Preparation and swelling characteristics of a superabsorbent nanocomposite based on natural guar gum and cation‐modified vermiculite

A series of novel superabsorbent nanocomposites were prepared by the solution radical polymerization of natural guar gum (GG), partially neutralized acrylic acid [sodium acrylate (NaA)], and cation‐exchanged vermiculite (Mⁿ⁺‐VMT) with ammonium persulfate as the initiator in the presence of the crosslinking agent N,N′‐methylene‐bis‐acrylamide. Fourier transform infrared analysis revealed that NaA was grafted onto the GG chains and that Mⁿ⁺‐VMT participated in the polymerization. X‐ray diffraction results showed that the occurrence of the cation‐exchange process changed the interlayer gap of vermiculite (VMT) and that Mⁿ⁺‐VMT was exfoliated during polymerization to form a nanocomposite. The exfoliated VMT led to better dispersion in the GG‐g‐poly(sodium acrylate) matrix, as shown by scanning electron microscopy and transmission electron microscopy analysis. Mⁿ⁺‐VMT improved the water absorption of the nanocomposite more remarkably than raw VMT, and Al³⁺‐VMT enhanced the water absorption to the highest degree. The nanocomposite exhibited intriguing overshooting swelling characteristics in a multivalent saline solution and acidic pH solution and showed switching pH‐responsive behaviors in buffer solutions between pH 2 and pH 7.2. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Synthesis,characterization and swelling behaviors of hydroxyethyl cellulose‐g‐poly(acrylic acid)/attapulgite superabsorbent composite

In this work, a series of novel hydroxyethyl cellulose‐ g‐poly(acrylic acid)/attapulgite (HEC‐g‐PAA/APT) superabsorbent composites were prepared through the graft polymerization of hydroxyethyl cellulose (HEC), partially neutralized acrylic acid (AA), and attapulgite (APT) in aqueous solution, and the composites were characterized by means of Fourier‐transform spectroscopy, scanning electron microscopy, and transmission electronmicroscopy. The effects of polymerization variables including concentrations of the initiator and crosslinker and APT content on water absorbency were studied, and the swelling properties in various pH solutions as well as the swelling kinetics in various saline solutions were also systematically evaluated. Results showed that the introduction of 5 wt% APT into HEC‐g‐PAA polymeric network could improve both water absorbency and water absorption rate of the superabsorbent composites. In addition, the superabsorbent composites retained high water absorbency over a wide pH range of 4–10, and the swelling kinetics of the superabsorbent composites in CaCl₂ and FeCl₃ solutions exhibited a remarkable overshooting phenomenon. POLYM. ENG. SCI., 2010. © 2010 Society of Plastics Engineers     

Utilization of plant ash for the fabrication of novel superabsorbent composites with potassium‐release characteristics

Design and synthesis of the agricultural and ecological superabsorbent materials with cost‐efficient and fertilizer‐release characteristics has recently attracted considerable interests. In this work, the novel poly(sodium‐potassium acrylate‐co‐acrylamide)/plant ash (PNa‐KA‐co‐AM/PA) superabsorbent composites with potassium‐release characteristics were prepared using partially neutralized acrylic acid (Na‐KA), acrylamide (AM), and plant ash (PA) as raw materials, ammonium persulfate (APS) as the initiator, and N,N′‐methylenebisacrylamide (MBA) as the crosslinker. The structure, morphologies, and thermal stability of the composites were characterized by Fourier transform infrared spectrophotometer, scanning electron microscopy, and TGA techniques, respectively. The effects of MBA concentration and PA content on water absorbency were studied, and the swelling properties of the composites in saline solutions and various pHs solution as well as their potassium‐release capabilities were also evaluated. Results indicate that the composites exhibit better thermal stability, salt‐resistant performance, pH‐stability, and potassium‐release properties, and can act as a fertilizer and an effective water‐saving material for agricultural and ecological application. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

GG-g-PAA/LOESS复合高吸水性树脂的制备与性能

以瓜尔胶(GG)、丙烯酸(AA)和黄土(LOESS)为原料,过硫酸铵(APS)为引发剂,N,N'-亚甲基双丙烯酰胺(MBA)为交联剂,采用水溶液聚合法制备了瓜尔胶接枝聚丙烯酸/黄土(GG-g-PAA/LOESS)复合高吸水性树脂。采用FTIR和SEM对其结构进行了表征,研究了LOESS的添加量对复合高吸水性树脂的溶胀能力和溶胀动力学的影响,考察了复合高吸水性树脂的保水性能、反复溶胀性以及在不同pH溶液中的吸水性能。结果表明,瓜尔胶、丙烯酸和LOESS发生了接枝共聚,体系中引入LOESS能够显著提高复合高吸水性树脂的吸水性能。当LOESS的质量分数为2%时,该树脂最高吸水倍率可达602 g/g,室温下6 d后,其保水率仍达28%,5次反复溶胀,吸水倍率仍能保持初始时的49%。此外,该复合高吸水性树脂还表现出优异的pH稳定性。     

Ethanol‐assisted dispersion of attapulgite and its effect on improving properties of alginate‐based superabsorbent nanocomposite

The dispersion of attapulgite (APT) as nanorod‐like single crystals is crucial to fully develop its functionality of one‐dimensional nanometer material as a filler of composite materials. In this study, APT was dispersed by the assistance of ethanol during the high‐pressure homogenization process to form individual nanorod‐like crystals. The dispersed APT was used to prepare new sodium alginate‐g‐poly(sodium acrylate‐co‐styrene)/attapulgite (NaAlg‐g‐P(NaA‐co‐St)/APT) superabsorbent nanocomposites. The effect of ethanol/water ratio on the dispersion of crystal bundles of APT was investigated by field emission scanning electron microscopy, and the results indicate that APT crystal bundles were effectively disaggregated in ν(CH₃CH₂OH) : ν(H₂O) ? 5 : 5 solution after homogenized at 50 MPa. The better dispersion of APT in NaAlg‐g‐P(NaA‐co‐St) matrix has clearly improved the gel strength (from 1300 Pa to 1410 Pa, ω = 100 rad/s), swelling capacity (442–521 g/g), swelling rate (3.3303–4.5736 g/g/s), and reswelling ability of the superabsorbent nanocomposite. Moreover, the nanocomposites showed fast swelling–deswelling responsive behavior in different saline solutions. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

pH‐sensitive crosslinked guar gum‐based superabsorbent hydrogels: Swelling response in simulated environments and water retention behavior in plant growth media

Crosslinked guar gum‐g‐polyacrylate (cl‐GG‐g‐PA) superabsorbent hydrogels were prepared to explore their potential as soil conditioners and carriers. The hydrogels were prepared by in situ grafting polymerization and crosslinking of acrylamide onto a natural GG followed by hydrolysis. Microwave‐initiated synthesis under the chosen experimental conditions did not exhibit any significant improvement over the conventional technique. The optimization studies of various synthesis parameters, namely, monomer concentration, crosslinker concentration, initiator concentration, quantity of water per unit reaction mass, particle size of backbone, and concentration of alkali were performed. The hydrogels were characterized by wide‐angle X‐ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, and solid‐state ¹³C‐NMR spectroscopy. Swelling behavior of a candidate hydrogel [GG‐superabsorbent polymer (SAP)] in response to external stimuli, namely, salt solutions, fertilizer solutions, temperature, and pH, was studied. The GG‐SAP exhibited significant swelling in various environments. The effect of GG‐SAP on water absorption and the retention characteristics of sandy loam soil and soil‐less medium were also studied as a function of temperature and moisture tensions. The addition of GG‐SAP significantly improved the moisture characteristics of plant growth media (both soil and soil‐less), showing that it has tremendous potential for diverse applications in moisture stress agriculture. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41060.     

Preparation of chitosan‐g‐poly(acrylamide)/montmorillonite superabsorbent polymer composites: Studies on swelling,thermal, and antibacterial properties

Superabsorbent composites based on chitosan‐g‐poly(acrylamide) and montorillonite (CTS‐g‐PAAm/MMT) were synthesized through in situ radical polymerization by grafting of crosslinked acrylamide onto chitosan backbone in presence of MMT at different contents. The formation of the grafted network was confirmed by attenuated total reflectance Fourier transform infrared spectroscopy (ATR‐FTIR), thermogravimetric analysis (TGA), and differential scanning calorimetery (DSC). The obtained porous structure was observed by scanning electron microscope (SEM). The presence of clay and its interaction with chitosan‐g‐poly(acrylamide) (CTS‐g‐PAAm) matrix was evidenced by ATR‐FTIR analysis. The morphology was investigated by both X‐ray diffraction (XRD) and SEM analyses. It was suggested the formation of mostly exfoliated structures with more porous structures. Besides, the thermal stability of these composites, observed by TGA analysis, was slightly affected by the clay loading as compared to the matrix. These hydrogel composites were also hydrolyzed to achieve anionic hydrogels with ampholytic properties. Swelling behaviors were examined in doubly distilled water, 0.9 wt % NaCl solution and buffer solutions. The water absorbency of all superabsorbent composites was enhanced by adding clay, where the maximum was reached at 5 wt % of MMT. Their hydrolysis has not only greatly optimized their absorption capacity but also improved their swelling rate and salt‐resistant ability. The hydrolyzed superabsorbent showed better pH‐sensitivity than the unhydrolyzed counterparts. The results of the antibacterial activity of these superabsorbents composites against Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli), assayed by the inhibitory zone tests, have showed moderate inhibition of the bacteria growth. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39747.     

Preparation of starch‐graft‐poly(acrylamide)/attapulgite superabsorbent composite

A novel starch‐graft‐poly(acrylamide)/attapulgite superabsorbent composite was synthesized by graft copolymerization reaction of starch, acrylamide (AM), and attapulgite micropowder using N.N‐methylene‐bisacrylamide (MBA) as a crosslinker and ammonium persulphate (APS) as an initiator in aqueous solution, followed by hydrolysis with sodium hydroxide. The effects on water absorbency, such as amount of crosslinker, initiator, attapulgite, weight ratio of acrylamide to starch in the feed, gelatinization conditions of starch and molar ratio of NaOH to acrylamide, and so forth, were investigated. These superabsorbent composites were characterized by Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA). The water absorbencies for these superabsorbent composites in water and saline solution were investigated, and water retention tests were carried out. Results obtained from this study showed that the water absorbency of superabsorbent composite synthesized under optimal synthesis conditions with an attapulgite content of 10% exhibit absorption of 1317 g H₂O/g sample and 68 g H₂O/g sample in distilled water and in 0.9 wt % NaCl solution, respectively. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1351–1357, 2005     

Preparation and Swelling Behavior of a pH-Responsive Psyllium-g-Poly(acrylic acid)/Attapulgite Superabsorbent Nanocomposite

In this study, a series of psyllium-g-poly(acrylic acid)/attapulgite (PSY-g-PAA/APT) superabsorbent nanocomposites were prepared. The effects of the content of APT on equilibrium water absorption, swelling rate, and the swelling behaviors of the nanocomposites in various cationic saline solutions and different pH solutions were also systematically investigated. The nanocomposite containing 10 wt% APT gives the best water absorption of 568 g/g in distilled water and 64 g/g in 0.9 wt% NaCl solution. The excellent responsive properties and reversible On-Off switching characteristics can be observed in various pH buffer solutions.     

Superabsorbent composite XXII: Effects of modified sepiolite on water absorbency and swelling behavior of chitosan‐g‐poly(acrylic acid)/sepiolite superabsorbent composite

In this work, a series of chitosan‐g‐poly(acrylic acid)/sepiolite (CTS‐g‐PAA/ST) superabsorbent composites containing raw sepiolite, acid‐activated sepiolite, and cation‐exchanged sepiolite were synthesized by free‐radical graft polymerization in aqueous solution, using N,N′‐methylenebisacrylamide as a crosslinker and ammonium persulfate as an initiator. The effects of raw sepiolite, acid‐activated sepiolite, and cation‐exchanged sepoilite on equilibrium water absorbency, swelling rate, and swelling behavior in different pH value solution of superabsorbent composites were systematically investigated. The results from FTIR spectra showed that chitosan and sepiolite participated in graft polymerization reaction with acrylic acid. The introduction of acid‐activated and cation‐exchanged sepiolite into chitosan‐g‐poly(acrylic acid) polymeric network could improve water absorbency and swelling rate compared with that of the raw sepiolite. All prepared samples have similar swelling behavior in different pH solutions and the equilibrium water absorbencies of samples keep roughly constant in the pH range from 4 to 12. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers     

Synthesis and characterization of starch‐g‐Poly(acrylic acid)/Organo‐Zeolite 4A superabsorbent composites with respect to their water‐holding capacities and nutrient‐release behavior

Novel superabsorbent composites were prepared using starch, acrylic acid, and organo‐zeolite 4A micropowder via aqueous solution graft copolymerization. The effects of organo‐zeolite 4A content on water absorbency were tested to determine the optimum conditions that ensure a high swelling ability. Under these conditions, the maximum swelling ability in distilled water was determined to be 511 g/g when the amount of organo‐zeolite 4A in the feed was 10 wt%. The prepared samples were characterized with Fourier transform infrared spectroscopy, X‐ray diffraction, and scanning electron microscope (SEM). The SEM characterization of the samples indicated that the superabsorbent composites had more pores and water than zeolite‐free superabsorbents. The swelling capacities in distilled water, various salt solutions, and aqueous urea were studied. The on–off switching behavior and the release of urea from the loaded starch‐g‐ poly(acrylic acid)/organo‐zeolite 4A were also determined. The results indicated that the novel composite was responsive to salts and exhibited on–off switching behavior, as evidenced by reversible swelling and de‐swelling. In addition, the slow nutrient release makes this material suitable for many potential applications in the fields of agriculture and horticulture. POLYM. COMPOS., 38:1838–1848, 2017. © 2015 Society of Plastics Engineers     

Synthesis and enhanced swelling properties of a guar gum-based superabsorbent composite by the simultaneous introduction of styrene and attapulgite

In current study, a series of novel guar gum-graft-poly(sodium acrylate-co-styrene)/attapulgite (GG-g-P(NaA-co-St)/APT) superabsorbent nanocomposites were prepared by the simultaneous graft copolymerization of partially neutralized acrylic acid (NaA), styrene (St) and attapulgite (APT) onto natural guar gum (GG), using ammonium persulfate (APS) as the initiator and N,N'-methylene-bis-acrylamide (MBA) as the crosslinking agent. Fourier Transform Infrared (FTIR) and ultravoilet (UV) spectra confirmed that NaA and St had been grafted onto GG backbones and APT participated in the polymerization reaction. The incorporation of St and APT clearly improved the surface porous morphology of the composites as exhibited by Filed Emission Scanning Electron Microscopy (FESEM). The effect of St and APT on the swelling properties and the swelling kinetics of the developed nanocomposite was investigated. Results showed that the simultaneous incorporation of proper amount of hydrophobic co-monomer St and inorganic nano-scale APT not only obviously enhanced the swelling capacity but highly improved the swelling rate, and the nanocomposite showed better salt-resistant capability and excellent pH-stability in various pH solutions.     

Synthesis and properties of a novel superabsorbent polymer composite from microwave irradiated waste material cultured Auricularia auricula and poly (acrylic acid‐co‐acrylamide)

A novel superabsorbent polymer composite was successfully synthesized from waste material cultured Auricularia auricula (WMCAA) and poly (acrylic acid‐co‐acrylamide) (P(AA‐co‐AM)) using microwave irradiation. Optimal synthesis conditions were determined by investigating the water absorbency of the superabsorbent composite. The effects associated with weight ratios of WMCAA, acrylamide (AM) monomers, initiators, and acrylic acid (AA) crosslinkers, as well as the degree of neutralization of AA were examined. The maximum water absorbencies were found to be 1548 g/g (distilled water) and 72 g/g (0.9% NaCl solution). Fourier transform infrared spectroscopy (FTIR) was applied to determine the molecular structure of the superabsorbent composite, and scanning electron microscopy (SEM) was used to demonstrate the characteristic compact and porous structure of the material. Further studies conducted via transmission electron microscopy (TEM) revealed the formation of a novel interpenetrating polymer network structure. Thermogravimetry/differential thermal (TG/DTG) analysis demonstrated improved thermal stability in the composite material compared with WMCAA. Additionally, high water absorption rates observed in the polymer during the swelling process indicated first‐order kinetics. The water absorption and adsorption of the superabsorbent composite were studied in a variety of fertilizer solutions, revealing an indirect relationship between water absorbing ability and fertilizer concentration. Conversely, a direct relationship was observed between absorbed fertilizer and fertilizer concentration. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 3674–3681, 2013     

Waste polystyrene foam‐graft‐acrylic acid/montmorillonite superabsorbent nanocomposite

A novel superabsorbent nanocomposite based on partially neutralized acrylic acid, waste polystyrene foam, and sodium type montmorillonite (Na‐MMT) powder was synthesized through emulsion polymerization using N, N′‐methylenebisacrylamide as a crosslinker, 2,2′‐azo‐bisiso‐butyronitrile, ammonium persulfate, and sodium sulfite as mixed redox initiators. The effects of such factors as amount of Na‐MMT, crosslinker, initiator, and neutralization degree on water absorbency of the superabsorbent were investigated. The composites were characterized by Fourier transform infrared spectroscope, X‐ray diffraction, thermo gravimetric analysis, and scanning electron microscope. The results show that acrylic acid monomer successfully grafted onto the polystyrene chain, the layers of Na‐MMT were exfoliated and dispersed in the composite at nano size after copolymerization. The introduction of waste polystyrene foam in the composite increased the water absorbency rate. The addition of Na‐MMT not only enhanced the thermal stability of the composites but also increased its water absorbency, and the optimal water absorbencies of distilled water and saline water (w_NaCl = 0.9%) of the nanocomposites were more than 1180 g H₂O/g and 72.6 g H₂O/g, respectively. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 2341–2349, 2007     

Synthesis,swelling behaviors,and slow‐release characteristics of a guar gum‐g‐poly(sodium acrylate)/sodium humate superabsorbent

Superabsorbents used in agricultural and ecological projects with low‐cost, slow‐release fertilizers and environmentally friendly characteristics have been extensively studied. The use of a natural polymer as the matrix and then further polymerization with some functional material has become the preferred method. In this work, with natural guar gum (GG), partially neutralized acrylic acid, and sodium humate (SH) as the raw materials, ammonium persulfate as the initiator, and N,N′‐methylenebisacrylamide (MBA) as the crosslinker, GG‐g‐poly(sodium acrylate) (PNaA)/SH superabsorbents were synthesized through a solution polymerization reaction and were characterized with Fourier transform infrared spectroscopy, scanning electron microscopy, and thermogravimetric analysis. The effects of the SH content and MBA concentration on the water absorbency were investigated. The results showed that the introduction of SH into the GG‐g‐PNaA system could improve the water absorbency, swelling rate, pH‐resistant property, and reswelling capability, and the superabsorbent containing 15 wt % SH had the highest water absorbency of 532 g/g of sample in distilled water and 62 g/g of sample in a 0.9 wt % NaCl solution. The slow release in water and water retention in sandy soil tests revealed that the superabsorbent could act as a fertilizer as well as an effective water‐saving material for agricultural applications. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

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     

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     

Synthesis,Characterization, and swelling behaviors of acrylic acid/carboxymethyl cellulose superabsorbent hydrogel by glow‐discharge electrolysis plasma

This article exploits a new approach for synthesis of acrylic acid/carboxymethyl cellulose (AA/CMC) superabsorbent hydrogel in aqueous solution by a simple one‐step using glow‐discharge electrolysis plasma, in which N,N′‐methylenebisacrylamide (MBA) was used as a crosslinking agent. The reaction parameters affecting the equilibrium swelling, that is, discharge voltage, discharge time, mass ratio of AA to CMC, content of crosslinker, and degree of neutralization, were systematically optimized to achieve a superabsorbent hydrogel with a maximum equilibrium swelling. The structure, thermal stability, and morphology of AA/CMC superabsorbent hydrogel were characterized by Fourier transform infrared spectroscopy, X‐ray diffraction analysis, thermogravimetric analysis, and scanning electron microscopy. The swelling kinetics in distilled water and swelling behaviors in various pH solutions and salts solutions (NaCl, KCl, MgCl₂, CaCl₂, AlCl₃, and FeCl₃) were investigated in detail. The effect of six cationic salt solutions on the equilibrium swelling had the following order K⁺ > Na⁺ > Mg²⁺ > Ca²⁺ > Al³⁺ > Fe³⁺. In addition, the pH‐reversibility was preliminarily investigated with alternating pH between 6.5 and 2.0. The results showed that the equilibrium swelling of AA/CMC was achieved in 90 min. The hydrogel was responsive to the pH and salts, and was reversible swelling and deswelling behavior. POLYM. ENG. SCI., 54:2310–2320, 2014. © 2013 Society of Plastics Engineers     

Hydrogel composites based on linear low‐density polyethylene‐g‐poly (acrylic acid)/Kaolin or halloysite nanotubes

Two series of superabsorbent hydrogel composites were prepared using waste linear low‐density polyethylene, acrylic acid, and two types of clays including kaolin and halloysite nanotube (HNT) through emulsion polymerization. The effects of the clay content on Water absorbency were investigated to obtain a high swelling capacity. The prepared samples were characterized using FTIR, SEM, thermogravimetric analysis, XRD, solid‐state ¹³C Nuclear Magnetic Resonance spectroscopy, and ²⁹Si NMR. SEM characterization of the samples showed that the hydrogel composites have more pores and a higher swelling ratio than the clay‐free hydrogels. The hydrogel composite containing kaolin had higher water absorbency compared to the hydrogel composites with HNT. The swelling behavior of the hydrogel composite was investigated in various saline solutions. The hydrogel composite containing 5 wt % kaolin had the highest water absorbency (760 g/g in distilled water). © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40101.     

Studies on poly(acrylic acid)/attapulgite superabsorbent composite. I. Synthesis and characterization

A novel poly(acrylic acid)/attapulgite superabsorbent composite was synthesized by graft copolymerization reaction of acrylic acid (AA) on attapulgite micropowder using N,N′‐methylenebisacrylamide (MBA) as a crosslinker and ammonium persulfate (APS) as an initiator in aqueous solution. The effects on water absorbency of such factors as reaction temperature, initial monomer concentration, degree of neutralization of AA, amount of crosslinker, initiator, and attapulgite were investigated. These crosslinked superabsorbent composites were characterized by thermogravimetetric analysis and scanning electron microscopy. The graft copolymerization reaction of AA on attapulgite micropowder was characterized by FTIR. The water absorbencies for these superabsorbent composites in water and saline solutions were investigated and water‐retention tests were carried out. Results obtained from this study show that the water absorbency of the superabsorbent composite synthesized under optimal synthesis conditions with an attapulgite content of 10% exhibited an absorption of 1017 g H₂O/g sample and 77 g H₂O/g sample in distilled water and in 0.9 wt % NaCl solution, respectively. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1596–1603, 2004