Superabsorbent Composite Research Articles

Synthesis, characterization, and swelling behavior of alginate‐g‐poly(sodium acrylate)/kaolin superabsorbent hydrogel composites

AbstractA novel superabsorbent composite based on sodium alginate and the inorganic clay kaolin was synthesized via the graft copolymerization of acrylic acid (AA) in an aqueous medium with methylene bisacrylamide (MBA) as a crosslinking agent and ammonium persulfate (APS) as an initiator. The effects of reaction variables, such as the MBA, AA, and APS concentrations and the alginate/kaolin weight ratio, on the water absorbency of the composite were systematically optimized. Evidence of grafting and kaolin interactions was obtained by a comparison of the Fourier transform infrared spectra of the initial substrates with that of the superabsorbent composite, and the hydrogel structure was confirmed with scanning electron microscopy. The results indicated that with an increasing alginate/kaolin weight ratio, the swelling capacity and gel content increased. The effects of various salt media were also studied, along with the swelling kinetics. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007

Study on superabsorbent composite. XI. Effect of thermal treatment and acid activation of attapulgite on water absorbency of poly(acrylic acid)/attapulgite superabsorbent composite

AbstractThe effect of acid activation and thermal treatment of attapulgite on water absorbency of superabsorbent composite were investigated. Under the same preparation conditions, superabsorbent composite prepared with natural attapulgite exhibited a water absorbency of 639 g/g and it merely kept 71% of its initial water absorbency after 5 times of swelling–deswelling–reswelling test. However, superabsorbent composites prepared with 2–10 M hydrochloric acid acidified attapulgite and 100–400°C thermal treated attapulgite respectively exhibited the water absorbency of 884–1,241 g/g and 701–1,515 g/g. Also, those superabsorbent composites can keep 87% and 85% of their initial water absorbency after 5 times of swelling–deswelling–reswelling test, respectively. These results showed that, compared with superabsorbent composite prepared with natural attapulgite, the comprehensive water‐absorbing properties of poly(acrylic acid)/ attapulgite superabsorbent composites were improved effectively by acid activation and thermal treatment of attapulgite. This improvement of water absorbencies and gel strength of superabsorbent composite may be due to synthetical factors such as changes in the crystalline structure and the specific surface area and improvement of the number and the activity of hydroxyl groups of attapulgite, which in turn influence the grafting efficiency of monomer, crosslinking density, and the structure of superabsorbent composite network. POLYM. COMPOS., 28:397–404, 2007. © 2007 Society of Plastics Engineers

Preparation and characterization of poly(acrylic acid)‐iron rich smectite superabsorbent composites

AbstractA novel poly(acrylic acid)‐iron rich smectite (IRS) superabsorbent composite was synthesized by graft copolymerization reaction of acrylic acid (AA) in the presence of N,N‐methylenebisacrylamide (MBA) as a crosslinker. IRS was used to strengthen the hydrogel products in the polymerization process. Water absorbencies for these superabsorbent composites in water and saline solutions were investigated. IRS caused a reduced equilibrium swelling as low as 8–26%. However, grafted IRS particles resulted in improved gel strength as high as 66% compared to the IRS‐free sample. IRS modified superabsorbent hydrogel composites exhibited higher thermal stability compared to the IRS‐free sample. The pH dependent reversible swelling behavior of hydrogels was also investigated. It is found that the swelling process is pH dependent and reversible for synthesized superabsorbent. Superabsorbent hydrogel composites were characterized by thermogravimetric analysis (TGA) and scanning electron microscopy (SEM). FTIR spectroscopy was confirmed grafting of acrylic chains onto the surface of IRS particles. From the standpoint of these results, these strengthened and thermostabilized hydrogels may be considered as good candidates for a controlled release study and agricultural applications. Copyright © 2007 John Wiley & Sons, Ltd.

Superabsorbent composite. XIII. Effects of Al3+‐attapulgite on hydrogel strength and swelling behaviors of poly(acrylic acid)/Al3+‐attapulgite superabsorbent composites

AbstractAl3+‐attapulgite (Al3+‐APT) was prepared by treating attapulgite (APT) with AlCl3 aqueous solution of various concentrations. The poly(acrylic acid)/Al3+‐attapulgite (PAA/Al3+‐APT) superabsorbent composite was prepared by reaction of partly neutralized acrylic acid, and Al3+‐APT in aqueous solution using N, N′‐methylenebisacrylamide as a crosslinker and ammonium persulfate as an initiator. The surface morphology of the composite was investigated by SEM, and the Al3+‐APT composite generated a relatively planar surface comparing the nature APT. The effects of Al3+‐APT on hydrogel strength and swelling behaviors, such as equilibrium water absorbency, swelling rate, and reswelling capability, of the superabsorbent composites were also studied. The hydrogel strength and reswelling capability were improved, however, the equilibrium water absorbency and swelling rate decreased with increasing AlCl3 solution concentration. The equilibrium water absorbency firstly increased, and then decreased with increasing Al3+‐APT content. The results indicate that Al3+‐APT acts as an assistant crosslinker in the polymeric network, which has great influences on hydrogel strength and swelling behaviors of the PAA/Al3+‐APT superabsorbent composites. POLYM. ENG. SCI., 47:619–624, 2007. © 2007 Society of Plastics Engineers.

Study on superabsorbent composite. XV. Effects of ion‐exchanged attapulgite on water absorbency of superabsorbent composites

AbstractA series of superabsorbent composite, polyacrylamide/attapulgite, from acrylamide (AM) and ion‐exchanged attapulgite (APT) was prepared by aqueous polymerization, using N,N′‐methylenebisacrylamide (MBA) as a crosslinker and ammonium persulfate (APS) as an initiator. The effects of ion‐exchanged APT on water absorbency of superabsorbent composites in distilled water and in 0.9 wt% NaCl solution were studied. The result indicates that higher cation‐exchange capacity (CEC) and lower specific surface area (SSA) of APT treated with various anions are of benefit for improving water absorbency in distilled water. The effects of AlCl3 solution concentration and Al3+‐exchanged APT content on water absorbency of the composite were also investigated. The concentration of AlCl3 solution has a great influence on water absorbency of the superabsorbent composite. Al3+‐exchange of APT could also enhance reswelling ability of the corresponding composite, which indicates that Al3+‐exchange of APT could improve gel strength and gives a direct evidence for its acting as an inorganic assistant crosslinker in the polymeric network. POLYM. COMPOS., 28:208–213, 2007. © 2007 Society of Plastics Engineers

The synthesis and electrical conductivity of a polyacrylamide/Cu conducting hydrogel

A polyacrylamide/Cu superabsorbent composite was synthesized by aqueous solution polymerization. Based on the electrical conductivity of Cu and the water absorbency of polyacrylamide, a novel conducting hydrogel with a conductivity of 1.08 mS m −1 was prepared. The effect of crosslinker, initiator, monomer, neutralization degree, Cu amount, water absorbency and reaction temperature on the electrical conductivity of the hydrogel was investigated. An appended network structure model of the polyacrylamide/Cu conducting hydrogel is proposed.

Preparation and properties of diatomite composite superabsorbent

AbstractA novel diatomite composite superabsorbent was synthesized by solution polymerization of partially neutralized acrylic acid and diatomite, using N,N′‐methylenebisacrylamide as a crosslinking agent and hydrogen peroxide and L‐ascorbic acid as a redox initial system. The influences of some reaction conditions, such as diatomite content, neutralization degree of acrylic acid, amount of initiator, amount of crosslinking agent, monomer concentration, and the reaction temperature on swelling characteristic were investigated. The water absorbency of the sample prepared at optimum conditions was 99 g/g in 0.9 wt% NaCl solution. The results of swelling rate measurement showed that diatomite composite superabsorbent had better swelling rate than that of poly(sodium acrylate) prepared in the same conditions. Other properties, i.e. water retention, reswelling ability and resistance to salt, were also examined. Copyright © 2007 John Wiley & Sons, Ltd.

Study on superabsorbent composite XVI. Synthesis, characterization and swelling behaviors of poly(sodium acrylate)/vermiculite superabsorbent composites

A series of superabsorbent composites were synthesized by copolymerization reaction of partially neutralized acrylic acid on unexpanded vermiculite (UVMT) micropowder using N, N′-methylenebisacrylamide (MBA) as a crosslinker and ammonium persulfate (APS) as an initiator in aqueous solution. And the samples were further characterized by means of fourier-transform spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and thermogravimetric analysis (TGA). The effects of vermiculite content on water absorbency were studied. Swelling behaviors of the superabsorbent composites in various cationic salt solutions (NaCl, CaCl 2 and FeCl 3), anionic salt solutions (NaCl, Na 2SO 4 and Na 3PO 4) and pH solutions were also systematically investigated. Results obtained showed that the equilibrium water absorbency increased with increasing UVMT content and the concentration of 20 wt.% clay gave the best absorption (1232 g/g in distilled water and 89 g/g in 0.9 wt.% NaCl). Data achieved also suggested that the water absorbency in various saline solutions decreased with an increase in the ionic strengths of these solutions. And it was found that at a higher ionic strength (>1 × 10 −3 M), the water absorbency in monovalent cationic solutions was higher than those in multivalent cationic solutions. However, at the same ionic strength (>1 × 10 −3 M), the effect of three anionic salt solutions on the swelling has the following order: NaCl < Na 2SO 4 < Na 3PO 4.

Preparation and swelling behavior of amphoteric superabsorbent composite with semi‐IPN composed of poly(acrylic acid)/Ca‐bentonite/poly(dimethyldiallylammonium chloride)

AbstractAmphoteric superabsorbent composite with semi‐interpenetrating polymer networks (semi‐IPN) composed of poly(acrylic acid) (PAA)/Ca‐bentonite/poly(dimethyldiallylammonium chloride) (PDMDAAC) was prepared by a combination of intercalative polymerization and a sequential IPN method and the effects of reaction parameters on the swelling capacity were studied. PDMDAAC was used as a polycation to modify bentonite and form semi‐IPN with lightly crosslinked PAA. FTIR and TG were used to characterize the amphoteric superabsorbent composites with semi‐IPN. The thermal stability of the product was not degraded as in the case of using small molecular surfactant to modify bentonite. The contents of carboxylic groups and nitrogen had been determined. This indicated that the product with certain content of carboxylic groups and nitrogen is inclined to exhibit excellent swelling capacity. The presence of PDMDAAC improved the swelling capacity. The resulting amphoteric superabsorbent composite showed excellent swelling capacity of 1578 g/g in distilled water and 136 g/g in 0.9 wt% NaCl solution. Copyright © 2007 John Wiley &amp; Sons, Ltd.

Preparation and water absorbency of a novel poly(acrylate‐co‐acrylamide)/vermiculite superabsorbent composite

AbstractA novel poly(acrylate‐co‐acrylamide)/expanded vermiculite (EVMT) superabsorbent composite was synthesized by aqueous solution polymerization method. The water absorbency of the superabsorbent composite still reaches 850 g/g when 50 wt % EVMT is added, which is significant in decreasing the production cost of the superabsorbent composites. By controlling the molar ratio of acrylic acid monomer and acrylamide monomer, and neutralization degree of acrylic acid, the hydrophilic groups on the composite can be adjusted, and it is found that the collaborative absorbent effect of CONH2, COOK, and COOH groups is superior to that of single CONH2, COOK, or COOH group. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 735–739, 2007

Synthesis and characterization of chitosan- g-poly(acrylic acid)/attapulgite superabsorbent composites

A novel chitosan- g-poly(acrylic acid)/attapulgite superabsorbent composite with water absorbency of 159.6 g g −1 in distilled water and 42.3 g g −1 in 0.9 wt% NaCl solution was prepared by graft polymerization with chitosan, acrylic acid and attapulgite in aqueous solution, using N, N′-methylenebisacrylamide as a crosslinker and ammonium persulfate as an initiator. Factors influencing water absorbency of the superabsorbent composite were investigated, such as average molecular weight of chitosan, weight ratio of acrylic acid to chitosan, dewatering method, the amount of crosslinker and attapulgite. The result from FTIR spectra showed that –OH of attapulgite, –OH, –NHCO and –NH 2 of chitosan participated in graft polymerization with acrylic acid. The introduced attapulgite enhanced thermal stability of the chitosan- g-poly(acrylic acid) superabsorbent and formed a loose and more porous surface. Introducing a small amount of attapulgite also enhanced water absorbency of the chitosan- g-poly(acrylic acid) superabsorbent.

Carrageenan-g-Poly(sodium Acrylate)/Kaolin Superabsorbent Hydrogel Composites: Synthesis, Characterisation and Swelling Behaviour

A novel superabsorbent hydrogel composite based on kappa-carrageenan (κC) was prepared by graft copolymerisation of acrylic acid (AA) in the presence of kaolin using methylenebisacrylamide (MBA) as a crosslinking agent and ammonium persulfate (APS) as an initiator. The synthetic variables (i.e. AA, MBA and APS concentration, and the amount of kaolin) affecting the water absorbency of the resulting superabsorbent composite were studied. Evidence of grafting and kaolin interaction was obtained by comparing the FTIR spectra of the initial substrates and of the superabsorbent composite. A new absorption band at 1722 cm−1 in the composite spectrum confirmed the kaolin-organic polymer linkage. Increasing the amount of kaolin and the MBA concentration caused the water absorbency of the superabsorbent composite to decrease. The effect of various salt media and pH on the swelling of the superabsorbent was studied. The swelling kinetics of the synthesised composite was also investigated.

A Conductive Hydrogel by Poly(Sodium Acrylate)/Montmorillonite Superabsorbent Composite

Poly(sodium acrylate)/montmorillonite superabsorbent composite was synthesised by an inverse suspension polymerisation method. A novel hydrogel electrolyte with conductivity of 100 mS·cm−1 was prepared by immersing the superabsorbent composite in 1 M KCl aqueous solution. The conductivity of the hydrogel electrolyte was investigated, and it was found that the hydrogel electrolyte exhibits liquid-like ionic conductivity. The conductivity depends mainly on the ionic intensity of the solution in which it is immersed and on the water absorbency of the superabsorbent.

Optimization of synthetic conditions CMC-g-poly (acrylic acid)/Celite composite superabsorbent by Taguchi method and determination of its absorbency under load

A novel biopolymer-based composite hydrogel was synthesized through chemical crosslinking by graft copoly- merization of partially neutralized acrylic acid onto the carboxymethyl cellulose (CMC). The Taguchi method, a robust experimental design, was employed for the optimization of the synthesis based on the swelling capacity of the hydrogels. This method was applied for the experiments and standard L16 orthogonal array with five factors and four levels. In the synthesis of the composite superabsorbent, N,N'-methylene bisacrylamide (MBA) as crosslinker, ammonium persulfate (APS) as initiator, acrylic acid (AA) as monomer, CMC/Celite weight ratio and neutralization percent (NU) were used as important factors. From the analysis of variance of the test results, the most effective factor controlling equilibrium swelling capacity was obtained and maximum water absorbency of the optimized final product was found to be 310 g/g. The surface morphology of the gel was examined using scanning electron microscopy. Furthermore in this research, swelling capacity of composite SAPs was determined under realistic condition (saline solution absorbency under load).

Controlled release NPK compound fertilizer with the function of water retention

Controlled release nitrogen, phosphorus and potassium (CRNPK) compound fertilizer with the function of water retention was prepared, which possessed the core/shell structure. Its core was urea formaldehyde (UF) and polyphosphate potassium (PAK) fertilizer, and the shell was P(acrylic acid-co-acrylamide)/kaolin (P(AA-co-AM)/kaolin) superabsorbent composite. Analysis results showed that the N, P and K contents were 11.3, 21.1 (shown by P 2O 5) and 8.6 (shown by K 2O) wt%, respectively. The synthesis conditions of inversion suspension polymerization were studied systematically. The water absorbency of the product was 91 g/g in tap water. The swelling rate, slow release and water retention properties of CRNPK were also investigated. Additionally, the effect of temperature on the nutrients release behaviors was studied. The results showed that the product had high initial swelling rate, and the product not only had a good slow release property but also excellent water retention ability, which could effectively improve the utilization of fertilizer and water resource at the same time.

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

AbstractA 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

Preparation and slow‐release property of a poly(acrylic acid)/attapulgite/sodium humate superabsorbent composite

AbstractA novel poly(acrylic acid)/attapulgite (APT)/sodium humate (SH) superabsorbent composite was synthesized through the graft copolymerization reaction of acrylic acid on APT micropowder and SH with N,N′‐methylene bisacrylamide as a crosslinker and ammonium persulfate as an initiator in an aqueous solution. Various effects on the water absorbency, including the amounts of the crosslinker, initiator, APT, and SH, were investigated. The superabsorbent composite was characterized with Fourier transform infrared spectroscopy and scanning electron microscopy. The superabsorbent composite synthesized under optimal synthesis conditions with an APT concentration of 20% and an SH concentration of 20% exhibited absorption of 583 g of H2O/g of sample and 63 g of H2O/g of sample in distilled water and in a 0.9 wt % NaCl solution, respectively. The slow‐release property of SH from the superabsorbent composite into water was measured, and a test of the water retention of the superabsorbent composite in soil was also carried out experimentally with and without the superabsorbent composite. The results showed that the superabsorbent composite had not only good water retention but also an additional slow‐release property of SH. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 37–45, 2007

Preparation of bentonite–poly[(acrylic acid)‐acrylamide] water superabsorbent by photopolymerization

AbstractA novel bentonite–poly[(acrylic acid)‐acrylamide] superabsorbent composite with water and salt solution absorbencies of 450 and 108 times its own weight, respectively, was successfully synthesized by photopolymerization of acrylic acid with acrylamide in the presence of bentonite powder using 30 min of ultraviolet irradiation at room temperature. The results show a synergetic effect of Michler's ketone and benzophenone mixed photoinitiators on the water absorbency, and incorporation of bentonite below 10 wt% into the water superabsorbent can slightly increase the water and salt solution absorbencies, and improve water retention, as demonstrated using thermogravimetric analysis and differential scanning calorimetry. Fourier transform infrared spectroscopy allowed the determination of the structure of the bentonite composite superabsorbent. Copyright © 2006 Society of Chemical Industry

CMC-g-Poly (Sodium Acrylate)/Kaolin Superabsorbent Hydrogel Composites: Synthesis, Characterization and Swelling Behaviour

A novel superabsorbent composite system based on carboxymethyl cellulose (CMC) was prepared by graft copolymerization of acrylic acid (AA) in the presence of kaolin powder using methylenebisacrylamide (MBA) as a crosslinking agent and ammonium persulfate (APS) as an initiator. The effect of reaction variables, such as MBA, AA, and APS concentration and CMC/kaolin ratio on the water absorbency of the composite were studied. Evidence of grafting and kaolin interaction was obtained by comparing the FT-IR spectra of the initial substrates with that of the superabsorbent composite. The results indicated that with increasing amount of kaolin, the swelling capacity was increased and then considerably decreased with further increase in amount. The effect of various salt media was also studied, along with swelling kinetics.

Synthesis and biodegradability of starch-g-ethyl methacrylate/sodium acrylate/sodium silicate superabsorbing composite

A new superabsorbent composite polymer (SAP) has been prepared by graft copolymerization reaction using starch, ethyl methacrylate (EMA), benzoyl peroxide (BPO) as initiator and sodium acrylate as crosslinking agent. Further, it is observed that the composite doped with sodium silicate exhibits higher waterabsorbency as the silicate can well disperse in the water and enter into the network structure of the composite, thereby increasing the porosity of the composite. Sodium acrylate plays an important role as the crosslinker forming a network structure of the superabsorbent composite. The composite was characterized by IR, TGA, and XRD methods. The biodegradability of these valuable novel materials was evaluated for their industrial and commercial importance. The surface morphology was compared by scanning electron microscopy (SEM) before and after biodegradation of the composite.