Biodegradable superabsorbent polymer composition with good absorption and retention properties

Abstract

The present invention generally relates to a method for the production of a superabsorbent composition comprising the process steps: i. production of a hydrogel by radical polymerization of an aqueous monomer solution containing at least one monomer ii. drying the hydrogel to obtain a water-absorbing polymer structure iii. surface crosslinking of the water-absorbing polymer structure to obtain a surface-crosslinked water-absorbing polymer structure, iv. incorporation of a starch compound in one or at least two of the variants V1 to V6, V1. in process step i. into the monomer solution V2. after process step i. and prior to process step ii. into the hydrogel V3. in process step ii. V4. after process step ii. and prior to process step iii. into the water-absorbing polymer structure V5. in process step iii V6. after process step iii onto the surface-crosslinked water-absorbing polymer structure. The present invention also related to a superabsorbent composition obtainable according to this method, a particulate superabsorbent composition and a composite, a sanitary article core and a sanitary item, furthermore chemical products and also the use of this superabsorbent composition in chemical products.

1 - 41 . (canceled) 
     
     
         42 . A particulate superabsorbent composition containing:
 a crosslinked inner region based on partially neutralized acrylic acid within a range of about 70 to about 95% by weight based on the superabsorbent composition   an outer region which is more strongly crosslinked than the inner region surrounding this inner region at least partially   whereby from about 5wt % to 20wt % of at least one water-soluble starch compound based on the weight of the superabsorbent composition wherein the powder starch compound is water-soluble if at least about 30 g of powder starch compound may be dissolved in a liter of deionized water at a temperature of 20° C. is incorporated into the superabsorbent composition in a quantity of least 1% by weight based on the superabsorbent composition; and wherein at least about 70% by weight of said starch compound has a particle size of less than about 100 μm;   whereby the superabsorbent composition possesses at least one of the following properties:
 z1 a retention (CRC) of at least about 25 g/g 
 z2 an absorption at pressure (AAP 0.7 ) of at least about 20 g/g 
 z3 a permeability (SFC) of at least about 20×10 −7  cm 3 sec/g 
 z4 a biodegradability determined according to the method described here after 28 days of at least about 25%. 
   
     
     
         43 . The particulate superabsorbent composition according to  claim 42 , whereby said starch compound comprises less than about 20% amylose and are more than about 75% carboxymethylated. 
     
     
         44 . The particulate superabsorbent composition according to  claim 42  whereby the starch compound is incorporated in the inner region. 
     
     
         45 . The particulate superabsorbent composition according to  claim 42  whereby a starch compound is incorporated in the outer region. 
     
     
         46 . The particulate superabsorbent composition according to  claim 42  whereby a further starch compound SII different from a first starch compound SI incorporated in the inner region is incorporated in the outer region. 
     
     
         47 . A method for the production of a superabsorbent composition comprising the process steps:
 i. producing a hydrogel by radical polymerization of an aqueous monomer solution containing an ethylenically unsaturated acid-group-containing monomer including acrylic acid and methacrylic acid and a crosslinking agent, wherein the monomer solution has a monomer content in the range from 20 to 30%;   ii. drying the hydrogel to obtain a water-absorbing polymer structure;   iii. surface post-crosslinking of the water-absorbing polymer structure with a post-crosslinking agent to obtain a surface-crosslinked water-absorbing polymer structure;   iv. incorporating from about 5 wt % to 20 wt % of a water-soluble powder starch compound based on the weight of the superabsorbent composition wherein the powder starch compound is water-soluble if at least about 30 g of powder starch compound may be dissolved in a liter of deionized water at a temperature of 20° C., in at least two of the following variants
 V2. after process step i. and prior to process step ii. into the hydrogel 
 V3. in process step ii 
 V5. in process step iii 
   wherein the starch compound comprises less than about 20% amylose and is more than about 75% carboxymethylated.   
     
     
         48 . The method according to  claim 47 , wherein the starch compound has at least one of the following properties:
 S1 a free absorption (FA) of at least about 9 g/g,   S2 a retention (CRC) of at least about 7 g/g,   S3 an absorption at pressure (AAP 0.3 ) of at least about 2 g/g,   S4 an absorption at pressure (AAP 0.7 ) of at least about 2 g/g, and   S5 a pH value in the range from about 9 to about 14.   
     
     
         49 . The method according to  claim 47 , wherein at least one first starch compound SI is incorporated in the variant V2. 
     
     
         50 . The method according to  claim 47 , wherein the starch compound is used in a quantity of a maximum of about 30% by weight based on the monomer used. 
     
     
         51 . The method according to  claim 47 , wherein the monomer solution has a monomer content in the range from 22.5 to 27.5% by weight based on the monomer solution. 
     
     
         52 . The method according to  claim 47 , wherein the starch compound has a solution viscosity according to the method specified herein in the range of from about 20,000 to about 50,000 mPas. 
     
     
         53 . The method according to  claim 47 , wherein the starch compound comprises less than about 10% by weight of cyclic or branched polysaccharides. 
     
     
         54 . A method for the production of a superabsorbent composition comprising the process steps:
 i. producing a hydrogel by radical polymerization of an aqueous monomer solution containing an ethylenically unsaturated acid-group-containing monomer including acrylic acid and methacrylic acid and a crosslinking agent, wherein the monomer solution has a monomer content in the range from 20 to 30%;   ii. drying the hydrogel to obtain a water-absorbing polymer structure;   iii. surface post-crosslinking of the water-absorbing polymer structure with a post-crosslinking agent to obtain a surface-crosslinked water-absorbing polymer structure;   iv. incorporating from about 5 wt % to 20 wt % of a water-soluble powder starch compound based on the weight of the superabsorbent composition wherein the powder starch compound is water-soluble if at least about 30 g of powder starch compound may be dissolved in a liter of deionized water at a temperature of 20° C., in at least two of the following variants
 V3. in process step ii 
 V4. after process step ii. and prior to process step iii. into the water-absorbing polymer structure 
 V5. in process step iii, 
 V6. after process step iii onto the surface-crosslinked water-absorbing polymer structure, 
   wherein the starch compound comprises less than about 20% amylose and is more than about 75% carboxymethylated.   
     
     
         55 . The method according to  claim 54 , wherein the starch compound has at least one of the following properties:
 S1 a free absorption (FA) of at least about 9 g/g,   S2 a retention (CRC) of at least about 7 g/g,   S3 an absorption at pressure (AAP 0.3 ) of at least about 2 g/g,   S4 an absorption at pressure (AAP 0.7 ) of at least about 2 g/g, and   S5 a pH value in the range from about 9 to about 14.   
     
     
         56 . The method according to  claim 54 , wherein the starch compound is used in a quantity of a maximum of about 30% by weight based on the monomer used. 
     
     
         57 . The method according to  claim 54 , wherein the monomer solution has a monomer content in the range from 22.5 to 27.5% by weight based on the monomer solution. 
     
     
         58 . The method according to  claim 54 , wherein the starch compound has a solution viscosity according to the method specified herein in the range of from about 20,000 to about 50,000 mPas. 
     
     
         59 . The method according to  claim 54 , wherein the starch compound comprises less than about 10% by weight of cyclic or branched polysaccharides.