Acidic superabsorbent hydrogels

Abstract

The present invention relates to novel hydrophilic swellable addition polymers comprising improved odor control, a process for their preparation and their use for absorbing aqueous fluids and a process for screening superabsorbents.

1 .- 16 . (canceled)  
   
   
       17 . A hydrogel-forming polymer capable of absorbing aqueous fluids and having a pH absorbency index pH AI  of at least 80 and a pH of not more than 5.7, wherein pH AI  is calculated as follows:  
       pH AI =ΔpH (AUL 0.7psi +CRC), wherein ΔpH=7−pH of product, AUL 0.7psi  is an absorbency under pressure at 0.7 psi, and CRC is a centrifuge retention capacity.    
   
   
       18 . The polymer of  claim 17  having a pH absorbency index pH AI  of at least 90.  
   
   
       19 . The polymer of  claim 17  having a pH absorbency index PHAI of at least 100.  
   
   
       20 . The polymer of  claim 17  having a pH of from 4 to 5.5.  
   
   
       21 . The polymer of  claim 17  having a pH of from 4.4 to 4.6 or from 5.1 to 5.3.  
   
   
       22 . The polymer of  claim 17  having a Nessler value of less than 60%.  
   
   
       23 . The polymer of  claim 17  having a Nessler value of less than 40%.  
   
   
       24 . The polymer of  claim 17  having a Nessler value of less than 30%.  
   
   
       25 . The polymer of  claim 17  having a CRC greater than 15 g/g.  
   
   
       26 . The polymer of  claim 17  having a CRC greater than 26 g/g.  
   
   
       27 . The polymer of  claim 17  having an AUL 0.7psi  greater than 13 g/g.  
   
   
       28 . The polymer of  claim 17  having an AUL 0.7psi  greater than 15 g/g.  
   
   
       29 . The polymer of  claim 17  obtainable from a base polymer having a pH of not more than 5.7.  
   
   
       30 . The polymer of  claim 17  being an acrylic acid (co)polymer partially neutralized with an alkali metal, an alkaline earth metal, ammonium, or an amine salt.  
   
   
       31 . The polymer of  claim 17  wherein the polymer is surface postcrosslinked.  
   
   
       32 . The polymer of  claim 17  having antimicrobial properties.  
   
   
       33 . A method of permanently or temporarily binding an aqueous fluid comprising a step of contacting the aqueous fluid with an absorbent article comprising a hydrogel-forming polymer of  claim 17 .  
   
   
       34 . A hydrogel-forming polymer prepared by polymerizating a partially neutralized acrylic acid with a crosslinking agent to form a gel, wherein 
 (i) partial neutralization is effected using 50% NaOH or an equivalent neutralizing agent: 20-30 mol % based on acrylic acid, and crosslinking is effected using polyethylene glycol 400 diacrylate: 0.005-1.0%, by weight, based on acrylic acid, or a different crosslinker that produces the same degree of crosslinking, or    (ii) partial neutralization is effected using NaHCO 3  or an equivalent neutralizing agent: 23-28%, by weight, based on acrylic acid, and crosslinking is effected using allyl methacrylate: 0.005-1.0%, by weight, based on acrylic acid, or a different crosslinker that produces the same degree of crosslinking, or    (iii) partial neutralization is effected using LiOH×H 2 O or an equivalent neutralizing agent:  15- 30%, by weight, based on acrylic acid, and crosslinking is effected using allyl methacrylate: 0.005-1.0%, by weight, based on acrylic acid, or a different crosslinker that produces the same degree of crosslinkng, or    (iv) partial neutralization is effected using NaHCO 3  or an equivalent neutralizing agent: 35-55%, by weight, based on acrylic acid, when 2-acryl-amido-2-methylpropanesulfonic acid is present at 30-55%, by weight, based on acrylic acid, and crosslinking is effected using allyl methacrylate: 0.005-1.0%, by weight, based on acrylic acid, or a different crosslinker that produces the same degree of crosslinking.    
   
   
       35 . A base polymer obtained by drying a gel prepared in  claim 36 .  
   
   
       36 . A base polymer obtained by surface postcrosslinking the dried base polymer of  claim 35 .  
   
   
       37 . A hydrogel-forming polymer having a pH absorbency index pH AI  of at least 80 and prepared by the method of  claim 35 .  
   
   
       38 . A hygiene article comprising 
 (A) a liquid pervious topsheet,    (B) a liquid impervious backsheet,    (C) a core positioned between (A) and (B), said core comprising 10% to 100%, by weight, of the hydrogel-forming polymer of  claim 17  and 0% to 90%, by weight, of hydrophilic fiber material,    (D) optionally a tissue layer positioned directly above and below said core (C), and    (E) optionally an acquisition layer positioned between (A) and (C).