Improvement in the water‐absorbing properties of superabsorbent polymers (acrylic acid‐co‐acrylamide) in supercritical CO2

Superabsorbent resins prepared by ultraviolet radiation‐inducing polymerization techniques with acrylic acid/acrylamide were treated with supercritical carbon dioxide (SC‐CO₂). The water‐absorbing properties of the treated resins were greatly improved. The water‐absorbing properties of resins treated with SC‐CO₂ in the pressure range of 10–35 MPa and the temperature range of 40–60°C were studied. The effects of the treatment time and depressurizing speed of CO₂ after treatment were also examined. Obviously, different results were found for particles of different sizes. Smaller particles were more efficient under the same treatment conditions. Samples were tested with differential scanning calorimetry. The results showed that the plasticizing effect of CO₂ reduced the glass‐transition temperature of the polymer, and it was proposed that the plasticization effect might have led to polymer chain redistribution and better flexibility. Minor changes in the surface morphology of the particles were observed with scanning electron microscopy. The extraction of the unpolymerized monomers by SC‐CO₂ was also studied. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2272–2278, 2002     

Adsorption of cationic dyes on poly(acrylic acid‐co‐sodium acrylate‐co‐acrylamide) superabsorbents

Inverse suspension polymerization was carried out to synthesize poly(acrylic acid‐co‐sodium acrylate‐co‐acrylamide) superabsorbent polymers (SAPs) crosslinked with ethylene glycol dimethacrylate (EGDMA). The equilibrium swelling capacities of the SAPs, determined by swelling them in DI water, were found to vary with the acrylamide (AM) content. The SAPs were used to adsorb four cationic dyes (Acriflavine, Auramine‐O, Azure‐I and Pyronin‐Y). The effect of AM content in the SAPs on the adsorption of the cationic dyes was investigated. Different initial concentrations of Azure‐I were used with the same amount of the SAP to explore the effect of initial dye concentration on the adsorption. The effect of the adsorbent amount was investigated by taking different amounts of SAP with a fixed initial concentration of Acriflavine. The kinetics of the dye adsorption was modeled by a first order model and the equilibrium amount of the dye adsorbed, adsorption rate coefficients, removal efficiency and partition coefficients were determined. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Preparation and Swelling Behavior of Fast‐Swelling Superabsorbent Hydrogels Based On Starch‐g‐Poly(acrylic acid‐co‐sodium acrylate)

Summary: A novel fast‐swelling porous superabsorbent hydrogel was prepared by grafting acrylic acid onto corn starch through free‐radical polymerization in aqueous solution using N,N′‐methylenebisacrylamide as a crosslinker, ammonium persulfate as an initiator, sodium dodecyl sulfate and p‐octyl poly(ethylene glycol)phenyl ether as pore‐forming agents. The graft polymerization and surface morphology of the porous superabsorbents were characterized by FTIR and SEM. The results indicate that the porous superabsorbents were endowed with higher equilibrium water absorbency and faster swelling rate (they needed only 10 min to reach 90% of their equilibrium water absorbency) compared with the nonporous superabsorbents. The dewatering method employed had a significant influence on the swelling behavior of the superabsorbents and dewatering agents were useful to preserve the pores formed during the polymerization process.

The equilibrium water absorbency in distilled water, for the porous and non‐porous starch‐g‐poly(acrylic acid‐co‐sodium acrylate) superabsorbent hydrogels dried through different procedures.     

Study on superabsorbent composites. XXI. Synthesis,characterization and swelling behaviors of chitosan‐g‐poly(acrylic acid)/organo‐rectorite nanocomposite superabsorbents

A novel chitosan‐g‐poly(acrylic acid)/organo‐rectorite (CTS‐g‐PAA/OREC) nanocomposite superabsorbent was synthesized by aqueous polymerization using N, N′‐methylenebisacrylamide as a crosslinker and ammonium persulfate as an initiator. Rectorite was organified with four different degree of hexadecyltrimethyl ammonium bromide, and the organification of rectorite was proved by FTIR and XRD. The effect of organification degree of rectorite on water absorbency of CTS‐g‐PAA/OREC with different organo‐rectorite content was investigated. The swelling behaviors in distilled water and various pH solutions were also studied. The results from IR spectroscopy and XRD data show that acrylic acid had been grafted polymerization with chitosan and organo‐rectorite and formed nanocomposite. Introducing organo‐rectorite into the CTS‐g‐PAA polymeric network can improved water absorbency and swelling rate of CTS‐g‐PAA/OREC. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Influence of reaction parameters on water absorption of neutralized poly(acrylic acid‐co‐acrylamide) synthesized by inverse suspension polymerization

Highly water‐absorbing polymers of neutralized poly(acrylic acid‐co‐acrylamide) were synthesized in an effort to investigate the influences of reaction parameters on water absorption. In addition, the extent of water absorption and the absorption rate were studied to determine their relationship with the reaction parameters. This article explains the synthesis technique, characterization of the water‐absorbing copolymers, and their properties. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 1349–1366, 1999     

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     

Synthesis of poly(acrylic acid)/sodium humate superabsorbent composite for agricultural use

A novel poly (acrylic acid)/sodium humate superabsorbent composite was synthesized by graft copolymerization reaction of acrylic acid (AA) on sodium humate micropowder using N,N′‐methylenebisacrylamide (MBA) as a crosslinker and potassium peroxydisulfate (KPS) as an initiator in aqueous solution. The effects on water absorbency of factors such as reaction temperature, initial monomer concentration, and degree of neutralization of AA, amount of crosslinker, initiator, and sodium humate were investigated. The superabsorbent composite was characterized by scanning electron microscopy, and the graft copolymerization reaction of AA on sodium humate micropowder was characterized by IR spectroscopy. Results obtained from this study show that the water absorbency of the superabsorbent composite synthesized under optimal conditions for synthesis with a sodium humate content of 5.3% exhibited absorption of 684 g H₂O/g sample in distilled water. Water‐retention in soil is enhanced by the use of the superabsorbent composite. The effect of superabsorbent composite on the growth of corn is reported. The superabsorbent composite may be of use as water management materials for agriculture purposes in desert and drought‐prone areas. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 5137–5143, 2006     

Absorbency and adsorption of poly(acrylic acid‐co‐acrylamide) hydrogel

Poly(acrylic acid‐co‐acrylamide) (PAAAM) hydrogels have been prepared from partly neutralized acrylic acid (AA) and acrylamide (AM) by solution polymerization, and their absorbency and adsorption in both CuCl₂ and FeCl₃ solutions have been investigated. PAAAM hydrogels and their complexes with Cu²⁺ or Fe³⁺ have been characterized by FTIR. The absorbency of PAAAM in both CuCl₂ and FeCl₃ solutions increases initially and then decreases as the absorbing time increases. The adsorption of PAAAM in both CuCl₂ and FeCl₃ solutions can be described by the pseudo‐second order chemisorption kinetics proposed by Ho and McKay, and the equilibrium uptake of Cu²⁺ on PAAAM can well be fit with the Langmuir adsorption isotherm. However, the equilibrium uptake of Fe³⁺ on PAAAM increases as the initial Fe³⁺ concentration increases for Fe³⁺ concentration smaller than 5.625 × 10^?3 mol/L, and then decreases with Fe³⁺ concentration. The largest uptakes for Cu²⁺ and Fe³⁺ are 247 and 173 mg/g, respectively. The results also show that the uptake of Cu²⁺ and Fe³⁺ on PAAAM increases remarkably when pH of the solution is changed from 2.3 to 4.2 and from 1.0 and 2.1, respectively. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Investigation of pH sensitivity of poly(acrylic acid‐co‐acrylamide) hydrogel

It was found that the upper critical solution temperature (UCST) of poly(acrylic acid‐co‐acrylamide) hydrogel decreases with increase in pH. The UCST of samples equilibrated in a buffer at pH 2.5 was 33.7 °C, whereas it shifted to below 0 °C when swollen in buffers above pH 10. FT‐IR showed that COOH group of acrylic acid ionized gradually in alkaline media. The morphology change of the hydrogel swollen in different buffers was studied by environmental scanning electron microscopy (ESEM). ESEM images showed that the pore size of the sample increased with increase in pH, and in strongly basic media the three‐dimensional network was replaced by a ‘sausage‐like’ or ‘desert‐like’ structure. A study of the pH‐dependent release of cefazolin sodium was also carried out. Copyright © 2003 Society of Chemical Industry     

壳聚糖交联聚丙烯酸/马来酸酐吸水树脂的制备

以马来酸酐(MA)、丙烯酸(AA)为原料,过硫酸铵(APS)和亚硫酸氢钠为引发剂,N-马来酰化壳聚糖(N-MACH)为交联剂,采用水溶液自由基聚合反应合成了高吸水树脂,并用正交实验法对合成条件进行了优化,得到最佳合成条件。结果表明,当单体浓度为20%,交联剂的用量为0.03 g,AA中和度为50%,m(MA)/m(AA)为5%时,可以合成具有较好吸水性的高吸水树脂,在蒸馏水中的吸水倍率为1 560.42 g/g;合成的吸水树脂具有较好的吸水速度;不同种类盐溶液浓度的变化对吸水树脂吸水率的影响较大。     

聚丙烯酸/丙烯酰胺高吸水性树脂吸附性能

用反相悬浮聚合法合成了聚丙烯酸/丙烯酰胺高吸水性树脂(PAAAM),讨论了其吸附CuCl₂、NiCl₂、CoCl₂溶液中金属离子的性能,考察了溶液pH值和初始浓度对金属离子吸附的影响。结果表明,PAAAM在不同pH值及浓度区间,对金属离子的吸附能力有较大差异,可被用于Cu(II)、Ni(II)、Co(II)的分离。同时还探讨了PAAAM在混合金属离子溶液中的吸附性能及反复利用的可能性,发现在混合溶液中PAAAM表现出对Cu（II）有较好的选择性吸附能力;4次循环后对Cu(II)、Ni(II)、Co(II) 离子的吸附量为最大吸附量的80%以上,重复使用效果理想。     

Synthesis and properties of electrically‐sensitive poly(acrylic acid‐co‐acetoacetoxy ethyl methacrylate) gels

A series of electric field sensitive copolymer P(AA‐co‐AAEM) gels of acrylic acid (AA) with acetoacetoxy ethyl methacrylate (AAEM) were prepared by free‐radical copolymerization, with N,N′‐methylene bisacrylamide (MBAAm) and ammounium persulfate (APS) as crosslinking agent and initiator, respectively. The structures and properties of the gels were tunable by changing the monomer feed weighty ratio (R) (R = W_AAEM/(W_AAEM + W_AA) of AAEM and AA. The influences of the NaCl concentration and pH buffer solutions on the equilibrium swelling ratios of the gels were studied in detail. It is shown that both NaCl concentration and pH value of the buffer solution affect the swelling properties of the P(AA‐co‐AAEM) gels greatly. Moreover, the gel deswelling behavior induced by a direct current electric field was investigated and an excellent electric‐sensitivity was found. Among all the samples, the gel with monomer feed weighty ratio (R) = 0.1479 showed the best electrical contraction properties. On the basis of the experimental results, the mechanism of the electricity‐induced deswelling behavior was presented. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

壳聚糖接枝聚丙烯酸钠/高岭土复合树脂的吸水性能

利用溶液聚合法制备了壳聚糖接枝聚丙烯酸钠/高岭土复合树脂,研究了复合树脂在蒸馏水中的吸水速率、重复吸水性能和人工尿液中的吸水倍率,以及在不同温度、不同电解质溶液离子强度和不同pH值的环境下复合树脂的吸水性能。结果表明,复合树脂的吸水速率较慢,在多次重复吸水后吸水性能也逐渐降低,在人工尿液中的吸水倍率高于聚丙烯酸钠树脂,低于壳聚糖接枝丙烯酸钠树脂;随着温度的升高,复合树脂的吸水能力增强,超过50℃后变化较小;树脂的吸液倍率随着电解质溶液浓度和价态的增大而下降;随着pH值的增大而出现驼峰,在pH=3.5和pH=8.5处分别出现吸液倍率最大值。     

Factors influencing absorbent properties of saponified starch‐g‐(acrylic acid‐co‐acrylamide)

Mixtures of acrylamide (AM) and acrylic acid (AA) were grafted onto gelatinized maize starch by using ceric ammonium nitrate (CAN) as an initiator. These graft copolymers were hydrolyzed with alkali to yield hydrogels. The effects of different reaction variables, such as the concentration of the initiator and crosslinker, initial dilution of monomers, gelatinization conditions of starch, and the ratio of AM and AA in the monomer feed, on the water absorption capacities of these hydrogels have been examined. Absorption increases on gelatinizing starch at a higher temperature for a longer time as smaller granules gelatinize only under these conditions. The higher proportion of AA in the monomer feed enhances absorption due to formation of polyelectrolyte. The optimum conditions for obtaining maximum water absorbency established in the present study are granular maize starch = 2.0 g; gelatinization temperature = 95°C; gelatinization time = 60 min; AM = 1.0 g; AA = 4.0 g; CAN = 0.008 mol/L; N,N′‐methylene bisacrylamide = 1%. The product so formed was saponified with NaOH and then precipitated in excess of methanol. The dried and finely powdered product showed the maximum water absorbency of 510 g/g. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2480–2485, 2000     

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     

pH‐reversible hydrogels. IV. Swelling behavior of the 2‐hydroxyethyl methacrylate‐co‐acrylic acid‐co‐sodium acrylate copolymeric hydrogels

A series of 2‐hydroxyethyl methacrylate (HEMA) and sodium acrylate (SA50) copolymeric gels were prepared from HEMA and the anionic monomer SA50 with various molar ratios. The influence of SA50 on the copolymeric gels on their swelling behavior in deionized water at different temperatures and various pH buffer solutions was investigated. Results indicated that the poly(2‐hydroxyethyl methacrylate) (PHEMA) hydrogels exhibited an overshooting phenomenon in their dynamic swelling behavior. The maximum overshooting value decreased with increasing of the temperature. The same results were also found in the HEMA/SA50 copolymeric gels with a lower SA50 content. On the contrary, the overshooting phenomenon for HEMA/SA50 copolymeric gels with a higher content of SA50 was exhibited only under higher temperature (over 35°C). These copolymer gels were used to assess drug release and drug delivery in this article. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 1360–1371, 2001     

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     

Determination of swelling behavior and morphological properties of poly(acrylamide‐co‐itaconic acid) and poly(acrylic acid‐co‐itaconic acid) copolymeric hydrogels

Poly(acrylamide‐co‐itaconic acid) (PAAmIA) and poly(acrylic acid‐co‐itaconic acid) (PAAIA) copolymeric hydrogels were prepared with different compositions via free‐radical polymerization. Ethylene glycol dimethacrylate (EGDMA) was used as an original crosslinker for these monomers. Gelation percentages of the monomers were studied in detail and it was found that addition of IA into the monomer mixture decreased the gelation percentage. The variation in swelling values (%) with time, temperature, and pH was determined for all hydrogels. PAA, which is the most swollen hydrogel, has the swelling percentage value of 2000% at pH = 7.4, 37°C. Swelling behaviors were explained with detailed SEM micrographs, which show the morphologic differences between dry and swollen hydrogels. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 5994–5999, 2006     

Swelling properties of CMC‐g‐poly (AAm‐co‐AMPS) superabsorbent hydrogel

A series of biopolymer‐based superabsorbent hydrogels based on carboxymethyl cellulose has been prepared by free‐radical graft copolymerization of acrylamide and 2‐acrylamido‐2‐methylpropan sulfonic acid (AMPS) in aqueous solution using methylenebisacrylamide as a crosslinking agent and ammonium persulfate as an initiator. The effect of variables on the swelling capacity such as: acrylamide/AMPS weight ratio, reaction temperature, and concentration of the initiator and crosslinker were systematically optimized. The results indicated that with increasing the amount of AMPS, the swelling capacity is increased. FT‐IR spectroscopy and scanning electron microscope analysis were used to confirm the hydrogel structure. Swelling measurements of the synthesized hydrogels in different salt solutions indicated considerable swelling capacity. The absorbency under load of the superabsorbent hydrogels was determined by using an absorbency under load tester at various applied pressures. A preliminary swelling and deswelling behaviors of the hydrogels were also studied. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Poly(acrylic acid)–poly(vinyl alcohol) copolymers with superabsorbent properties

Biodegradable polyacrylates were produced by a series of novel copolymerization and/or crosslinking techniques using poly(vinyl alcohol) (PVA) moieties modified by the incorporation of olefinic structures. PVA was modified by a tosylation and/or detosylation reaction. The functionalized PVA was copolymerized and/or crosslinked with acrylic acid or its partially neutralized form to give crosslinked polyacrylates that could swell in water. Their swelling behavior was determined under load. Degradation studies were performed in α-chymotrypsin, trypsin, and papain solutions. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 817–829, 1998