Enhancing absorption rates of superabsorbents by incorporating a blowing agent
AssigneeNalco Chemical Company
InventorEric J. Lind
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Abstract
An improved superabsorbent polymer having increased rate of water absorption is obtained by the addition, preferably prior to polymerization, of a carbonate blowing agent to a monomer solution of the monomers used to form the superabsorbent polymer. Preferred monomers include (meth)acrylic acids, preferably partially neutralized prior to polymerization and appropriate cross-linking agents. The carbonate cross-linking agents are any carbonate salt soluble or dispersible in the monomer solution, prior to polymerization. The multi-valent cationic salts of carbonate are preferred, especially the complex carbonates, for example, of magnesium.
Claims6
A method of improving the rate of water absorption of a dry superabsorbent substantially water-insoluble, cross-linked, hydrogel-forming polymer composition, which method comprises:
- (1) forming a monomer solution containing at least one carboxylic acid monomer and water soluble salts thereof effective water insolubilizing amount of a cross-linking agent, and an effective microcellular forming amount of about 0.05 to about 2.5 weight per cent of a carbonate blowing agent, based on the total weight of the carbonated monomer solution,
- (2) having dispersed or dissolved said carbonate blowing agent throughout the solution to form said carbonated monomer solution and then
- (3) initiating free radical polymerization of said carbonated solution, by adding a free radical initiator to said solution thereby forming a microcellular aqueous gel of hydrogel polymer, and then
- (4) chopping said hydrogel into pieces having a diameter ranging from about 0.1 mm diameter to about 5.0 cm., and then
- (5) drying said pieces at a temperature ranging from 85.degree. C. to about 210.degree. C., then grinding said dry pieces to a size of from about 0.05 mm to about 5.0 mm thereby forming a dry superabsorbent polymer having increased rate of water absorption.
A superabsorbent polymer having improved rate of water absorption, which polymer is manufactured by adding an effective microcellular gel forming amount of a carbonate blowing agent to a monomer solution containing carboxylic acid monomers, or their salts, and a cross-linking agent, thereby forming a carbonated monomer solution, said solution containing from about 0.05 to about 2.5 weight percent of the carbonate blowing agent and then adding a free radical polymerization initiator and polymerizing, at temperature ranging from about 0.degree.-110.degree. C., thereby forming a microcellular expanded hydrogel in volume, compared to the volume of the monomer solution, from 1.01 to about 10 times;
- and then chopping and drying the expanded hydrogel at temperatures ranging from about 85.degree. C. to about 210.degree. C., to form dried gel pieces, and then grinding said pieces to within a particle size range of from about 0.05 mm to about 5.0 mm, thereby forming the superabsorbent polymer.
The polymer of claim 7 wherein the carbonate blowing agent is selected from the group consisting of CO.sub.2, Na.sub.2 CO.sub.3, K.sub.2 CO.sub.3, (NH.sub.4).sub.2 CO.sub.3, MgCO.sub.3, (MgCO.sub.3).sub.4. Mg(OH).sub.2.5H.sub.2 O, CaCO.sub.3, ZnCO.sub.3, and mixtures thereof.
Dependencies are inferred from the claim text.