Water-absorbent polymer structures based on renewable resources and method for producing said structures

Abstract

The present invention relates to a process for the production of polymers, such as water-absorbing polymer structures, by radical polymerization of acrylic acid, whereby the acrylic acid has been obtained by a synthesis process which comprises as a process step the splitting of an organic material by means of an enzyme or at least one component of an enzyme. The invention also relates to the water-absorbing polymers obtainable by this process, water-absorbing polymers which are based to at least about 25 wt % upon partially neutralized acrylic acid, a composite, a process for the production of a composite, the composite obtainable by this production, the use of acrylic acid in the production of polymers, preferably in the production of water-absorbing polymer structures, a device for the production of acrylic acid, and a process for the production of acrylic acid.

1 - 29 . (canceled) 
     
     
         30 . A water-absorbing polymer structure, which is based to at least about 25 wt. % upon partially neutralized acrylic acid, wherein at least about 80 wt. % of the acrylic acid monomers used in the production of the water-absorbing polymer structure was obtained by a synthetic process comprising the steps of:
 A) forming β-hydroxypropionic acid by splitting an organic material comprising a carbohydrate in the presence of a microorganism and a nutrient solution comprising carbon sources, nitrogen sources, and salts thereof for the nutrition of microorganism by means of an enzyme or at least one component of an enzyme;   B) purifying the product of step A) including the step of removing the β-hydroxypropionic acid of step A) from the nutrient solution to provide β-hydroxypropionic acid;   C) dehydrating the β-hydroxypropionic acid of step B) to form an aqueous acrylic acid solution;   D) purifying the aqueous acrylic acid solution of step C) by crystallization to have a benzaldehyde content of less than 0.1 ppm, a maleic acid or maleic acid anhydride content of less than about 5 ppm, an acetic acid content of less than 0.1 ppm and a ketone content of less than about 5 ppm wherein the purification includes removal of water from the aqueous acrylic acid solution to form acrylic acid; and   E) polymerizing the acrylic acid of step D) by radical polymerization to produce the polymer.   
     
     
         31 . The water-absorbing polymer structures according to  claim 30 , wherein the polymer structures are based to at least about 25 wt. %, based on the total weight of the water-absorbing polymer structures, upon natural, biodegradable polymers. 
     
     
         32 . The water-absorbing polymer structure of  claim 30 , which is characterized by the following properties:
 (β1) the polymer structure is based to at least about 25 wt. % on acrylic acid, whereby at least about 80 wt. % of the acrylic acid monomers used in the preparation of the water-absorbing polymer structures has been obtained by a synthesis process which comprises the process step of splitting an organic material by means of an enzyme or at least one component of an enzyme,   (β2) the polymer structure has a biodegradability determined according to the modified Sturm Test according to Appendix V of Guideline 67/548/EWG after 28 days of at least about 25%;   (β3) the polymer structure has a CRC value determined according to ERT 441.2-02 of at least about 20 g/g.   
     
     
         33 . The water-absorbing polymer structures according to  claim 32 , which are based to at least about 10 wt. %, based upon the polymer structure, upon acrylic acid, and which are characterized by the following properties:
 (ε1) the polymer structure has a sustainability factor of at least about 10;   (ε2) the polymer structure has a biodegradability determined according to the modified Sturm Test according to Appendix V of Guideline 67/548/EWG after 28 days of at least about 25%;   (ε3) the polymer structure has a CRC value determined according to ERT 441.2-02 of at least about 20 g/g.   
     
     
         34 . The water-absorbing polymer structures according to  claim 30  wherein step E1 comprises the steps of:
 i) polymerizing the acrylic acid of step D) by radical polymerization in the presence of a crosslinker to form a polymer gel; 
 ii) comminuting the polymer gel; 
 iii) drying of the polymer gel to obtain water-absorbing polymer structures; and 
 iv) surface post-treating the water-absorbing polymer structure. 
 
     
     
         35 . The water-absorbing polymer structures according to  claim 30  wherein at least about 75 wt % of the organic material is a carbohydrate. 
     
     
         36 . The water-absorbing polymer structures according to  claim 30  wherein step C) comprises
 catalytic dehydration of the β-hydroxypropionic acid. 
 
     
     
         37 . The water-absorbing polymer structures according to  claim 36  wherein a porous carrier brought into contact with an inorganic acid is used as a catalyst. 
     
     
         38 . The water-absorbing polymer structures according to  claim 33  wherein at least about 90 wt % the porous carrier is a silicon oxide. 
     
     
         39 . The water-absorbing polymer structures according to  claim 37  wherein the inorganic acid is phosphoric acid. 
     
     
         40 . The water-absorbing polymer structures according to  claim 37  wherein the porous carrier has a surface area within a range from about 0.005 m 2 /g to about 450 m 2 /g. 
     
     
         41 . The water-absorbing polymer structures according to  claim 30  wherein at least about 80% of the acrylic acid is obtained by a synthetic process comprising the process step splitting of an organic material by means of an enzyme or at least one component of an enzyme to make the acrylic acid. 
     
     
         42 . A hygiene article comprising an upper layer, a lower layer, and an intermediate layer arranged between the upper layer and the lower layer, which comprises water-absorbing polymer structures according to  claim 30 .