Method for preparing super absorbent resin

Abstract

The present invention discloses a method for preparing a super absorbent resin including the following steps: 1) adding an inner-crosslinking agent, an active promoter, and an initiator to a solution of an unsaturated monomer in water, deoxygenating by bubbling nitrogen therethrough, and then undergoing free radical polymerization to obtain a gel; 2) reacting the gel with a neutralizing agent, extruding, and granulating to obtain a product; 3) drying, pulverizing, sieving, and fixing the particle size combination of the product to obtain powdered raw particles; 4) adding a surface crosslinking agent to the powdered raw particles and performing surface crosslinking by heating to obtained crosslinked particles; and 5) subjecting the crosslinked particles to anti-caking treatment to obtain a super absorbent resin.

Claims

1. A method for preparing a super absorbent resin, comprising: step 1) adding an inner-crosslinking agent, an active promoter, and an initiator to a solution of an unsaturated monomer in water to obtain a mixture solution, deoxygenating the mixture solution by bubbling nitrogen therethrough, and subjecting the mixture solution to a free radical polymerization to obtain a gel, wherein the active promoter is one selected from the group consisting of a fatty acid ester, a fatty acid salt, an alkyl sulfonate salt, and a mixture of the fatty acid ester, the fatty acid salt, and the alkyl sulfonate salt; the free radical polymerization is initiated at a temperature ranging from 3 C. to 5 C.; the initiator is a mixture of a redox initiator and a thermally decomposable initiator, wherein the redox initiator is a combination of ascorbic acid and ferrous chloride; and the thermally decomposable initiator is one selected from the group consisting of hydrogen peroxide, phthalimide peroxide, a persulfate, an ammonium persulfate, an alkali metal persulfate, 2,2-azobis(2-amidinopropane) dihydrochloride, 2,2-azodiisobutylamidine dihydrochloride, 2,2-azobis(N,N-dimethyleneisobutylamidine) dihydrochloride, and 2,2-azo[2-methyl-N-(2-hydroxyethyl)]propenamine; the unsaturated monomer is acrylic acid, methacrylic acid, maleic acid, or fumaric acid; step 2) reacting the gel with a neutralizing agent to obtain an intermediate product; extruding and granulating the intermediate product to obtain a product; step 3) drying, pulverizing, sieving, and fixing a particle size distribution after the sieving to obtain a plurality of powdered raw particles, wherein the particle size distribution after sieving is 100-800 m; an average particle size of the powdered raw particles obtained after fixing the particle size distribution is 300-450 m; and the bulk density is 0.55-0.63 g/mL, step 4) adding a surface crosslinking agent to the plurality of powdered raw particles and performing surface crosslinking by heating to obtain a plurality of crosslinked particles; and step 5) subjecting the plurality of crosslinked particles to an anti-caking treatment, wherein the anti-caking treatment comprises adding an aqueous solution of aluminum sodium sulfate to the plurality of crosslinked particles to obtain a mixed particle, and then adding fumed silica to the mixed particle and heating, to obtain a super absorbent resin.

2. The method for preparing a super absorbent resin according to claim 1, wherein the inner-crosslinking agent is a compound having two or more unsaturated double bonds and/or a compound having two or more epoxy groups.

3. The method for preparing a super absorbent resin according to claim 1, wherein, the unsaturated monomer is the acrylic acid and in step 1), a neutralizing agent is further added; and the neutralizing agent is added in an amount of 0-5 mol % based on exclusively the acrylic acid in a solution of the acrylic acid in water.

4. The method for preparing a super absorbent resin according to claim 1, wherein the neutralizing agent is an alkali metal hydroxide or carbonate.

5. The method for preparing a super absorbent resin according to claim 1, wherein the surface crosslinking agent is one of a compound having two or more epoxy groups, a polyol, a polyamine, or a mixture thereof.

6. The method for preparing a super absorbent resin according to claim 1, wherein the particle size distribution after sieving is 150-710 m.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The specific embodiments of the present invention will be further described in detail with reference to the accompanying drawings.

(2) FIG. 1 is a photograph of an existing super absorbent resin under a high power microscope.

(3) FIGS. 2 and 3 are photographs of the super absorbent resins according to the present invention under a high power microscope.

DETAILED DESCRIPTION OF THE INVENTION

(4) In order to make the present invention clearer, the present invention will be further described below in conjunction with the preferred embodiments. It should be understood by those skilled in the art that the following detailed description is illustrative rather than restrictive, and should not be construed as limiting the protection scope of the present invention.

(5) Performance Test Standards

(6) The performance indices of the super absorbent resin are tested following the steps as described in the method in China national standard GB/T 22905-2008 Super absorbent resin for diaper and in European Disposables and Nonwovens Association EDANA442.2-2002, as well as in beyond-standard methods generally accepted in the industry, referred to here as the market methods.

(7) The absorption capacity, that is, the absorbency and water retention capacity, are tested following the steps as described in the tea bag test method in GB/T 22905-2008 Super absorbent resin for diaper, and EDANA442.2-2002 Determination of the absorbency and water retention capacity of super absorbent resins. Five measurements are made, and then averaged after removing the maximum and minimum values. The test steps are as follows. 1.0 g (accurate to 0.002 g) of the super absorbent resin is weighed into a tea bag, and soaked for 60 min in a 0.9% aqueous NaCl solution at 255 C. Then, the soaked tea bag is gently pulled out, suspended from a clip, stood for 15 min to allow for the dripping of water, and then weighed. The absorbency is obtained by subtracting the weight of the blank tea bag without the super absorbent resin from the value obtained, and then dividing by the weight of the super absorbent resin before soaking. The tea bag that has completed the determination of absorbency is placed in a centrifuge and centrifuged for 90 s at 150 G, and weighed. The water retention capacity after centrifugation is obtained by subtracting the weight of the wet empty tea bag after centrifugation from the value obtained, and then dividing by the weight of the super absorbent resin before soaking.

(8) The high pressure resistance is expressed as the water absorbency under pressure, and determined following the steps as described in the method in GB/T 22905-2008 Super absorbent resin for diaper and EDANA442.2-2002 Super absorbent resin-determination of absorbency under pressure. The pressure load is 0.3 PSI (that is, 2068 Pa or 21.099 g/cm.sup.2), and then further increased to 0.6 PSI (that is, 4137 Pa or 42.197 g/cm.sup.2), and 0.9 PSI (that is, 6206 KPa or 63.296 g/cm.sup.2) for determination. The determination steps are as follows. 0.160 g (accurate to 0.001 g) of the super absorbent resin powder is accurately weighed into a cylindrical body with a screen bottom, and a pressure of 0.3 PSI, 0.6 PSI, and 0.9 PSI is respectively applied to the powder. Then, the cylindrical body is placed on an absorbency tester, and the super absorbent resin powder is allowed to absorb a 0.9 wt % aqueous NaCl solution for 1 hr. The absorbency under pressure is obtained by dividing the weight value obtained after the water absorption by the weight of the super absorbent resin powder. and then the value obtained by measuring the water absorption weight is divided by the weight of the high water-absorbent resin powder

(9) The liquid absorption rate is expressed as absorption capacity within a fixed time interval, which is tested according to GB/T 22905-2008 Super absorbent resin for diaper and EDANA442.2-2002 Vortex method, and market method generally accepted in the industry.

(10) The vortex method may be made reference to the method as described in GB/T 22905-2008 Super absorbent resin for diaper and EDANA442.2-2002 Determination of absorption rate of super absorbent resin. The absorption rate of the super absorbent resin is preferably determined at a temperature of (252) C. with a relative humidity of (4510)%. The super absorbent resin sample was quickly added to a 0.9% NaCl solution of known volume with stirring, and then a gel is formed after the saline solution is absorbed by the SAP sample. The time from when the SAP was added to the time when a liquid gel is formed, the vortex generated by stirring disappears, and finally the gel surface becomes smooth is recorded. (50.01.0) ml of a 0.9% NaCl solution is measured into a 100 ml beaker. A rotor is placed and the NaCl solution is stirred on a magnetic stirrer at 600 rpm. (2.0000.001) g of super absorbent resin is weighed on weigh paper and poured into the vortex in one portion. After addition, timing is started. As the sample absorbs saline, the vortex in the middle portion begins to disappear. The vortex is disappeared and the liquid level becomes planar. This is used as an endpoint, and the time required to reach the end point is measured in seconds. Three parallel tests are performed for each sample.

(11) In the market method generally accepted in the industry, 0.9 wt % saline is used for testing the absorption capacity within a fixed time interval. The test steps are as follows. 1.0 g (accurate to 0.002 g) of the sample is weighed. All the sample is poured into the bottom of the tea bag. The sample attached to the inner side of the tea bag should also be poured into the bottom of the tea bag. The tea bag is soaked in 0.9% saline adjusted to a temperature of 250.5 C. Timing is started when the tea bag is soaked. The tea bag is slightly shaken up and down for 10 times in the saline to disperse the sample. At 1 min, 3 min, and 5 min after soaking, the soaked tea bag is lifted from the saline and hung on a drip rack until no water is dripped from the tea bag. The tea bag is weighed. A value is obtained by subtracting a blank weight from the weight of the tea bag obtained after the tea bag is completely soaked in saline, and hung until no water is dripped off from the tea bag, and recorded. Two replicates are set for each sample.

(12) In the market method generally accepted in the industry, pure water is used for testing the absorption capacity within a fixed time interval. The method comprises the following test steps. 1.0 g (accurate to 0.002 g) of the sample is weighed. All the sample is poured into the bottom of a tea bag (18 mm25 mm), and then opening of the tea bag is tied tightly. Then, the tea bag is soaked in pure water adjusted to a temperature of 250.5 C., and shaken gently three times up and down, and seven times left and right. Timing is started while soaking. At 1 min, 3 min, and 5 min after soaking, the soaked tea bag is lifted from the pure water and hung on a drip rack until no water is dripped from the tea bag. The tea bag is weighed. A value is obtained by subtracting a blank weight from the weight of the tea bag obtained after the tea bag is completely soaked in saline, and hung until no water is dripped off from the tea bag, and recorded. Two replicates are set for each sample.

(13) The apparent density of the super absorbent resin is determined by using a densimeter following the method as described in GB/T 22905-2008 Super absorbent resin for diaper and EDANA442.2-2002. Before being removed for testing, the sample needs to be stored in a closed container that reaches equilibrium with the test temperature in the laboratory. The recommended test conditions are a temperature of (252) C. and a relative humidity of (5010)%.

(14) The average particle size is determined according to the method described in GB/T 22905-2008 Super absorbent resin for diaper and EDANA 442.2-2002. The determination method is as follows. A series of standard sieves and logarithmic probability paper are used. The particle size (mesh size, m) is set as the horizontal axis, and the cumulative mass % on the sieve is is set to the right vertical axis. Each point is connected with a straight line, and the particle size (m) on the horizontal axis corresponding to 50% on the right vertical axis is the average particle size of the sample.

(15) The particle size distribution is determined following the steps as described in GB/T 22905-2008 Super absorbent resin for diaper and EDANA442.2-2002 Determination of the particle size distribution of super absorbent resin. The super absorbent resin of different particle sizes is separated by using a series of standard sieves, and weighed separately. The mass percentages of the high-absorbent resin at various levels are calculated, to obtain the particle size distribution of the super absorbent resin.

(16) The flow-through rate of saline is a rate at which the saline passes through a gel layer under pressure after the super absorbent resin absorbs the saline and swells to form the gel layer. 0.3200.005 g of the super absorbent resin sample is weighed, and transferred to a 250 ml beaker. 150 ml of saline is added, stirred for 1 min at 12020 rpm (that is, two rounds per second), and then stood for 30 min at room temperature, to allow the SAP sample to swell fully. Into a chromatographic separation tube, saline is added to above the 60 ml mark, and then the time required for the liquid to drop from the 60 ml mark to the 40 ml mark is determined. This time is set as T0 seconds. The swollen gel is poured into the chromatographic separation tube, and the beaker previously holding the gel is directly positioned beneath the chromatographic separation tube. The piston is opened to discharge the gas so that the liquid level in the chromatographic separation tube drops to 5 cm above the 60 ml mark. At this point, the gel washed off by the saline in the beaker is poured into the chromatographic separation tube. Be sure to pour all the gel into the chromatographic separation tube. After 1 minute, the piston was opened, and the time required for the liquid in the tube to drop from the 60 ml mark (upper mark) to the 40 ml mark (lower mark) is measured with a stopwatch. This time was set as T1 seconds. The liquid flow-through rate is calculated according to the following formula:
Liquid flow-through rate (ml/min)=2060/(T1T0)

(17) Two measurements are performed at the same time, and the arithmetic average is taken as the measurement result. The result is rounded off to an integer. Two measurements are performed with the swollen gel. If the results of the two measurements are highly different, the measurement is repeated.

(18) Dry touch sensation: the amount of reverse osmosis within a fixed time interval after the super absorbent resin absorbs a liquid is determined according to a market method generally accepted in industry. The determination of the amount of reversely osmosed liquid absorbed can be determined based on the amount of the reversely osmosed liquid transferred to filter paper under pressure. The test steps are as follows. 2.0 g (accurate to 0.002 g) of a sample is weighed. The sample is poured into a 90 mm petri dish (upper lid), 50 ml of 0.9% saline is slowly added, and timing is started when it is poured. When the saline is added, the petri dish (upper lid) is slowly and equally rotated, to distribute the sample evenly. After 5 min, ten pieces of 90 mm filter paper that have been weighed (ml) are placed on the sample, on which a 90 mm Petri dish (base plate) equipped with a 300 g balance weight is pressed. The weight of the filter paper is exactly weighed at 0.5, 1, 2, 4, 8, 12, 16, 20, and 24 hrs from the starting time, from which the weight of the blank filter paper is subtracted.

(19) The hydrolysis resistance is expressed as the extractable content, and determined following the method as described in GB/T 22905-2008 Super absorbent resin for diaper and EDANA442.2-2002 Super absorbent resindetermination of extractable content. The steps are as follows. 200 ml of saline is accurately measured, and poured into a 250 ml beaker. A stirring rod is added. 1 g (accurate to 0.001 g) of the super absorbent resin is weighed and poured into the beaker. The beaker is sealed with a paraffine film, and the magnetic stirrer is started to stir at 500 rpm for 16 hrs. 200 ml of saline is used as a blank control. After 16 hrs, the stirring is stopped, the gel is deposited, and the supernatant is filtered out using a Buchner funnel with filter paper. Not less than 50 ml of the liquid is left for test. 50 ml of the liquid is titrated with a standard NaOH solution until the pH is 10.0, as measured with a pH meter. The volume of NaOH solution consumed is recorded. Then, the liquid is titrated with a HCl solution until the pH is 2.7. The volume of the HCl solution consumed is recorded. At the same time, the blank solution is titrated.

(20) Calculation of Results

(21) 1) The total amount of carboxylic acid (e.g. polycarboxylic acid), n.sub.COOH expressed as moles in the filtrate is calculated by a formula below:
n.sub.COOH=(V.sub.NaOH,sV.sub.NaOH,b)c.sub.NaOH

(22) in which:

(23) V.sub.NaOH,svolume (unit: mL) of the sodium hydroxide solution needed for titrating the filtered sample supernatant to pH 10.0;

(24) V.sub.NaOH,bvolume (unit: mL) of the sodium hydroxide solution needed for titrating the filtered blank solution to pH 10.0; and

(25) c.sub.NaOHconcentration (unit: moL/L) of the sodium hydroxide solution.

(26) 2) The total content of carboxylate n.sub.tot expressed as moles in the filtrate is calculated by a formula below:
n.sub.tot=(V.sub.HCl,sV.sub.HCl,b)c.sub.HCl

(27) in which:

(28) V.sub.HCl,svolume (unit: mL) of the hydrochloric acid solution needed for titrating the sample filtrate from pH 10 to pH 2.7;

(29) V.sub.HCl,bvolume (unit: mL) of the hydrochloric acid solution needed for titrating the blank solution from pH 10 to pH 2.7; and

(30) c.sub.HClconcentration (unit: moL/L) of the hydrochloric acid solution.

(31) 3) The total amount of carboxylic acid neutralized in the filtrate n.sub.COONa expressed as moles is calculated by a formula below:
n.sub.cooNa=n.sub.totn.sub.COOH

(32) 4) Weight of the carboxylic acid m.sub.COOH expressed in g, is calculated by a formula below:
m.sub.COOH=n.sub.COOHm.sub.COOHF.sub.dil
m.sub.COONa=n.sub.COONam.sub.COONaF.sub.dil

(33) in which:

(34) m.sub.COOHmolar mass of acrylic acid, that is, 72.0 g/moL;

(35) m.sub.COONamolar mass of sodium acrylate, that is, 94.0 g/moL;

(36) F.sub.dildilution factor, that is, 200/50=4.

(37) 5) The extractable content w expressed in percent by weight in the super absorbent resin is calculated by a formula below:

(38) $w=\frac{m_{\mathrm{COOH}}+m_{\mathrm{COONa}}}{m_{s}1000}100\%$

(39) in which

(40) m.sub.sweight of the test sample, unit: g.

(41) 6) If the super absorbent resin is known to have a degree of neutralization, the extractable content w expressed in percent by weight is calculated by a formula below:

(42) $w=\frac{\left(V_{\mathrm{HCl},s}-V_{\mathrm{HCl},b}\right)C_{\mathrm{HCl}}{M}_{\mathrm{acr}}{F}_{\mathrm{dil}}}{m_{s}1000}100\%$

(43) in which

(44) V.sub.HCl,svolume (unit: mL) of the hydrochloric acid solution needed for titrating the sample filtrate from pH 10 to pH 2.7;

(45) V.sub.HCl,bvolume (unit: mL) of the hydrochloric acid solution needed for titrating the blank solution from pH 10 to pH 2.7;

(46) C.sub.HClconcentration (unit: moL/L) of the hydrochloric acid solution;

(47) m.sub.acrmolar mass of acrylate (87.46 g/mol);

(48) m.sub.smass of the sample, unit: g.

(49) Two measurements are performed at the same time, and the arithmetic average is taken as the measurement result. The result is rounded off to one decimal place.

Example 1

(50) A method for preparing a super absorbent resin is provided, which comprises the following steps.

(51) 1) Acrylic acid (300 g) was formulated into a 25 wt % aqueous solution, cooled to 3-2 C., and slowly poured into a 2000 ml glass beaker wound with a heat insulation layer on the outer surface. The beaker was sealed with a plastic wrap, into which a nitrogen tube, and a thermometer were inserted.

(52) 2) Trimethylolpropane triacrylate (0.616 g), a solution containing 2-azobis(2-methylpropylamidine) dihydrochloride (0.110 g), and a solution containing sucrose fatty acid ester (0.03 g) were injected into the beaker respectively by using a syringe, and deoxygenated by bubbling nitrogen therethrough at 5 ml/min while stirring.

(53) 3) After 15 min, an aqueous solution containing sodium persulfate (0.6 g), an aqueous solution containing ascorbic acid/ferrous chloride (0.05 g), and a 48.5% aqueous sodium hydroxide solution (17.210 g) were respectively injected, and nitrogen was continuously bubbled therethrough for another 2 min while stirring. Several minutes later, the free radical polymerization was initiated and incubated for eight hours.

(54) 4) The gel obtained after reaction was cut into thin strips, sprayed with a 30% aqueous sodium carbonate solution (302 g) preheated to 45 C. or above, and broken, neutralized and granulated in a small neutralization extrusion granulator.

(55) 5) The granules were dried to a constant weight at a temperature ranging from 150 to 200 C. and then pulverized. Particles of 100-125 meshes were sieved by using a standard sieve, and formulated according to a fixed particle size combination, to obtain powdered raw super absorbent resin particles.

(56) 6) The raw super absorbent resin particles (100 g) were weighed. Propylene glycol:ethylene glycol diglycidyl ether:water at a ratio of 1.600 g:0.090 g:3.470 g were sprayed, uniformly mixed with the raw particles, and heated for 30 min at a temperature of 135 C.

(57) 7) The material was sprayed with a 15% solution of aluminium sodium sulfate (2.46 g) in water and uniformly mixed. Then, fumed silica (0.36 g) was added and heated for 2 min at a temperature of 135 C., to obtain a high-performance super absorbent resin.

(58) 8) Steps 6) and 7) were repeated to obtain a super absorbent resin (about 410 g).

Example 2

(59) A method for preparing a super absorbent resin is provided, which comprises the following steps.

(60) 1) Acrylic acid (300 g) was formulated into a 30 wt % aqueous solution, cooled to 3-2 C., and slowly poured into a 2000 ml glass beaker wound with a heat insulation layer on the outer surface. The beaker was sealed with a plastic wrap, into which a nitrogen tube, and a thermometer were inserted.

(61) 2) Pentaerythrityl triallyl ether (0.958 g), a solution of 2,2-(1,2-diazenediyl)bis[N-(2-hydroxyethyl)-2-methylpropionamide (0.117 g) in water, and a solution containing linear sodium dodecylbenzenesulfonate (0.03 g) were injected into the beaker respectively by using a syringe, and deoxygenated by bubbling nitrogen therethrough at 5 ml/min while stirring.

(62) 3) After 15 min, hydrogen peroxide (0.02 g), an aqueous solution containing ascorbic acid and ferrous chloride (0.09 g), and a 48.5% aqueous sodium hydroxide solution (17.210 g) were respectively injected, and nitrogen was continuously bubbled therethrough for another 2 min while stirring. Several minutes later, the free radical polymerization was initiated and incubated for eight hours.

(63) 4) The gel obtained after reaction was cut into thin strips, sprayed with a 48.5% aqueous sodium hydroxide solution (238.5 g), and broken, neutralized and granulated in a small neutralization extrusion granulator.

(64) 5) The granules were dried to a constant weight at a temperature ranging from 150 to 200 C. and then pulverized. Particles of 100-125 meshes were sieved by using a standard sieve, and formulated according to a fixed particle size combination, to obtain powdered raw super absorbent resin particles.

(65) 6) The raw super absorbent resin particles (100 g) were weighed. Propylene glycol:ethylene glycol diglycidyl ether:water at a ratio of 1.560 g:0.090 g:3.470 g were sprayed, uniformly mixed with the raw particles, and heated for 30 min at a temperature of 135 C.

(66) 7) The material was sprayed with a 15% solution of aluminium sodium sulfate (2.46 g) in water and uniformly mixed. Then, fumed silica (0.36 g) was added and heated for 5 min at a temperature of 135 C., to obtain a high-performance super absorbent resin.

(67) 8) Steps 6) and 7) were repeated to obtain a super absorbent resin (about 410 g).

Example 3

(68) A method for preparing a super absorbent resin is provided, which comprises the following steps.

(69) 1) Acrylic acid (300 g) was formulated into a 35 wt % aqueous solution, cooled to 3-2 C., and slowly poured into a 2000 ml glass beaker wound with a heat insulation layer on the outer surface. The beaker was sealed with a plastic wrap, into which a nitrogen tube, and a thermometer were inserted.

(70) 2) N,N, -methylene-bisacrylamide (0.071 g), acrylamide (0.071 g), a solution of 2,2-(1,2-diazenediyl)bis[N-(2-hydroxyethyl)-2-methylpropionamide (0.117 g) in water, and a solution of linear sodium dodecylbenzenesulfonate (0.03 g) in water were injected into the beaker respectively by using a syringe, and nitrogen was bubbled therethrough.

(71) 3) After 15 min, hydrogen peroxide (0.02 g), an aqueous solution containing ascorbic acid and ferrous chloride (0.09 g), and a 48.5% aqueous sodium hydroxide solution (17.210 g) were respectively injected, and nitrogen was continuously bubbled therethrough for another 2 min while stirring. Several minutes later, the free radical polymerization was initiated and incubated for eight hours.

(72) 4) The gel obtained after reaction was cut into thin strips, sprayed with a 48.5% aqueous sodium hydroxide solution (238.5 g), and broken, neutralized and granulated in a small neutralization extrusion granulator.

(73) 5) The granules were dried to a constant weight at a temperature ranging from 150 to 200 C. and then pulverized. Particles of 100-125 meshes were sieved by using a standard sieve, and formulated according to a fixed particle size combination, to obtain powdered raw super absorbent resin particles.

(74) 6) The raw super absorbent resin particles (100 g) were weighed. Propylene glycol:ethylene glycol diglycidyl ether:water at a ratio of 1.600 g:0.090 g:3.470 g were sprayed, uniformly mixed with the raw particles, and heated for 30 min at a temperature of 135 C.

(75) 7) The material was sprayed with a 15% solution of aluminium sodium sulfate (2.46 g) in water and uniformly mixed. Then, magnesia (0.15 g) and fumed silica (0.26 g) was added and heated for 2 min at a temperature of 135 C., to obtain a high-performance super absorbent resin.

(76) 8) Steps 6) and 7) were repeated to obtain a super absorbent resin (about 410 g).

Example 4

(77) A method for preparing a super absorbent resin is provided, which comprises the following steps.

(78) 1) Acrylic acid (300 g) was formulated into a 25 wt % aqueous solution, cooled to 3-2 C., and slowly poured into a 2000 ml glass beaker wound with a heat insulation layer on the outer surface. The beaker was sealed with a plastic wrap, into which a nitrogen tube, and a thermometer were inserted.

(79) 2) Trimethylolpropane triacrylate (0.616 g), a solution containing 2-azobis(2-methylpropylamidine) dihydrochloride (0.110 g), and a solution containing straight-chain sodium fatty alcohol polyoxyethylene ether sulphate (0.03 g) were injected into the beaker respectively by using a syringe, and deoxygenated by bubbling nitrogen therethrough at 5 ml/min while stirring.

(80) 3) After 15 min, a solution of sodium persulfate (0.6 g) in water, and a solution of ascorbic acid/ferrous chloride (0.05 g) in water were respectively injected, and nitrogen was continuously bubbled therethrough for another 2 min while stirring. Several minutes later, the free radical polymerization was initiated and incubated for eight hours.

(81) 4) The gel obtained after reaction was cut into thin strips, sprayed with a 48.5% aqueous sodium hydroxide solution (255.7 g), and broken, neutralized and granulated in a small neutralization extrusion granulator.

(82) 5) The granules were dried to a constant weight at a temperature ranging from 150 to 200 C. and then pulverized. Particles of 100-125 meshes were sieved by using a standard sieve, and formulated according to a fixed particle size combination, to obtain powdered raw super absorbent resin particles.

(83) 6) The raw super absorbent resin particles (100 g) were weighed. 1,4-butylene glycol:ethylene glycol diglycidyl ether:water at a ratio of 1.912 g:0.090 g:3.470 g were sprayed, uniformly mixed with the raw particles, and heated for 30 min at a temperature of 135 C.

(84) 7) The material was sprayed with a 15% solution of aluminium sodium sulfate (2.46 g) in water and uniformly mixed. Then, fumed silica (0.36 g) was added and heated for 2 min at a temperature of 135 C., to obtain a high-performance super absorbent resin.

(85) 8) Steps 6) and 7) were repeated to obtain a super absorbent resin (about 410 g).

Example 5

(86) A method for preparing a super absorbent resin is provided, which comprises the following steps.

(87) 1) Acrylic acid (300 g) was formulated into a 31 wt % aqueous solution, cooled to 3-2 C., and slowly poured into a 2000 ml glass beaker wound with a heat insulation layer on the outer surface. The beaker was sealed with a plastic wrap, into which a nitrogen tube, and a thermometer were inserted.

(88) 2) Pentaerythrityl triallyl ether (0.958 g), and a solution of 2,2-(1,2-diazenediyl)bis[N-(2-hydroxyethyl)-2-methylpropionamide (0.117 g) in water were injected respectively by using a syringe, and deoxygenated by bubbling nitrogen therethrough at 5 ml/min while stirring.

(89) 3) After 15 min, hydrogen peroxide (0.02 g), and a solution of ascorbic acid and ferrous chloride (0.09 g) in water were respectively injected, and nitrogen was continuously bubbled therethrough for another 2 min while stirring. Several minutes later, the free radical polymerization was initiated and incubated for eight hours.

(90) 4) The gel obtained after reaction was cut into thin strips, sprayed with a 30% aqueous sodium carbonate solution (547 g) preheated to 45 C. or above, and broken, neutralized and granulated in a small neutralization extrusion granulator.

(91) 5) The granules were dried for 2 hrs at a temperature ranging from 150 to 200 C. and then pulverized. Particles of 100-125 meshes were sieved by using a standard sieve, and formulated according to a fixed particle size combination, to obtain powdered raw super absorbent resin particles.

(92) 6) The raw super absorbent resin particles (100 g) were weighed. Propylene glycol:neopentyl glycol polydiglycidyl ether:water at a ratio of 1.600 g:0.123 g:3.470 g were sprayed, uniformly mixed with the raw particles, and heated for 25 min at a temperature of 145 C.

(93) 7) The material was sprayed with a 15% solution of aluminium sodium sulfate (2.46 g) in water and uniformly mixed. Then, fumed silica (0.36 g) was added and heated for 2 min at a temperature of 135 C., to obtain a high-performance super absorbent resin.

(94) 8) Steps 6) and 7) were repeated to obtain a super absorbent resin (about 410 g).

Example 6

(95) A method for preparing a super absorbent resin is provided, which comprises the following steps.

(96) 1) Acrylic acid (300 g) was formulated into a 35 wt % aqueous solution, cooled to 3-2 C., and slowly poured into a 2000 ml glass beaker wound with a heat insulation layer on the outer surface. The beaker was sealed with a plastic wrap, into which a nitrogen tube, and a thermometer were inserted.

(97) 2) N,N, -methylene-bisacrylamide (0.071 g), acrylamide (0.071 g), and a solution of 2,2-(1,2-diazenediyl)bis[N-(2-hydroxyethyl)-2-methylpropionamide (0.117 g) in water were injected into the beaker respectively by using a syringe, and nitrogen was bubbled therethrough.

(98) 3) After 15 min, hydrogen peroxide (0.02 g), an aqueous solution containing ascorbic acid and ferrous chloride (0.09 g), and a 48.5% aqueous sodium hydroxide solution (17.210 g) were respectively injected, and nitrogen was continuously bubbled therethrough for another 2 min while stirring. Several minutes later, the free radical polymerization was initiated and reacted for eight hours.

(99) 4) The gel obtained after reaction was cut into thin strips, sprayed with a 48.5% aqueous sodium hydroxide solution (255.7 g), and broken, neutralized and granulated in a small neutralization extrusion granulator.

(100) 5) The granules were dried to a constant weight at a temperature ranging from 150 to 200 C. and then pulverized. Particles of 100-125 meshes were sieved by using a standard sieve, and formulated according to a fixed particle size combination, to obtain powdered raw super absorbent resin particles.

(101) 6) The raw super absorbent resin particles (100 g) were weighed. Propylene glycol:ethylene glycol diglycidyl ether:water at a ratio of 1.600 g:0.090 g:3.470 g were sprayed, uniformly mixed with the raw particles, and heated for 30 min at a temperature of 135 C.

(102) 7) The material was sprayed with a 15% solution of aluminium sodium sulfate (2.46 g) in water and uniformly mixed. Then, fumed silica (0.36 g) was added and heated for 2 min at a temperature of 135 C., to obtain a high-performance super absorbent resin.

(103) 8) Steps 6) and 7) were repeated to obtain a super absorbent resin (about 410 g).

Example 7

(104) A method for preparing a super absorbent resin is provided, which comprises the following steps.

(105) 1) Acrylic acid (300 g) was formulated into a 25 wt % aqueous solution, cooled to 3-2 C., and slowly poured into a 2000 ml glass beaker wound with a heat insulation layer on the outer surface. The beaker was sealed with a plastic wrap, into which a nitrogen tube, and a thermometer were inserted.

(106) 2) Trimethylolpropane triacrylate (0.616 g), a solution containing 2-azobis(2-methylpropylamidine) dihydrochloride (0.110 g), and a solution containing sucrose fatty acid ester (0.03 g) were injected into the beaker respectively by using a syringe, and deoxygenated by bubbling nitrogen therethrough at 5 ml/min while stirring.

(107) 3) After 15 min, an aqueous solution containing sodium persulfate (0.6 g), an aqueous solution containing ascorbic acid/ferrous chloride (0.05 g), and a 48.5% aqueous sodium hydroxide solution (17.210 g) were respectively injected, and nitrogen was continuously bubbled therethrough for another 2 min while stirring. Several minutes later, the free radical polymerization was initiated and incubated for eight hours.

(108) 4) The gel obtained after reaction was cut into thin strips, sprayed with a 48.5% aqueous sodium hydroxide solution (238.5 g), and broken, neutralized and granulated in a small neutralization extrusion granulator.

(109) 5) The granules were dried to a constant weight at a temperature ranging from 150 to 200 C. and then pulverized. Particles of 100-125 meshes were sieved by using a standard sieve, and formulated according to a fixed particle size combination, to obtain powdered raw super absorbent resin particles.

(110) 6) The raw super absorbent resin particles (100 g) were weighed. Propylene glycol:ethylene glycol diglycidyl ether:water at a ratio of 1.600 g:0.090 g:3.470 g were sprayed, uniformly mixed with the raw particles, and heated for 30 min at a temperature of 135 C.

(111) 7) The material was sprayed with a 15% solution of aluminium sodium sulfate (2.46 g) in water and uniformly mixed. Then, fumed silica (0.36 g) was added and heated for 2 min at a temperature of 135 C., to obtain a high-performance super absorbent resin.

(112) 8) Steps 6) and 7) were repeated to obtain a super absorbent resin (about 410 g).

Example 8

(113) A method for preparing a super absorbent resin is provided, which comprises the following steps.

(114) 1) Acrylic acid (300 g) was formulated into a 30 wt % aqueous solution, cooled to 3-2 C., and slowly poured into a 2000 ml glass beaker wound with a heat insulation layer on the outer surface. The beaker was sealed with a plastic wrap, into which a nitrogen tube, and a thermometer were inserted.

(115) 2) Pentaerythrityl triallyl ether (0.958 g), and a solution of 2,2-(1,2-diazenediyl)bis[N-(2-hydroxyethyl)-2-methylpropionamide (0.117 g) in water were injected respectively by using a syringe, and deoxygenated by bubbling nitrogen therethrough at 5 ml/min while stirring.

(116) 3) After 15 min, hydrogen peroxide (0.02 g), an aqueous solution containing ascorbic acid and ferrous chloride (0.09 g), and a 48.5% aqueous sodium hydroxide solution (17.210 g) were respectively injected, and nitrogen was continuously bubbled therethrough for another 2 min while stirring. Several minutes later, the free radical polymerization was initiated and reacted for eight hours.

(117) 4) The gel obtained after reaction was cut into thin strips, sprayed with a 48.5% aqueous sodium hydroxide solution (238.5 g), and broken, neutralized and granulated in a small neutralization extrusion granulator.

(118) 5) The granules were dried to a constant weight at a temperature ranging from 150 to 200 C. and then pulverized. Particles of 100-125 meshes were sieved by using a standard sieve, and formulated according to a fixed particle size combination, to obtain powdered raw super absorbent resin particles.

(119) 6) The raw super absorbent resin particles (100 g) were weighed. Propylene glycol:ethylene glycol diglycidyl ether:water at a ratio of 0.525 g:0.090 g:1.485 g were sprayed, uniformly mixed with the raw particles, and heated for 30 min at a temperature of 135 C.

(120) 7) The material was sprayed with a 15% solution of aluminium sodium sulfate (2.25 g) in water and uniformly mixed. Then, fumed silica (0.25 g) was added and heated for 5 min at a temperature of 130 C., to obtain a high-performance super absorbent resin.

(121) 8) Steps 6) and 7) were repeated to obtain a super absorbent resin (about 410 g).

Example 9

(122) A method for preparing a super absorbent resin is provided, which comprises the following steps.

(123) 1) Acrylic acid (300 g) was formulated into a 35 wt % aqueous solution, cooled to 3-2 C., and slowly poured into a 2000 ml glass beaker wound with a heat insulation layer on the outer surface. The beaker was sealed with a plastic wrap, into which a nitrogen tube, and a thermometer were inserted.

(124) 2) N,N,-methylene-bisacrylamide (0.071 g), acrylamide (0.071 g), and a solution of 2,2-(1,2-diazenediyl)bis[N-(2-hydroxyethyl)-2-methylpropionamide (0.117 g) in water were injected into the beaker respectively by using a syringe, and nitrogen was bubbled therethrough.

(125) 3) After 15 min, hydrogen peroxide (0.02 g), an aqueous solution containing ascorbic acid and ferrous chloride (0.09 g), and a 48.5% aqueous sodium hydroxide solution (17.210 g) were respectively injected, and nitrogen was continuously bubbled therethrough for another 2 min while stirring. Several minutes later, the free radical polymerization was initiated and reacted for eight hours.

(126) 4) The gel obtained after reaction was cut into thin strips, sprayed with a 48.5% aqueous sodium hydroxide solution (255.7 g), and broken, neutralized and granulated in a small neutralization extrusion granulator.

(127) 5) The granules were dried to a constant weight at a temperature ranging from 150 to 200 C. and then pulverized. Particles of 100-125 meshes were sieved by using a standard sieve, and formulated according to a fixed particle size combination, to obtain powdered raw super absorbent resin particles.

(128) 6) The raw super absorbent resin particles (100 g) were weighed. Propylene glycol:ethylene glycol diglycidyl ether:water at a ratio of 1.600 g:0.090 g:3.470 g were sprayed, uniformly mixed with the raw particles, and heated for 30 min at a temperature of 135 C.

(129) 7) The material was sprayed with a 15% solution of aluminium sodium sulfate (2.46 g) in water and uniformly mixed. Then, fumed silica (0.36 g) was added and heated for 2 min at a temperature of 135 C., to obtain a high-performance super absorbent resin.

(130) 8) Steps 6) and 7) were repeated to obtain a super absorbent resin (about 410 g).

Examples 10-12

(131) The preparation method in these examples was the same as that in Example 1, except that methacrylic acid, maleic acid, and fumaric acid monomer were respectively used to replace the acrylic acid monomer, and cooled to 3-5 C.

Examples 13-14

(132) The preparation method in these examples was the same as that in Example 1, except that in Step 5), the drying temperature was 130-140 C. and 200 C.300 C. respectively.

Example 15

(133) The preparation method in these examples was the same as that in Example 1, except that in Step 6), sorbitol polyglycidyl ether was used to replace ethylene glycol diglycidyl ether, and heated for 40 min at a temperature of 90-100 C.

Example 16

(134) The preparation method in these examples was the same as that in Example 1, except that in Step 6), diglycerol polyglycidyl ether was used to replace ethylene glycol diglycidyl ether, and heated for 10 min at a temperature of 170-180 C.

Example 17

(135) The preparation method in these examples was the same as that in Example 1, except that in Step 6), ethylenediamine was used to replace ethylene glycol diglycidyl ether.

(136) FIG. 1 is a photograph of an existing super absorbent resin having a solid structure under a high power microscope. FIGS. 2 and 3 are photographs of the super absorbent resins having a porous structure according to the present invention under a high power microscope. The performance test results of the super absorbent resin according to the present invention are shown in Tables 1-4.

(137) TABLE-US-00001 TABLE 1 Test results of absorption capacity, water retention capacity and pressure resistance. Water retention capacity Water retention Pressure resistance Absorption capacity capacity after Absorbency under Absorbency centrifugation pressure (0.9% Pure at 150G saline) water 0.9% saline 0.9% saline 0.6 psi: 0.9 psi: Sample g/g g/g g/g g/g g/g Example 1 620 67.3 42.2 14.5 10.3 Example 2 438 60.1 36.2 22.2 16.8 Example 3 415 58.0 33.8 23.5 17.1 Example 4 643 67.9 42.7 14.1 11.4 Example 5 450 60.8 33.5 24.8 17.7 Example 6 430 58.5 34.3 24.6 18.1 Example 7 679 69.2 44.8 13.3 9.8 Example 8 470 67.7 42.6 15.0 10.4 Example 9 455 59.7 34.7 23.7 16.4 Existing 430 56.5 35.3 26.6 19.2 product

(138) TABLE-US-00002 TABLE 2 Test results of liquid absorption rate, liquid diffusivity, and bulk density Liquid absorption rate Absorption Absorption capacity capacity within a Liquid Bulk within a fixed time fixed time interval Absorption rate diffusivity density interval (pure water) (0.9% saline) Static Vortex Flow-through Apparent 1 min 3 min 5 min 1 min 3 min 5 min method method rate density Sample g/g g/g g/g g/g g/g g/g s s ml/min g/ml Example 1 189 321 397 31 49 56 24/48 26 18 0.62 Example 2 210 370 428 34 50 55 25/48 26 55 0.59 Example 3 203 353 410 33 48 54 26/49 27 89 0.60 Example 4 207 334 408 32 49 57 24/49 27 26 0.61 Example 5 201 341 397 33 49 54 24/49 24 86 0.60 Example 6 207 346 406 32 48 53 26/50 28 93 0.60 Example 7 214 354 420 33 51 55 23/47 25 12 0.60 Example 8 227 431 459 35 51 57 25/47 23 17 0.59 Example 9 213 359 412 34 50 55 26/49 25 9 0.59 Existing 63 160 226 17 31 39 66/133 61 14.6 0.66 product

(139) TABLE-US-00003 TABLE 3 Test results of particle size, particle size distribution, and hydrolysis resistance Particle size and particle size distribution Hydrolysis Particle size distribution resistance Average >25 25-35 35-50 50-100 <100 Extractable particle size meshes meshes meshes meshes meshes content Sample m % % % % % % Example 1 444 0.6 38.0 49.1 11.9 0.4 5.22 Example 2 404 0.1 21.1 59.5 19.0 0.3 3.12 Example 3 402 0.6 25.0 52.0 21.2 1.1 4.82 Example 4 403 0.7 26.4 50.2 16.3 0.4 4.92 Example 5 396 0.5 25.7 52.1 20.3 1.5 2.35 Example 6 405 4.2 41.2 39.2 15.1 0.1 4.07 Example 7 406 3.7 44.5 40.3 11.4 0.1 5.42 Example 8 407 0.3 34.3 52.4 12.2 0.6 3.67 Example 9 407 0.3 34.3 52.4 12.2 0.6 5.37 Existing product 405 4.2 41.2 39.2 15.1 0.1 17.84

(140) TABLE-US-00004 TABLE 4 Test results of reverse osmosis of liquid absorbed Reverse osmosis of liquid absorbed Quantity of reverse osmosis 1 hr 4 hrs 8 hrs 16 hrs 24 hrs Sample g g g g g Example 1 0.84 1.76 2.01 2.73 3.12 Example 2 0.82 1.82 2.19 2.81 3.09 Example 3 0.91 1.94 2.31 3.01 3.12 Example 4 0.82 1.81 2.14 2.87 3.26 Example 5 0.77 1.61 2.17 2.52 2.64 Example 6 0.89 1.91 2.28 3.05 3.17 Example 7 1.02 2.13 2.74 3.21 4.11 Example 8 0.93 1.83 2.23 2.91 3.32 Example 9 0.92 2.01 2.35 3.44 4.83 Existing product 0.97 2.25 4.28 5.46 5.92

(141) Through various tests, it has been confirmed that the super absorbent resin of the present invention has excellent physical properties and can be used in agricultural and forestry soil water retention agents, as water absorbents in hygiene products such as diapers, adult incontinence products and feminine hygiene products, and in preservation applications for food preservation.

(142) Obviously, the above examples are merely provided for elucidating the present invention, and not intended to limit the implementations of the present invention. Other variations or changes in various forms can be made by those skilled in the art based on the above description, which are not enumerated herein. Any obvious changes or variations derived from the technical solutions of the present invention are still within the protection scope of the present invention.