Superabsorbent polymer and method for making same

Abstract

A process for the preparation of superabsorbent polymer containing clay, the process including the steps of (I) polymerizing a polymerization mixture comprising: (a) one or more ethylenically unsaturated carboxyl-containing monomers, (b) one or more crosslinking agents, (c) optionally one or more comonomers copolymerizable with the carboxyl-containing monomer, (d) neutralizing agent to partially neutralize the polymer to from about 50% to about 99%, by weight, and (e) a polymerization medium, to form a crosslinked partially neutralized hydrogel, (II) admixing a clay with the crosslinked partially neutralized hydrogel to form partially neutralized superabsorbent polymer-clay hydrogel; (III) drying the crosslinked partially neutralized hydrogel at a temperature from about 190° C. to about 210° C. and for a time period of from about 15 minutes to about 120 minutes, and (IV) comminuting the dried partially neutralized superabsorbent polymer-clay hydrogel to particles.

1 - 34 . (canceled) 
     
     
         35 . A superabsorbent polymer containing kaolin particulate comprising:
 a) a superabsorbent polymer particulate comprising an intimately admixed blend of from about 90 wt % to about 99.5 wt % of a superabsorbent polymer hydrogel, wherein the superabsorbent polymer hydrogel is neutralized to from about 50 to about 80 mole %, and from about 0.5 wt % to about 10 wt % of a kaolin; wherein the admixed blend is dried and comminuted into superabsorbent polymer particulate;   b) wherein the superabsorbent polymer particulate of a) is surface treated with from about 0.001 wt % to about 5 wt % of a surface crosslinking agent to form a surface crosslinked superabsorbent polymer particulate;   c) wherein the surface crosslinked particulate composition of b) is surface treated with from about 0.01 wt % to about 5 wt % of a multivalent salt to form the superabsorbent polymer containing kaolin particulate;   d) wherein the superabsorbent polymer particulate composition of b), c), or b) and c) is further surface treated with an additive selected from an odor-binding compound, cyclodextrin, zeolite, anti-caking additive, multivalent metal salt, or a surfactant.   
     
     
         36 . The superabsorbent polymer containing kaolin particulate of  claim 35  wherein at least about 40% by weight of the superabsorbent polymer particulate have a particle size from about 300 μm to about 600 μm as measured by screening through a U.S. standard 30 mesh screen and retained on a U.S. standard 50 mesh screen. 
     
     
         37 . The superabsorbent polymer containing kaolin particulate of  claim 35  further comprising e) from about 0.01 wt % to about 0.5 wt % of a thermoplastic polymer. 
     
     
         38 . The superabsorbent polymer containing kaolin particulate of  claim 35  wherein the additive is an odor-binding substance. 
     
     
         39 . The superabsorbent polymer containing kaolin particulate of  claim 35  wherein the additive is an odor-binding substance comprising an organic salt. 
     
     
         40 . The superabsorbent polymer containing kaolin particulate of  claim 35  having a centrifuge retention capacity of from about 25 g/g to about 40 g/g as measured by the Centrifuge Retention Capacity Test. 
     
     
         41 . The superabsorbent polymer containing kaolin particulate of  claim 35  having an absorption under load at 0.9 psi of from about 10 g/g to about 20 g/g as measured by the Absorbency Under Load (AUL0.9 psi) Test. 
     
     
         42 . The superabsorbent polymer containing kaolin particulate of  claim 35  having a free swell gel bed permeability of from about 10 Darcy to about 100 Darcy as measured by the Free Swell Gel Bed Permeability Test. 
     
     
         43 . The superabsorbent polymer containing kaolin particulate of  claim 35  having a vortex time of from about 30 seconds to about 70 seconds. 
     
     
         44 . The superabsorbent polymer containing kaolin particulate of  claim 35  wherein the multivalent metal salt of d) comprises an aluminum salt. 
     
     
         45 . The superabsorbent polymer containing kaolin particulate of  claim 35  wherein said superabsorbent polymer containing kaolin particulate has a water content of up to about 10% by weight. 
     
     
         46 . A process for the preparation of superabsorbent polymer containing kaolin, the process comprising the steps of:
 (I) polymerizing a polymerization mixture comprising: (a) one or more ethylenically unsaturated carboxyl-containing monomers, (b) one or more crosslinking agents, (c) optionally one or more comonomers copolymerizable with the carboxyl-containing monomer, (d) neutralizing agent to partially neutralize the polymer to from about 50 to about 80 mole %, and (e) a polymerization medium, to form a crosslinked partially neutralized hydrogel,   (II) admixing kaolin with the crosslinked partially neutralized hydrogel to form a partially neutralized superabsorbent polymer-kaolin hydrogel comprising an intimately admixed blend of from about 90 wt % to about 99.5 wt % of a superabsorbent polymer hydrogel and from about 0.5 wt % to about 10 wt % of a kaolin;   (III) drying the crosslinked partially neutralized hydrogel at a temperature from about 190° C. to about 210° C. and for a time period of from about 15 minutes to about 120 minutes; and   (IV) comminuting the dried partially neutralized superabsorbent polymer kaolin hydrogel into superabsorbent polymer containing kaolin particulate; and   (V) surface treating the superabsorbent polymer particulate with from about 0.001 wt % to about 5 wt % of a surface crosslinking agent to form a surface crosslinked superabsorbent polymer containing kaolin particulate;   (VI) wherein the surface crosslinked particulate composition of step (V) is surface treated with an additive selected from an odor-binding compound, cyclodextrin, zeolite, anti-caking additive, multivalent metal salt, or a surfactant; and   
       wherein the superabsorbent polymer containing kaolin particulate has a free swell gel bed permeability of at least about 10 Darcy, as measured by the Free Swell Gel Bed Permeability Test. 
     
     
         47 . The process for the preparation of superabsorbent polymer containing kaolin of  claim 46  wherein the superabsorbent polymer is present in an amount of about 90% to about 98%, by weight, and the kaolin is present in an amount from about 0.5% to about 10%, by weight. 
     
     
         48 . The process for the preparation of superabsorbent polymer containing kaolin of  claim 46 , further comprising the step of grinding the superabsorbent polymer kaolin hydrogel into superabsorbent polymer particulate having a particle size from about 150 μm to about 850 μm as measured by screening through a U.S. standard 20 mesh screen and retained on a U.S. standard 100 mesh screen. 
     
     
         49 . The process for the preparation of superabsorbent polymer containing kaolin of  claim 46  wherein at least about 40% by weight of the superabsorbent polymer particulate has a particle size from about 300 μm to about 600 μm as measured by screening through a U.S. standard 30 mesh screen and retained on a U.S. standard 50 mesh screen. 
     
     
         50 . The process for the preparation of superabsorbent polymer containing kaolin of  claim 46  wherein the kaolin is a swelling kaolin selected from the group consisting of montmorillonite, saponite, nontronite, laponite, beidelite, hectorite, sauconite, stevensite, vermiculite, volkonskoite, magadite, medmontite, kenyaite, and mixtures thereof. 
     
     
         51 . The process for the preparation of superabsorbent polymer containing kaolin of  claim 46  wherein the kaolin is a nonswelling kaolin selected from the group consisting of a kaolin mineral, a serpentine mineral, a mica mineral, a chlorite mineral, sepolite, palygorskite, bauxite, and mixtures thereof. 
     
     
         52 . The process for the preparation of superabsorbent polymer containing kaolin of  claim 46  wherein said monomer solution includes water-soluble ethylenically unsaturated monomer mixtures or salts thereof. 
     
     
         53 . The process for the preparation of superabsorbent polymer containing kaolin of  claim 46  wherein said polymer is a cross linked polymer of polyacrylic acid, sodium polyacrylate or copolymers thereof, cross linked with a polyvinyl monomer. 
     
     
         54 . The process for the preparation of superabsorbent polymer containing kaolin of  claim 46  wherein said polymerizing step produces a water-swellable, aqueous fluid absorbent polymer or copolymer gel. 
     
     
         55 . The process for the preparation of superabsorbent polymer containing kaolin of  claim 46  wherein the multivalent metal salt of (VI) comprises aluminum sulfate.