SYNTHESIS AND PROPERTIES OF ACRYLIC-BASED SUPERABSORBENTS WITH ENHANCED CROSSLINKING ON PARTICLE SURFACE

A series of acrylic-based superabsorbent resins were synthesized by inverse suspension polymerization, using potassium persulfate as the initiator, N, N＇-methylene bisacrylamide （BIS） and divinylbenzene （DVB） as the multiple crosslinking agents. The morphology of the resulting superabsorbent resins revealed by SEM demonstrated that a hard shell layer was indeed formed due to surface crosslinking. The swelling and deswelling properties, and the mechanical strength of superabsorbents were investigated. The results indicated that the adding time of DVB and the amount of DVB participated in the crosslinking show a significant influence on the properties of superabsorbents. When DVB was added in polymerization later, the amount of DVB participated in reaction decreases and the surface crosslinked shell becomes thinner. It is suitable for DVB to be introduced in the later stage of the polymerization process, because the absorption rate of resin is efficiently improved in conjunction with higher water absorption. Furthermore, it was found that the mechanical strength of swollen superabsorbent with surface crosslinking was indeed enhanced in comparison with that of the conventional one.     

Study on superabsorbent of maleic anhydride/acrylamide semi‐interpenetrated with poly(vinyl alcohol)

A series of superabsorbents of maleic anhydride (MAH)/acrylamide (AM) interpenetrated with poly(vinyl alcohol) (PVA) were prepared by aqueous polymerization, using N,N‐methylenebiacrylamide (NNMBA) as a crosslinker and ammonium persulfate (APS) as an initiator. The samples were characterized by Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), and scanning electron microscope (SEM). The effects of reaction variables on the water absorbency of the superabsorbents in distilled water and in 0.9 wt% NaCl solution were investigated. In addition, the effect of the PVA content on the swelling rate and sensitivity to saline of the superabsorbents were also investigated. The results showed that the absorbency, both in 0.9 wt% NaCl solution and in distilled water, first decreased and then increased with increasing PVA content. Moreover, the resultant superabsorbent had a higher absorption rate and it became less sensitive to saline by incorporating certain amount of PVA into the network of the hydrogel. Copyright © 2009 John Wiley & Sons, Ltd.     

Temperature Sensitive Superabsorbent Hydrogels from Poly(N-t-butyl acrylamide-co-acrylamide) Grafted on Sodium Alginate

Temperature-sensitive hydrogels based on N-t-butylacrylamide (TBA), acrylamide (AAm), and sodium alginate were prepared by free radical polymerization method. Methylenebisacrylamide (MBA) and amonium persulfate (APS) were applied as water soluble crosslinker and initiator, respectively. The chemical structure of the hydrogels was confirmed by FT-IR spectroscopy and thermogravimetric analysis (TGA) methods. Morphology of the samples was examined by scanning electron microscopy (SEM). By changing the initial TBA/AAm mole ratios, hydrogels with different swelling properties were obtained. The rate parameters were found to be 2.0, 2.4, and 3.5 min for the superabsorbents with AAm/TBA weight ratio of 1.0, 1.3 and 2.0 respectively. The swelling behavior in distilled water and different pH solutions was investigated. A preliminary swelling kinetics and the absorbency under load (AUL) were also studied. At the applied pressure (2.07 kPa), maximum swelling was found to be 17, 19, and 21 (g/g) for the superabsorbent hydrogels with AAm/TBA weight ratios of 1.0, 1.5 and 2.0, respectively.     

Different types of microfibrillated cellulose as filler materials in polysodium acrylate superabsorbents

Three types of microfibrillated cellulose(MFC)with differences in structure and surface charge were used at low concentration as filler materials in polysodium acrylate superabsorbents(SAPs).The swelling of the composite hydrogels was determined in 0.9%NaCl solution as well as in deionized water.The shear modulus of the samples was determined through uniaxial compression analysis after synthesis and after swelling in 0.9%NaCl solution.Furthermore,the ability to retain filler effects after washing was investigated.The results showed that all of the investigated MFCs had a strong reinforcing effect on the shear modulus after synthesis.The filler effect on swelling and on the associated shear modulus of swollen samples showed a more complicated dependence on structure and surface charge.Finally,it was found that the filler effects were reasonably retained after washing and subsequent drying.The results confirm that MFC holds great potential as a filler material in superabsorbent applications.Furthermore,the results provide some insight on how the structural properties and surface charge of MFC will affect gel properties depending on swelling conditions.This information should be useful in evaluating the use of different types of MFC in future applications.     

Evaluation of the degree of cross-linking of cellulose-based superabsorbent hydrogels: a comparison between different techniques

Three different techniques have been applied to the evaluation of the degree of cross-linking of superabsorbent cellulose-based hydrogels obtained from water solutions of carboxymethylcellulose sodium salt (CMCNa) and hydroxyethylcellulose (HEC), chemically cross-linked with divinyl sulfone. These polyelectrolyte hydrogels are biodegradable and have the same sorption capacity as acrylate-based superabsorbents on the market. A ¹³C solid state NMR analysis was carried out on dry samples of hydrogel to obtain the degree of cross-linking, an important parameter that affects the swelling and mechanical properties of a hydrogel. Dynamic mechanical analysis was performed during the hydrogel cross-linking using a parallel plate rheometer under oscillatory deformations in order to monitor the evolution of the hydrogel viscoelastic properties during the synthesis. The value of |G*| and the slope of the stress-deformation ratio plots from uniaxial compression tests were used to evaluate the elastically effective degree of cross-linking according to classical rubber elasticity theory. Moreover, a dynamic mechanical analysis was carried out on cross-linked hydrogels at different degrees of swelling in order to investigate the influence of the swelling on the mechanical properties and the application of rubber elasticity theory to swollen hydrogels.     

pH-Responsive Nanocomposites From Methylcellulose and Attapulgite Nanorods: Synthesis,Swelling and Absorption Performance on Heavy Metal Ions

A pH-responsive methylcellulose-g-poly(sodium acrylate)/attapulgite (MC-g-PNaA/APT) nanocomposite superabsorbent was prepared by the free-radical solution polymerization of methylcellulose (MC), sodium acrylate (NaA) and nanoscale attapulgite (APT) in the presence of the crosslinker N,N′-methylene-bis-acrylamide (MBA). The structure and morphology of the nanocomposite were characterized by FTIR, FESEM, TEM, XRD and EDS techniques, and the effects of the amount of MBA, MC and APT nanorods on swelling behaviors were also evaluated. Results indicate that NaA has been grafted onto MC macromolecular chains and APT nanorods participated in polymerization by its active silanol groups, and APT led to a better dispersion in the MC-g-PNaA matrix. The incorporation of APT clearly enhanced the swelling capacity and rate of the superabsorbent. In addition, the nanocomposite exhibited excellent absorption capacity on heavy metal ions, and its absorption amounts on Ni²⁺, Cu²⁺ and Zn²⁺ ions reached 9.86, 7.66 and 21.86 times greater than active carbon (AC). The biopolymer-based nanocomposite superabsorbents can be used as a potential water-saving material and candidate of AC for heavy metal ion absorption.     

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

Amphoteric 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 & Sons, Ltd.     

Preparation and Properties of Novel Slow-release PK Agrochemical Formulations Based on Carboxymethylcellulose-Graft-Poly(acrylic acid-co-itaconic acid) Superabsorbents

To improve the utilization of fertilizer and water resources at the same time, a new slow-release PK compound fertilizer (SRCF) with the function of water retention was prepared. Element analysis results showed that the product contained 20.46% potassium (shown by K₂O) and 15.45% phosphorus (shown by P₂O₅), which were trapped in the matrix of carboxymethylcellulose-graft-poly(acrylic acid-co-itaconic acid) superabsorbent polymer. Major factors affecting the water absorbency of SRCF such as weight ratio of itaconic acid (IA) to acrylic acid (AA), contents of crosslinker, K₂HPO₄, and carboxymethylcellulose (CMC) were investigated and optimized. The water absorbency of the product was 130 times its own weight if it was allowed to swell in tap water at room temperature for 1 h. Fourier transform infrared spectroscopy (FTIR) and Thermogravimetric/Differential thermal analysis (TG/DTA) confirmed that AA and IA monomers were graft-copolymerized onto CMC backbone and presented the improved thermal stability. The water evaporation of the fertilizer-containing superabsorbents, as well as their nutrients release in sandy soil was carried out, and a possible slow-release mechanism was proposed. Additionally, compressive modulus measurements revealed that the introduction of CMC could improve the mechanical properties of the superabsorbents. These studies showed that the product with good slow-release and water retention properties, being economical and environment-friendly, could be expected to have wide potential applications in modern agriculture and horticulture.     

Fine coal dewatering using pH- and temperature-sensitive superabsorbent polymers

Water is a necessary medium in most coal preparation processes, but its presence in the final product has a negative impact on transporation costs, handling and specific energy value. A major contribution to the total moisture content may be attributed to the proportion of fine coal in the total product, which presents the greatest dewatering problem. This paper describes a novel process that seeks to reduce the moisture content of fine coal cakes to a level comparable to that achieved by thermal drying. In this process, superabsorbent polymers, which are granular highly crosslinked synthetic copolymers with excellent water-absorbing properties, are employed to draw water from moist fine coal. The drying or dewatering process is characterized by three main stages: (a) contacting of superabsorbents with high-moisture fine coal; (b) separation of dried fine coal from superabsorbents by screening; and (c) regeneration of used superabsorbent polymer, taking advantage of its response to changes in such conditions as pH, temperature or electric field. Depending on the polymer type, the dosage and the polymer/coal contact time, the moisture content of coal filter cake can readily be reduced from, say, 25% to 10% by mass or less. The results of laboratory and pilot scale tests conducted using pH- and temperature-sensitive superabsorbent polymers are discussed in this paper. © 1997 John Wiley & Sons, Ltd.     

Synthesis of bio‐based internal and external cross‐linkers based on tannic acid for preparation of antibacterial superabsorbents

Recent researches focus on the synthesis of new cross‐linkers from natural resources. In the current work, functionalized tannic acid was employed as a replacement of petroleum‐based cross‐linkers because of its outstanding biochemical properties. Alkene‐ and epoxy‐functionalized tannic acids were synthesized as internal and external cross‐linkers, respectively. Cross‐linker structures were characterized with Ft‐IR and ¹HNMR analysis. Different amounts, as well as different numbers of alkene functional group, were incorporated during the superabsorbent synthesis. Moreover, the internal cross‐linked superabsorbent was surface cross‐linked with different amounts of epoxy‐functionalized tannic acid and increased the absorbency under load about 10 g g^?1. Free absorption properties in water and saline solution, absorbency under load, and rheological properties of superabsorbents were investigated. In addition, the antibacterial activity of the internal and external cross‐linked superabsorbent was studied against Escherichia coli and Staphylococcus aureus bacteria via different methods and compared with that of conventional superabsorbent.     

粉煤灰复合聚丙烯酸钠凝胶的制备及其溶胀性能

粉煤灰(CFA)存在的情况下,采用自由基溶液聚合法,以过硫酸钾(KPS)为引发剂,N,N'-亚甲基双丙烯酰胺(NNMBA)为交联剂,制备了粉煤灰复合聚丙烯酸钠凝胶(CFAPAANa)。 以丙烯酸单体质量为基准,当交联剂用量为0.08%,引发剂用量为0.4%,粉煤灰用量为3%,丙烯酸中和度为70%,聚合温度为70 ℃时,所合成的粉煤灰复合聚丙烯酸钠凝胶在蒸馏水和生理盐水中平衡溶胀比最高,分别为1556(g/g)和168(g/g)。 考察了复合凝胶在不同介质溶液中的溶胀动力学,保水性能以及在土壤中的降解行为。 溶胀动力学研究表明,蒸馏水中溶胀初期复合凝胶聚合物链段的扩散运动能够调控凝胶溶胀的快慢及程度,而生理盐水中水分子的平移和对流运动在凝胶的溶胀过程中起着关键性作用。 保水和降解实验结果表明,25 ℃时,50 h凝胶保水率为64%,土壤中50 d时降解率达60%。 相比于聚丙烯酸钠凝胶,粉煤灰复合凝胶保水率提高了8%。     

Preparation and properties of superabsorbent containing starch and sodium humate

Starch and sodium humate were utilized as raw material for synthesizing starch‐g‐poly(acrylic acid)/sodium humate (St‐g‐PAA/SH) superabsorbent by graft copolymerization reaction of starch (St) and acrylic acid (AA) in the presence of sodium humate (SH) in aqueous solution. The effect of weight ratio of AA to St, initial monomer concentration, neutralization degree of AA, amount of crosslinker, initiator and SH on water absorbency of the superabsorbent were studied. The swelling rate and swelling behavior in NaCl solution as well as reswelling ability of the superabsorbent were systematically investigated. The results showed that the superabsorbent synthesized under optimal conditions with SH content of 7.7 wt% and St content of 11.5 wt% exhibits water absorbency of 1100 g/g in distilled water and 86 g/g in 0.9 wt% NaCl solution, respectively. Introducing SH into the St‐g‐PAA polymeric network can improved the swelling rate and reswelling capability of the superabsorbent. Copyright © 2008 John Wiley & Sons, Ltd.     

Study on the swelling kinetics of superabsorbent using open circuit potential measurement

Open circuit potential measurement was used to trace the swelling kinetics of superabsorbent. The calibration curve and its fitting result showed the validity of the method in determining the concentration of chloride ion in aqueous solution. According to the regression analysis and theoretical derivation, the relationship between the open circuit potential change and the swelling ratio was obtained. Comparing with tea bag method, it was verified that open circuit potential measurement could be employed to trace the swelling kinetics of superabsorbent. The hysteresis effect of solute entering into superabsorbent and the overflow of soluble parts of hydrogel were also observed. Besides, we found that the entrance of solute and water were almost synchronal, and the concentration of solution absorbed by superabsorbent was lower than that of swelling medium. Moreover, the swelling model of superabsorbent in salting liquid was slightly modified.     

Study on superabsorbent composite. IV. Effects of organification degree of attapulgite on swelling behaviors of polyacrylamide/organo-attapulgite composites

A novel kind of superabsorbent composite, polyacrylamide/organo-attapulgite, from acrylamide (AM) and attapulgite (APT) was prepared by aqueous polymerization, using N,N′-methylenebisacrylamide (MBA) as a crosslinker and ammonium persulfate (APS) as an initiator. APT was organified with five different degree of hexadecyltrimethyl ammonium bromide (HDTMABr), and the organification degree of APT was proved by FTIR, TGA and XRD. The effects of organification degree of APT on water absorbency and swelling rate of the superabsorbent composite in distilled water and in various saline solutions were investigated in this study. The effect of organification degree on reswelling ability of the superabsorbent composites was also investigated. The results indicate that the organification degree of APT had remarkable influence on swelling behaviors of the superabsorbent composites. The superabsorbent composite acquired its highest water absorbency when the organification degree of APT is 8.02 wt.%.     

Study on superabsorbent composite—VII. Effects of organification of attapulgite on swelling behaviors of poly(acrylic acid‐co‐acrylamide)/sodium humate/organo‐attapulgite composite

A novel multifunctional superabsorbent composite from acrylic acid (AA), acrylamide (AM), sodium humate (SH) and organo‐attapulgite (organo‐APT), PAA‐AM/SH/organo‐APT, was synthesized by aqueous solution polymerization, using N,N′‐methylenebisacrylamide (MBA) as a crosslinker and ammonium persulfate (APS) as an initiator. The organification of APT with hexadecyltrimethyl ammonium bromide (HDTMABr) was proved by FT‐IR. The effects of organo‐APT (HDTMA‐APT) content in the superabsorbent composite and organification degree of it on water absorbency of the superabsorbent composite were studied. The effects of incorporated HDTMA‐APT on swelling rate, water absorbency in various saline solutions and reswelling capability of the superabsorbent composite were also investigated. The results indicate that organification of APT had a remarkable influence on swelling behaviors of the superabsorbent composites. Comparing with the composite doped with APT, water absorbency for the composite incorporated with 10 wt% HDTMA‐APT was enhanced from 996 to 1282 g g^?1 in distilled water and from 63 to 68 g g^?1 in 0.9 wt% NaCl solution, respectively. The superabsorbent composite acquired its highest water absorbency when the organification degree of APT was 8.02 wt%. Water absorbency of the composites in various saline solutions decreased with the increasing concentration, especially for the multivalent cations. In addition, swelling rate and reswelling capability of the superabsorbent composite were also improved by introducing HDTMA‐APT into the composite compared with that of incorporating APT. Copyright © 2006 John Wiley & Sons, Ltd.     

交联剂分子量对高吸水性树脂性能的影响

通过丙烯酰氯对聚乙二醇的封端反应合成了一系列分子量不同、结构类似的交联剂———聚乙二醇二丙烯酸酯 (PEGDA) ,并用于聚丙烯酸高吸水性树脂的制备 .运用FTIR对PEGDA进行了分析 .吸水性能实验结果表明 ,交联剂的分子量越大 ,则高吸水性树脂的吸水倍率越高 ,吸水速率越大 ,而相对吸水速率降低 .同时 ,PEGDA与常用的交联剂N ,N′ 亚甲基双丙烯酰胺 (MBA)相比 ,前者制备的高吸水性树脂的吸水倍率远高于后者 ;线型可溶性聚合物及残留单体的含量 ,前者也低于后者     

碳纳米管复合聚丙烯酸钠的制备及吸水性能

以过硫酸铵(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碳纳米管/聚丙烯酸钠高吸水树脂。系统考察了碳纳米管质量分数、引发剂、交联剂和聚合温度对树脂吸水性能的影响。结果表明,以单体丙烯酸质量为基准,当交联剂,引发剂和碳纳米管质量分数分别为0.04%、0.3%和0.3%,聚合温度75℃时,所合成树脂的吸水性能最佳。添加碳纳米管后树脂表面粗糙和形成孔结构导致了其吸水性能的变化,使得碳纳米管/聚丙烯酸钠的吸水量和吸水速率明显提高,其吸去离子水和生理盐水能力分别达到1423和104g/g。该树脂重复吸水5次后,其吸水能力为1081.5g/g,达到最大吸水倍数的76.0%。     

高吸水性树脂研究进展

介绍了高吸水性树脂的结构、性能及其表征,结合经典理论与最新研究从热力学和动力学角度阐述其吸水机理,着重分析合成条件,组份和方法对高吸水性树脂性能的影响机制,简略地介绍了高吸水性树脂三十年来的发展及广阔的应用领域,并预测其研究与开发前景     

Preparation and properties of diatomite composite superabsorbent

A 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.     

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

A 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.