DESC:TECHNICAL FIELD
[0001] The present disclosure relates generally to the field of super absorbent polymers (SAPs). More particularly, the present disclosure provides an improved method for processing of polyacrylate SAP fines.

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 crosslinked partially neutralized polymer, including crosslinked polyacrylic acids, 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] Typically, the polyacrylate superabsorbent polymers (SAPs) are made at an industrial scale by reacting vinyl carboxylic acid monomer or sodium salt of vinyl carboxylic acid with a cross-linker of different chain lengths to produce the polyacrylate superabsorbent polymers (SAPs). These SAP particles exhibit wide range of particle size distribution, wherein typically 5-15% of particles may have particle size of less than 150 microns. Such particles (with particle size less than 150 micron) are called “polyacrylate fines”. The polyacrylate fines differ significantly from the SAP particles in terms of its Absorption Under Load (AUL), Centrifuge Retention Capacity (CRC) and the like properties and hence, generally cannot be utilized directly in preparation of the end product. This leads to production of significant amount of wastage that contributes toward significant loss of energy and productivity.
[0005] Accordingly, there remained a need in the state of art for a method of processing of polyacrylate fines to produce polyacrylate SAP therefrom.

OBJECTS OF THE INVENTION
[0006] An object of the present disclosure is to provide a method of processing of polyacrylate fines to produce polyacrylate SAP therefrom.
[0007] Another object of the present disclosure is to provide a method of processing of polyacrylate fines to produce polyacrylate SAP therefrom that can be utilized directly in preparation of the end product.
[0008] Another object of the present disclosure is to provide a method of processing of polyacrylate fines to produce polyacrylate SAP therefrom that aids in reduction of wastage, conserves energy and improves overall productivity.
[0009] Further object of the present disclosure is to provide a method of processing of polyacrylate fines that is economical.
[0010] Yet another object of the present invention is to provide a process that is technically and commercially feasible.
[0011] Other objects of the present invention will be apparent from the description of the invention herein below.

SUMMARY
[0012] The present disclosure relates generally to the field of super absorbent polymers (SAPs). More particularly, the present disclosure provides an improved method for processing of polyacrylate SAP fines. Aspects of the present disclosure provide method of processing of polyacrylate fines to produce polyacrylate SAP particles therefrom.
[0013] An aspect of the present disclosure provides a method of processing polyacrylate fines to produce polyacrylate SAP particles, said method including the steps of : (a) taking polyacrylate fines, wherein at least 80% of the particles exhibit particle size of less than 150 micron; (b) effecting agglomeration of said polyacrylate fines to produce agglomerated particles, wherein at least 80% of the agglomerated particles exhibit particle size ranging from 150 micron to 850 micron; and (c) effecting surface crosslinking of said agglomerated particles to produce the polyacrylate SAP particles, wherein said polyacrylate SAP particles exhibit Absorption Under Load (AUL) of more than 19 g/g at 0.3 psi. In an embodiment, the polyacrylate SAP particles exhibit Absorption Under Load (AUL) of more than 20 g/g at 0.3 psi. In an embodiment, the polyacrylate SAP particles exhibit free swelling of more than 45 g/g in 0.9 Nacl Solution.
[0014] In an embodiment, the step of effecting agglomeration of the polyacrylate fines to produce agglomerated particles includes chemical agglomeration of SAP fines. In an embodiment, the chemical agglomeration is effected by treating the polyacrylate fines with a solution of crosslinking agent. In an embodiment, the step of treating the polyacrylate fines with a solution of crosslinking agent comprises spraying the solution of crosslinking agent onto the polyacrylate fines. In an embodiment, the solution of crosslinking agent is prepared by dissolving the crosslinking agent in an aqueous solvent. In an embodiment, the solution of crosslinking agent is prepared by dispersing the crosslinking agent in an aqueous solvent. In an embodiment, the solution of crosslinking agent comprises less than 20% v/v of water. In an embodiment, the solution of crosslinking agent comprises equal to or less than 10% v/v of water. In an embodiment, the solution of crosslinking agent is sprayed onto the polyacrylate fines for less than 3 minutes.
[0015] In an embodiment, the crosslinking agent is one or a combination of polyols such as polyether polyols. In an embodiment, the polyether polyols exhibit molecular weight of less than 2000. In an embodiment, the step of effecting agglomeration of the polyacrylate fines to produce agglomerated particles further includes exposing the agglomerated particles to a high temperature. In an embodiment, the step of exposing the agglomerated particles to a high temperature includes exposing the agglomerated particles to a temperature of more than 170°C for a time period ranging from 30 minutes to 60 minutes. In an embodiment, the step of exposing the agglomerated particles to a high temperature includes exposing the agglomerated particles to a temperature of more than 170°C for about 40 minutes.
[0016] In an embodiment, the step of effecting surface crosslinking of said agglomerated particles to produce the polyacrylate SAP particles includes treating the agglomerated particles with a surface cross-linker composition. In an embodiment, the surface cross-linker composition comprises a surface cross-linker in a concentration ranging from 0.1% to 3% by dry weight of the agglomerated particles. In an embodiment, the surface cross-linker composition comprises a surface cross-linker in a concentration ranging from 0.1% to 0.5% by dry weight of the agglomerated particles. In an embodiment, the surface cross-linker is selected from any or a combination of cyclic carbonate esters, di-functional alcohols and tri-functional alcohols. In an embodiment, the surface cross-linker is an in-situ product generated by reaction between glycerol and ethylene carbonate at a temperature ranging from 150oC to 200oC. In an embodiment, the surface cross-linker composition includes less than 10% of water by dry weight of the agglomerated particles. In an embodiment, the surface cross-linker composition includes less than 5% of water by dry weight of the agglomerated particles.

DETAILED DESCRIPTION
[0017] 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.
[0018] 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.
[0019] 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.
[0020] 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.
[0021] 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.
[0022] 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 10 times their weight, or at least about 15 times their weight, or at least about 25 times their weight in an aqueous solution containing 0.9 weight percent sodium chloride.
[0023] 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 grams of liquid absorbed per gram weight of the sample (g/g) at an applied pressure.AUL is determined as follows: 0.9 g of weighed SAP sample is placed in a plastic cylinder having inner diameter of 6 cm and height of 5 cm with a nylon screen fabric (mesh size 400 mesh) at bottom. The SAP particles are uniformly dispersed and initial weight of the setup was measured (A). A Teflon made plastic plate with a metal piston is placed on test substance. Thereafter, the entire testing setup is placed on a ceramic filter plate (porosity=0) covered with a Whatman filter paper (porosity =25) and soaked with 0.9% NaCl solution upto top edge of filter plate and the SAP sample is allowed to absorb liquid for 60 minutes. Afterwards, the testing set up is slowly moved out of NaCl solution and gently remove the wet SAP sample which is stuck to the Teflon plate. The weight of the swollen testing setup without Teflon plate and metal piston was recorded (B). The gram amount of the NaCl solution that had been retained per gram of sample was calculated according to the following equation:
AUL=
Where AUL is in g/g at 0.3 psi and C is the actual weight of SAP sample in grams.
[0024] 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 grams of liquid retained per gram weight of the sample (g/g). CRC testing may be conducted at an assigned testing temperature for an assigned period of testing time, noted as CRC (testing temperature, testing time). For example, CRC (23° C, 0.5 hr) refers to a CRC with a testing temperature of about 23°Cand a testing time of 0.5 hour. CRC of SAP samples is determined by standard method no. ISO 17190-6. 0.2 g of weighed SAP samples are placed in non-woven bags of dimension 6 cm X 8 cm and submerged in beaker containing 0.9% NaCl solution for half an hour. Empty bags are used as controls and treated in similar way. The bags are then placed in centrifuge basket and centrifuged at 250 g for 3 min. The bags are removed and weighed. CRC of the samples are measured by using following equation:
CRC = (w1 – w2 –w3) / w3
Where, w1 is the weight of wet sample and bag, w2 is the weight of empty bag and w3 is the weight of dry sample.
[0025] Free swelling is the ability of the particulate superabsorbent polymer (SAP) to absorb the liquid and is expressed as grams of liquid absorbed per gram weight of the sample (g/g). The free swelling capacity of SAP is measured by standard method no. ISO 17190-5. The procedure is same as CRC, except, instead of centrifugation step, excess solution is removed by hanging the bags for ten minutes.
[0026] The term “polyacrylate fines” or “polyacrylate SAP fines” or “SAP fines” as used herein synonymously and interchangeably throughout the present disclosure denotes the polyacrylate SAP particles that exhibit particle size of less than 150 microns.
[0027] The present disclosure relates generally to the field of super absorbent polymers (SAPs). More particularly, the present disclosure provides an improved method for processing of polyacrylate SAP fines.
[0028] Aspects of the present disclosure provide method of processing of polyacrylate fines to produce polyacrylate SAP particles therefrom.
[0029] An aspect of the present disclosure provides a method of processing polyacrylate fines to produce polyacrylate SAP particles, said method including the steps of : (a) taking polyacrylate fines wherein at least 80% of the particles exhibit particle size of less than 150 micron; (b) effecting agglomeration of said polyacrylate fines to produce agglomerated particles, wherein at least 80% of the agglomerated particles exhibit particle size ranging from 150 micron to 850 micron; and (c) effecting surface crosslinking of said agglomerated particles to produce the polyacrylate SAP particles, wherein said polyacrylate SAP particles exhibit Absorption Under Load (AUL) of more than 19 g/g at 0.3 psi.
[0030] In an embodiment, the polyacrylate SAP particles exhibit Absorption Under Load (AUL) of more than 20 g/g at 0.3 psi. In an embodiment, the polyacrylate SAP particles exhibit free swelling of more than 45 g/g in 0.9 Nacl Solution.
[0031] In an embodiment, the step of effecting agglomeration of the polyacrylate fines to produce agglomerated particles includes chemical agglomeration of SAP fines. In an embodiment, the chemical agglomeration is effected by treating the polyacrylate fines with a solution of crosslinking agent. In an embodiment, the step of treating the polyacrylate fines with a solution of crosslinking agent comprises spraying the solution of crosslinking agent onto the polyacrylate fines. In an embodiment, the solution of crosslinking agent is prepared by dissolving the crosslinking agent in an aqueous solvent. In an embodiment, the solution of crosslinking agent is prepared by dispersing the crosslinking agent in an aqueous solvent. In an embodiment, the solution of crosslinking agent comprises less than 20% v/v of water. In an embodiment, the solution of crosslinking agent comprises equal to or less than 10% v/v of water. In an embodiment, the solution of crosslinking agent is sprayed onto the polyacrylate fines for less than 3 minutes.
[0032] In an embodiment, the crosslinking agent is one or a combination of polyols such as polyether polyols. In an embodiment, the polyether polyols exhibit molecular weight of less than 2000 (e.g. PEG 600, PEG 1000, PEG 1500 and the likes). In an embodiment, the polyether polyols exhibit Poly-Dispersity Index (PDI) of less than 1.5. In an embodiment, the step of effecting agglomeration of the polyacrylate fines to produce agglomerated particles further includes exposing the agglomerated particles to a high temperature. In an embodiment, the step of exposing the agglomerated particles to a high temperature includes exposing the agglomerated particles to a temperature of more than 170°C for a time period ranging from 30 minutes to 60 minutes. In an embodiment, the step of exposing the agglomerated particles to a high temperature includes exposing the agglomerated particles to a temperature of more than 170°C for about 40 minutes.
[0033] In an embodiment, the step of effecting surface crosslinking of said agglomerated particles to produce the polyacrylate SAP particles includes treating the agglomerated particles with a surface cross-linker composition. In an embodiment, the surface cross-linker composition comprises a surface cross-linker in a concentration ranging from 0.1% to 3% by dry weight of the agglomerated particles. In an embodiment, the surface cross-linker composition comprises a surface cross-linker in a concentration ranging from 0.1% to 0.5% by dry weight of the agglomerated particles. In an embodiment, the surface cross-linker is selected from any or a combination of cyclic carbonate esters (for example, ethylene carbonate, propylene carbonate), di-functional alcohols (for example, ethylene glycol, propylene glycol) and tri-functional alcohols (for example, glycerol). In an embodiment, the surface cross-linker is an in-situ product generated by reaction between glycerol and ethylene carbonate at a temperature ranging from 150oC to 200oC. In an embodiment, the surface cross-linker composition includes less than 10% of water by dry weight of the agglomerated particles. In an embodiment, the surface cross-linker composition includes less than 5% of water by dry weight of the agglomerated particles.
[0034] 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.
[0035] Production of SAP (Polymerization Reaction)
[0036] 2 kg acrylic acid was neutralized with 3.4 kg of 22 % sodium hydroxide solution in a jacketed vessel. Subsequently, 30 g of TMPTA cross-linker was added to the neutralization solution. 60 g of 1% potassium persulfate solution, 45g of 0.5% H2O2 solution and 35 g of 0.1% ascorbic acid solution were prepared and transferred to the preheated kneader reactor through the feeder. The aqueous monomer and TMPTA mixture was continuously fed into the reactor. Polymerization starts in the kneader reactor immediately, as the reactor was preheated at desired temperature of 80oC. The reactor was kept under nitrogen blanket for the whole reaction period and the gel obtained was few mm in size due to chopping effect of the twin shaft. This gel was immediately dried in hot air dryer at 150-200 oC with desired air flow rates. Brittle cake obtained were broken down into few cm size by a shredder and then subjected to milling and sieving to obtain desired particle size range (150-850 µm). SAP particles which are below 150µm were considered as SAP fines. Particle size distribution (PSD) of the resultant fines is shown in Table 1 below, wherein about 95% of particles exhibited particle size ranging from 90-150 µm, and about 4.6% of particles exhibited particle size ranging from 45-90 µm (cumulatively, about 99.6% particles exhibited particle size ranging from 45 to 150 µm), and about 0.4% particles exhibited particle size ranging from 20-45 µm. Median Particle Size of the SAP fines was found to be 134 µm.
[0037] EXAMPLE 1
[0038] Preparation of agglomerated particles from the polyacrylate fines (Ex-1)
[0039] In a kitchen aid mixer, 400 g of polyacrylate fines/SAP fines (with particle size <150 µm) are chemically treated with a mixture of 2 g of PEG-600 and 40 g of water through compressed sprayer system for 3 min, under continuous mixing conditions. The PEG treated SAP fines were heated to 170oC - 180oC for 30 min in a forced air convection oven. Thereafter, the treated and agglomerated particles were sieved through vibratory sieve shaker for obtaining particles with particle size ranging from 150 µm to 850 µm. The overall conversion of fines to particles with desired size (i.e. 150 µm to 850 µm) was around 70%. Particle size distribution (PSD) of the resultant aggregated particles is shown in Table 1 below, wherein about 36.8% of agglomerated particles were having a particle size in the range of 150-300 µm, about 39.6% particles were having particle size in the range of 300-600 µm, and about 21.7% of particles were having particle size in the range of 600-850 µm. Median Particle Size of the agglomerated particles was found to be 376 µm.
[0040] Preparation of polyacrylate SAP particles from the agglomerated particles (Ex-1-sxl-1)
[0041] In a further step of crosslinking (SXL), 200 g of chemically agglomerated SAP particles were crosslinked with 0.4 g of ethylene carbonate (EC) and 8 g of water in plough shear mixer under controlled spraying and continuous agitation conditions (Step-4). In the step of surface treatment, the wet SAP mixture is heated to 180oC for 20-25 min in a forced convection oven (Esco Isotherm model) (Step-4). The dry SAP was size sorted through Retsch AS 200 vibratory sieve shaker as per the ISO 17190-3 method (Step-5). Particle size distribution (PSD) of the resultant SAP particles is shown in Table 1 below, wherein about 33.6% of particles were in the range of 150-300 µm, about 31.6% of particles were in the range of 300-600 µm, and about 30.9% of particles were in the range of 600-850 µm. Median Particle Size of the SAP particles was found to be 443 µm.
Table 1: Particle Size Distribution (PSD) and Median particle size of SAP Fines, Agglomerated particles and SAP particles
Particle Size (µm) SAP fines (%) Agglomerated particles
(After PEG treatment) (%) SAP particles
(%)
850 or more 0 1.1 3.3
600-850 0 21.7 30.9
300- 600 0 39.6 31.6
150-300 0 36.8 33.6
45-150
(90-150)
(45-90) 99.6
(95)
(4.6) 0.78 1.68
20-45 0.4 0 0
<20 0 0 0
Median particle Size 134 376 443
Table 2: Properties of agglomerated particles and SAP particles
sample Chemical Agglomeration Surface
Crosslinking
Free swelling
(0.9%, Nacl) CRC* (g/g) AUL (g/g at 0.3 PSI)
Ex-1 PEG-600 (0.5 wt%) +
water (10 wt%) - 41 31.5 13.9
Ex-1-sxl-1 PEG-600 (0.5 wt%) +
water (10 wt%) EC-0.2wt%+
H2O-4wt%/20min 46.5 26 19
Ex-1-sxl-2 PEG-600 (0.5 wt%) +
water (10 wt%) EC-0.4wt% +
H2O-4wt% /20min 49 25 19
Ex-1-sxl-3 PEG-600 (0.5 wt%) +
water (10 wt%) EC-0.8wt% +
H2O-4wt%/20min 42 22.2 20.3
Ex-1-sxl-4 PEG-600 (0.5 wt%) +
water (10 wt%) EC-0.4wt% +
H2O-8wt%/20min 44 23.4 19.1
Ex-2 PEG-1000 (1.5wt%)+ water (10 wt%) - 46 29.8 14.6
Ex-2-sxl-1 PEG-1000 (1.5wt%)+ water (10 wt%) EC-1wt%+
H2O-4wt% 43.8 22.6 20.6
Ex-3 PEG-1500 (1.5wt%)+ water (10 wt%) - 51 28.7 14.5
Ex-3-sxl-1 PEG-1500 (1.5wt%)+ water (10 wt%) EC-1wt%+
H2O-4wt% 44 21.8 20.3

[0042] 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
[0043] The present disclosure provides a method of processing of polyacrylate fines to produce polyacrylate SAP therefrom that can be utilized directly in preparation of the end product.
[0044] The present disclosure provides a method of processing of polyacrylate fines to produce polyacrylate SAP therefrom that aids in reduction in wastage, conserves energy and improves overall productivity.
[0045] The present disclosure provides a method of processing of polyacrylate fines that is economical.
[0046] The present disclosure provides a process that is technically and commercially feasible.
,CLAIMS:1. A method of processing polyacrylate fines to produce polyacrylate SAP particles, said method comprising the steps of:
(a) taking polyacrylate fines, wherein at least 80% of the particles exhibit particle size of less than 150 micron;
(b) effecting agglomeration of said polyacrylate fines to produce agglomerated particles, wherein at least 80% of the agglomerated particles exhibit particle size ranging from 150 micron to 850 micron; and
(c) effecting surface crosslinking of said agglomerated particles to produce the polyacrylate SAP particles, wherein said polyacrylate SAP particles exhibit Absorption Under Load (AUL) of more than 19 g/g at 0.3 psi.
2. The method as claimed in claim 1, wherein the polyacrylate SAP particles exhibit Absorption Under Load (AUL) of more than 20 g/g at 0.3 psi, and free swelling of more than 45 g/g in 0.9 Nacl Solution.
3. The method as claimed in claim 1, wherein the step of effecting agglomeration of the polyacrylate fines to produce agglomerated particles comprises chemical agglomeration of SAP fines.
4. The method as claimed in claim 3, wherein the chemical agglomeration is effected by treating the polyacrylate fines with a solution of crosslinking agent.
5. The method as claimed in claim 4, wherein the step of treating the polyacrylate fines with the solution of crosslinking agent comprises spraying the solution of crosslinking agent onto the polyacrylate fines.
6. The method as claimed in claim 4, wherein the solution of cross-linking agent is prepared by dissolving the cross-linking agent in an aqueous solvent.
7. The method as claimed in claim 4, wherein the solution of cross-linking agent is prepared by dispersing the cross-linking agent in an aqueous solvent.
8. The method as claimed in claim 4, wherein the solution of cross-linking agent comprises less than 20% v/v of water.
9. The method as claimed in claim 4, wherein the solution of cross-linking agent comprises equal to or less than 10% v/v of water.
10. The method as claimed in claim 5, wherein the solution of cross-linking agent is sprayed onto the polyacrylate fines for less than 3 minutes.
11. The method as claimed in claim 4, wherein the cross-linking agent is one or a combination of polyols.
12. The method as claimed in claim 11, wherein the one or a combination of polyols comprise polyether polyols with molecular weight of less than 2000.
13. The method as claimed in claim 1, wherein the step of effecting agglomeration of the polyacrylate fines to produce agglomerated particles further comprises exposing the agglomerated particles to a high temperature.
14. The method as claimed in claim 13, wherein the step of exposing the agglomerated particles to a high temperature comprises exposing the agglomerated particles to a temperature of more than 170°C for a time period ranging from 30 minutes to 60 minutes.
15. The method as claimed in claim 13, wherein step of exposing the agglomerated particles to a high temperature comprises exposing the agglomerated particles to a temperature of more than 170°C for about 40 minutes.
16. The method as claimed in claim 1, wherein the step of effecting surface crosslinking of said agglomerated particles to produce the polyacrylate SAP particles comprises treating the agglomerated particles with a surface cross-linker composition.
17. The method as claimed in claim 16, wherein the surface cross-linker composition comprises a surface cross-linker in a concentration ranging from 0.1% to 3% by dry weight of the agglomerated particles.
18. The method as claimed in claim 16, wherein the surface cross-linker is selected from any or a combination of cyclic carbonate esters, di-functional alcohols, and tri-functional alcohols.
19. The method as claimed in claim 16, wherein the surface cross-linker is an in-situ product generated by reaction between glycerol and ethylene carbonate at a temperature ranging from 150oC to 200oC.
20. The method as claimed in claim 1, wherein the surface cross-linker composition comprises less than 10% of water by dry weight of the agglomerated particles.