Study on superabsorbent composite. III. Swelling behaviors of polyacrylamide/attapulgite composite based on acidified attapulgite and organo-attapulgite

A novel kind of salt-resistant superabsorbent composite, polyacrylamide/attapulgite, from acrylamide (AM) and attapulgite (APT) was prepared by free-radical aqueous 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 FTIR and XRD. The effects of acidified APT (H⁺-APT), organo-APT (HDTMABr-APT) and the content of APT in the superabsorbent composite on the water absorbency and the initial swelling rate for the superabsorbent composite in distilled water and in various saline solutions were studied. The effects of incorporated HDTMABr-APT and H⁺-APT on the reswelling ability of the superabsorbent composites were investigated. The results indicate that the incorporation of APT had remarkable influence on the improvement of water absorbency and swelling rate of the composites. Comparing with the composite doped with H⁺-APT, the water absorbency for the composite doped with 10 wt% HDTMABr-APT was enhanced from 2140 g g⁻¹ to 2800 g g⁻¹ in distilled water and from 100 g g⁻¹ to 121 g g⁻¹ in 0.9 wt% NaCl solution, respectively. The water absorbency of the composites in various saline solutions decreased with the increasing concentration, especially for the multivalent cations. In addition, the reswelling ability of the superabsorbent composites is also improved evidently by adding a small amount of HDTMABr-APT into the composite, comparing with that of incorporated with H⁺-APT.     

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.     

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.%.     

Synthesis and properties of clay-based superabsorbent composite

A novel superabsorbent composites based on acrylic acid, acrylamide, and inorganic clay mineral-attapulgite were synthesized through a solution polymerization to improve water and saline absorbencies. The superabsorbent composite was characterized by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA) and scanning electron microscopy (SEM). The effects of saline solutions, amount of initiator, crosslinker and attapulgite on the water absorbency of superabsorbent composites were investigated. The water retention test of superabsorbent composites were also carried out. The superabsorbent composite exhibited improved water and saline absorbencies compared with that of crosslinked poly(acrylic acid-co-acrylamide) superabsorbent polymer. The water absorbency of the superabsorbent composite synthesized under optimal synthesis conditions with an attapulgite content of 10% reaches more than 1400 g H₂O/g and 110 g H₂O/g in distilled water and 0.9% NaCl solution, respectively.     

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.     

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 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, CaCl₂ and FeCl₃), anionic salt solutions (NaCl, Na₂SO₄ and Na₃PO₄) 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 < Na₂SO₄ < Na₃PO₄.     

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 a Superabsorbent Polymer Prepared by Copolymerization of Sodium Acrylate with Sodium 1‐(Acryloyloxy)propan‐2‐yl Phosphate

A novel monomer, 1‐(acryloyloxy)propan‐2‐yl phosphoryl dichloride, was synthesized and characterized in this work. Thereafter, the monomer was neutralized with sodium hydroxide and copolymerized with sodium acrylate to obtain a superabsorbent polymer. The superabsorbent polymer was then modified to improve its swelling properties (i.e., the water absorbency under load, the hydrogel strength, the resilience and the dispersion). Both single factor and orthogonal design experiments were adopted to obtain optimal conditions. The superabsorbent polymer prepared under the optimal conditions showed improved water absorbency in physiological saline [17 g · g^?1 under load (P = 2 × 10³ Pa) and 65 g · g^?1 at atmospheric pressure] and other swelling properties, such as hydrogel strength, resilience and dispersion, also improved.

     

Fabrication and properties of a novel superabsorbent composite based on coco peat and poly (acrylic acid) cross‐linked trimethylolpropane trimaleate under ultraviolet irradiation

A series of novel poly(acrylic acid)/coco peat (PAA/CP) superabsorbent composites were prepared via the ultraviolet irradiation copolymerization of acrylic acid monomer (PAA) and coco peat cellulose (CP) in the presence of the cross‐linker trimethylolpropane trimaleate. The physico‐chemical structures of obtained PAA/CP were characterized by Fourier transform infrared spectroscopy, thermogravimetry/derivative thermogravimetry, X‐ray diffraction, and scanning electron microscopy, respectively. The critical parameters of affecting the water absorbency of PAA/CP, including the cross‐linker level, amount of CP and reaction time, were studied in detailed. The experimental results showed that the PAA/CP samples exhibited the maximum swelling value of 523.09 g/g in distilled water and 40.52 g/g in 0.9 wt % NaCl solution. The swelling behaviors of PAA/CP were significantly relied on the concentration of salt solution and the pH of external solution. The effect of ions species on the swelling performance was in the order: Na⁺ > Ca²⁺ > Fe³⁺ , and in pH 2.2 and 7.2 aqueous solutions PAA/CP composites displayed better pH‐responsiveness and reversible on‐off switching characteristics. Urea, as an agrochemical model, was loaded into PAA/CP substrate to supply with nitrogen nutrient. The test of their loading and releasing diffusion performance of urea suggested that the urea loading percentage of PAA/CP was remarkably dependent on the concentration of aqueous urea solutions and the release of urea from loaded PAA/CP samples in water followed a non‐Fickian mechanism. Owing to their considerable good water absorption capacity, slow urea release, economical and environment‐friendly merits, PAA/CP composites could be exploited for the agriculture applications. Copyright © 2016 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.     

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.     

Osmotic and Activity Coefficients of the {<Emphasis Type="Italic">x</Emphasis>ZnCl<Subscript>2</Subscript>+(1−<Emphasis Type="Italic">x</Emphasis>)ZnSO<Subscript>4</Subscript>}(aq) System at 298.15 K

Isopiestic vapor pressure measurements were made for {xZnCl₂+(1−x)ZnSO₄}(aq) solutions with ZnCl₂ molality fractions of x=(0,0.3062,0.5730,0.7969, and 1) at the temperature 298.15 K, using KCl(aq) as the reference standard. These measurements cover the water activity range 0.901–0.919≤a _w≤0.978. The experimental osmotic coefficients were used to evaluate the parameters of an extended ion-interaction (Pitzer) model for these mixed electrolyte solutions. A similar analysis was made of the available activity data for ZnCl₂(aq) at 298.15 K, while assuming the presence of equilibrium amounts of ZnCl⁺(aq) ion-pairs, to derive the ion-interaction parameters for the hypothetical pure binary electrolytes (Zn²⁺,2Cl⁻) and (ZnCl⁺,Cl⁻). These parameters are required for the analysis of the mixture results. Although significant concentrations of higher-order zinc chloride complexes may also be present in these solutions, it was possible to represent the osmotic coefficients accurately by explicitly including only the predominant complex ZnCl⁺(aq) and the completely dissociated ions. The ionic activity coefficients and osmotic coefficients were calculated over the investigated molality range using the evaluated extended Pitzer model parameters.     

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.     

Stability of the valinomycin - lithium complex in nitrobenzene saturated with water

Summary From extraction experiments and γ-activity measurements, the extraction constant corresponding to the equilibrium Li⁺(aq)+NaL⁺(nb) ↔LiL⁺(nb)+Na⁺(aq) taking place in the two-phase water-nitrobenzene system (L = valinomycin; aq = aqueous phase, nb = nitrobenzene phase) was evaluated as logK_ex(Li⁺,NaL⁺)=-1.1. Further, the stability constant of the valinomycin-lithium complex species in nitrobenzene saturated with water was calculated: logβ_nb(LiL⁺)=6.3.     

Stability of complex of Na+ with 18-crown-6 in nitrobenzene saturated with water

From extraction experiments and γ-activity measurements, the extraction constant corresponding to the equilibrium Na⁺(aq)+HL⁺(nb)⇆NaL⁺(nb)+H⁺(aq) taking place in the two-phase water-nitrobenzene system (L=18-crown-6; aq=aqueous phase, nb=nitrobenzene phase) was evaluated as logK _ex (Na⁺,HL⁺)=0.1. Further, the stability constant of the 18-crown-6-sodium complex in nitrobenzene saturated with water was calculated: logβ _nh(NaL⁺)=8.0.     

Swelling characteristics of konjac glucomannan superabsobent synthesized by radiation-induced graft copolymerization

Graft copolymerization of konjac glucomannan (KGM) and acrylic acid was induced by ⁶⁰Co-γ irradiation at room temperature. The effects of radiation dose and monomer-to-KGM ratio on grafting yield and equilibrium water absorbency were investigated. The KGM-based superabsorbent polymer (KSAP) could absorb water 625 times of its dry weight when the radiation dose was 5.0 kGy and monomer-to-KGM ratio was 5. The structure of KSAP was characterized by FTIR, XRD, and SEM. KSAP showed a lower crystallinity than KGM. The porous microstructure of KSAP was revealed by SEM. The diffusion mechanism of water in the hydrogel is consistent with the anomalous diffusion model. Cations, especially multivalent cations, greatly reduced water absorbency of KSAP. Rising temperature, acidic or basic solutions are not favorable for the swelling of KSAP.     

Extraction of silver from water into nitrobenzene using sodium dicarbollylcobaltate in the presence of valinomycin

Summary From extraction experiments andg-activity measurements, the extraction constant corresponding to the Ag⁺(aq) + NaL⁺(nb)?AgL⁺(nb) + Na⁺(aq) equilibrium in the two-phase water-nitrobenzene system (L=valinomycin; aq=aqueous phase, nb=nitrobenzene phase) was evaluated as log K_ex(Ag⁺,NaL⁺)=-0.6±0.1. The stability constant of the valinomycin-silver complex in nitrobenzene saturated with water was calculated: log b_nb(AgL⁺)=4.6±0.1. The stability constants of complexes of some univalent cations with valinomycin were summarized and discussed.     

Preparation of composites and nanocomposites based on bentonite and poly(sodium acrylate). Effect of amount of bentonite on the swelling behaviour

A series of composite and nanocomposite hydrogels were synthesized by copolymerization reaction of partially neutralized acrylic acid (SA) on bentonite micropowder (BT) using N,N′-methylenebisacrylamide (MBA) as a crosslinker and potassium persulfate (I) as an initiator in aqueous solution. The influences of Na⁺-BT, organoBT (O-BT), and the content of the BT in the copolymeric gels on the swelling behaviour in deionized water and saline solution (0.2 wt.% NaCl_(aq)) were investigated. Results showed that the equilibrium swelling (W_∞) was decreased by adding a small amount of the BT, however, at higher BT contents, the W_∞ increased with the increase of the amount of clay. It was found that a concentration of 14 wt.% Na⁺-BT gave the best results absorption (955 g/g). Moreover, the amount of swelling for these absorbents in saline solution was smaller than that in deionized water. These hydrogels were characterized by X-ray diffraction and scanning electron microscopy. Finally, the thermogravimetric analysis indicated that introduction of clay to the polymer network resulted in an increase in thermal stability.     

Stability of the ammonium-p-tert-butylcalix[4]arene-tetrakis (N,N-diethylacetamide) complex in nitrobenzene saturated with water

Summary From extraction experiments andg-activity measurements, the extraction constant corresponding to the equilibrium NH(aq)+NaL⁺(nb)?NH₄L⁺(nb)+Na⁺(aq) taking place in the two-phase water-nitrobenzene system (L = p-tert-butylcalix[4]arene-tetrakis (N,N-diethylacetamide); aq = aqueous phase, nb = nitrobenzene phase) was evaluated as logK_ex(NH,NaL⁺)=-1.8. Further, the stability constant of the p-tert-butylcalix[4]arene-tetrakis (N,N-diethylacetamide)-ammonium complex in nitrobenzene saturated with water was calculated for a temperature of 25 °C: logb_nb(NH₄L⁺)=6.7.