Particulate superabsorbent polymer composition having improved stability and fast absorption

A particulate superabsorbent polymer composition comprising a particulate superabsorbent polymer comprising an internal crosslinker agent comprising a silane compound comprising at least one vinyl group or allyl group and at least one Si—O bond wherein the vinyl group or allyl group is directly attached to a silicon atom, and from 0.01 wt % to about 5 wt % based on the particulate superabsorbent polymer composition weight of a neutralized aluminum salt applied to the surface of the particulate superabsorbent polymer, in the form of an aqueous neutralized aluminum salt solution having a pH value from about 5.5 to about 8;

• wherein the particulate superabsorbent polymer composition has a Centrifuge Retention Capacity (CRC) of from about 25 grams to about 40 grams of 0.9 weight percent sodium chloride aqueous per gram of the particulate superabsorbent polymer composition, wherein the CRC is measured either before or after subjecting the superabsorbent polymer composition to a Processing Test, and an absorbency under load at 0.9 psi prior to subjecting the particulate superabsorbent polymer composition to the Processing Test of from 15 g/g to 21 g/g;
• and an original Free Swell Gel Bed Permeability (FSGBP) of from about 30×10−8 cm2 to about 200×10−8 cm2 prior to subjecting the particulate superabsorbent polymer composition to the Processing Test;
• and a permeability stability index of about 0.60 to 0.99 when subjecting the particulate superabsorbent polymer composition to a Processing Test, and a compressibility of from 1.30 mm2/N to about 4 mm2/N as measured by the Compression Test, and a Centrifuge Retention Capacity (CRC) Increase of at least 2 g/g or more based on CRC Increase=CRC(bt,5 hr)-CRC(rt,0.5 hr) wherein CRC Increase measures the increase in the CRC that occurs and is calculated as the difference between the second CRC Test and first CRC Test, and bt refers to body temperature and rt refers to room temperature.

A process for the production of a particulate superabsorbent polymer composition comprising the following steps:

• a) preparing an aqueous monomer solution of a mixture of a polymerizable unsaturated acid group containing monomer and an internal crosslinking agent monomer wherein the aqueous monomer solution comprises dissolved oxygen;
• b) sparging the aqueous monomer solution of step a) including adding an inert gas to the aqueous monomer solution of step a) to replace the dissolved oxygen of the aqueous monomer solution;
• c) polymerizing the aqueous monomer solution of step b) including the steps of c1) adding to the aqueous monomer solution of step a):
• i) an aqueous solution comprising from about 0.05 to about 2.0 wt. % based on the total amount of the polymerizable unsaturated acid group containing monomer solution of a foaming agent;
• and ii) an aqueous solution comprising from about 0.001 to about 1.0 wt. % based on the total amount of the polymerizable unsaturated acid group containing monomer solution of a mixture of a lipophile surfactant and a polyethoxylated hydrophilic surfactant;
• c2) treating the monomer solution of step c1) to high speed shear mixing to form a treated monomer solution, wherein the components i) an aqueous solution comprising from about 0.1 to about 1.0 wt. % of a foaming agent;
• and ii) an aqueous solution comprising from about 0.001 to about 1.0 wt. % of a mixture of a lipophile surfactant and a polyethoxylated hydrophilic surfactant are added to the aqueous monomer solution after step b) of sparging the aqueous monomer solution and before step c2) of high speed shear mixing of the aqueous monomer solution;
• c3) forming a hydrogel by adding a polymerization initiator to the treated monomer solution of step c2) wherein the initiator is added to the treated monomer solution after the foaming agent and the mixture of surfactants, wherein the polymer is formed to include bubbles of the foaming agent into the polymer structure;
• and d) drying and grinding the hydrogel of step c) to form particulate superabsorbent polymer;
• and e) surface crosslinking the particulate superabsorbent polymer of step d) with a surface crosslinking agent;
• b) preparing a neutralized aluminum salt in the form of an aqueous solution having a pH value from about 5.5 to about 8;
• and;
• c) applying the aqueous neutralized aluminum salt solution on the surface of the particulate superabsorbent polymer composition;
• and wherein the particulate superabsorbent polymer composition has a degree of neutralization of from about 50% mol to about 80 mol %;
• and the particulate superabsorbent polymer composition has a Centrifuge Retention Capacity of from about 25 grams to about 40 grams of 0.9 weight percent sodium chloride aqueous per gram of the particulate superabsorbent polymer composition, wherein the CRC is measured either before or after subjecting the particulate superabsorbent polymer composition to a Processing Test, and an absorbency under load at 0.9 psi prior to subjecting the particulate superabsorbent polymer composition to the Processing Test of from 15 g/g to 21 g/g;
• and a Free Swell Gel Bed Permeability (FSGBP) of about 30×10−8 cm2 to about 200×10−8 cm2 prior to subjecting the treated particulate superabsorbent polymer composition to the Processing Test;
• and wherein the particulate superabsorbent polymer composition has a permeability stability index of from 0.60 to 0.99 when subjecting the particulate superabsorbent polymer composition to a Processing Test, and a compressibility from 0.30 mm2/N to about 4 mm2/N as measured by the Compression Test, and wherein the particulate superabsorbent polymer composition has a vortex time of from about 25 sec to about 60 sec as measured by the Vortex Test.