‘Gel collapse’ in the saponified starch-g-polyacrylonitrile/water-alcohol system

2006

Macro Materials & Eng

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.

Section: Resultssupporting

confidence: 84%

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

Zhang

2006

Macro Materials & Eng

“…Beyond 50 vol% ethanol, the hydrogel almost lost its swelling capacity. According to Rodehed and Ranby, [32] the first transition may be attributed to the polymer-polymer affinity, which expels some absorbed free liquid from the swollen hydrogels by increasing the concentration of external ethanol solution. The second transition (the gel collapse) is due to an interaction between the polar groups of the solvent and the ionic groups in the polymer, and the collapse of the gel results from the total depletion of absorbed fluid from the solvated polymeric network.…”

Section: Influence Of Hydrophilic Organic Solvents On Swelling Capacitymentioning

confidence: 98%

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

Journal of Macromolecular Science, Part B

2011

A series of superabsorbent composites, guar gum-g-poly(sodium acrylate-costyrene)/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.

“…The swelling behaviors of superabsorbent gels in hydrophilic solvent–water mixtures were also investigated by various workers. The swelling behaviors of saponified starch‐ g ‐polyacrylonitrile polymer gel11 and a crosslinked poly(acrylic acid‐ co ‐acrylamide) gel12 in various organic solvent–water mixtures were reported in a previous study. Murase and Fujita13 reported on the swelling of a superabsorbent in alcohol (methanol, ethanol, isopropyl alcohol, or glycerol)–water mixtures.…”

Section: Introductionmentioning

confidence: 94%

Studies on poly(acrylic acid)/attapulgite superabsorbent composites. II. Swelling behaviors of superabsorbent composites in saline solutions and hydrophilic solvent–water mixtures

J of Applied Polymer Sci

Chen

2004

ABSTRACT:The effect of the attapulgite content on the swelling for a series of poly(acrylic acid)/attapulgite superabsorbent composites in water was studied. The effects of the temperature and pH values on the water absorbency of the superabsorbent composites were investigated. The swelling behavior of the superabsorbent composites in various saline solutions was also investigated. The water absorbency in various salt solutions decreased with an increase in the ionic strength of the solutions. At a high ionic strength (Ͼ1 ϫ 10 Ϫ3 M), the water absorbency in monovalent cationic solutions was higher than that in multivalent cation solutions. This dramatic reduction of the water absorbency in multivalent cationic solutions of high ionic strength may have been due to the complexing ability of the carboxylate groups inducing the formation of intramolecular and intermolecular complexes, which resulted in an increased crosslink density of the network. The swelling behavior of the superabsorbent composites in mixtures of water and hydrophilic solvents, including methanol, acetone, ethanol, and dimethyl sulfoxide (DMSO), was also investigated. The water absorbency decreased with an increase in the concentration of any of the four organic solvents, and two transitions were observed in the superabsorbent composite/hydrophilic solvent-water mixture systems. The main transition for the four hydrophilic solvent-water mixtures was a collapse of the swollen gel (at 50 -80% methanol, 30 -80% acetone, 50 -80% ethanol, and 50 -80% DMSO). For the methanol-water system, the magnitudes of the first and second transitions for the poly(acrylic acid)/attapulgite superabsorbent composites containing lower proportions of attapulgite were larger than those for the superabsorbent composites with higher attapulgite contents. The effect of the mixture temperature on the water absorbency of the superabsorbent composites in 10 min was also reported.