ABSORPTION RATE

TECHNICAL FIELD

[0001] The present disclosure relates generally to the field of super absorbent polymers (SAPs). More particularly, the present disclosure provides polyacrylate super absorbent polymer (SAP) particles with enhanced absorption rate and method of production thereof.

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, including cross-linked 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 “Modem 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, with median particle size ranging from 300 to 600 microns, typically exhibit absorption rate of more than about 20 seconds. Table A below illustrates the properties of the commercial products available from Sumitomo Seika Chemicals Co. Ltd. under the name“AQUA KEEP”. Table A:Properties of the commercial products available from Sumitomo Seika Chemicals Co. Ltd. under the name“AQUA KEEP”

[0005] To the best of the knowledge of inventors of the present application, no SAP particles with median particle size ranging from 300 to 600 microns are reported in the art that exhibit enhanced absorption rate or vortex time (less than about 15 seconds).

[0006] Accordingly, there remains a need in the state of art for polyacrylate superabsorbent polymer (SAP) particles that exhibits enhanced absorption rate. Need is also felt of method of production of polyacrylate superabsorbent polymer (SAP) particles that exhibits enhanced absorption rate.

OBJECTS OF THE INVENTION

[0007] An object of the present disclosure is to provide polyacrylate superabsorbent polymer (SAP) particles that exhibits enhanced absorption rate.

[0008] Another object of the present disclosure is to providea method of production of polyacrylate superabsorbent polymer (SAP) particlesthat exhibits enhanced absorption rate.

[0009] Yet another object of the present disclosure is to provide a process that is technically and commercially feasible.

[0010] Still further object of the present disclosure is to provide polyacrylate superabsorbent polymer (SAP) particles that are economical.

[0011] Still further object of the present disclosure is to providea method of production of polyacrylate superabsorbent polymer (SAP) particles that is economical. [0012] Other objects of the present invention will be apparent from the description of the invention herein below.

SUMMARY

[0013] The present disclosure relates generally to the field of super absorbent polymers

(SAPs). More particularly, the present disclosure provides polyacrylate super absorbent polymer (SAP) particles with enhanced absorption rate and method of production thereof.Aspects of the present disclosure provide polyacrylate super absorbent polymer (SAP) particles having median particle size 300-600 microns that exhibit Absorption rate or Vortex time of less than about 13 seconds and a method of production thereof.

[0014] An aspect of the present disclosure provides polyacrylate super absorbent polymer

(SAP) particles having median particle size ranging from about 300 microns to about 600 microns that exhibit (i) Absorption rate or Vortex time of less than about 13 seconds, and (ii) AUL of more than about 20 g/g at 0.3 psi. In an embodiment, the SAP particles exhibit free swelling of more than about 45 g/gin 0.9 NaCl Solution.

[0015] Another aspect of the present disclosure relates to a method of production of polyacrylate SAP particles with enhanced absorption rate, said method including the steps of: (a) taking polyacrylate SAP particles that exhibit median particle size less than about 150 microns; (b) effecting agglomeration of said polyacrylate SAP particles to produce agglomerated SAP particles; and (c) effecting surface crosslinking of said agglomerated particles to produce the polyacrylate SAP particles to produce polyacrylate super absorbent polymer (SAP) particles having median particle size 300-600, wherein said polyacrylate SAP particles exhibit (i) Absorption rate or Vortex time of less than about 13 seconds, and (ii) AUL of more than about 20 g/g at 0.3 psi. In an embodiment, the SAP particles exhibit free swelling of more than about 45 g/gin 0.9 NaCl Solution.

[0016] In an embodiment, the step of effecting agglomeration of the polyacrylate SAP particles to produce agglomerated particles includes chemical agglomeration of the polyacrylate SAP particles. In an embodiment, the chemical agglomeration is effected by treating the polyacrylate SAP particles with a solution of cross-linking agent. In an embodiment, the step of treating the polyacrylate SAP particles with a solution of cross- linking agent comprises spraying the solution of cross-linking agent onto the polyacrylate SAP particles. In an embodiment, the solution of cross-linking agent is prepared by dissolving the cross-linking agent in an aqueous solvent. In an embodiment, the solution of cross-linking agent is prepared by dispersing the cross-linking agent in an aqueous solvent. In an embodiment, the solution of cross-linking agent comprises less than 20% v/v of water.In an embodiment, the solution of cross-linking agent comprises equal to or less than 10%v/v of water. In an embodiment, the solution of cross-linking agent is sprayed onto the polyacrylate SAP particles for less than 3 minutes.

[0017] In an embodiment, the cross-linking agent isone 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 SAP particles 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.

[0018] 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- linkercomposition comprises a surface cross-linkerin a concentration ranging from 0.1% to 1% by dry weight of the agglomerated particles. In an embodiment, the surface cross-linker composition comprises a surface cross-linkerin a concentration ranging from 0.1% to 3% 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 150°C to 200°C.In an embodiment, the surface cross-linkercomposition 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.

BRIEF DESCRIPTION OF DRAWINGS

[0019] FIG. 1 illustrates an exemplary drawing showing chemical aggregation of SAP particles. DETAILED DESCRIPTION

[0020] 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.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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 What man 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:

Where AUL is in g/g at 0.3 psi and C is the actual weight of SAP sample in grams.

[0027] 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 = (wi - W2 -W3) / W3

Where, wi is the weight of wet sample and bag, w ₂ is the weight of empty bag and w ₃ is the weight of dry sample.

[0028] 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 rate/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.

[0029] The term“Absorption rate” or“vortex time” as used herein synonymously and interchangeably throughout the present disclosure, denotes the method to evaluate swelling rate of SAP particles. This test measures the time required for 2 grams of a super absorbent polymer to close a vortex created by stirring 50 ml of saline solution (0.9%) at 600 revolutions per minute on a magnetic stir plate. The time it takes to disappearance of vortex is an indication of absorption rate of super absorbent particle. Absorption rate may be determined by using 100 ml Beaker (Borosil ®) and 50 ml graduated cylinder, Programmable magnetic stir plate, capable of providing 600 revolutions per minute (such as Cole-Parmer model), Magnetic stir bar without rings(e.g. 32mm x 7.9mm, Teflon®), Stopwatch, Balance, accurate to +/-0.001 g (e.g. Sartorius AG make, model no: CPA224), Saline solution, 0.9 w/w % at standard atmospheric conditions: Temp=25°C± 1°C and Relative Humidity = 49% (±1 %) and following the exemplary method: 50 ml of 0.9% Nacl solution is taken into 100 ml beaker with a magnetic bar and RPM of 600 was set on programmable magnetic stir plate. Ensure that bottom of the vortex should be near the top of the stir bar by adjusting the beaker on the center of the magnetic plate. The test begins when 2 g of thoroughly dried SAP sample to be tested is added directly into 0.9% NaCl solution, and stop the watch when the vortex disappears. The time recorded in seconds is considered as Vortex time or the Absorption rate.

[0030] The present disclosure relates generally to the field of super absorbent polymers (SAPs). More particularly, the present disclosure provides polyacrylate super absorbent polymer (SAP) particles with enhanced absorption rate and method of production thereof.Aspects of the present disclosure provide polyacrylate super absorbent polymer (SAP) particles having median particle size 300-600 microns that exhibit Absorption rate or Vortex time of less than about 13 seconds and a method of production thereof.

[0031] Without wishing to be bound by the theory, the inventors of the present application believes that, the controlledchemical aggregation not only results in increase in the particle size, but also significantly increases the porosity (or void formation), which in turn improves the penetration of the water or aqueous fluids leading to significant improvement in absorption rate of the polyacrylate SAP particles. FIG. 1 illustrates an exemplary drawing showing chemical aggregation of SAP particles.

[0032] An aspect of the present disclosure provides polyacrylate super absorbent polymer (SAP) particles having median particle size ranging from about 300 microns to about 600 microns that exhibit (i) Absorption rate or Vortex time of less than about 13 seconds, and (ii) AUL of more than about 20 g/g at 0.3 psi. In an embodiment, the SAP particles exhibit free swelling of more than about 45 g/gin 0.9 NaCl Solution.

[0033] Another aspect of the present disclosure relates to a method of production of polyacrylate SAP particles with enhanced absorption rate, said method including the steps of: (a) taking polyacrylate SAP particles that exhibit median particle size less than about 150 microns; (b) effecting agglomeration of said polyacrylate SAP particles to produce agglomerated SAP particles; and (c) effecting surface crosslinking of said agglomerated particles to produce the polyacrylate SAP particles to produce polyacrylate super absorbent polymer (SAP) particles having median particle size 300-600, wherein said polyacrylate SAP particles exhibit (i) Absorption rate or Vortex time of less than about 13 seconds, and (ii) AUL of more than about 20 g/g at 0.3 psi. In an embodiment, the SAP particles exhibit free swelling of more than about 45 g/gin 0.9 NaCl Solution.

[0034] In an embodiment, the step of effecting agglomeration of the polyacrylate SAP particles to produce agglomerated particles includes chemical agglomeration of the polyacrylate SAP particles. In an embodiment, the chemical agglomeration is effected by treating the polyacrylate SAP particles with a solution of cross-linking agent. In an embodiment, the step of treating the polyacrylate SAP particles with a solution of cross- linking agent comprises spraying the solution of cross-linking agent onto the polyacrylate SAP particles. In an embodiment, the solution of cross-linking agent is prepared by dissolving the cross-linking agent in an aqueous solvent. In an embodiment, the solution of cross-linking agent is prepared by dispersing the cross-linking agent in an aqueous solvent. In an embodiment, the solution of cross-linking agent comprises less than 20% v/v of water.In an embodiment, the solution of cross-linking agent comprises equal to or less than 10%v/v of water. In an embodiment, the solution of cross-linking agent is sprayed onto the polyacrylate SAP particles for less than 3 minutes.

[0035] In an embodiment, the cross-linking agent isone 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 step of effecting agglomeration of the polyacrylate SAP particles 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.

[0036] 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- linkercomposition comprises a surface cross-linker in a concentration ranging from 0.1% to 1% by dry weight of the agglomerated particles. In an embodiment, the surface cross-linker composition comprises a surface cross-linkerin a concentration ranging from 0.1% to 3% 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), tri-functional alcohols (for example, glycerol) or combination thereof. 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 150°C to 200°C.In an embodiment, the surface cross-linkercomposition 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.

[0037] 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.

[0038] Production of polyacrylate SAP particles (Polymerization Reaction)

[0039] 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% H O 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 35°C. 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°C - 200°C 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 (150-850pm). SAP particles which are below 150pm were considered as SAP fines. Particle size distribution (PSD) of the resultant SAP particle size(i.e. initial SAP particles) is shown in Table 1 below, wherein Median Particle Size of the initial SAP particles was found to be 134 pm.

[0040] EXAMPLE 1

[0041] Preparation of Agglomerated SAP particles from the Initial polyacrylate SAP particles (Ex-1)

[0042] In a kitchen-aid mixer, 400 g of polyacrylate SAP particles with particle size <150 pmwere chemically treated with a mixture of 2 g of PEG-600 and 40 g ofwater through compressed sprayer system for 3 min, under continuous mixing conditions. The PEG treated SAP particleswere heated to 170°C - 180°C for 30 min in a forced air convection oven. Thereafter, the treated and agglomerated particles were sieved through vibratory sieve shaker for obtaining particleswith particle size ranging from 150 pm to 850 pm . Median Particle Size of the agglomerated particles was found to be 376 pm.

[0043] Surface crosslinking of Agglomerated SAP particles (Ex-l-sxl-1)

[0044] In a further step of cross-linking (SXL), 200 g of agglomerated SAP particles produced above were cross-linked with 0.4 g of ethylene carbonate (EC) and 8 g of water in plough shear mixer under controlled spraying and continuous agitation conditions. In the step of surface treatment, the wet SAP mixture is heated to 180°C for 20-25 min in a forced convection oven (Esco Isotherm model). The dry SAP was size sorted through Retsch AS 200 vibratory sieve shaker as per the ISO 17190-3 method. Median Particle Size of the resultant SAP particles was found to be 443 pm. Table 1 below illustrates particle size distribution of the initial SAP particles, agglomerated SAP particles and the final SAP particles. Table 1: Particle Size Distribution (PSD) and Median particle size of Initial SAP particles, Agglomerated SAP particles and final SAP particles

Table 2:Properties of agglomerated SAP particles and final SAP particles

[0045] 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 5 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 10 therein.

ADVANTAGES

[0046] The present disclosure provides polyacrylate superabsorbent polymer (SAP) particles that exhibits enhanced absorption rate.

15 [0047] The present disclosure providesa method of production of polyacrylate superabsorbent polymer (SAP) particlesthat exhibits enhanced absorption rate.

[0048] The present invention provides a process that is technically and commercially feasible.

[0049] The present disclosure provides polyacrylate superabsorbent polymer (SAP) 20 particles that are economical.

[0050] The present disclosure providesa method of production of polyacrylate superabsorbent polymer (SAP) particlesthat is economical.