Equilibrium Swelling Capacity Research Articles

Equilibrium Swelling Study of Cationic Acrylamide-Based Hydrogels: Effect of Synthesis Parameters, and Phase Transition in Polyelectrolyte Solutions

Cationic copolymer gels of acrylamide and [(methacrylamido) Propyl] trimethyl ammonium chloride (MAPTAC) were synthesized by free radical aqueous solution polymerization. The Taguchi method, a robust experimental design, was employed for the optimization of the synthesis based on the equilibrium swelling capacity of the hydrogels. Based on Taguchi method a standard L16 orthogonal array with five factors at four levels was designed and experiments were done in accordance with it. The effects of network composition such as cross-linker density, ionizable monomer and total monomer concentration together with the initiator concentration on the equilibrium swelling capacity of hydrogels in distilled water were studied. From the analysis of variance (ANOVA) of the test results, the most effective factor controlling equilibrium swelling capacity was obtained and maximum water absorbency of the optimized hydrogel was found to be 3570 g/g. The presence of counterions in the external solution suppressed swelling of optimized hydrogel and this effect was pronounced with bivalent counterions. By using the thermodynamic model, the experimental data were analyzed and the cross-linking efficiency for the polymerization reaction was calculated to be about 40%.

Swelling Behavior of Guar Gum-g-Poly(Sodium Acrylate -co-Styrene)/Attapulgite Superabsorbent Composites

A series of superabsorbent composites, guar gum-g-poly(sodium acrylate-co- styrene)/attapulgite [GG-g-P(NaA-co-St)/APT], were prepared by simultaneous grafting partially neutralized acrylic acid and hydrophobic styrene (St) onto guar gum in the presence of attapulgite as an inorganic component. Equilibrium swelling capacity strongly depended on the concentration of St, drastically increasing with increasing St concentration to 24.3 mmol/L and then decreasing. The influence of St concentration on the swelling kinetics of the superabsorbent was studied by means of a Schott's second-order model. The proper amount of St is of benefit for the improvement of the initial swelling rate in either distilled water or saline solution. The influence of St concentration on the swelling behaviors in various external media (the aqueous solutions of various salts, pHs, hydrophilic organic solvent/water mixture and surfactants) was also investigated systematically. Results showed that the concentration of St is the key factor influencing equilibrium swelling capacity of the superabsorbent composites in each swelling media, and moderate amounts of St could enhance the responsiveness of the corresponding superabsorbent composite to external stimulation.

Effect of crosslinker concentration on characteristics of superporous hydrogel

Aim:Synthesis of superporous hydrogel with different concentrations of crosslinker was carried out using solution polymerization to study its effect on characteristics of superporous hydrogel. Methylene-bis-acrylamide was used as a crosslinker.Materials and Methods:The characterization studies were performed by measurement of apparent density, porosity, swelling studies, mechanical strength studies, and scanning electron microscopy analysis. Results and Discussion: As the concentration of crosslinker increased from 7.37% to 14.36 % the porosities decreased. In double distilled water, superporous hydrogels showed good increase in equilibrium swelling capacity compared to that in simulated gastric fluid. Scanning electron microscopic images clearly indicated the formation of interconnected pore and capillary channels. Characterization studies revealed that the increase in crosslinker concentration is beneficial from the mechanical stability point of view, but at the same time the decrease in porosity may lead to decrease in drug release rate by diffusion through these capillary channels. Batches B1 and B2 with low concentrations of crosslinker provide good porous structure, swelling characteristics, and mechanical strength appropriate for further applications of superporous hydrogel-based drug delivery systems.Conclusion:The concentration of crosslinker affects the porous structure, swelling characteristics and mechanical strength. By setting appropriate degree of crosslinking it is possible to prepare superporous hydrogel having desired characteristics, which will provide a platform to design the drug delivery systems based on it.

Superabsorbent nanocomposite hydrogels based on intercalation of chitosan into activated bentonite

Superabsorbent polymers, composed of acrylamide (Am) and 2-acrylamido-2-methyl-1-propane sulfonic acid, were prepared by the solution crosslinking polymerization technique. The effect of the ionic monomer content was correlated with the equilibrium swelling capacity. The swelling capacity was augmented up to 94 g/g by increasing the concentration of the ionic monomer. Intercalation of bentonite clay, by chitosan solution, was performed by two techniques, namely, microwave irradiation and heating. The basal spacing of bentonite increased from 1.21 to 1.31 nm for the former and to 1.4 nm for the latter. Specific interaction of bentonite with –OH group of chitosan through hydrogen bonding was estimated by FT-IR. Also, TEM showed a layered morphology due to the penetration of chitosan chains into bentonite silicate layers. Different amount of the intercalated clay was dispersed in the aforementioned monomers aiming at preparing superabsorbent composites. The clay showed an exfoliated structure in the polymer matrix while the composite was porous, with a three-dimensional interconnected microstructure as proved by SEM. The prepared composites had a higher absorption capacity up to 180 g/g and a better thermal stability than the corresponding hydrogel.

Effects of solvent treatments on characteristics of superporous hydrogels

The synthesis of an acrylamide-based superporous hydrogels (SPHs) was carried out by solution polymerization. SPHs were submerged in one of the organic solvents: diethyl ether, acetone, absolute ethanol, or hexane for 48 h. The characterization studies were performed by measurement of apparent density, porosity, swelling, mechanical strength, and scanning electron microscopy (SEM). The swelling ratio was calculated based on the mass of SPHs in the swollen state and in the dried state. The penetration pressure of the SPHs was measured from the force required for complete fracture of SPH. SPHs showed porosities of more than 60%. In double distilled water SPHs showed tremendous increase in equilibrium swelling capacity. But, when the same SPHs were placed in artificial gastric fluid for swelling, they showed very low equilibrium swelling capacity. The solvent treated SPHs showed good swelling characteristics in both the swelling media compared to that of SPH without solvent treatment. When an artificial gastric fluid was used as a swelling medium, ethanol- and hexane-treated SPHs showed higher penetration pressure compared to SPH without solvent treatment, while diethyl ether- and acetone-treated SPHs showed less penetration pressure. SEM images clearly indicate the formation of interconnected pore and capillary channels. The characterization studies revealed that the SPHs treated with solvents showed remarkable effects on their characteristics compared to SPH without solvent treatment. The results of the present study provide background for the selection of solvent for SPH treatment to improve characteristics that will lead to modification of the available SPH-based gastric retention devices. Keywords: superporous hydrogel, solvent, scanning electron microscopy, swelling, penetration pressure

Preparation and characterization of chitosan-based superporous hydrogel composite

The synthesis of superporous hydrogel composites (SPHCs) with various concentrations of chitosan as a composite material was carried out by solution polymerization. The characterization studies were performed by measurement of apparent density, porosity, swelling studies, mechanical strength studies, and scanning electron microscopy (SEM). In double distilled water, SPHCs showed tremendous increase in their equilibrium swelling capacity. But, when the same SPHCs were placed into simulated gastric fluid for swelling, they showed very less equilibrium swelling capacity. The chitosan altered swelling characteristics in both the swelling media. SPHCs showed improved mechanical strength as the chitosan concentration increased. SEM images clearly indicated the formation of interconnected pore, capillary channels, and the cross-linked chitosan molecules were observed around the peripheries of pores.

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.

Ground particle size influence on the swelling of a copolymer of AA/AMPS in water

AbstractThe influence of the ground particle size on the swelling behavior of a copolymer of AA/AMPS in water was observed to determine the best size considering water absorbency in view of fastest and highest equilibrium swelling. The copolymer gel, from acrylamide and 2‐acrylamido‐2‐methyl‐propanosulfonic acid and synthesized in the presence of N,N‐methylene‐bis‐acrylamide, was obtained by a radical solution technique, and identified by FTIR spectroscopy. By grinding, various particle diameters were obtained, and then separated by sieves. Studies of dynamic and equilibrium swelling in deionized water at 20°C showed the influence of the particle size on the kinetics of swelling and its equilibrium swelling capacity. A mathematical model for the absorption, including diffusion and relaxation modes, permitted to assess the absorption mechanism, and offered quantitative information about water diffusivity in the copolymer. The fastest swelling was obtained with diameters of 22.5–215 μm. Particle sizes ranging from 67.5 to 355 μm yielded the greatest equilibrium swelling, with mass ratios of about 1100. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

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).

Optimization of synthetic conditions of a novel collagen-based superabsorbent hydrogel by Taguchi method and investigation of its metal ions adsorption

A novel biopolymer-based superabsorbent hydrogel was synthesized through chemical crosslinking by graft copolymerization of partially neutralized acrylic acid onto the hydrolyzed collagen, in the presence of a crosslinking agent and a free radical initiator. The Taguchi method, a robust experimental design, was employed for the optimization of the synthesis reaction based on the swelling capacity of the hydrogels. This method was applied for the experiments and standard L16 orthogonal array with three factors and four levels were chosen. The critical parameters that have been selected for this study are crosslinker (N,N′-methylene bisacrylamide), initiator (potassium persulfate), and monomer (acrylic acid) concentration. From the analysis of variance of the test results, the most effective factor to control equilibrium swelling capacity was obtained and maximum water absorbency of the optimized final product was found to be 500 g/g. The surface morphology of the gel was examined using scanning electron microscopy. Furthermore, the sorption capacity of the hydrogel toward bivalent metal ions was evaluated. Therefore, the hydrogel may be considered as a candidate to develop as an efficient biopolymer-based chelating hydrogel for water treatment. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4878–4885, 2006

Graft copolymerization of acrylic acid onto cellulose: Effects of pretreatments and crosslinking agent

AbstractThe graft copolymerization of acrylic acid (AA) and 2‐acrylamido 2‐methylpropane sulfonic acid (AASO3H) onto cellulose, in the presence or absence of crosslinking agent N,N′‐methylene bisacrylamide (NMBA), by using different concentrations of ceric ammonium nitrate (CAN) initiator in aqueous nitric acid solution at either 5 or 30°C was investigated. To investigate the effect of pretreatment of cellulose on the copolymerization, before some grafting reactions cellulose was pretreated with either 2 or 20 wt % NaOH solutions or heated in distilled water/aqueous nitric acid (2.5 × 10−3 M) at 55°C. To determine how the excess of initiator affects the grafting and homopolymerization, separate reactions were carried out by removing the excess of ceric ions by filtration of the mixture of initiator solution and cellulose before the monomer addition. Extraction‐purified products were characterized by grafting percentage and equilibrium swelling capacity. Pretreatment of cellulose with NaOH solutions decreased the grafting percentage of copolymers. In the case of AA–AASO3H mixtures, nonpretreated cellulose gave a higher grafting percentage than NaOH‐pretreated cellulose. Filtration also lowered the grafting of AA on the cellulose in the cases of pretreatment with either water or nitric acid. Copolymers with the highest grafting percentage (64.8%) and equilibrium swelling value (105 g H2O/g copolymer) were obtained in grafting reactions carried out in the presence of NMBA at 5°C. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2267–2272, 2001

Synthesis and Characterization of Surface‐Hydrophobic Ion‐Exchange Microspheres and the Effect of Coating on Drug Release Rate

Biodegradable, dextran‐based ion‐exchange microspheres (IE‐MS) have been used for localized delivery of anticancer drugs and chemosensitizers. Because of their hydrophilic nature, the IE‐MS release their payload quickly. The purpose of this work was to develop an IE‐MS system that could provide a broad range of release rates for in vitro and in vivo applications. Sulfopropylated dextran microspheres (SP C25 MS) were surface‐modified by acylation. These hydrophobically modified sulfopropylated dextran microspheres (HM‐MS) were further coated with the cationic acrylic polymer Eudragit RL100 (EU‐MS). The changes in chemical composition after the surface modification and coating were characterized by X‐ray photoelectron spectroscopy. The effects of the modification and coating on the surface hydrophobicity, equilibrium swelling, surface morphology, and drug loading capacity were investigated. The HM‐MS showed little change in swelling and functionality, despite significantly increased affinity to oil and carbon content on the surface. The coated microspheres (EU‐MS) exhibited a profoundly decreased swelling ratio, an even higher affinity to oil, a higher loading capacity, and a lower drug release rate. Through further coating of the EU‐MS with different amounts of corn oil, the rate of drug release could be tailored to cover a relatively wide range. These results suggest that a versatile delivery system with various release profiles can be prepared by a combination of hydrophobic modification, polymer coating, and oil coating. © 2000 Wiley‐Liss, Inc. and the American Pharmaceutical Association J Pharm Sci 89: 807–817, 2000

Kinetics of absorption of N‐alkyl phthalate plasticizers into PVC resin particles

AbstractThe kinetics of plasticizer absorption by suspension polymerized polyvinylchloride (PVC) have been investigated. The volume swelling ratios of individual PVC particles, immersed in excess plasticizer, were recorded over a period of time using an optical microscope equipped with a high speed camera, Absorption of din‐decylphthalate was studied in the range 70 < T < 100°C. The study shows that the uptake of plasticizer proceeds in three steps: (1) a slow initial absorption into glassy PVC, which is a thermally activated rate process, wherein the polymer is being progressively solvated and evolving toward the rubbery state, (2) the considerable faster diffusion of plasticizer into a rubbery, dynamic polymer matrix, and (3) the asymptotic approach to the equilibrium swelling capacity. Temperature dependency of rate of absorption in the slow initial step was fitted to an Arrhenius expression, and an activation energy for plasticizer uptake was calculated.

On factors determining the swelling ability of crosslinked polymers

AbstractMacronet isoporous styrene polymers were obtained by a cross‐linking process (using monochlorodimethyl ether as the cross‐linking agent) applied to both dissolved linear polystyrene and swollen styrene copolymers with 0.3–1.0% divinylbenzene at the same polymer‐solvent weight ratio for all the systems. The lower equilibrium swelling capacity of copolymer‐based three‐dimensional structures as compared to that of linear polystyrene cross‐linked to an equal extent is explained by the presence in the initial swollen styrenedivinylbenzene copolymers of internal strains inhibiting an increase in the volume of the final polymer network. Cross‐linking of the linear polystyrene by means of a partially chloromethylated polystyrene shows that irregularity in the distribution of cross‐linking bridges enhances the equilibrium swelling capacity of the final gels.