A PROCESS FOR THE PREPARATION OF SUPERABSORBENT POLYMER

Abstract

The present invention relates to a process for preparing a superabsorbent polymer with a high fluid absorption capacity. The present invention also relates to a composition comprising said superabsorbent polymer and its use for absorbing aqueous fluids, for example, in the agricultural industry.

Description

A PROCESS FOR THE PREPARATION OF SUPERABSORBENT POLYMER FIELD OF INVENTION The present invention relates to a process for preparing a superabsorbent polymer with a high fluid absorption capacity. The present invention also relates to a composition comprising said superabsorbent polymer and its use for absorbing aqueous fluids, for example, in the agricultural industry. BACKGROUND OF THE INVENTION Superabsorbent polymers absorb water or fluids several times their weight. Superabsorbent polymers (SAPs) improve water retention in the soil and are therefore used in agriculture. In the art, various superabsorbent polymers are known. Such superabsorbent polymers can be manufactured from polyacrylamide copolymer, crosslinked carboxymethylcellulose, polyvinyl alcohol copolymer, crosslinked polyethylene oxide, polyacrylonitrile starch grafted copolymer, etc. It is known that the water absorbance of most superabsorbent polymers decreases considerably in the presence of salts. Superabsorbent polymers incorporated into the soil or mixed with fertilizers are known to suffer a decrease in absorption capacity due to the presence of salts in the soil or fertilizer. Studies have been conducted to investigate the effect of salts, such as those carried out by Daniel C. Bowman, Richard Y. Evans, and J.L. Paul, J. Amer. Soc. Hort. Sci. May 1990 115:382-386, "Fertilizer Salts Reduce Hydration of Polyacrylamide Gels and Affect Physical Properties of Gel-Amended Container Media."The article discusses the decrease in the polymer's absorption capacity when mixed with salts. It was observed that soluble salts dramatically affect absorption by hydrophilic polyacrylamide gels. Agriculture requires the use of many compounds to ensure good yields and healthy crops. Most fertilizers and nutrients added to the soil are salts that contribute to crop improvement. Salts are also naturally present in the soil, which also contributes to increased soil salinity. In drought-prone areas and areas where water management is essential, soil salinity is higher because the water required to leach these salts is scarce. In such soils, where water is scarce, where water management is required, or even where normal salts are added to the soil, the addition of superabsorbent polymers cannot produce the desired effect of increased water availability. The salts in the environment surrounding the superabsorbent polymer influence the polymer's performance capacity. The known preparation process for such superabsorbent polymers includes a reverse-phase suspension polymerization process and an aqueous solution polymerization process. U.S. Patent No. 7459501 describes and claims a process for preparing SAP, wherein the SAP is prepared by graft polymerization of a monomer onto starch in the presence of a thermal initiator such as ammonium persulfate at 170 °F. U.S. Patent No. 8507607 describes a continuous process for grafting a carbohydrate with an α,β-unsaturated carboxylic acid derivative in the presence of a catalyst, wherein the polymerization is a thermally initiated polymerization under substantially adiabatic conditions. Patent No. WO2019 / 011793 relates to a process for producing superabsorbent polymer particles, comprising surface post-crosslinking, sorting of surface post-crosslinked superabsorbent polymer particles, deagglomeration of the separated oversize fraction using a roller crusher, and recycling of the disintegrated oversize fraction before or during sorting of the surface post-crosslinked superabsorbent polymer particles. Therefore, there is a need in the art for a simple and industrially viable process for preparing superabsorbent polymer in granular form. Consequently, the present invention provides a feasible and economical route for preparing superabsorbent polymer by overcoming the problem encountered during the preparation of superabsorbent polymers (SAPs). Surprisingly, the present invention has been found to provide a superabsorbent polymer with the desired properties; specifically, the superabsorbent polymer particles have high absorption capacity and retention properties for aqueous fluids. oczn ιη / ζζηζ / Β / γίΛΐ BRIEF DESCRIPTION OF THE INVENTION In one aspect, the present invention provides a process for the preparation of superabsorbent polymer. Another aspect of the present invention is to provide an efficient method for the production of a superabsorbent polymer that shows an increase in production capacity, is a simple, cost-effective and environmentally friendly technique. Another object of the present invention is to provide a superabsorbent polymer having a high water absorption capacity. In another aspect, the present invention provides a process for the preparation of a superabsorbent polymer comprising grafting a monomer onto starch in the presence of a redox catalytic system. In another aspect, the present invention provides a process for the preparation of a superabsorbent polymer comprising grafting a monomer onto starch in the presence of a redox catalytic system at room temperature. In another aspect, the present invention provides a process for preparing a superabsorbent polymer comprising grafting an acrylic acid compound monomer onto a polysaccharide using a redox catalyst system comprising ammonium persulfate, hydrogen peroxide, and ascorbic acid. In another aspect, the present invention provides a process for the preparation of polysaccharide-g-poly (2-propenamide-co-2-propenoic acid) or salts thereof. In another aspect, the present invention provides a process for the preparation of starch-g-poly(2-propenamide-co-2-propenoic acid) or salts thereof. In another aspect, the present invention provides a method for the production of a superabsorbent polymer comprising a) graft the monomer onto the surface of the polysaccharide in the presence of a redox catalytic system and a crosslinking agent to form a copolymer and b) neutralize the copolymer to obtain granulated superabsorbent polymer. In one aspect, the present invention provides a superabsorbent polymer having a particle size, for example, in the range of 7500 microns to 75 microns, which is approximately mesh 3 to mesh 200. oczn ιη / ζζηζ / Β / γίΛΐ In one aspect, the present invention provides superabsorbent polymers that have water absorbance capacity in the range of 200-2000 g / g. Typically, the water absorbance capacity of the superabsorbent polymer can be measured by a method known in the art and one such method is described in H. Omidiana et al., Polymer 40 (1999) 1753-1761. In another aspect, the present invention provides starch-grafted polyacrylic / acrylamide acid having a high water absorption capacity ranging from 500 g / g to 980 g / g, preferably in the range of 650 g / g to 800 g / g. In one aspect, the present invention provides a composition comprising at least one superabsorbent polymer produced by the present invention. In one aspect, the present invention provides a composition comprising at least one superabsorbent polymer of the present invention and optionally at least one plant-advantageous additive. In one aspect, the present invention provides a multi-package agricultural product comprising: i) a container comprising at least one superabsorbent polymer of the present invention and optionally at least one plant-advantageous additive. i) an instruction manual that instructs the user to manage the content to a locus. In one aspect, the present invention provides a method for increasing the water absorption capacity of a superabsorbent polymer; the method comprises bringing the superabsorbent polymer produced by the present invention into contact with a plot of soil. In another aspect, the present invention provides a superabsorbent polymer produced by the present method that has a water absorbance capacity ranging from 500 g / g to 980 g / g. DETAILED DESCRIPTION OF THE INVENTION Within the context of this specification, each term or phrase below will include the following meaning or meanings: oczn Ln / zznz / e / YiAi For the purposes of the following detailed description, it is understood that the invention may assume several alternative variants and sequences of steps, except where expressly specified otherwise. Furthermore, apart from any operational example, or where otherwise indicated, all numbers expressing, for example, quantities of materials / ingredients used in the specification are understood to be modified in all cases by the term “approximately”. Therefore, before describing the present invention in detail, it should be understood that this invention is not limited to the particularly exemplified systems or process parameters, which, of course, may vary. It should also be understood that the terminology used herein is for the purpose of describing particular embodiments of the invention and is not intended to limit the scope of the invention in any way. The use of examples anywhere in this specification that include examples of any of the terms discussed herein is for illustrative purposes only and in no way limits the scope and meaning of the invention or of any term exemplified. Likewise, the invention is not limited to the various embodiments given in this specification.Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by a person skilled in the art to which this invention pertains. In case of conflict, the present document, including its definitions, shall prevail. Those skilled in the art will recognize that the methods and compositions described herein can be implemented without one or more of the specific details outlined, or with other methods, components, materials, etc. In some cases, well-known materials, components, or method steps are not shown or described in detail. Furthermore, the method steps, compositions, etc., described herein can be combined in any suitable manner in one or more modalities. It will also be readily understood that the methods and compositions of the modalities as generally described herein could be arranged and designed in a wide variety of different configurations. The order of the steps or actions of the methods described in relation to the modalities described may be changed, as will be evident to those skilled in the art. Therefore, any order in the detailed description is for illustrative purposes only and is not intended to imply a required order. It should be noted that, as used in this specification, the singular forms “a,” “an,” and “the” include plural referents unless the content clearly indicates otherwise. The terms “preferred” and “preferably” refer to embodiments of the invention that may provide certain benefits under certain circumstances. As used in the present description, the terms “comprising”, “including”, “having”, “containing”, “implying” and the like should be understood as open-ended, meaning that they include, but are not limited to, what is included. As used in this description, the term “ambient temperature” refers to temperatures, for example, from 15°C to 40°C, 15°C to 30°C, and 15°C to 24°C, 16°C to 21°C, 20°C to 30°C, 30°C to 35°C. Such temperatures may vary from +5 to -5°C. The term “SAP”, as used in this description, means superabsorbent polymer. The term “water absorption,” as used herein, means the property of absorbing water when the superabsorbent polymer is exposed to water. Water absorption capacity (WAC) testing involves adding water or an aqueous solution to a material, followed by sieving and quantifying the water retained by the gelled material on the sieve. In any aspect or embodiment described below, the phrase “comprising” may be replaced by the phrases “consisting of,” “consisting essentially of,” or “containing.” In these aspects or embodiments, the described combination or composition includes, comprises, consists of, essentially of, or substantially consists of specific components mentioned in this description, or adjuvants or excipients not specifically mentioned herein. The terms “superabsorbent polymer” or “SAP” or “polymer gel” refer to water-expandable polymers that can absorb many times their weight in an aqueous solution. Beyond theory, the term superabsorbent polymers also applies to polymers that absorb water and reabsorb the water they have absorbed. A superabsorbent polymer can be selected from, but is not limited to, water-expandable or water-retaining polymers such as crosslinked polymers that expand without dissolving in the presence of water and can absorb at least 10, 100, 1000, or more times their weight in water. The term “a redox catalytic system” referred to in this description is a catalytic system comprising ammonium persulfate, hydrogen peroxide, and ascorbic acid. In one aspect, the present invention provides a method for the production of superabsorbent polymer. In one aspect, the present invention provides a process for the preparation of a superabsorbent polymer comprising grafting an acrylic acid monomer and a polysaccharide in the presence of a redox catalytic system. In one embodiment, the process comprises grafting a monomer onto a starch to form a starch graft copolymer, wherein the monomer comprises at least one carboxylic acid or α,β-unsaturated nitrile derivative. Typically, the monomer is selected from acrylic acid, acrylamide, methacrylamide, 2-acrylamido-2-methylpropanesulfonic acid, methacrylic acid, vinylsulfonic acid, ethyl acrylate, potassium acrylate, derivatives thereof, or mixtures thereof. Examples of monomers used in the invention include, but are not limited to, acrylic acid or methacrylic acid, acrylamide or methacrylamide, sulfonic acids such as 2-acrylamido-2-methylpropanesulfonic acid (AMPS), vinylsulfonic acid, acrylates such as ethyl acrylate and potassium acrylate. In one embodiment, the monomer is acrylic acid. In another form, the monomer is a mixture of acrylic acid and acrylamide. In alternative applications, acrylic acid can be grafted onto a starch or other polysaccharide without the aid of acrylamide. In one form, the polysaccharide is a superabsorbent polymer. In one embodiment, the superabsorbent polymer is a starch-based superabsorbent polymer. In one form, the superabsorbent polymer is Zeba™. In one form, the polysaccharide is starch. The starch used in the method described above includes starches, flours, and ground grains. For example, starches include native starches (e.g., corn starch (Puré Food Powder, manufactured by AE Staley), waxy corn starch (Waxy 7350, manufactured by AE Staley), wheat starch (Midsol 50, manufactured by Midwest Grain Products), potato starch (Avebe, manufactured by AE Staley)), dextrin starches (e.g., Stadex 9, manufactured by AE Staley), dextran starches (e.g., Grade 2P, manufactured by Pharmachem Corp.), corn flour, peeled cassava root, unpeeled cassava root, oat flour, plantain flour, and tapioca flour. Starch may be gelatinized to provide optimal absorbency. An illustrative starch is gelatinized corn starch. Furthermore, according to one modality, the molar ratio of starch to monomer is in the range of approximately 1:1 to approximately 1:7. In alternative formulations, other polysaccharides, such as cellulose, can be used instead of starch. Consequently, the monomers described so far can be polymerized by grafting onto cellulose for agricultural applications. In one embodiment, the redox catalyst system may comprise initiators, for example, cerium(+4) salts, such as ammonium ceric nitrate; ammonium persulfate; sodium persulfate; potassium persulfate; ferrous peroxide; ferrous ammonium sulfate-hydrogen peroxide; L-ascorbic acid; and potassium permanganate-ascorbic acid. Other suitable initiators known to those skilled in the art, such as alternative persulfates and peroxides, as well as vanadium, manganese, etc., may be used. The amount of initiator used may vary based on the chosen initiator, the selected monomer, and the chosen starch. The initiator may be added in one or multiple stages at room temperature. In one embodiment, the process for preparing superabsorbent polymer comprises grafting a monomer onto a starch in the presence of a redox catalytic system to form the starch graft copolymer at room temperature. In another modality, the process for preparing superabsorbent polymer comprises the steps of a) grafting a monomer onto a starch in the presence of a redox catalytic system to form the starch graft copolymer; b) neutralize the starch graft copolymer and c) isolate the granular superabsorbent polymer. In one embodiment, the monomer is polymerized by grafting onto a starch in the presence of a redox catalytic system at room temperature. oczn ιη / ζζηζ / Β / γίΛΐ The grafting polymerization process also includes a crosslinking agent. Examples of crosslinking agents include: glycerides; diepoxides; diglycidyls; cyclohexadiamide; methylene bis-acrylamide; bis-hydroxyalkylamides, such as bis-hydroxypropyl adipamide; formaldehydes, such as urea-formaldehyde and melamine-formaldehyde resins; isocyanates, including di- or triisocyanates; epoxy resins, typically in the presence of a base catalyst; and derivatives and mixtures thereof. In one aspect, the present invention provides a process for the preparation of a superabsorbent polymer comprising grafting an acrylic acid monomer and a polysaccharide in the presence of a redox catalytic system and a crosslinking agent at room temperature. In one embodiment, the redox catalytic system comprises ammonium persulfate, hydrogen peroxide, and ascorbic acid. In one embodiment, the crosslinking agent is methylene bis-acrylamide. In one modality, the process for preparing superabsorbent polymer is either a batch process or a continuous process. Advantageously, the catalytic system used in the process helps to achieve polymerization at room temperature and provides the product with better strength and water absorption capacity. Another advantage associated with the present invention is that the utilities required to heat and cool the thermally initiated catalytic system are completely avoided, resulting in a reduction of process costs on a commercial scale. In one embodiment, once a starch graft copolymer is formed, its pH can be adjusted to a desired value for the particular agricultural application. Alternative pH values ​​may be desirable depending on the soil type and the crop to which the resulting SAPs will be applied. The resulting pH for most agricultural applications will typically range from approximately 6.0 to approximately 8.0, preferably 7.0. In one embodiment, the neutralization of the starch graft copolymer is carried out by using potassium hydroxide, potassium methoxide, or a mixture of these. oczn Ln / zznz / e / γΐΛΐ In one embodiment, after neutralization, the starch graft copolymer can be isolated. In an illustrative method, the neutralized polymer mass is washed with a solvent, for example, alcohol, to obtain a granulated product. In an illustrative method, the neutralized mass of the exiting polymer is granulated by mixing it with solvent, for example, methanol, in a twin-screw reactor continuously to obtain SAP product granules. For example, the SAP product may have a particle size smaller than approximately 200 mesh. The desired particle size may depend on the specific intended agricultural application. In an embodiment for agricultural applications that deposit the starch grafting copolymer directly into the soil, the particle size may be smaller than 50 mesh, more specifically, between approximately 5 and 50 mesh, or between approximately 5 and 25 mesh, or between approximately 8 and 25 mesh. In another aspect, the present invention provides a method for increasing the water absorption capacity of a superabsorbent polymer. The method comprises contacting the superabsorbent polymer produced by the present invention with a soil sample. Typically, the superabsorbent polymer product can be mixed with a solvent, such as water, to form a suspension. The resulting suspension can be applied to an agricultural medium, such as a plant, root, seed, seedling, or directly to the soil in which a plant, root, seed, or seedling will be planted. In one modality, a fertilizer or micronutrient can be added to the SAP product. The agricultural application of SAPs produced using the methods described above can result in earlier seed germination and / or flowering, reduced irrigation requirements, increased propagation, enhanced crop growth, higher crop yields, and decreased soil crusting. Therefore, SAPs produced using the methods described herein are desirable for large-scale agricultural applications. The advantage of the present invention also lies in retaining the desired water absorption properties without undergoing plasticizing conditions. oczn Ln / zznz / e / YiAi It is understood that the specification and examples are illustrative but not limiting of the present invention, and that other embodiments within the spirit and scope of the invention will be obvious to those skilled in the art. Other embodiments may be practiced that are also within the scope of the present invention. The following examples illustrate the invention but are in no way intended to limit the scope of the claims. Examples Example 1 Batch process Starch (82 g) was placed in water (700 g) in a homogenizer for 1 hour. The resulting mass was then transferred to a reaction kettle. The reaction mixture was stirred at 25–30 °C, and acrylic acid (82 g, 100%) was added, followed by a mixture of acrylamide (41 g), methylene bisacrylamide (200 mg), and ammonium persulfate (200 mg). Hydrogen peroxide (160 mg) and ascorbic acid solution (100 mg in 3 mL of water) were added to the reaction mixture. The thick mass was stirred for 1 hour and then neutralized with potassium hydroxide solution to a pH of 7.2. The mass was washed by stirring with methanol (3.0 kg) to produce a granulated product. Weight-260 g, yield-97% with moisture content at 6-7% Water absorption capacity: 562 g / g Example 2 Continuous process Starch (82 g) was placed in water (700 g) in a homogenizer for 1 hour. Acrylic acid (82 g) was added to this resulting mass, followed by the addition of acrylamide (41 g), methylene bisacrylamide (200 mg), ammonium persulfate (200 mg), and hydrogen peroxide (160 mg). This mixture was fed into a continuous twin-screw reactor at a rate of 38.1 mL / min at 25 °C. Simultaneously, a 0.0031 M ascorbic acid solution was introduced into the reactor through another port at a feed rate of 10 mL / min. The material exiting the reactor was progressively neutralized in a neutralization chamber where a potassium hydroxide solution was fed at a rate of 7 mL / min. The neutralized mass was then granulated by mixing it with methanol in another continuous twin-screw reactor. Weight-260 g / h, yield-97% with moisture content at 6-7% Water absorption capacity: 540 g / g Example 3 Eighty-two grams of starch were mixed with 700 grams of water in a homogenizer for 1 hour. The resulting mass was then transferred to a reactor equipped with ribbon paddle blades. The reaction mixture was stirred at 25–30 °C, and 82 grams (100%) of acrylic acid were added, followed by a mixture of 41 grams of acrylamide, 200 mg of methylene bisacrylamide, and 200 mg of ammonium persulfate. Then, 160 mg of hydrogen peroxide was added. Finally, 100 mg (in 3 mL of water) of ascorbic acid solution was added. The thick mass was stirred for 1–1.5 hours, then neutralized with KOH solution to a pH of 7.2. The mass was washed by stirring with methanol (3.0 kg) to produce a granulated product. Weight-200 g, yield-74% with moisture content at 6-7% Water absorption capacity: 445 g / g Example 4 Reaction in the absence of ascorbic acid. Eighty-two grams of starch were placed in 700 grams of water in a homogenizer for 1 hour. The resulting mass was then transferred to a reaction kettle equipped with a Teflon-coated blade. The reaction mixture was stirred at 25–30 °C, and 82 g (100%) of acrylic acid were added, followed by the addition of a mixture of 41 g of acrylamide, 100 mg of methylene bisacrylamide, and 200 mg of ammonium persulfate. Then, 160 mg of hydrogen peroxide was added, and the mixture was stirred for 2 hours. No polymerization occurred even after 2 hours. Example 5 Eighty-two grams of starch were placed in 700 grams of water in a homogenizer for 1 hour. The resulting mass was then transferred to a reaction kettle. The reaction mixture was stirred, and 82 grams (100%) of acrylic acid were added, followed by the addition of a mixture of 41 grams of acrylamide, 50 mg of methylene bisacrylamide, and 200 mg of ammonium persulfate. Next, 160 mg of hydrogen peroxide was added under stirring to 100 mg (in 3 mL of water) of ascorbic acid solution. The thick mass was stirred for 1 hour, then neutralized with KOH solution to a pH of 7.2. The mass was washed with 3.0 kg of methanol to produce a granulated product. Weight: 240 g (yield - 92%) with moisture content at 6-7% Water absorption capacity: 265 g / g Example 6 Eighty-two grams of starch were placed in 700 grams of water in a homogenizer for 1 hour. The resulting mass was then transferred to a reaction kettle. The reaction mixture was stirred, and 82 grams of acrylic acid were added, followed by a mixture of 41 grams of acrylamide, 100 mg of methylene bisacrylamide, and 200 mg of ammonium persulfate. Next, 160 mg of hydrogen peroxide were added under stirring. Finally, 100 mg (in 3 mL of water) of ascorbic acid solution was added. The thick mass was stirred for 1 hour, then neutralized with KOH solution to a pH of 7.2. The mass was washed with methanol (3.0 kg) to produce a granulated product. Weight: 256 g with a moisture content of 6-7% Water absorption capacity: 780 g / g Example 7 Eighty-two grams of starch were placed in 700 grams of water in a homogenizer for 1 hour. The resulting mass was then transferred to a reaction kettle. The reaction mixture was stirred at 25–30 °C, and 82 grams of acrylic acid were added, followed by a mixture of 41 grams of acrylamide, 100 mg of methylene bisacrylamide, and 240 mg of AIBA (2,2'-Azobis(2-methylpropionamide) dihydrochloride). This was followed by the addition of 160 mg of hydrogen peroxide under stirring. One hundred milliliters (in 3 mL) of ascorbic acid solution in water were then added. The thick mass was stirred for 1 hour, then neutralized with KOH solution to a pH of 7.2. The mass was washed with methanol (3.0 kg) to produce a granulated product. Weight 259 g (yield >98%) with moisture content at 6-7% oczn ιη / ζζηζ / Β / γίΛΐ Water absorption capacity: 700 g / g. Example 8 Continuous process 1207 g of starch were placed in 11.666 g of water in a homogenizer for 1 h. To this resulting mass, 1839 g of acrylic acid were added, followed by 7.67 g of tetraethylene glycol diacrylate, 0.345 g of AIBA (2,2'-Azobis(2-methylpropionamidine) dihydrochloride), and 0.16 g of hydrogen peroxide. This mixture was fed into a continuous twin-screw reactor at a rate of 38.1 mL / min at 30–32 °C. Simultaneously, an ascorbic acid solution (3.658 g dissolved in 5 L of water) was introduced through another port at a feed rate of 10 mL / min. The reactor was maintained under an inert atmosphere with slow bubbling of nitrogen. The material leaving the reactor was progressively neutralized in the next neutralization chamber where a 22.5% potassium hydroxide solution is fed at a rate of 7 ml / min. Then, the neutralized mass that comes out is granulated by mixing it with methanol in another twin-screw reactor continuously and is dried. Weight-520 g / h, yield-95% with moisture content at 5-7%. Water absorption capacity (WAC): 540 g / g.

Claims

1o) A method for the production of superabsorbent polymer comprising a) grafting a monomer onto the surface of the polysaccharide in the presence of a redox catalytic system to form a copolymer and b) neutralizing the copolymer to obtain granulated superabsorbent polymer. 2o) The method as claimed in claim 1 wherein said monomer is selected from acrylamide, methacrylamide, 2-acrylamido-2-methylpropanesulfonic acid, methacrylic acid, vinylsulfonic acid, ethyl acrylate, potassium acrylate or derivatives thereof. 3) The method as claimed in claim 1 wherein said superabsorbent polymer is selected from acrylamide-sodium acrylate copolymer; hydrolyzed starch-polyacrylonitrile; 2-propenenitrile homopolymer, hydrolyzed, sodium salt or poly(acrylamide co-sodium acrylate) or poly(2-propenamide-co-2-propanoic acid, sodium salt); starch-γ-poly(2-propenamide-co-2-propanoic acid, mixed sodium and aluminum salts); starch-γ-poly(2-propenamide co-2-propanoic acid, potassium salt); poly(2-propenamide co-2-propanoic acid, sodium salt); poly-2-propanoic acid, sodium salt; starch-γ-poly(acrylonitrile) or poly(2-propenamide co-sodium acrylate); starch / acrylonitrile copolymer; crosslinked copolymers of acrylamide and sodium acrylate; crosslinked polymers of acrylamide / sodium polyacrylate; anionic polyacrylamide; starch-grafted sodium polyacrylates; polymers of acrylic acid, sodium salt;Crosslinked potassium polyacrylate / polyacrylamide copolymers; sodium polyacrylate; laminates and composites of superabsorbent polymers; partial sodium salt of crosslinked polypropenoic acid; potassium polyacrylate, slightly crosslinked; sodium polyacrylates, slightly crosslinked; sodium polyacrylates; poly(sodium acrylate) homopolymer; polymers of polyacrylamide, carrageenan, agar, alginic acid, guar gums and their derivatives, and gellan gum; Specific superabsorbent polymers include crosslinked acrylamide and potassium acrylate copolymer. oczn Ln / zznz / e / YiAi; 4o) The method as claimed in claim 1 wherein said superabsorbent polymer is starch-g-poly (2-propenamide-co-2-propenoic acid) or salts thereof. 5o) The method as claimed in claim 1 wherein said redox catalyst system comprises cerium (+4) salts, preferably ammonium ceric nitrate; ammonium persulfate; sodium persulfate; potassium persulfate; ferrous peroxide; ferrous ammonium sulfate-hydrogen peroxide; ascorbic acid and potassium permanganate-ascorbic acid. 6o) The method as claimed in claim 1 wherein said redox catalytic system comprises ammonium persulfate, hydrogen peroxide and ascorbic acid. 7o) The method as claimed in claim 1 wherein said graft polymerization further comprises a crosslinking agent. 8o) The method as claimed in claim 1 wherein said crosslinking agent is selected from glycerides; diepoxides; diglycidyls; cyclohexadiamide; methylene bis-acrylamide; bis-hydroxyalkylamides, preferably bis-hydroxypropyl adipamide; formaldehydes, such as urea-formaldehyde and melamine-formaldehyde resins; isocyanates including di- or triisocyanates; epoxy resins. 9o) The method as claimed in claim 1 wherein said graft polymerization is carried out at room temperature. 10°) The method as claimed in claim 1 wherein said method is carried out in a continuous or batch process. 11°) The method as claimed in claim 1 wherein said superabsorbent polymer has a water absorbance capacity in the range of 500 g / g to 900 g / g. 12° ) A method for increasing the water absorption capacity of a superabsorbent polymer, wherein said superabsorbent polymer is produced by graft polymerization of a monomer onto a starch in the presence of a redox catalytic system at room temperature. 13o) A superabsorbent polymer produced by the method as claimed in any one of the preceding claims having a water absorbance capacity ranging from 500 g / g to 900 g / g.