixtures, which was due to the different solvent interactions between water/DO and water/DMSO. The additional important factor influencing the swelling behavior in water/aprotic solvent mixtures was the hydrophilicity of the UAA networks, which was different than the water–UAA network interaction. The microstructure of UAA networks prepared with the water/aprotic solvent mixtures was greatly influenced by the water–solvent interactions. Unlike the water/DO mixtures, which had a relatively weak water–DO interaction, the strong water–DMSO interaction largely restricted the ability of DMSO to solvate the UAA chain, which resulted in an increase in the aggregation of the hydrophobic segment and the hydrophilic/hydrophobic microphase separation. Thus, UAASG and UAADG networks showed very different swelling behaviors in the same swelling medium because of the microstructural difference between these gels, which was confirmed by dynamic mechanical measurements. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 608–620, 2001     

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     

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     

Synthetic polymeric absorbent for dye based on chemically crosslinked acrylamide/mesaconic acid hydrogels

Adsorption properties of copolymers of acrylamide and mesaconic acid (CAME) in aqueous Basic Blue 12 (Nile blue chloride) solution have been investigated. Chemically crosslinked CAME hydrogels with various compositions were prepared from ternary mixtures of acrylamide (A), mesaconic(ME) acid, and water by free radical polymerization in aqueous solution, using a multifunctional crosslinker such as ethylene glycol dimethacrylate (EGDMA). Dynamic swelling tests in water was applied to the hydrogels. Weight swelling ratio (S) values have been calculated. Sorption of Basic Blue 12 (BB 12) onto CAME hydrogels was studied by batch sorption technique at 25°C. In the experiments of the sorption, L type sorption in the Giles classification system was found. Some binding parameters such as initial binding constant (K_i), equilibrium constant (K), monolayer coverage (n), site‐size (u), and maximum fractional occupancy (Ô) for CAME hydrogels‐BB 12 binding system were calculated by using Klotz, Scatchard, and Langmuir linearization methods. Finally, the amount of sorbed BB 12 per gram of dry hydrogel (q) was calculated to be 2.28 × 10^?6–7.91× 10^?6 mol BB 12 per gram for hydrogels. Sorption % was changed range 16.09–58.86%. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 405–413, 2006     

Bioerodible hydrogels based on 2‐hydroxyethyl methacrylate: Synthesis and characterization

Biocompatible polymers with specific shape and tailored hydrogel properties were obtained by polymerization of mixtures of 2‐hydroxyethyl methacrylate (HEMA) with 1–8 wt % ethylene glycol dimethacrylate (EGDMA) or tetra(ethylene glycol) diacrylate (TEGDA) as crosslinking agents, by using a redox initiator. Introduction of charged positive and negative groups was easily achieved by direct polymerization of appropriate monomer mixtures and by chemical transformation of preformed hydrogels. Investigation of the swelling behavior of the prepared hydrogels evidenced an appreciable dependence on both solvent type and polymer chemical structure. Additionally, the solvation process resulted in being controlled by solvent diffusion, according to a Fickian II mechanism. The presence of several types of water with different melting behavior was observed in fully swollen hydrogels. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2729–2741, 2002     

Swelling characteristics of GMZ bentonite and its mixtures with sand

Gaomiaozi (GMZ) bentonite produced in Inner Mongolia has been chosen as a matrix material of buffer/backfill materials in the deep geological disposal to isolate the high level radioactive waste in China. Swelling characteristics of GMZ bentonite and bentonite–sand mixtures inundated with distilled water were studied by experimental methods. The test result shows that the relation between the void ratio and the swelling pressure of compacted GMZ bentonite–sand mixtures at full saturation is independent of the initial conditions such as the initial dry density and initial water content, and dependent on bentonite/sand ratio. An empirical equation is proposed to predict the swelling deformation and swelling pressure of the mixtures with different densities and bentonite/sand ratios. Finally, the swelling capacities of GMZ, Kunigel-V1 and MX-80 bentonites are compared.     

A cellulose‐based hydrogel as a potential bulking agent for hypocaloric diets: An in vitro biocompatibility study on rat intestine

A number of over‐the‐counter slimming products are currently available on the market. However, there is no scientific consensus over their effectiveness in promoting and sustaining weight loss. The need to develop an alternative dietary supplement for the treatment of obesity and overweight makes attractive a polyelectrolyte cellulose‐based hydrogel, crosslinked through a water soluble carbodiimide, as a potential bulking agent or stomach filler for hypocaloric diets. The hydrogel is envisaged to be administered orally to absorb water in the stomach, thus swelling and giving a sense of fullness, and to be finally expelled by fecal way. To this purpose, a preliminary assessment of hydrogel swelling capacity in distilled water has been performed, and the biocompatibility of the material with respect to intestinal tissues has been evaluated in vitro. The direct contact with the intestinal mucosa in vivo has been simulated by contacting the hydrogel with the jejunum tract of rat intestine, and the capacity of the material to maintain the epithelial barrier integrity has been monitored by means of transepithelial electric resistance measurements and lactate dehydrogenase release assay. The reported results evidence that the hydrogel is well tolerated by the intestinal tissue during the expected time of contact in vivo. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1524–1530, 2006