Superabsorbent polymers in agricultural applications

Abstract

Superabsorbent polymer (SAP) products for use in agricultural applications, and methods of making and using the same are disclosed. Certain of the SAPs include a monomer or a mixture of monomers, other than acrylonitrile, that is graft polymerized onto a starch in the presence of an initiator to form a starch graft copolymer that is cross-linked and the SAP product is isolated.

1 . A superabsorbent polymer product, comprising: 
 a polysaccharide; and    a monomer that is graft polymerized onto the polysaccharide in the presence of an initiator, forming a polysaccharide graft polymer;    wherein the polysaccharide graft polymer is cross-linked and further isolated in an alcohol-free environment.    
   
   
       2 . The superabsorbent polymer product of  claim 1 , wherein the monomer is at least one of the following: acrylic acid, acrylamide, methacrylamide, 2-acrylamido-2-methyl-propanesulfonic acid, methacrylic acid, vinyl sulfonic acid, ethyl acrylate, potassium acrylate, and derivatives and mixtures thereof.  
   
   
       3 . The superabsorbent polymer product of  claim 1 , wherein the monomer is a mixture of acrylic acid and acrylamide.  
   
   
       4 . The superabsorbent polymer product of  claim 3 , wherein the mixture is about two or more parts acrylic acid to about one part acrylamide by weight.  
   
   
       5 . The superabsorbent polymer product of  claim 1 , wherein the monomer is 2-acrylamido-2-methyl-propanesulfonic acid and derivatives thereof.  
   
   
       6 . The superabsorbent polymer product of  claim 1 , wherein the polysaccharide is a starch.  
   
   
       7 . The superabsorbent polymer product of  claim 6 , wherein the starch is at least one of the following: corn starch, waxy maize starch, wheat starch, potato starch, dextrin starch, dextran starch, corn meal, yucca root, oat flour, banana flour, and tapioca flour.  
   
   
       8 . The superabsorbent polymer product of  claim 6 , wherein the weight ratio of starch to monomer is in the range of between about 1:1 and about 1:6.  
   
   
       9 . The superabsorbent polymer product of  claim 1 , wherein the initiator is ammonium persulfate.  
   
   
       10 . The superabsorbent polymer product of  claim 1 , wherein the initiator is at least one of the following: cerium (+4) salt, ammonium persulfate, sodium persulfate, potassium persulfate, ferrous peroxide, ferrous ammonium sulfate-hydrogen peroxide, L-ascorbic acid, and potassium permanganate-ascorbic acid.  
   
   
       11 . A method for preparing a superabsorbent polymer, comprising: 
 graft polymerizing a monomer onto a starch in the presence of an initiator to form a starch graft copolymer;    cross-linking the starch graft copolymer; and    isolating the starch graft copolymer in an alcohol-free environment.    
   
   
       12 . The method of  claim 11 , further comprising drying the starch graft copolymer.  
   
   
       13 . The method of  claim 11 , further comprising adjusting a pH of the starch graft copolymer.  
   
   
       14 . The method of  claim 13 , wherein the pH is adjusted to within a range of about 6.0 to about 8.0.  
   
   
       15 . The method of  claim 11 , wherein isolating the starch graft copolymer comprises granularizing the starch graft copolymer.  
   
   
       16 . The method of  claim 11 , wherein isolating the starch graft copolymer comprises extruding the starch graft copolymer.  
   
   
       17 . The method of  claim 11 , wherein isolating the starch graft copolymer comprises pelletizing the starch graft copolymer.  
   
   
       18 . The method of  claim 11 , wherein isolating the starch graft copolymer comprises drying the starch graft copolymer.  
   
   
       19 . The method of  claim 11 , wherein the monomer is a mixture of acrylic acid and acrylamide.  
   
   
       20 . The method of  claim 11 , wherein the monomer is at least one of the following: acrylic acid, acrylamide, methacrylamide, 2-acrylamido-2-methyl-propanesulfonic acid, methacrylic acid, vinyl sulfonic acid, ethyl acrylate, potassium acrylate, and derivatives and mixtures thereof.  
   
   
       21 . The method of  claim 11 , wherein cross-linking the starch graft copolymer comprises adding a cross-linking agent.  
   
   
       22 . A method for preparing a superabsorbent polymer product for agricultural applications, comprising: 
 graft polymerizing a mixture of acrylic acid and acrylamide onto a starch in the presence of an initiator to form a starch graft copolymer;    adding a cross-linking agent to form a cross-linked starch graft copolymer;    adjusting a pH of the cross-linked starch graft copolymer to within a pH range of about 6.0 and about 8.0; and    isolating the superabsorbent polymer product through drying or extruding the cross-linked starch graft copolymer.    
   
   
       23 . A method of using a superabsorbent polymer product, comprising: 
 obtaining a cross-linked starch graft copolymer product isolated in an alcohol-free environment; and    applying the cross-linked starch graft copolymer product to an agricultural medium to increase plant growth.    
   
   
       24 . The method of  claim 23 , wherein applying the cross-linked starch graft copolymer product to an agricultural medium comprises applying the cross-linked starch graft copolymer to soil.  
   
   
       25 . The method of  claim 23 , wherein applying the cross-linked starch graft copolymer product to an agricultural medium comprises coating a seed with the cross-linked starch graft copolymer.  
   
   
       26 . The method of  claim 23 , wherein applying the cross-linked starch graft copolymer product to an agricultural medium comprises coating a plant root with granulated cross-linked starch graft copolymer.  
   
   
       27 . The method of  claim 23 , further comprising forming a slurry of the cross-linked starch graft copolymer product with a solvent, wherein applying the cross-linked starch graft copolymer product to an agricultural medium comprises applying the slurry to at least one of the following: a plant, a root, a seed, a seedling, and soil.  
   
   
       28 . The method of  claim 23 , wherein the cross-linked starch graft copolymer product comprises a mixture of acrylic acid and acrylamide that is graft polymerized onto a starch.