Swelling Behavior of pH-Sensitive Copolymers Containing 2-Acrylamido-2-Methyl Propane Sulfonic Acid and Acrylic Acid Crosslinked with Vinyl Trimethoxy Silane Crosslinker

Copolymers of 2-acrylamido-2-methyl propane sulfonic acid and acrylic acid were crosslinked in the presence of different mol% of either vinyl trimethoxy silane (VTMS) as the crosslinking agent under acidic conditions or N,N-methylenebisacrylamide (MBA) as crosslinker using solution radical polymerization. The resultant xerogels were characterized by extracting the soluble fractions and measuring the equilibrium water content. Soluble fractions of the crosslinked networks were reduced by varying the MBA and VTMS concentrations. The surface morphology of the crosslinked polymers was observed by scanning electron microscope. The influence of pH on the swelling behavior of gels was investigated. The swelling behaviors of the resulting gels show pH sensitivity.     

Synthesis,characterization and water absorbency properties of poly(acrylic acid)/sodium humate superabsorbent composite

A novel poly(acrylic acid)/sodium humate superabsorbent composite was synthesized by aqueous solution polymerization of acrylic acid using N, N′‐methylenebisacrylamide as a crosslinker and ammonium persulfate as an initiator in the presence of sodium humate. The effects on water absorbency such as initial monomer concentration, degree of neutralization of acrylic acid, amount of crosslinker, initiator and sodium humate, etc. were investigated. The water absorbency of the superabsorbent composite synthesized under optimal synthesis conditions with a sodium humate content of 20% exhibited an absorption of 1268 g H₂O/g sample and 93 g H₂O/g sample in distilled water and in 0.9 wt% NaCl solution, respectively. Swelling rate and water retention tests were also carried out. The results show that sodium humate, as a kind of functional filler, can enhance comprehensive properties of superabsorbent composite and reduce the product cost significantly. Copyright © 2005 John Wiley & Sons, Ltd.     

Modified carrageenan 3. Synthesis of a novel polysaccharide-based superabsorbent hydrogel via graft copolymerization of acrylic acid onto kappa-carrageenan in air

A novel biopolymer-based superabsorbent hydrogel was synthesized through chemically crosslinking graft copolymerization of acrylic acid (AA) onto kappa-carrageenan (κC), in the presence of a crosslinking agent and a free radical initiator. A proposed mechanism for κC-g-polyacrylic acid was suggested and the affecting variables onto graft polymerization (i.e. the crosslinker, the monomer and the initiator concentration, the neutralization percent and reaction temperature) were systematically optimized to achieve a hydrogel with swelling capacity as high as possible. Maximum water absorbency of the optimized final product was found to be 789 g/g. The swelling capacity of the synthesized hydrogels was also measured in various salt solutions. The time-temperature profile of the polymerization reaction, in order to investigate the effect of molecular oxygen was conducted in terms of the absence and presence of the atmospheric oxygen. The overall activation energy (E_a) of the graft polymerization reaction was found to be 2.93 KJ/mol.     

钻井液用交联-接枝淀粉的制备及性能

以N,N′-亚甲基双丙烯酰胺为交联剂,过硫酸铵为引发剂,采用“溶剂法”工艺合成了高粘度抗剪切丙烯酸钠接枝淀粉(St),考察了单体、引发剂和交联剂用量、丙烯酸中和度、反应时间及反应温度对合成交联丙烯酸钠接枝淀粉糊液粘度的影响。 结果表明,其优化反应条件为：m(淀粉)∶m(丙烯酸）=1∶1.5,乙醇质量分数为80%,过硫酸铵的用量为单体总质量的1%,交联剂为单体总质量的0.6%,反应时间2.5 h,反应温度为55 ℃,丙烯酸中和度为70%。 该交联接枝淀粉糊液具有良好的触变性,在4%盐水泥浆中的添加量为14.0 g/L时,表观粘度为26.0 mPa·s,滤失量为7.2 mL;在饱和盐水泥浆中添加量为23.5 g/L时,表观粘度为54.5 mPa·s,滤失量为3.1 mL;在80 ℃高温下老化16 h其表观粘度及滤失量等性能基本保持不变,表现出良好的增粘、降失水作用和抗盐、抗老化性能。     

Radiation Synthesis of Superabsorbent Hydrogels Based on Chitosan and Acrylic Acid for Controlled Drug Release

Superabsorbent hydrogels based on the natural polymer chitosan and acrylic acid (CS/AAc) was prepared using ⁶⁰Co gamma radiation as a source of initiation and crosslinking. The factors, which affect the preparation of CS/AAc hydrogels such as irradiation dose, CS/AAc ratios, and acrylic acid monomer concentrations, to get the best optimum conditions, were investigated. The kinetic studies of the swelling of CS/AAc hydrogel showed that it follows a Fickian type of water diffusion. The Fickian constant value ‘n’ was more than 0.5 with a high swelling capacity of 300 g/g as superabsorbent hydrogel. In addition, the suitability of CS/AAc hydrogel as carrier material for the drug Chlortetracycline-HCl has been investigated by adsorption isotherm studies. The performance of drug release from hydrogel systems, influenced by acrylic acid ratio and the effect of pH of the medium was studied.     

Inverse Suspension Polymerization of Partially Neutralized and Lightly Cross-Linked Acrylic Acid: Effect of Reaction Parameters

An inverse suspension polymerization was carried out in laboratory in one Liter Buchi glass reactor to produce superabsorbent polymers (SAPs) based on acrylic monomers for hygiene applications. Strongly water absorbing polymers, based on acrylic acid, sodium acrylate were prepared by copolymerization using potassium per sulfate as initiator and N-N′ methylene-bisacrylamide (MBA) as crosslinking agent. The effect of varying monomer, crosslinker, initiator, dispersant concentration, time of reaction and degree of neutralization, on absorption capacities was investigated. In the present studies, the continuous hydrocarbon phase was taken as 50:50 mixture of n-heptane and cyclohexane (aliphatic-alicyclic) because the availability of crosslinker in the aqueous phase is controlled by the partition coefficient of the crosslinker between the aqueous phase and the continuous hydrocarbon phase. The SAPs were evaluated for their free absorption capacities in distilled water, saline (0.9% NaCl), and also absorption under load (AUL). The experimental results show that these SAPs have good absorbency both in water and NaCl solutions. It was observed that SAP synthesized from acrylic acid with about 70% degree of neutralization, containing 1% cross-linker, and 0.5–1.0% initiator concentration with 10% dispersant exhibited absorption capacities in water, saline and AUL as 220 g/g, 70 g/g and 27 g/g respectively.     

Investigation of Water Uptake Behavior of Superabsorbent Polymers Composed of N‐Vinyl‐2‐pyrrolidone and Partially Neutralized Acrylic Acid

Fast‐swelling micrometer sized superabsorbents were synthesized through a rapid solution polymerization of n‐vinyl‐2‐pyrrolidone (NVP) and partially neutralized acrylic acid (PNAAc) under normal atmospheric conditions using N,N'‐methylene bisacrylamide (MB) as crosslinker and sodium bicarbonate as porogen. The effect of various parameters such as crosslinker concentration, degree of neutralization of monomer acid, concentration of initiator have been evaluated. Water retention capacity of superabsorbents under varying loads was also examined. The drying behavior of polymers at 37°C was also studied. The gels showed sharp volume transition in solutions of divalent metal ions. The superabsorbents were also characterized by FTIR and TGA.     

Synthesis and Properties of a Novel Diverting Agent Derived From the Copolymerization of Acrylamide with Sodium Acrylate

A novel diverting agent, which derived from the copolymer of poly(acrylamide-co-sodium acrylate) [P(AM-co-SA)], was synthesized by using aluminium nitrate [Al(NO₃)₃] as crosslinker, L-ascorbic acid/peroxide hydrogen [Vc/H₂O₂] as initiator, and methanol as temperature regulator. Thereafter, as key investigation points, the aging time and water absorbency of the resulting diverting agent were recruited, the amount of crosslinker and initiator, the ratios between acrylic acid and acrylamide, the neutralization of acrylic acid, the feeding ratios of methanol, the temperature and the reaction time were investigated. The dependency relationship between the water absorbency and aging time on each factor was also obtained.     

Graft Copolymerization of Artemisia Seed Gum with Acrylic Acid under Microwave and its Water Absorbency

A super‐absorbent polymer was prepared by grafting copolymerization of acrylic acid onto Artemisia seed gum, using microwave irradiation and ammonium persulfate as an initiator. The effect of various preparation conditions on its water absorbency, such as the ratio of acrylic acid to Artemisia seed gum, degree of acrylic acid neutralization, amount of initiator and microwave irradiation time, was investigated by orthogonal tests. The optimal reaction conditions were 3 min (irradiation time), 70% neutralization degree of acrylic acid and 2% initiator on the basis of the mass of acrylic acid used. When the mass ratio of acrylic acid to Artemisia seed gum is 5:0.5, the product has a water absorbency close to 400 times at room temperature in distilled water, this indicated that is has a high water absorbency. The structure of the graft copolymer was confirmed by Fourier transform infrared spectrometer (FT‐IR) and thermogravimetric analysis (TGA). Further more, this microwave irradiation processing method to prepare water absorbent materials has no industrial cast off produced, that is to say, this method is environmentally friendly.     

A Way to Prepare Core‐Shell Biocompatible Polymeric Nano‐Particles from Gelatin and Acrylic Acid

Narrowly distributed core‐shell nano‐particles at relatively high concentration (30 mg/mL) were prepared via in situ polymerization of acrylic acid in an aqueous solution of biocompatible gelatin. These polymeric nano‐particles, in aqueous solution, had cores mainly comprised of an insoluble inter‐polymer complex of poly(acrylic acid, PAA) and gelatin and shells comprised of soluble gelatin (denoted as gelatin/PAA nano‐particles). Dynamic light scattering and electrophoretic light scattering techniques were used to trace the in situ polymerization process. The structure of the gelatin/PAA nano‐particle was further locked‐in via shell crosslinking; i.e., the reaction between glutaraldehyde and gelatin. Scanning force microscopy (SFM) was used to observe the morphologies of the particles before and after cross‐linking. Furthermore, the pH responsive behaviors of the gelatin/PAA nano‐particles before and after shell crosslinking were studied.     

Preparation and swelling properties of hydrolysis-resistant superabsorbent composite based on acrylic acid and sodium bentonite

Abstract

A novel hydrolysis-resistant superabsorbent composite was prepared via the solution polymerization based on acrylic acid (AA) and sodium bentonite (SBT) as monomers, tetraallylammonium bromine (TAAB) as crosslinker and ammonium persulfate (APS) as initiator. The mechanism of polymerization and the structure of the superabsorbent polymer (SAP) were studied by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (X-ray), and scanning electron microscopy (SEM). The reaction conditions such as different mass ratios of APS to AA, TAAB to AA, SBT to AA, neutralization degree of AA were optimized by orthogonal experiment, and the influence of each reaction condition on the capacity of water absorption at 150?°C was investigated via single-factor controlled experiment. The hydrolysis resistance and swelling kinetics of the SAP were studied in different solutions at 150?°C. Compared to traditional SAPs, the SAP synthesized with TAAB as crosslinker performed a more excellent hydrolysis resistance and water absorbency capacity at high temperatures. The water absorbency in distilled water or 0.1?mol L^?1 NaCl solution could reach 392.6 and 145.2?g g^?1at 150?°C, respectively. The SAP maintaining high swelling capacity in the pH range of 5–9 indicated its wide application values in the acidic or alkaline environment at high temperature. In addition, the SAP exhibited good reusability which could still retain about 73% of its initial water absorbency after reswelling six times at 150?°C.     

Synthesis and Properties of Poly(acrylic acid)/Mica Superabsorbent Nanocomposite

A novel poly(acrylic acid)/mica superabsorbent composite was synthesized by graft polymerization reaction between partially neutralized acrylic acid and ultrafine mica mineral powder. The water absorbency of the composite is higher than 1 100 g H₂O/g. The influence of the neutralization degree of acrylic acid, as well as of the amounts of mica and crosslinker on the absorbing properties are discussed in this paper.     

Preparation and Properties of Biodegradable Slow-Release PAA Superabsorbent Matrixes for Phosphorus Fertilizers

Biodegradable superabsorbent matrixes for a slow-release fertilizer were prepared by using crosslinked acrylic acid and water-soluble granular phosphorus fertilizer KH₂PO₄. The effects of the amount of crosslinker, initiator and phosphorus fertilizer concentration on water absorption were investigated and optimized. The products show excellent slow release and water-retention capacity, being nontoxic in soil and environment-friendly, and could be useful especially in agricultural and horticultural applications. The results showed that the hydrogel structure and swelling capacity was affected by various factors, such as concentration of crosslinker and initiator, as well as by the amount of KH₂PO₄.     

Preparation of Homogeneous Hydrogels by Controlling the Crosslinker Reactivity and Availability

Network microstructures of polyacrylamide (PAAm) hydrogels were investigated by static light scattering measurements. The gels were prepared by free‐radical crosslinking polymerization of acrylamide (AAm). To suppress the degree of gel inhomogeneity, the crosslinker reactivity during gelation was controlled by decreasing its availability in the reaction system. Our first approach was the addition of the crosslinker N,N′‐methylenebis(acrylamide) (BAAm) in one or three portions during the course of the gelation reactions. As a second approach, a slightly water soluble crosslinker, namely ethylene glycol dimethacrylate (EGDM) was used as a crosslinker in AAm polymerization. Due to the low water solubility of EGDM, EGDM phase in the gelation system act as a reservoir of crosslinker so that the crosslinker can be supplied continuously to the aqueous reaction zone during the course of gelation. It was found that the delayed crosslinker addition technique further increases the degree of inhomogeneity of PAAm hydrogels. The results were explained with increasing viscosity of the reaction solution at the time of the crosslinker addition so that the crosslinking reactions are limited to local regions in the reaction system. The second approach, namely use of the slightly water soluble crosslinker EGDM significantly increases the degree of structural homogeneity of PAAm hydrogels.     

Preparation and characterization of cellulose acetate‐coated compound fertilizer with controlled‐release and water‐retention

A novel cellulose acetate‐coated compound fertilizer with controlled‐release and water‐retention (CAFCW) was prepared, which possessed the three‐layer structure. Its core was water‐soluble compound fertilizer granular, the inner coating was cellulose acetate (CA), and the outer coating was poly(acrylic acid‐co‐acrylamide)/unexpanded vermiculite (P(AA‐co‐AM)/UVMT) superabsorbent composite. The effects of the amount of acrylamide, crosslinker, initiator, degree of neutralization of acrylic acid (AA), and unexpanded vermiculite concentration on water absorbency were investigated and optimized. The water absorbency of CAFCW was 72 times its own weight if it was allowed to swell in tap water at room temperature for 90 min. Element analysis and atomic absorption spectrophotometer results showed that the product contained 11% nitrogen, 6% phosphorus (shown by P₂O₅), 9% potassium (shown by K₂O), 1% calcium (shown by CaO), and 0.4% magnesium (shown by MgO). Swelling rate, slow‐release, and water‐retention properties of CAFCW were also investigated. This product with good controlled‐release and water‐retention capacity, being degradable in soil and environmentally friendly, could be especially useful in agricultural and horticultural applications. Copyright © 2008 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.     

Synthesis of fast-swelling superabsorbent hydrogels: effect of crosslinker type and concentration on porosity and absorption rate

Fast-swelling highly porous superabsorbent hydrogels were synthesized through a rapid solution polymerization of concentrated partially neutralized acrylic acid under normal atmospheric conditions. Acetone and sodium bicarbonate were used as porosity generators (porogens) during polymerization process for porosity generation. N,N^′-methylenebisacrylamide (MBA) and 1,4-butanedioldiacrylate were used as the water- and the oil-soluble crosslinkers, respectively. The temperature changing of the reaction mixture during polymerization and foam formation process was monitored and investigated in details. Time and sequence of addition of the porogens and gelation time were recognized to be important to increase efficiency of the porogens. The concentration of the crosslinkers on gelation time was optimized to achieve highly porous products. It was found that higher crosslinker concentration, especially in the case of MBA, causes decreased gelation times. Shorter gelation time resulted in more porogen bubbles trapped in the viscose reaction mixture led to products with higher porosity. The effect of type and concentration of the crosslinking agents on the process and swelling behavior of the hydrogels (in water and saline solutions) were investigated. Power law relationships were found for the variation of swelling in terms of either crosslinker or saline concentration. Less sensitivity to the change of salinity was achieved by employing higher amount of crosslinker.     

Syntheses and properties of superabsorbent composites based on natural guar gum and attapulgite

Utilization of raw materials available in nature and their application to derive other useful products without any adverse impact on the environment has long been a desired goal. In this work, guar gum (GG) and attapulgite (APT) clay were used as raw materials for preparing guar gum‐g‐poly(acrylic acid)/attapulgite (GG‐g‐PAA/APT) superabsorbent composites through the graft copolymerization of GG, partially neutralized acrylic acid (AA) and APT in aqueous solution. The effects of reaction conditions such as concentrations of the initiator and crosslinker, APT content, etc. on water absorbency were investigated. The composite prepared under optimal conditions gave the best absorption of 529 g/g sample in distilled water and 61 g/g sample in 0.9 wt% NaCl solution. Swelling behaviors revealed that the superabsorbent composites retained a high water absorbency over a wide pH range of 4–11, and the developed composites also exhibited improved reswelling and water‐retention capabilities. The superabsorbent composites can be utilized as eco‐friendly water‐manageable materials for agricultural and horticultural applications. Copyright © 2008 John Wiley & Sons, Ltd.     

Taguchi optimized synthesis of collagen-g-poly(acrylic acid)/kaolin composite superabsorbent hydrogel

A novel biopolymer-based hydrogel composite was synthesized through chemical crosslinking by graft copolymerization of partially neutralized acrylic acid onto the hydrolyzed collagen. 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, neutralization percent (NU), and collagen/kaolin weight ratio 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 674 g/g. The surface morphology of the gel was examined using scanning electron microscopy. Furthermore in this research, swollen gel strength of composite SAPs already swollen under realistic conditions (saline solution absorbency under load) was determined.     

Synthesis and Characterization of Montmorillonite-Graft-Acrylic Acid Superabsorbent by Using Glow-Discharge Electrolysis Plasma

Crosslinking graft polymerization of poly acrylic/montmorillonite superabsorbent composite in aqueous solution was prepared by using glow-discharge electrolysis plasma, in which acrylic acid and acid-activated montmorillonite were used as starting materials, N,N-methylenebisacrylamide as a crosslinking agent. To optimize the synthetic conditions, seven important parameters of the graft-polymerization were examined in detail, such as the discharge voltage, discharge time, the neutralization of acrylic acid, post polymerization temperature, amounts of crosslinking agent, montmorillonite and acrylic acid used in this study. The structure, thermal stability and morphology of product were characterized by Fourier transform infrared spectroscopy, thermogravimetric analysis, scanning electron microscopy, respectively. The absorbency of poly acrylic/montmorillonite superabsorbent was examined to yield the following results: 1,834 g/g for distilled water, 116 g/g for 0.05 mol/L and 75 g/g for 0.15 mol/L sodium chloride solution. Such excellent character could be important to use in many fields, for example, in agricultural and horticultural applications.