Claims:1. A method for production of an absorbent polymer, the method comprising the steps of:
(a) dissolving a first monomer and a second monomer in a polar solvent to obtain a first mixture;
(b) adding an initiator to the first mixture under stirring maintaining a temperature ranging from 65°C to 70°C to obtain a reaction mixture;
(c) exposing the reaction mixture to a temperature ranging from 70°C to 90°C for a time period ranging from 1 hour to 6 hours;
(d) adding a catalyst to the reaction mixture from step (c) maintaining said reaction mixture at a temperature ranging from 70°C to 90°C;
(e) allowing formation of a polymer by maintaining the reaction mixture from step (d) at a temperature ranging from 25°C to 50°C for a time period ranging from 4 hours to 16 hours;
(f) adding a crosslinker to the polymer to form a gel; and
(g) drying the gel at a temperature ranging from 50°C to 180°C to obtain the absorbent polymer, said first monomer being diacetone acrylamide (DAAM) and said crosslinker being adipic acid dihydrazide (ADH).
2. The method as claimed in claim 1, wherein the first monomer is diacetone acrylamide (DAAM) and the second monomer is any of acrylic acid and acrylamide.
3. The method as claimed in claim 1, wherein the initiator is potassium persulfate (KPS).
4. The method as claimed in claim 1, wherein the catalyst includes potassium persulfate (KPS) and sodium metabisulphite (SMBS).
5. The method as claimed in claim 1, wherein the polar solvent is water.
6. The method as claimed in claim 1, wherein diacetone acrylamide (DAAM) and adipic acid dihydrazide (ADH) are in a molar ratio ranging from 1:0.1 to 1:2.
7. A super absorbent polymer (SAP) obtainable by a method comprising the steps of:
(a) dissolving a first monomer and a second monomer in a polar solvent to obtain a first mixture;
(b) adding an initiator to the first mixture under stirring maintaining a temperature ranging from 65°C to 70°C to obtain a reaction mixture;
(c) exposing the reaction mixture to a temperature ranging from 70°C to 90°C for a time period ranging from 1 hour to 6 hours;
(d) adding a catalyst to the reaction mixture from step (c) maintaining said reaction mixture at a temperature ranging from 70°C to 90°C;
(e) allowing formation of polymer by maintaining the reaction mixture from step (d) at a temperature ranging from 25°C to 50°C for a time period ranging from 4 hours to 16 hours;
(f) adding a crosslinker to the polymer to form a gel; and
(g) drying the gel at a temperature ranging from 50°C to 180°C to obtain the absorbent polymer,
said first monomer being diacetone acrylamide (DAAM), said second monomer being any of acrylic acid and acrylamide, and said crosslinker being adipic acid dihydrazide (ADH).
8. A super absorbent polymer (SAP), said super absorbent polymer (SAP) being a co-polymer of diacetone acrylamide (DAAM) and acrylic acid, said co-polymer being cross-linked with adipic acid dihydrazide (ADH).
9. The super absorbent polymer (SAP) as claimed in claim 8, wherein the super absorbent polymer (SAP) exhibits AUL ranging from 4 to 15 ml/g at 0.3 psi, absorbency ranging from 3 to 25 g/g, CRC(23° C, 0.5 hr) ranging from 5 to 30 and bulk density ranging from 0.5 to 0.9 gm/cc.
10. A super absorbent polymer (SAP), said super absorbent polymer (SAP) being a co-polymer of diacetone acrylamide (DAAM) and acrylamide, said co-polymer being cross-linked with adipic acid dihydrazide (ADH).

11. The super absorbent polymer as claimed in claim 10, wherein the super absorbent polymer exhibits AUL ranging from 4 to 15 ml/g at 0.3 psi, absorbency ranging from 3 to 25 g/g, CRC(23° C, 0.5 hr) ranging from 5 to 30 and bulk density ranging from 0.5 to 0.9 gm/cc.

, Description:TECHNICAL FIELD
[0001] The present disclosure relates generally to the field of absorbent polymers, particularly, super absorbent polymers (SAPs). More particularly, the present disclosure provides a method for production of SAP that may find utility in sanitary napkins, agricultural products, cooling gel packs and the likes.

BACKGROUND
[0002] Background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.
[0003] A superabsorbent polymer is a cross-linked partially neutralized polymer capable of absorbing large amounts of aqueous liquids and body fluids, such as urine or blood, with swelling and the formation of hydrogels, and of retaining the aqueous liquids under a certain pressure in accordance with the general definition of superabsorbent polymer. Superabsorbent polymer may be formed into particles, generally referred to as particulate superabsorbent polymer. The acronym SAP may be used in place of superabsorbent polymer, superabsorbent polymer composition, and particles hereof. A primary use of superabsorbent polymer and superabsorbent polymer compositions is in sanitary articles, such as babies' diapers, incontinence products, or sanitary towels. A comprehensive survey of superabsorbent polymers, and their use and manufacture, is given in F. L. Buchholz and A. T. Graham (editors) in “Modern Superabsorbent Polymer Technology,” Wiley-VCR, New York, 1998.
[0004] In the recent years, SAPs have attracted worldwide attention owing to their applicability in a variety of fields with liquid absorbing needs such as agriculture, personal hygiene products, waste-water treatment, horticulture, and controlled release of drugs. For instance, CN103570463A relates to a water holding slow release fertilizer comprising absorbent resin which plays an important role in improvement of soil in arid areas. Therefore, with the focus to achieve improved water absorbency, higher strength and retention capacity, considerable amount of research has been done in the direction to modify the SAP molecular structures and compositions.
[0005] Multiple methods for preparing cross-linked polymers have been devised, for example, using water-in-oil emulsified aqueous monomer solutions (or emulsion polymerization), or polymerization by suspending aqueous monomers in hydrophobic solvents. In addition, cast polymerization process is also being employed. However, such methods often mandate usage of large amounts of organic solvents, which may pose difficulty in purification and disposal. Moreover, such solvents are also highly dangerous in view of the possible accidents and plausible health hazards associated with their prolonged exposure.
[0006] In an effort to make thinner sheets of SAPs for sanitary napkins and diapers, and to meet the consumer demand of improved retention capacity, the ratio of cross-linked polymer is increased, however, this often leads to gel blocking under high fluid load. In order to increase the absorption under load (AUL), the crosslinking density has to be increased to enable SAPs to withstand the load. However, a very highly cross-linked polymer also faces the issues of insufficient permeability, non-uniform absorption and reduced water retention capacity. SAP forming material such as clays, polysachharides and polyvinyl alcohol are commonly used, but have the resultant SAP could achieve only limited success as regards the desired absorbing characteristics. Moreover, other additives such as sulfuric acid, fillers, and various inorganic materials, for example, montmorillonite and metakaolin, often result in SAPs with compromised mechanical strength after absorption, thereby making the swollen SAPs difficult to handle and transport.
[0007] CN103374094A relates to an antibacterial super absorbent polymer (SAP) and a preparation method thereof, wherein the SAP is prepared by copolymerizing and crosslinking an unsaturated amine oxide amphoteric ion monomer, an anionic monomer acrylic acid neutralized by alkali parts and an acrylamide non-ionic monomer in a redox initiation system by adopting N,N'-methylene bisacrylamide as a crosslinking agent, wherein the copolymerisation involves use of organic solvents.
[0008] US6187828B1 relates to a continuous process of making superabsorbent polymer using a variety of reaction vessel shapes containing at least 50% of volume capacity of super absorbent polymer (SAP).
[0009] US4625001 relates to a method for continuous production using a vessel provided with a plurality of mutually parallel rotary stirring shafts each fitted with stirring blades. The process includes finely dividing a water-containing gel polymer issuing from the polymerization in progress by the shearing force of stirring blades generated by the rotation of said stirring shafts while allowing the radical aqueous solution polymerization to proceed without interruption, and continuously discharging the resultant finely divided water-containing gel polymer out of said vessel.
[0010] US6500947 relates to a superabsorbent hydrogel made from sulfated polymers including cellulose, lignocellulose, and polysachharide. CN109970917A relates to a super absorbent resin and preparation method thereof comprising sodium carboxymethylcellulose] and montmorillonite.
[0011] Despite the rigorous research done in the technical field of SAPs, the conventional methods suffer from several fold shortcoming including – the issues of environment damage, high cost, and lower energy inefficiency. Moreover, the conventional processes fail to provide absorbent polymers/SAPs having high retention capacity and performance to satisfy the present demands. Consequently, there is a persistent need in the state of the art for a method that not only provides a superior quality absorbing polymer, but which is also non-polluting, energy saving and cost-efficient at both the industrial and the retail level.
[0012] Each of the documents referred in the background section are incorporated herein, in its entirety, by way of reference. Further, none of the abovementioned documents are to be construed as relevant prior-art for the invention as embodied in the present disclosure. The sole intention of referring to and providing the abovementioned documents is to highlight some of the work already done in the technical field of super absorbent polymers (SAPs).
OBJECTS OF THE INVENTION
[0013] An object of the present disclosure is to provide a method of production of SAP that alleviates one or more shortcomings associated with the conventional methods.
[0014] Another object of the present disclosure is to provide a method of production of SAP that aids in conserving energy and improves overall productivity.
[0015] Another object of the present disclosure is to provide a method of production of SAP that precludes/obviates, at least in part, requirement of usage or organic solvent(s).
[0016] Further object of the present disclosure is to provide a method of production of SAP that is economical.
[0017] Still further object of the present disclosure is to provide a process that is technically and commercially feasible.
[0018] Still further object of the present disclosure is to provide a process that affords novel SAP material(s).
[0019] Still further object of the present disclosure is to provide a new SAP material(s) that exhibits improved characteristics.
[0020] Other objects of the present invention will be apparent from the description of the invention herein below.

SUMMARY
[0021] The present disclosure relates generally to the field of absorbent polymers, particularly, super absorbent polymers (SAPs). More particularly, the present disclosure provides a method for production of SAP that may find utility in sanitary napkins, agricultural products, cooling gel packs and the likes.
[0022] An aspect of the present disclosure provides a method for production of an absorbent polymer, the method comprising the steps of: (a) dissolving a first monomer and a second monomer in a polar solvent to obtain a first mixture; (b) adding an initiator to the first mixture under stirring maintaining a temperature ranging from 65°C to 70°C to obtain a reaction mixture; (c) exposing the reaction mixture to a temperature ranging from 70°C to 90°C for a time period ranging from 1 hour to 6 hours; (d) adding a catalyst to the reaction mixture from step (c) maintaining said reaction mixture at a temperature ranging from 70°C to 90°C; (e) allowing formation of polymer by maintaining the reaction mixture from step (d) at a temperature ranging from 25°C to 50°C for a time period ranging from 4 hours to 16 hours; (f) adding a crosslinker to the polymer to form a gel; and (g) drying the gel at a temperature ranging from 50°C to 180°C to obtain the absorbent polymer, said first monomer being diacetone acrylamide (DAAM) and said crosslinker being adipic acid dihydrazide (ADH).
[0023] In an embodiment, the first monomer is diacetone acrylamide (DAAM) and the second monomer is any of acrylic acid and acrylamide. In an embodiment, the initiator is potassium persulfate (KPS). In an embodiment, the catalyst includes potassium persulfate (KPS) and sodium metabisulphite (SMBS). In an embodiment, the polar solvent is water. In an embodiment, said absorbent polymer is a super absorbent polymer (SAP). In an embodiment, diacetone acrylamide (DAAM) and adipic acid dihydrazide (ADH) are in a molar ratio ranging from 1:0.1 to 1:2, preferably, in a molar ratio ranging from 1:0.4 to 1:2, more preferably, in a molar ratio ranging from 1:0.5 to 1:2 and most preferably in a molar ratio of about 1:1. In an embodiment, the initiator is in an amount ranging from 0.05 to 10% by weight, preferably, in an amount ranging from 0.1 to 5% by weight, and more preferably, in an amount ranging from 0.5 to 1% by weight. In an embodiment, the catalyst is in an amount ranging from 0.025 to 10% by weight, preferably, in an amount ranging from 0.05 to 5% by weight, and more preferably, in an amount ranging from 0.1 to 1% by weight.
[0024] Another aspect of the present disclosure relates to a super absorbent polymer (SAP) obtainable by a method comprising the steps of: (a) dissolving a first monomer and optionally, a second monomer in a polar solvent to obtain a first mixture; (b) adding an initiator to the first mixture under stirring maintaining a temperature ranging from 65°C to 70°C to obtain a reaction mixture; (c) exposing the reaction mixture to a temperature ranging from 70°C to 90°C for a period of time ranging from 1 hour to 6 hours; (d) adding a catalyst to the reaction mixture from step (c) maintaining said reaction mixture at a temperature ranging from 70°C to 90°C; (e) allowing formation of polymer by maintaining the reaction mixture from step (d) at a temperature ranging from 25°C to 50°C for a time period ranging from 4 hours to 16 hours; (f) adding a crosslinker to the polymer to form a gel; and (g) drying the gel at a temperature ranging from 50°C to 180°C to obtain the absorbent polymer, said first monomer being diacetone acrylamide (DAAM), said second monomer being any of acrylic acid and acrylamide and said crosslinker being adipic acid dihydrazide (ADH).
[0025] Further aspect of the present disclosure provides a super absorbent polymer (SAP), said super absorbent polymer (SAP) being a co-polymer of diacetone acrylamide (DAAM) and acrylic acid, said co-polymer being cross-linked with adipic acid dihydrazide (ADH). In an embodiment, the super absorbent polymer (SAP) exhibits AUL ranging from 4 to 15 ml/g at 0.3 psi. In an embodiment, the super absorbent polymer (SAP) exhibits absorbency ranging from 3 to 25 g/g. In an embodiment, the super absorbent polymer (SAP) exhibits CRC(23° C, 0.5 hr) ranging from 5 to 30. In an embodiment, the super absorbent polymer (SAP) exhibits bulk density ranging from 0.5 to 0.9 gm/cc.
[0026] Still further aspect of the present disclosure provides a super absorbent polymer (SAP), said super absorbent polymer (SAP) being a co-polymer of diacetone acrylamide (DAAM) and acrylamide, said co-polymer being cross-linked with adipic acid dihydrazide (ADH). In an embodiment, the super absorbent polymer (SAP) exhibits AUL ranging from 4 to 15 ml/g at 0.3 psi. In an embodiment, the super absorbent polymer (SAP) exhibits absorbency ranging from 3 to 25 g/g. In an embodiment, the super absorbent polymer (SAP) exhibits CRC(23° C, 0.5 hr) ranging from 5 to 30. In an embodiment, the super absorbent polymer (SAP) exhibits bulk density ranging from 0.5 to 0.9 gm/cc.

DETAILED DESCRIPTION
[0027] The following is a detailed description of embodiments of the disclosure depicted in the accompanying drawings. The embodiments are in such detail as to clearly communicate the disclosure. However, the amount of detail offered is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present disclosure as defined by the appended claims.
[0028] Each of the appended claims defines a separate invention, which for infringement purposes is recognized as including equivalents to the various elements or limitations specified in the claims. Depending on the context, all references below to the “invention” may in some cases refer to certain specific embodiments only. In other cases it will be recognized that references to the “invention” will refer to subject matter recited in one or more, but not necessarily all, of the claims.
[0029] As used in the description herein and throughout the claims that follow, the meaning of “a,” “an,” and “the” includes plural reference unless the context clearly dictates otherwise. Also, as used in the description herein, the meaning of “in” includes “in” and “on” unless the context clearly dictates otherwise.
[0030] All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g. “such as”) provided with respect to certain embodiments herein is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention otherwise claimed. No language in the specification should be construed as indicating any non-claimed element essential to the practice of the invention.
[0031] Various terms as used herein are shown below. To the extent a term used in a claim is not defined below, it should be given the broadest definition persons in the pertinent art have given that term as reflected in printed publications and issued patents at the time of filing.
[0032] The term “SAP” or “superabsorbent polymer” as used herein synonymously and interchangeably, throughout the present disclosure, denotes natural, semi-synthetic or synthetic polymeric materials that can absorb large amount of a liquid relative to its own mass. Such superabsorbent polymer (SAP) may be water-swellable, water-insoluble organic or inorganic materials including superabsorbent polymers and superabsorbent polymer compositions capable, under the most favorable conditions, of absorbing at least about 3 times their weight, or at least about 10 times their weight, or at least about 20 times their weight in an aqueous solution containing 0.9 weight percent sodium chloride.
[0033] The term “Absorption Under Load” or “AUL” as used herein synonymously and interchangeably, throughout the present disclosure, is a measure of the ability of a superabsorbent polymer to absorb fluid under an applied pressure and is stated as ml of liquid absorbed per gram weight of the sample (ml/g) at an applied pressure. AUL is determined using the procedure as set out in ISO 17190 – Part 7.
[0034] The term “Centrifuge Retention Capacity” or “CRC” as used herein synonymously and interchangeably, throughout the present disclosure, is the ability of the particulate superabsorbent polymer (SAP) to retain liquid therein after being saturated and subjected to centrifugation under controlled conditions and is stated as ml of liquid retained per gram weight of the sample (ml/g). CRC is determined using the procedure as set out in ISO 17190 – Part 6.
[0035] The term “acrylic acid” or “acrylic acid monomer” as used herein synonymously and interchangeably throughout the present disclosure denotes the acrylic acid monomers, glacial acrylic acid monomers, salt of acrylic acid monomers such as monovalent metal salts, divalent metal salts, ammonium salts or organic amine salts of acrylic acid and the like monomers with acrylate moiety that may find utility in preparation of the polymer as detailed herein.
[0036] The present disclosure relates generally to the field of absorbent polymers, particularly, super absorbent polymers (SAPs). More particularly, the present disclosure provides a method for production of SAP that may find utility in sanitary napkins, agricultural products, cooling gel packs and the likes.
[0037] An aspect of the present disclosure provides a method of preparing an absorbent polymer, the method comprising the steps of: (a) dissolving a first monomer and a second monomer in a polar solvent to obtain a first mixture; (b) adding, an initiator to the first mixture under stirring maintaining a temperature ranging from 65°C to 70°C to obtain a reaction mixture; (c) exposing the reaction mixture to a temperature ranging from 70°C to 90°C for a time period ranging from 1 hour to 6 hours; (d) adding a catalyst to the reaction mixture from step (c) maintaining said reaction mixture at a temperature ranging from 70°C to 90°C; (e) allowing formation of a polymer by maintaining the reaction mixture from step (d) at a temperature ranging from 25°C to 50°C for a time period ranging from 4 hours to 16 hours; (f) adding a crosslinker to the polymer to form a gel; and (g) drying the gel at a temperature ranging from 50°C to 180°C to obtain the absorbent polymer, said first monomer being diacetone acrylamide (DAAM) and said crosslinker being adipic acid dihydrazide (ADH). In an embodiment, said absorbent polymer is a super absorbent polymer (SAP).
[0038] In an embodiment, the first monomer is diacetone acrylamide (DAAM) and the second monomer is acrylic acid, wherein the said polymer is a co-polymer of diacetone acrylamide (DAAM) and acrylic acid. In an embodiment, the first monomer is diacetone acrylamide (DAAM) and the second monomer is acrylamide, wherein the said polymer is a co-polymer of diacetone acrylamide (DAAM) and acrylamide. In an embodiment, diacetone acrylamide (DAAM) is used an amount ranging from 1 to 50 wt.% with respect to the total weight of the monomers, preferably, in an amount ranging from 1.5 to 35 wt. %, more preferably, in an amount ranging from 2 to 20 wt. % and most preferably, in an amount ranging from 2.5 to 10 wt. %. In an embodiment, acrylic acid is used an amount ranging from 50 to 99 wt.% with respect to the total weight of the monomers, preferably, in an amount ranging from 70 to 98 wt. %. In an embodiment, acrylamide is used an amount ranging from 50 to 99 wt.% with respect to the total weight of the monomers, preferably, in an amount ranging from 70 to 98 wt. %.
[0039] In an embodiment, the initiator is potassium persulfate (KPS). However, any other initiator as known to or appreciated by a person skilled in the art can also be used in the process of the instant disclosure. In an embodiment, the initiator is added in an amount ranging from 0.05 to 10% by weight, preferably, in an amount ranging from 0.1 to 5% by weight, and more preferably, in an amount ranging from 0.5 to 1% by weight of the monomer.
[0040] In an embodiment, the catalyst includes potassium persulfate (KPS) and sodium metabisulphite (SMBS). A person skilled in the art would realize that addition of catalyst may aid in reactivating the unreacted monomers and thus help in decreasing the free monomer content of the resultant polymer, and consequently, any suitable catalyst as known to or appreciated by the skilled person can also be used in the process of the instant disclosure. In an embodiment, the catalyst is in an amount ranging from 0.025 to 10% by weight, preferably, in an amount ranging from 0.05 to 5% by weight, and more preferably, in an amount ranging from 0.1 to 1% by weight of the monomer.
[0041] In an embodiment, the polar solvent is water. Advantageously, the method of the present disclosure precludes the necessity of usage of organic solvent(s). However, if desired one can use any other conventionally known polar solvent without detriment to the method of the present disclosure.
[0042] In an embodiment, diacetone acrylamide (DAAM) and adipic acid dihydrazide (ADH) are used in a molar ratio ranging from 1:0.1 to 1:2, preferably, in a molar ratio ranging from 1:0.4 to 1:2, more preferably, in a molar ratio ranging from 1:0.5 to 1:2 and most preferably in a molar ratio of about 1:1.
[0043] In an embodiment, the first mixture is neutralized to a pH ranging from 5.5 to 7.5 before addition of the initiator thereto. In an embodiment, the first mixture is neutralized by addition of an aqueous solution of a base thereto. In an embodiment, the first mixture is neutralized by addition of 50% w/w solution of NaOH under stirring.
[0044] In an embodiment, the gel has a solid content ranging from 5 to 50 wt.% with respect to total weight of the gel, preferably, ranging from 7 to 40 wt.% and more preferably, ranging from 8 to 31 wt.%.
[0045] In an embodiment, the absorbent polymer has a particle size ranging from 140 to 860 microns, preferably, ranging from 145 to 855 microns.
[0046] In an embodiment, the absorbent polymer has a moisture content ranging from 1 to 15% by weight of the absorbent polymer, preferably, ranging from 2 to 13% and more preferably, ranging from 2.9 to 11%.
[0047] In an embodiment, the step of drying the gel is done for a time period ranging from 6 to 72 hours at a temperature ranging from 50°C to 180°C, preferably, for a time period ranging from 40 to 52 hours in an oven or in vacuum. For example, the gel can be dried in an oven at a temperature ranging from 80°C to 130°C for a time period ranging from 20 to 72 hours. If vacuum is applied, the drying can be effected at a temperature, for example, ranging from 50°C to 110°C for a time period ranging from 6 to 48 hours.
[0048] The method of the present disclosure involves: (a) dissolving diacetone acrylamide (DAAM) and acrylic acid (or acrylamide) in water to obtain a first mixture; (b) adding an initiator to the first mixture under stirring maintaining a temperature ranging from 65°C to 70°C to obtain a reaction mixture and to initiate the polymerization reaction; (c) allowing the polymerization reaction to continue by exposing the reaction mixture to a temperature ranging from 70°C to 90°C for a time period ranging from 1 hour to 6 hours; (d) adding a catalyst to the reaction mixture from step (c) maintaining said reaction mixture at a temperature ranging from 70°C to 90°C, which may aid in reactivating the monomers, and which in turn aid in reduction of content of free monomer in the resultant polymer, reducing the need of or precluding the need of post reaction processes such as vacuum application or extraction for free monomer removal; (e) allowing formation of polymer by maintaining the reaction mixture from step (d) at a temperature ranging from 25°C to 50°C for a time period ranging from 4 hours to 16 hours; (f) adding a crosslinker to the polymer affording a cross-linked polymer, forming a gel; and (g) drying the gel at a temperature ranging from 50°C to 180°C to obtain the absorbent polymer.
[0049] Without wishing to be bound by the theory, it is believed that diacetone acrylamide (DAAM) is monofunctional (one reactive ketonic group on one molecule, other being sterically hindered does not take part in the cross-linking reaction), and adipic acid dihydrazide (ADH) is difunctional (each molecule has 2 reactive –NH2 groups), and the cross-linking reaction between the co-polymer of DAAM/acrylic acid or DAAM/acrylamide with ADH may proceed as depicted hereunder:

[0050] It could further be noted during the experiments that usage of the crosslinker in excess affords complete dispersion of the polymer and the crosslinker solution, and increases the kinetic probability of reaction leading to the increased cross-linking. Increased cross-linking may, in turn, result in improved absorption properties of the resultant absorbent polymer/SAP.
[0051] It could also be noted that the advantageous absorbent polymer/super absorbent polymer (SAP) produced by the method of the present disclosure exhibits AUL ranging from 4 to 15 ml/g at 0.3 psi, absorbency ranging from 3 to 25 g/g and CRC(23° C, 0.5 hr) ranging from 5 to 30. The absorbent polymer/super absorbent polymer (SAP) so produced exhibits bulk density ranging from 0.5 to 0.9 gm/cc.
[0052] Accordingly, another aspect of the present disclosure relates to a super absorbent polymer (SAP) obtainable by a method comprising the steps of: (a) dissolving a first monomer and a second monomer in a polar solvent to obtain a first mixture; (b) adding an initiator to the first mixture under stirring maintaining a temperature ranging from 65°C to 70°C to obtain a reaction mixture; (c) exposing the reaction mixture to a temperature ranging from 70°C to 90°C for a time period ranging from 1 hour to 6 hours; (d) adding a catalyst to the reaction mixture from step (c) maintaining said reaction mixture at a temperature ranging from 70°C to 90°C; (e) allowing formation of polymer by maintaining the reaction mixture from step (d) at a temperature ranging from 25°C to 50°C for a time period ranging from 4 hours to 16 hours; (f) adding a crosslinker to the polymer to form a gel; and (g) drying the gel at a temperature ranging from 50°C to 180°C to obtain the absorbent polymer, said first monomer being diacetone acrylamide (DAAM), said second monomer being any of acrylic acid and acrylamide, and said crosslinker being adipic acid dihydrazide (ADH).
[0053] Another aspect of the present disclosure relates to a super absorbent polymer (SAP) obtainable by a method comprising the steps of: (a) dissolving a first monomer and optionally, a second monomer in a polar solvent to obtain a first mixture; (b) adding an initiator to the first mixture under stirring maintaining a temperature ranging from 65°C to 70°C to obtain a reaction mixture; (c) exposing the reaction mixture to a temperature ranging from 70°C to 90°C for a period of time ranging from 1 hour to 6 hours; (d) adding a catalyst to the reaction mixture from step (c) maintaining said reaction mixture at a temperature ranging from 70°C to 90°C; (e) allowing formation of polymer by maintaining the reaction mixture from step (d) at a temperature ranging from 25°C to 50°C for a time period ranging from 4 hours to 16 hours; (f) adding a crosslinker to the polymer to form a gel; and (g) drying the gel at a temperature ranging from 50°C to 180°C to obtain the absorbent polymer, said first monomer being diacetone acrylamide (DAAM), said second monomer being any of acrylic acid and acrylamide and said crosslinker being adipic acid dihydrazide (ADH).
[0054] Further aspect of the present disclosure provides a super absorbent polymer (SAP), said super absorbent polymer (SAP) being a co-polymer of diacetone acrylamide (DAAM) and acrylic acid, said co-polymer being cross-linked with adipic acid dihydrazide (ADH). In an embodiment, the super absorbent polymer (SAP) exhibits AUL ranging from 4 to 15 ml/g at 0.3 psi. In an embodiment, the super absorbent polymer (SAP) exhibits absorbency ranging from 3 to 25 g/g. In an embodiment, the super absorbent polymer (SAP) exhibits CRC(23° C, 0.5 hr) ranging from 5 to 30. In an embodiment, the super absorbent polymer (SAP) exhibits bulk density ranging from 0.5 to 0.9 gm/cc.
[0055] Still further aspect of the present disclosure provides a super absorbent polymer (SAP), said super absorbent polymer (SAP) being a co-polymer of diacetone acrylamide (DAAM) and acrylamide, said co-polymer being cross-linked with adipic acid dihydrazide (ADH). In an embodiment, the super absorbent polymer (SAP) exhibits AUL ranging from 4 to 15 ml/g at 0.3 psi. In an embodiment, the super absorbent polymer (SAP) exhibits absorbency ranging from 3 to 25 g/g. In an embodiment, the super absorbent polymer (SAP) exhibits CRC(23° C, 0.5 hr) ranging from 5 to 30. In an embodiment, the super absorbent polymer (SAP) exhibits bulk density ranging from 0.5 to 0.9 gm/cc.
[0056] While the foregoing describes various embodiments of the invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof. The scope of the invention is determined by the claims that follow. The invention is not limited to the described embodiments, versions or examples, which are included to enable a person having ordinary skill in the art to make and use the invention when combined with information and knowledge available to the person having ordinary skill in the art.
EXAMPLES
[0057] EXAMPLE 1
[0058] Method of preparing absorbent polymer/SAP
[0059] An absorbent polymer/SAP was prepared by following method: Step 1: A reactor assembly was set up; a heating coil was immersed in a water bath having water level little above the recator reactant quantity level; the reactor was put in the water bath and the height of the overhead was adjusted; a temperature probe was then dipped in the reactor and water bath and fastened; and the necks of the lid were closed with a stopper, when not required. Step 2: A 50% w/w aqueous solution of NaOH was prepared by dissolving appropriate amounts of NaOH pellets in de-ionised water with stirring on a magnetic stirrer. Step 3: A solution of acrylic acid (or acrylamide) and diacetone acrylamide (DAAM) was prepared with de-ionised water to obtain a first mixture; the first mixture was neutralized by adding the NaOH solution in the first mixture with stirring to adjust the pH of about 6. Step 4: The reaction solution obtained in step 3 was then added to the reactor assembly set in step 1, keeping stirring speed of 200 to 250 rpm and water bath temperature of 80oC. Step 5: A solution of potassium persulfate (initiator) was prepared in water and slowly transferred to the solution of step 4 having temperature 67oC to obtain a reaction mixture. Step 6: The polymerization reaction in the reacting mixture was allowed to take place for next 1 hour. Subsequently, it was allowed to cook for 4 hours at 80oC temperature. Step 7: Two separate solutions of sodium metabisulfite and potassium persulfate (catalyst) were prepared by dissolving appropriate quantities of sodium metabisulfite and potassium persulfate in water and the same were added to the solution obtained in step 6 at 80oC temperature with constant stirring. The reaction mixture was further kept for cooking overnight at an ambient temperature of about 35°C to obtain a polymer and solid content of the polymer was determined. Step 8: A solution of adipic acid dihydrazide (crosslinker, ADH) was prepared by dissolving it in de-ionised water, and this crosslinker solution was added to the polymer from step 7, to a form a gel. Step 9: The gel was dried in an oven at 105oC for about 48 hours to form a brittle cake of the absorbent polymer/SAP. The cake was then ground and sieved to obtain absorbent polymer/SAP particles having size in the range of 140-860µ.
[0060] EXAMPLE 2
[0061] By following the method as detailed in Example 1 above, different absorbent polymers/SAPs were prepared varying the amount of acrylic acid (AAc), diacetone acrylamide (DAAM), potassium persulfate initiator (KPS), as shown in Table 1 below. Total amount of monomer content (AAc and DAAM) was kept at 30g, with the percentage of DAAM varying between 0% to 50% by weight of the total monomer content. The DAAM:ADH ratio was maintained at 1:0.5 and 1:1 by adding appropriate amounts of ADH. The KPS initator concentration was maintained at 0.3 g per 10 g water (indicated as “0.3/10” in the table) i.e. 1% by weight of the monomer. Neutralization was done with aqueous solution of NaOH. A solution of KPS and SMBS having 0.2 g of each of KPS and SMBS in 20 g water (indicated as “0.2/10”) was added as the catalyst i.e. 0.67% of each of KPS and SMBS by weight of the monomer. The pH was recorded for the de-ionised water, acrylic acid solution, and after neutralization with NaOH. The solid content of the polymer before crosslinking and after crosslinking (with ADH) was measured and compared.
Table 1: Preparation of different absorbent polymers/SAPs
Exp No 1 2 3 4 5 6 7 8
DAAM% 0 1.5 3.3 3.3 5 10 20 50
Acrylic acid (AAc) [g] 30 29.55 29 29 28.5 27 24 15
Diacetone acrylamide DAAM(g) 0 0.45 1 1 1.5 3 6 15
RO water [g] 216 217 218 218 218 219 222 228
Initiator (KPS) [g]/DIW 0.3/10 0.3/10 0.3/10 0.15/10 0.3/10 0.3/10 0.3/10 0.3/10
Catalyst (KPS) & (SMBS) [g]/DIW 0.2/10 0.2/10 0.2/10 0.2/10 0.2/10 0.2/10 0.2/10 0.2/10 0.2/10 0.2/10 0.2/10 0.2/10 0.2/10 0.2/10 0.2/10 0.2/10
NaOH [g]/DIW (70% neutralization) 11.5/23 11.5/23 11.3/22 11.3/22 11.1/22 10.5/21 9.3/18 5.8/12
Solid content (%) 13.9 13.9 21.1 21.1 17.6 15.3 17.5 13.3
Adipicdihyrazide (ADH) (g) 0.1 0.1 0.3 0.3 0.5 0.8 1.8 3.4
Solid content after cross linking (%) 14.5 14.5 17.2 17.2 14.8 10.9 16.2 13.12

[0062] It could be noted that sample 1 (having only acrylic acid, without DAAM and crosslinker) was soluble in water. Samples 2 to 8 prepared using acrylic acid, DAAM and ADH were tested for their properties such as moisture content, absorbency, absorption under load (AUL), centrifuge retention capacity (CRC), pH and bulk density. The results obtained for the absorbent polymers/SAPs having DAAM:ADH ratio 1:0.5 and 1:1 are given in Table 2 and Table 3, respectively, wherein pH was determined in accordance with ISO 17190 – Part 1, amount of residual monomers was determined in accordance with ISO 17190 – Part 2, particle size distribution by sieve fractionation was determined in accordance with ISO 17190 – Part 3, moisture content (%) by mass loss upon heating was determined in accordance with ISO 17190 – Part 4, Gravimetric determination of free swell capacity in saline solution (Absorbency) was done in accordance with ISO 17190 – Part 5, Gravimetric determination of fluid retention capacity in saline solution after centrifugation (CRC) was done in accordance with ISO 17190 – Part 6, Gravimetric determination of absorption under pressure (AUL) (0.3 psi) was done in accordance with ISO 17190 – Part 7, and Gravimetric determination of density (bulk density) was done in accordance with ISO 17190 – Part 9.
Table 2: Properties of absorbent polymers/SAPs (DAAM:ADH – 1:0.5)
Sample number DAAM% (DAAM: ADH) Moisture (%) pH Absorbency (g/g) AUL (ml/g) Bulk Density (g/cc) CRC (ml/g)
2
1.5 (1:0.5) 7.9 5.8 10.3 4.1 0.7 9.2
3 3.3 (1:0.5) 9.1 5.8 9.8 5.5 0.8 7.8
5 5 (1:0.5) 4.5 5.9 10.9 9.2 0.8 8.6
6 10 (1:0.5) 13.6 6.0 11.4 11.4 0.8 9.4
7 20 (1:0.5) 9.1 5.8 9.5 9.9 0.9 9.6
8 50 (1:0.5) 11.2 5.9 5.3 8.6 0.8 5.4

Table 3: Properties of absorbent polymers/SAPs (DAAM:ADH – 1:1)
Sample
number DAAM% (DAAM: ADH) Moisture (%) pH Absorbency (g/g) AUL (ml/g) Bulk Density (g/cc) CRC (ml/g)
9 1.5 (1:1) 4.9 5.9 20.3 3.3 0.8 18.0
10 3.3 (1:1) 4.5 6.0 22.8 10.2 0.7 21.5
11 5 (1:1) 4.0 6.0 22.3 10.5 0.8 17.6
12 10 (1:1) 4.8 6.0 21.5 10.0 0.7 18.9
13 20 (1:1) 4.8 6.0 16.1 11.5 0.7 14.6
14 50 (1:1) 4.0 6.1 6.7 9.0 0.6 6.9

[0063] It could be observed that absorbent polymers/SAPs prepared using DAAM:ADH in a molar ratio of 1:1 have lesser percentage of moisture, better absorbency, better AUL and better CRC as compared to the absorbent polymers/SAPs prepared using DAAM:ADH in a molar ratio of 1:0.5. Further, the absorbent polymers/SAPs prepared using DAAM:ADH in a molar ratio of 1:1 exhibits pH of about 6, have less bulk density (as compared to the absorbent polymers/SAPs prepared using DAAM:ADH in a molar ratio of 1:0.5) and have free monomer content of less than about 15 ppm.
[0064] It could further be observed that amongst the absorbent polymers/SAPs prepared using DAAM:ADH in a molar ratio of 1:1, the SAP having 3.3% DAAM (Sample 10) exhibit highest values of absorbency of about 22.8 g/g and CRC of about 21.5 ml/g. FIG. 1 illustrates exemplary comparative IR spectra of Sample 3 and 10. Further experiments were conducted keeping the DAAM:ADH molar ratio at 1:1 and using 3.3% DAAM while varying the amount of initiator (KPS). Table 4 below provides characteristics of the resultant polymers/SAPs, wherein, it could be noted that Sample 10 was showing better characteristics.
Table 4: Characteristics of the polymers/SAPs
Sample number DAAM% (DAAM: ADH) Initiator % Moisture
(%) pH Absorbency
(g/g) AUL (ml/g) Bulk Density
(g/cc) CRC
(ml/g)
10 3.3 (1:1) 1.0% 4.5 6.0 22.8 10.2 0.7 21.5
15 3.3 (1:1) 0.5% 5.6 5.8 11.2 4.2 0.7 8.4

[0065] The dried and ground SAP (Sample 10) was also subjected for particle size distribution study, result whereof is provided in the Table 5 below:
Table 5: Particle Size Distribution
Particle Size Range Approx. wt%
<150 µm 2
<200 µm & >150 µm 5
<300 µm & >200 µm 6
<400 µm & >300 µm 18
<500 µm & >400 µm 23
<600 µm & >500 µm 23
<710 µm & >600 µm 22
<850 µm & >710 µm 1

[0066] During the course of experiments, it could further be noted that the polymer formed using only DAAM as monomer i.e. the polymer - poly(DAAM) is water insoluble, while poly(acrylic acid) and sodium salt of poly(acrylic acid) are water soluble.
[0067] EXAMPLE 3
[0068] By following the method as detailed in Example 1 above, different absorbent polymers/SAPs were prepared using acrylamide and diacetone acrylamide (DAAM) as monomers. The total monomer amount was kept at 15 g, wherein wt. % of DAAM was varied at 0.5g (3.3%) and 1g (6.67%) by weight of the total monomers. The properties of the resultant absorbent polymers/SAPs including retention capacity, absorbency, absorption under load, residual monomer amount and polymer particle size were measured. Table 6 below provides details of the parameters and properties of the resultant polymers.
Table 6: Parameters and Properties of the resultant polymers
Parameter/property Sample 17 Sample 18
Acrylamide [g] 14.5 14
Diacetone acrylamide (DAAM) [g] 0.5 1
RO water [g] (de-ionized water) 150 150
Initiator (KPS & SMBS) [g] 0.08/5 0.08/5 0.08/5 0.08/5
Solid content (%) 13.4 9.1
Adipic acid dihydrazide (ADH) [g]
(DAAM : ADH 1 : 1) 0.42/20 0.63/20
Solid content (%) [after crosslinking] 11.22 8.24
Moisture content (%) 10.9 3.0
Retention capacity (ml/g) 31.0 30.8
Absorbency (g/g) 29.3 4.8
Absorption under load (0.3 psi) [ml/g] 18.5 6.5
Bulk density (g/cc) 0.7 0.8
Residual monomer (ppm) <10 <10
Particle size (µ) 150 to 700 150 to 700
pH 5.8 4.9

[0069] It could be noted that Sample 17 having 3.3% DAAM showed better results for absorbency and absorbency under load (AUL), while sample 18 having 6.67% DAAM had much reduced moisture content of about 3%. Both the samples exhibited comparable retention capacity, bulk density and particle size. The free monomer content was also appreciably less with only <10 ppm.
[0070] Although the subject matter has been described herein with reference to certain preferred embodiments thereof, other embodiments are possible. As such, the spirit and scope of the appended claims should not be limited to the description of the preferred embodiment contained therein. Furthermore, precise and systematic details on all above aspects are currently being made. Work is still underway on this invention. It will be obvious to those skilled in the art to make various changes, modifications and alterations to the invention described herein. To the extent that these various changes, modifications and alterations do not depart from the scope of the present invention, they are intended to be encompassed therein.

ADVANTAGES
[0071] The present disclosure provides a method of production of SAP that precludes/obviates, at least in part, requirement of usage or organic solvent(s)
[0072] The present disclosure provides a method of production of SAP that conserves energy and improves overall productivity.
[0073] The present disclosure provides a method of production of SAP that is economical.
[0074] The present disclosure provides a method that is technically and commercially feasible.
[0075] The present disclosure provides new SAP(s) that exhibit improved characteristics.