Superabsorbent polymer having increased rate of water absorption
The invention relates to a superabsorbent polymer wherein an increased rate of water absorption is obtained by the addition of an encapsulated blowing agent. The invention relates to a superabsorbent polymer including an encapsulating blowing agent and having a vortex time of 40 seconds or less. In particular, the superabsorbent polymer includes from about 55 to about 99.9 wt. % of polymerizable unsaturated acid group containing monomers; from about 0.001 to about 5.0 wt. % of internal crosslinking agent; wherein the wherein the composition has a degree of neutralization of more than about 20%; and from about 0.05 to about 10.0 wt. % of an encapsulated blowing agent.
1. A method of preparing superabsorbent polymers comprising the steps of
a) dissolving at least one acrylic acid monomer and/or its sodium salt and a cross-linking agent in an aqueous solution to form a monomer solution;
b) adding to the monomer solution a resin encapsulated carbonate blowing agent in sufficient amount to form, when polymerized to a hydrogel, a microcellular expanded polymer gel, wherein said resin is selected from natural or synthetic resins, acrylonitrile-butadiene rubbers, viscous settable ceramic materials, polyolefins, polyethylene gylcol, olefin copolymers, polyaromatic olefins, styrenic compounds or polymerized halo-diolefins, and wherein the resin encapsulated blowing agent provides a controllable delayed release of the blowing agent; and
c) initiating polymerization by adding to the monomer solution either immediately before or immediately after, or simultaneously with the addition of the encapsulated blowing agent, an effective amount of at least one free radical initiator and polymerizing at temperatures ranging from about 0° C. to about 130° C. to form a microcellular hydrogel wherein said superabsorbent polymers have a vortex time of about 32 seconds of less, a AUL (0.9 psi) of about 10 g/g or more and a tea bag retention of about 20 g/g or more.
2. The method of claim 1 further comprising the step of
d) chopping or grinding said microcellular hydrogel into gel pieces having a particle diameter size ranging from about 0.1 mm to about 5.0 mm.
3. The method of claim 2 further comprising the step of
e) drying said gel pieces at temperatures ranging from about 85° C. to about 210° C. to form dry pieces, which dry pieces, are ground to a size of from 0.05 mm to 5.0 mm diameter to form an improved dry superabsorbent polymer.