Study on superabsorbent composites. IX: Synthesis,characterization and swelling behaviors of polyacrylamide/clay composites based on various clays

A series of clay-based superabsorbent composite from acrylamide (AM) and various clays, such as attapulgite, kaolinite, mica, vermiculate and Na⁺-montmorillonite, was prepared by free-radical aqueous polymerization, using N,N′-methylenebisacrylamide (MBA) as a crosslinker and ammonium persulfate (APS) as an initiator, and then saponified with sodium hydroxide solution. In this paper, the reaction mechanism and thermal stability of the superabsorbent composites incorporated with various clays were characterized by FTIR, XRD and TGA, respectively. The effects of clay kind and clay content on equilibrium water absorbency of these composites were also investigated and compared. In addition, the influences of clay kind on comprehensive swelling behaviors of the PAM/clay superabsorbent composites were studied. The results indicated that the introduced clays could influence physicochemical properties of obtained superabsorbent composites. Mica could improve thermal stability of corresponding superabsorbent composites to the highest degree comparing with the other clays. The PAM/clay superabsorbent composites incorporated with 10 wt% clay of various kinds were all endowed with equilibrium water absorbency of more than 1300 g g⁻¹. The equilibrium water absorbency decreases with increasing clay content and correlates with the kind of clay. Attapulgite-based superabsorbent composite was endowed with higher water absorbency in univalent cationic saline solution, however, the vermiculite- and the kaolinite-based ones acquired the highest water absorbency in CaCl₂ and FeCl₃ aqueous solution, respectively. Moreover, the superabsorbent composites incorporated with Na⁺-montmorillonite have higher swelling rate and that of doped with mica was endowed with higher reswelling capability.     

Synthesis of acrylamide‐co‐(itaconic acid) superabsorbent polymers and associated silica superabsorbent polymer composites

Superabsorbent polymers (SAPs) were synthesized from acrylamide (AM) and itaconic acid (IA) via a crosslinking polymerization. SAP composites (SAPCs) were formed by the incorporation of silica with three particle sizes into the polymerization to increase the gel strength of SAPs. Effects of AM: IA molar ratios, silica types and concentrations on water absorbency, absorbency rate and absorbency under loadings (AUL) of the composites were investigated. The highest water absorbency of the SAP is 233 ± 8 g g^?1 at an AM: IA molar ratio of 97:3 with absorbency of 149 ± 2 g g^?1 within 15 min. The highest AUL of the SAPC with 0.5%–2.0% w w^?1 silica is 13 g g^?1 by 1.93 × 10³ Pa load. A pseudo‐second‐order kinetics for water absorbency was found in both SAPs and in situ SAPCs. In situ SAPCs and the mechanically mixed SAPCs in vertical and horizontal direction yielded similar water absorbency values. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers     

Removal of methylene blue from aqueous solution by sorption on lignocellulose-g-poly(acrylic acid)/montmorillonite three-dimensional cross-linked polymeric network hydrogels

Batch lignocellulose-g-poly(acrylic acid)/montmorillonite (LNC-g-PAA/MMT) hydrogel nanocomposites were applied as adsorbents. The nanocomposites were characterized by FTIR, XRD, SEM, and TEM. The results showed that montmorillonite (MMT) could react with the monomers and change the structure of polymeric network of the traditional superabsorbent materials, an exfoliated structure was formed in the nanocomposites. The effect of process parameters such as MMT content (wt%), contact time (t), initial concentration of dye solution (C ₀), adsorption temperature (T), and pH value (pH) of the dye solution for the removal of methylene blue (MB) from aqueous solution were also studied. The results showed that the adsorption capacity for MB increased with increasing contact time, initial dye concentration, and pH value, but decreased with increasing MMT content and temperature. The adsorption kinetics were better described by the pseudo-second-order equation, and their adsorption isotherms were better fitted for the langmuir equation. By introducing 20 wt% MMT into LNC-g-PAA polymeric network, the obtaining hydrogel composite showed the high adsorption capacity 1994.38 mg/g and economic advantage for MB. The desorption studies revealed that the composite provided the potential for regeneration and reuse after MB dye adsorption, which implied that the composite could be regarded as a potential adsorbent for cationic dye MB removal in a wastewater treatment process.     

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.     

Removal of Congo red from aqueous solution using a chitosan/organo‐ montmorillonite nanocomposite

To further improve the adsorption capacity of chitosan (CTS), a series of novel chitosan/organo‐montmorillonite nanocomposites (CTS/OMMT) were synthesized and the adsorption abilities for Congo red (CR) investigated in this study. The nanocomposites were characterized by Fourier transform infrared spectroscopy (FTIR), X‐ray diffraction analysis (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and the results indicated that an exfoliated nanostructure was formed in CTS/OMMT nanocomposites. Compared with the adsorption capacity of OMMT (192.4 mg g^?1), CTS/OMMT with an amount of cetyltrimethylammonium bromide equal to 0.75 CEC of MMT and molar ratio of CTS to OMMT of 1:10 exhibited the higher adsorption capacity (290.8 mg g^?1). The adsorption behaviours of OMMT and CTS/OMMT showed that the adsorption kinetics and isotherms were in good agreement with a pseudo‐second‐order equation and the Langmuir equation, respectively. The IR spectra revealed that a chemical interaction occurred between CTS/OMMT and CR. The adsorption capacity of CTS/OMMT nanocomposite was higher than that of other absorbents; this study suggested that the CTS/OMMT nanocomposite could be used as an adsorbent to remove CR dye from aqueous solution. Copyright © 2007 Society of Chemical Industry     

Study on superabsorbent composite. VIII. Effects of acid‐ and heat‐activated attapulgite on water absorbency of polyacrylamide/attapulgite

A novel superabsorbent composite, polyacrylamide/attapulgite, from acrylamide (AM) and attapulgite (APT), was prepared by free‐radical polymerization, using N,N′‐methylenebisacrylamide (MBA) as a crosslinker and ammonium persulfate (APS) as an initiator. The effects of hydrochloric acid (HCl) concentration, acidification time, and acidification temperature while acidifying APT and temperature and APT heat‐activation on water absorbency of the superabsorbent composite in distilled water and in 0.9 wt % NaCl solution were studied. The water absorbency first decreases with increasing the HCl concentration while acidifying APT, and then increases with further increasing the HCl concentration. Prolongation of acidification time is of benefit to the increase of water absorbency. At a given HCl concentration, water absorbency for the composite increases with increasing acidification temperature. An important increase in water absorbency was observed after incorporating heat‐activated APT into the polymeric network, reaching a maximum of 1964 g g^?1 with the APT heat‐activated at 400°C. Acid‐ and heat‐activation can influence chemical composition, crystalline structure, cation exchange capacity (CEC), and specific surface area of APT according XRF, XRD, FTIR analysis, and physicochemical properties test, and then on water absorbency of corresponding PAM/APT superabsorbent composite. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2419–2424, 2007     

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

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

Synthesis and swelling behaviors of semi‐IPNs superabsorbent resin based on chicken feather protein

A novel chicken feather protein‐g‐poly (potassium acrylate)/polyvinyl alcohol (CFP‐g‐PKA/PVA) semi‐IPNs superabsorbent resin (SAR) based on feather protein, acrylic acid (AA), and polyvinyl alcohol (PVA) was synthesized by graft copolymerization and semi‐interpenetrating technology. The results from FTIR, SEM, and TGA analysis showed that both CFP and PVA reacted with PKA during the polymerization process. The effects of AA, PVA, initiator and crosslinker content on water absorbency of semi‐IPNs SAR were studied. The swelling behavior in various pHs and saline solutions were also investigated. The water absorbency of SAR reached the maximum at pH = 6. The effect of the five cations on swelling had the following order: Al³⁺ > Ca²⁺ > Mg²⁺ > K⁺ > Na⁺. The highest water absorbency in distilled water and 0.9 wt % NaCl solutions were 714.22 and 70.08 g g^?1, respectively. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39748.     

Methylene blue adsorption from aqueous solutions to flexible poly(vinyl chloride) silica composites

Methylene blue (MB) adsorption studies were performed with poly(vinyl chloride)‐(dioctyl phthalate)‐silica composites, which were obtained by using plastisol‐plastigel technology. The films were flexible, having elastic modulus of 1.0–1.5 GPa. Diminishing MB concentration in the aqueous phase was followed as the adsorption process advanced by using visible spectroscopy. Contributions of the individual components of the composites to adsorption were also investigated. Although the MB adsorption capacity was extensively high for silica, it was moderate for the composite, most likely owing to the occlusion of pores of silica by plasticizer to some extent. The improvement of MB adsorption capacity of the composites as the silica ratio increased was explicitly deduced from the optical microscopy photographs. The diffusion coefficients of MB through the composites were 5 × 10^?13, 6 × 10^?13, and 3 × 10^?13 m² s^?1 with regression coefficients of 0.73, 0.89, and 0.88 for 0, 2, and 16% silica‐containing composites, respectively. Because of the slow diffusion of MB in poly(vinyl chloride)‐silica composites, using them as dynamic column adsorbent was not practical. However, these versatile plastics can be used as plastic labels, colored clothing, leather substitutes, antimicrobial medical devices, and laser printable surfaces. J. VINYL ADDIT. TECHNOL., 21:42–50, 2015. © 2014 Society of Plastics Engineers     

Starch/rice husk ash based superabsorbent composite: high methylene blue removal efficiency

Superabsorbent hydrogels composites based on the biopolymer starch (ST) and rice husk ash (RHA) were successfully developed and tested towards the removal of methylene blue (MB), a cationic dye. RHA content hit the morphology, mechanical and water uptake properties of the composite. Batch adsorption experiments, carried out under pH 5 at 33 °C and with 2000 mg L^?1 as the initial concentration of MB, showed that at 5 wt% RHA the composite exhibited a remarkable adsorption capacity reaching up to 1906.3 mg g^?1 within 60 min. The adsorption kinetics followed the pseudo-second-order model and intraparticle diffusion was involved in this process. The Langmuir adsorption isotherm suggested a monolayer formation and spontaneous process. Thermodynamic parameters confirmed the spontaneity of the adsorption and suggested electrostatic interaction among the cationic dye molecules and the anionic adsorption sites on the adsorbent surface. FTIR analysis confirmed the adsorption process occurs via electrostatic mechanism associated with hydrophobic interactions. The adsorbents showed reusability with slight loss of adsorption capacity in five consecutive adsorption/desorption cycles. These results demonstrate ST/RHA superabsorbent composite as a low-cost, eco-friendly, robust and powerful adsorbent material for wastewater remediation.     

Preparation and swelling properties of semi‐IPN hydrogels based on chitosan‐g‐poly(acrylic acid) and phosphorylated polyvinyl alcohol

The phosphorylated poly(vinyl alcohol) (P‐PVA) samples with various substitution degrees were prepared through the esterification reaction of PVA and phosphoric acid. By using chitosan (CTS), acrylic acid (AA) and P‐PVA as raw materials, ammonium persulphate (APS) as an initiator and N,N‐methylenebisacrylamide as a crosslinker, the CTS‐g‐PAA/P‐PVA semi‐interpenetrated polymer network (IPN) ssuperabsorbent hydrogel was prepared in aqueous solution by the graft copolymerization of CTS and AA and followed by an interpenetrating and crosslinking of P‐PVA chains. The hydrogel was characterized by Fourier transform infrared (FTIR), scanning electron microscopy (SEM), and differential scanning calorimetry (DSC) techniques, and the influence of reaction variables, such as the substitution degree and content of P‐PVA on water absorbency were also investigated. FTIR and DSC results confirmed that PAA had been grafted onto CTS backbone and revealed the existence of phase separation and the formation of semi‐IPN network structure. SEM observations indicate that the incorporation of P‐PVA induced highly porous structure, and P‐PVA was uniformly dispersed in the polymeric network. Swelling results showed that CTS‐g‐PAA/P‐PVA semi‐IPN superabsorbent hydrogel exhibited improved swelling capability (421 g·g^?1 in distilled water and 55 g·g^?1 in 0.9 wt % NaCl solution) and swelling rate compared with CTS‐g‐PAA/PVA hydrogel (301 g·g^?1 in distilled water and 47 g·g^?1 in 0.9 wt % NaCl solution) due to the phosphorylation of PVA. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Study on superabsorbent composites. XVIII. Preparation,characterization, and property evaluation of poly(acrylic acid‐co‐acrylamide)/organomontmorillonite/sodium humate superabsorbent composites

A series of novel multifunctional poly (acrylic acid‐co‐acrylamide) (PAA‐AM)/organomontmorillonite (O‐MMT)/sodium humate (SH) superabsorbent composites were synthesized by the graft copolymerization reaction of partially neutralized acrylic acid and acrylamide on O‐MMT micropowder and SH with N,N′‐methylene bisacrylamide as a crosslinker and ammonium persulfate as an initiator in an aqueous solution. The superabsorbent composites were characterized by means of Fourier transform infrared spectroscopy, X‐ray diffraction, scanning electron microscopy, and thermogravimetric analysis. The effect of the relative weight ratio of SH to O‐MMT on the water absorbency was studied, and the results indicated that the best water absorbency of 591 g/g in distilled water was obtained when an O‐MMT content of 20 wt % and an SH content of 30 wt % were incorporated. The superabsorbent composite possessed a good capacity for water retention; even after 30 days, 24.4 wt % of water could still be saved by the sand soil containing 1.0 wt % superabsorbent composite. The results from this study show that the water absorbency of a superabsorbent composite is improved by the simultaneous introduction of O‐MMT and SH into a PAA‐AM network in comparison with the incorporation of only O‐MMT or SH. Also, in comparison with PAA‐AM/MMT/SH, an appropriate amount of O‐MMT can benefit the developed composites with respect to their water absorbency, salt resistance, and capacity for water retention in sand soil. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Interaction of functional groups of gelatin and montmorillonite in nanocomposite

As an amphoteric polyelectrolyte, gelatin could intercalate into the galleries of montmorillonite (MMT). In this paper, sodium laurate/MMT composites and sodium laurate/dehydroxylated MMT composites were introduced as low molecular simulation to investigate the interaction functional groups of gelatin and MMT. The composites were characterized by X‐ray diffraction (XRD), Fourier transform infrared spectra (FTIR), thermogravimetric analysis (TGA) and ¹³C nuclear magnetic resonance (¹³C NMR). Furthermore, the effect of interaction between gelatin and MMT on the mechanical properties of the composites was investigated. The results indicated that ? COO^?, not ? COOH, in gelatin chains could interact strongly with the MMT sheets. The reactive sites on MMT were hydroxyl groups, which could interact with ? COO^? in gelatin chains by forming hydrogen bonds. The gelatin/MMT composites prepared in alkalic media have better mechanical properties due to stronger interaction. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1556–1561, 2006     

Swelling study of superabsorbent PAA‐co‐PAM/clay nanohydrogel

A series of superabsorbent composites were prepared from acrylic acid (AA), acrylamide (AM), and Cloisite® 30B by aqueous solution polymerization technique using ammonium peroxodisulfate (APS) as initiator. The interaction of the organically modified nanoclay with PAA‐co‐PAM copolymer was verified by FTIR, whereas the morphology of the composite was studied by Scanning Electron Microscopy (SEM). The water absorbency in deionized water and saline water of the synthesized nanohydrogels was measured by calculating their percentage swelling ratio. The effects of copolymerization, monomer ratio, clay content, and temperature on the water absorbency were studied. The results indicated a considerable increase in swelling ratio by proper monomer proportion and incorporation of optimum clay percentage into the copolymer matrix. It was found that the nanohydrogel acquired highest water absorbency with 2% clay loading. The reswelling ability and water retention capacity of the PAA‐co‐PAM hydrogel and PAA‐co‐PAM/clay nanohydrogel were also measured. The water absorbency was found to increase after each reswelling for which it may be useful as recyclable superabsorbent material. The results of water retention capacity of the nanohydrogel were also encouraging and find application in agriculture, especially in drought‐prone areas. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Adsorption and heat‐energy‐aid desorption of cationic dye on a new thermo‐sensitive adsorbent: Methyl cellulose/calcium alginate beads

The adsorption and heat‐energy‐aid desorption of methylene blue (MB) on a thermo‐sensitive adsorbent of methyl cellulose/calcium alginate beads (MC/CABs) has been studied. The addition of methyl cellulose intensified the desorption ability of adsorbent, and boosted the difference of adsorption capacity of adsorbent between low temperature and high temperature. At the mass ratio of methyl cellulose to sodium alginate of 2:1, the difference of adsorption capacity of MC/CABs between 20 and 60°C reached 20.48 mg g^?1. The effects of temperature, time and initial MB concentration on adsorption performance were investigated in detail. The MB adsorption on MC/CABs followed the pseudo‐second‐order kinetic model. The equilibrium data was fitted well with Langmuir isotherm. The maximum adsorption capacity of 336.70 mg g^?1 exhibited MC/CABs had a good adsorption capability. Thermodynamic analyses showed high temperature was not favorable to MB adsorption, and MC/CABs had a distinct superiority in desorption of adsorbate with heat‐energy‐aid. Lastly, the possible mechanisms involving in adsorption and heat‐energy‐aid desorption were presented. POLYM. ENG. SCI., 56:1382–1389, 2016. © 2016 Society of Plastics Engineers     

Improving properties of superabsorbent composite induced by using alkaline protease hydrolyzed‐sericin (APh‐sericin)

A series of superabsorbent polymer composites based on sericin hydrolyzed with alkaline protease (AP) were prepared by grafting with acrylic acid (AA) and acrylamide (AM). The properties of the superabsorbent polymers (SAP) by using hydrolyzed sericin with different amount of alkaline protease (nAPh‐sericin) were compared. It was found that the polymer prepared from 5APh‐sericin (the mass ratio of AP to sericin was 5.0 mg g⁻¹) showed the highest graft percentage and water absorbency, this phenomenon may be attributed to the change of molecular weight of resulting sericin molecules. The molecular structure of the grafted polymers was proved by thermal gravimetric analysis (TGA) and Fourier transform infrared spectroscopy (FTIR) measurements. Comparing with PAA‐AM (poly AA‐co‐AM) and 0APh‐sericin/PAA‐AM polymer, 5APh‐sericin/PAA‐AM polymer had the most excellent water retention capacity and enzyme degradability. The morphological features of the polymers with different drying methods were evidenced by SEM images. The water absorbencies of 5APh‐sericin/PAA‐AM polymer prepared with freeze‐drying were 896 g g⁻¹ in deionized water, 424 g g⁻¹ in tap water, and 83 g g⁻¹ in 0.9 wt% aqueous NaCl solution. POLYM. COMPOS., 35:509–515, 2014. © 2013 Society of Plastics Engineers     

Application of response surface methodology for modeling of reactive dye removal from solution using starch‐montmorillonite/polyaniline nanocomposite

In this study, starch‐montmorillonite/polyaniline (St‐MMT/PANI) nanocomposite was synthesized by chemical oxidative polymerization of aniline in the presence of St‐MMT nanocomposite dispersion. The prepared ternary nanocomposite was characterized using FTIR, XRD, and SEM techniques. Adsorption properties of the nanocomposite were investigated for removal of reactive blue (RB 194) as a model reactive dye from aqueous solution. Response surface methodology was employed for the modeling of adsorption capacity of the nanocomposite. A second‐order empirical relationship between adsorption capacity and independent variables (initial dye concentration, amount of the nanocomposite, and pH of the solution) was obtained. Pareto analysis for identification of the factors effect on the system revealed that initial dye concentration was the most effective parameter. The adsorption capacity value of reactive dye on St‐MMT/PANI nanocomposite was 91.74 mg g^?1. Further investigations indicated that the adsorption experimental data were well fitted to the Langmuir isotherm and pseudo‐second‐order kinetic model. POLYM. ENG. SCI., 54:1595–1607, 2014. © 2013 Society of Plastics Engineers     

Study on Superabsorbent Composite, 14

Summary: Organo‐attapulgite (organo‐APT) was prepared by modifying APT using four quaternary ammonium salts with various lengths of the alkyl group, including (octyl)trimethylammonium bromide (OTMABr) and (stearyl)trimethylammonium chloride (STMACl), etc. A series of composite hydrogels, poly(acrylic acid)/organo‐APT, from acrylic acid (AA), and organo‐APT was prepared by aqueous polymerization, using N,N′‐methylenebisacrylamide (MBA) as a crosslinker and ammonium persulfate (APS) as an initiator. The organification and organification degree of APT as well as the corresponding composites were characterized by FTIR, TGA, and XRD. The effects of the length of the alkyl group for different quaternary ammonium salts, organification degree of APT, and organo‐APT content on water absorbency and swelling behaviors in various electrolyte solutions were investigated in this study. Equilibrium water absorbency strongly depends on chain length of the alkyl group of quaternary ammonium salts, organification degree of APT as well as organo‐APT content. Longer alkyl group, higher organification degree, and proper organo‐APT content are of benefit for the improvement of equilibrium water absorbency. Equilibrium water absorbency in distilled water for PAA/APT was enhanced from 350.1 to 562.1 g · g^?1 after 10 wt.‐% organo‐APT, modified with STMACl for the highest degree, was introduced. The kind of cation is the key factor influencing equilibrium water absorbency of these composite hydrogels in electrolyte solutions. Organification of APT could enhance responsiveness of the corresponding composite hydrogel to electrolyte solutions.

Schematic structure of PAA/organo‐APT composite in a dry state (left) and in a swollen state (right).     

Biosorption of phenolic compounds from aqueous solutions onto chitosan–abrus precatorius blended beads

BACKGROUND: This research focuses on understanding the biosorption process and developing a cost‐effective technology for the treatment of water contaminated with phenolic compounds (phenol, 2‐chlorophenol and 4‐chlorophenol), which are discharged into the aquatic environment from a variety of sources and are highly toxic. In order to remove phenolic compounds from water, a new biobased sorbent is developed, blending chitosan with abrus precatorius, both naturally occurring biopolymers. The resulting chitosan–abrus precatorius blended beads (CS/Ab) were characterized by Brunauer, Emmett and Teller (BET) analysis, Fourier Transform Infrared (FTIR) spectroscopy and scanning electron microscopy (SEM) techniques under batch equilibrium and column flow experimental conditions. The binding capacity of the biosorbent was investigated as a function of initial pH, contact time, initial concentration of adsorbate and dosage of adsorbent. RESULTS: The percentage removal of phenol, 2‐CP and 4‐CP increased with increasing adsorbent dose, while the adsorption capacity at equilibrium, q_e (mg g^?1) (amount of phenol, 2‐CP and 4‐CP loaded per unit weight of adsorbent) decreased. The equilibrium time was found to be 240 min for full equilibration of all adsorbates. Adsorption kinetic and isotherm studies showed that the pseudo‐first‐order model and the Langmuir isotherm were the best choices to describe the adsorption behaviors. The maximum monolayer adsorption capacity of phenol, 2‐CP and 4‐CP on to the (CS/Ab) beads was found to be 156 mg g^?1, 204 mg g^?1 and 278 mg g^?1, respectively. CONCLUSION: The experimental results suggested that (CS/Ab) blended beads are effective in the removal of phenolic compounds from aqueous medium. Copyright © 2009 Society of Chemical Industry     

Fast-swelling porous starch-g-poly(acrylic acid) superabsorbents

The fast-swelling porous starch-g-poly(acrylic acid) (St-g-PAA) superabsorbents were prepared simply by free-radical graft polymerization between acrylic acid and potato starch in the aqueous phase by using Triton X-100 as the pore-forming agent. The porous superabsorbents were characterized by FTIR and scanning electron microscopy. The effects of weight ratio of acrylic acid to starch and the Triton X-100 content on water absorbency were investigated. In addition, the effects of Triton X-100 on swelling rate, water absorbency in 0.9 % NaCl and in the artificial urine solution, and reswelling ability were studied in detail. The superabsorbent prepared with an acrylic acid/starch ratio of 6:1 and a Triton X-100 content of 0.4 % has a water absorbency of 683 g g^?1 in distilled water and 72.8 g g^?1 in 0.9 % NaCl. The content of Triton X-100 has great influence on the water absorbency and the swelling rate. The porous sample prepared with 0.4 % Triton X-100 only needs about 5 min to reach 80 % of its equilibrium water absorbency which is obviously shorter in comparison with the nonporous sample (about 90 min). The porous samples also show nice urine absorbency and excellent reswelling ability. We believe the reported method may find some applications in preparing novel porous hydrogels.