CN111621039A - Water-absorbent resin and preparation method thereof - Google Patents
Water-absorbent resin and preparation method thereof Download PDFInfo
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Abstract
The invention relates to a water-absorbent resin and a preparation method thereof, comprising the following steps: a. and (3) fine powder granulation: mixing the water-absorbent resin micro powder prepared by aqueous solution polymerization and reversed-phase suspension polymerization processes with lignocellulose according to a certain proportion, adding deionized water and a swelling aid to uniformly swell the mixture and form hydrogel particles; b. and (3) drying: drying the hydrogel particles prepared in the step a until the moisture content is lower than 3%; c. grinding and screening: grinding and screening the dried particles prepared in the step b to obtain raw powder with the particle size distribution of 150-850 microns; d. surface crosslinking: and c, uniformly spraying surface cross-linking treatment liquid into the raw powder obtained in the step c, and carrying out heat treatment to obtain a finished product. The water-absorbent resin prepared by the invention has special appearance and excellent comprehensive performance, has high diffusion, high pressurization, high absorption speed and high water retention, effectively recycles micro powder, reduces dust pollution and lowers production cost.
Description
Technical Field
The invention relates to the field of water-absorbent resins, in particular to a water-absorbent resin with better absorption, diffusion and conductivity prepared by granulating fine powder and a preparation method thereof.
Background
The super absorbent resin is a high polymer material with strong water absorption capacity and water retention capacity, is widely used in the field of sanitary materials such as paper diapers and sanitary towels, and can also be used as a water-blocking material for cables, a water-retaining agent special for agriculture, forestry and gardening, and the like.
The common water-absorbent resins mainly include partially neutralized products of polyacrylic acid, neutralized products of starch-acrylic acid graft polymers, hydrolyzed products of starch-acrylonitrile graft polymers, saponified products of vinyl acetate-acrylic ester copolymers, and the like.
As a method for producing such a water-absorbent resin, an aqueous solution polymerization method, a reversed-phase suspension polymerization method, and the like are known. The water-absorbent resins prepared by different polymerization processes have different shapes and properties, and the product prepared by the aqueous solution polymerization process has high pressurized absorption and liquid passing rate; the product prepared by the reversed phase suspension polymerization process has extremely high liquid absorption rate. The particle size of the water-absorbent resin in the field of physiological hygiene is required to be 150-850 μm, but the water-absorbent resin with a particle size smaller than this range is inevitably generated in the preparation process, and is called as micropowder. The micro powder has small particle size, is easy to cause dust pollution, and also has cracking performance.
At present, around the problem of micropowder of water-absorbent resin, people generally swell the water-absorbent resin with water and then add other auxiliary agents to carry out fine powder granulation (Chinese patents CN100333826C and CN1636629A, European patents EP0309187 and EP0844270) so as to obtain normal products with the particle size of 150-850 microns again; or directly added into acrylic acid neutralized liquid for repolymerization (Chinese patents CN105131314B and CN106574006A, U.S. Pat. No. 4,985,692). The fine powder granulation methods only aim at the water-absorbent resin micro powder with single shape and performance, and either lack the liquid passing performance or lack the water retention capacity, so that the water-absorbent resin with balanced comprehensive performance cannot be finally obtained.
Therefore, how to effectively utilize the fine powder, reduce the cost and improve the performance is a very valuable research field.
Disclosure of Invention
In view of the disadvantages of these conventional methods, an object of the present invention is to provide a water-absorbent resin and a method for producing the same, by which a water-absorbent resin having high dispersion, high absorption rate and high liquid permeability can be obtained easily and efficiently.
The invention provides a preparation method of water-absorbent resin for solving the existing technical problems, which comprises the following steps:
a. and (3) fine powder granulation: mixing the water-absorbent resin micro powder prepared by an aqueous solution polymerization method, the water-absorbent resin micro powder prepared by an inverse suspension polymerization method and lignocellulose according to a certain proportion, and adding deionized water and a swelling aid to uniformly swell the mixture and form hydrogel particles;
b. and (3) drying: drying the hydrogel particles prepared in the step a to the moisture content of less than 3%, wherein the drying temperature is preferably 100-300 ℃, and more preferably 180-240 ℃; the drying time is preferably 10-60 min;
c. grinding and screening: grinding and screening the dried particles prepared in the step b to obtain raw powder with the particle size distribution of 150-850 microns;
d. surface crosslinking: and c, uniformly spraying a surface crosslinking treatment solution into the raw powder obtained in the step c, and carrying out heat treatment at 80-180 ℃ for 0.5-2h to obtain a water-absorbent resin finished product.
The fine powder of the present invention refers to a raw water-absorbent resin powder having a particle size distribution of 150 μm or less, and preferably, the fine powder is a raw water-absorbent resin powder having a particle size distribution of 150 μm or less without being subjected to surface cross-linking.
The amount of the fine powder of the water-absorbent resin produced by the reversed-phase suspension polymerization method of the present invention is 10 to 100%, preferably 10 to 99%, more preferably 20 to 80%, and still more preferably 30 to 70% of the total mass of the fine powder.
The addition amount of the lignocellulose is 0.1-10% of the total mass of the two micro powders, and the addition amount is preferably 0.5-3%.
The lignocellulose of the invention has an average fiber length of 100-1000 μm, more preferably 200-800 μm, such as 300 μm, 400 μm, 500 μm, 600 μm, 700 μm.
The volume density of the lignocellulose is 10-100g/L, more preferably 20-50g/L, such as 30g/L, 45g/L, 55g/L, 65g/L and 80 g/L.
In step a of the invention, the swelling aid is selected from one or more of 1, 3-propylene glycol, 1, 4-butanediol, 1, 2-propylene glycol and glycerol, and the addition amount is 0.1-10% of the total mass of the two micro powders, preferably 1-5%.
The adding amount of the deionized water is 50-500% of the total mass of the two micro powders, and preferably 100-200%.
The surface crosslinking treatment liquid in the step d) is an aqueous epoxy dispersion, preferably, the solid content of the aqueous epoxy dispersion is 30-60%, the viscosity is 300-1200cP, and the particle size is 500-1000 nm.
The addition amount of the aqueous epoxy dispersion is 0.2-5%, preferably 0.5-2% of the total mass of the two micro powders.
The aqueous epoxy dispersion of the present invention can be prepared by an existing preparation method, or a commercially available aqueous epoxy dispersion can be directly purchased.
The aqueous epoxy dispersion of the present invention comprises: epoxy resin, cosolvent, emulsifier and water.
Preferably, the content of each component is 30-60% of epoxy resin, 5-15% of cosolvent, 5-15% of emulsifier and 30-50% of water based on the total weight of the aqueous epoxy dispersion.
The epoxy resin is one or more of E-20, E-44 or E-51.
The emulsifier is one or more of modified epoxy resin, polyethylene glycol, polyether amine or conventional anionic surfactant (such as sodium dodecyl sulfate).
The modified epoxy resin is epoxy resin containing hydroxyl, carboxyl or amino, and can be prepared by reacting epoxy resin with a compound containing hydroxyl, carboxyl or amino.
The cosolvent is one or more of ethylene glycol methyl ether, propylene glycol methyl ether, ethylene glycol dimethyl ether and propylene glycol dimethyl ether.
The preparation method of the aqueous epoxy resin dispersion comprises the steps of adding the emulsifier and the cosolvent into epoxy resin according to a proportion, adding water to disperse the emulsifier and the cosolvent, and performing phase inversion to form the epoxy resin aqueous dispersion. The aqueous dispersion can also be prepared by a one-step process, i.e. mixing the emulsifier, the cosolvent, the compound containing hydroxyl, carboxyl or amino groups, and the epoxy resin, and then adding water for dispersion.
The present invention further relates to a water-absorbent resin obtained by the above production method, which has a centrifuge water retention of 29g/g or more, a 1min pure water absorption of 180g/g or more, a vertical diffusion absorption capacity of 8.0g/ml or more, and an absorption under a load of 4.14kpa of 18g/g or more.
The preparation method and the prepared water-absorbent resin have the following advantages:
the water-absorbent resin and the micro powder thereof prepared by the aqueous solution polymerization process and the reversed-phase suspension polymerization process have different shapes and properties. From the aspect of appearance, the former presents irregular blocks; the latter are uniform spherical particles; from the aspect of performance, the micro powder granulation product obtained by the former has poor water retention (the damage of a partial cross-linked network structure caused by over-drying and grinding), and has better pressurizing and liquid passing performance; the micro powder granulation product obtained by the latter has poor liquid passing performance (poor strength, high absorption speed and easy gel blockage), and has excellent water retention and absorption speed performance. The invention combines the advantages of the two components together, the prepared water-absorbent resin has special appearance and excellent comprehensive performance, has high diffusion, high pressurization, high absorption speed and high water retention, effectively recycles the micro powder, reduces dust pollution and lowers the production cost.
On one hand, lignocellulose with a loose porous structure is introduced into a system, so that the flow guiding effect and the conduction performance inside the resin are enhanced by virtue of natural dispersion and wetting and good flow guiding and diffusing properties (capillary effect); on the other hand, the water-based epoxy dispersoid is used as the surface crosslinking treatment liquid, and the absorption speed of the water solution of the common glycidyl ether surfactant is very high, so that the added surface crosslinking liquid is easy to have the defects of uneven distribution such as caking and the like, or the defects of different penetration depths and the like, and the comprehensive performance of the product is influenced. The epoxy dispersion is adopted, so that the purpose of uniform diffusion and distribution can be achieved, the epoxy dispersion and the added lignocellulose are combined, the surface cross-linking liquid slowly permeates to form a core-shell structure with uniform shell thickness distribution and uniform outer layer cross-linking network density distribution, and fine powder mixed granulation by different processes is adopted to make up respective performance defects, so that a product with excellent comprehensive performance is obtained.
Drawings
FIG. 1 is a schematic view showing the structure of an assay device x;
FIG. 2 shows SEM of the product of micro powders A and B after granulation of mixed fine powders;
Detailed Description
In order to better understand the present invention, the following examples are further provided to illustrate the content of the present invention, but the content of the present invention is not limited to the following examples.
The properties of the water absorbent resins in the following examples were measured by the following methods:
(1) physiological saline absorption (g/g) under load of 4.14kpa
The saline absorption capacity under a load of 4.14kPa was measured by the measuring apparatus x outlined in FIG. 1 below.
First, the valve 12 and the valve 13 of the measuring cylinder 1 were closed, physiological saline adjusted to 25 ℃ was injected from the upper part of the measuring cylinder 10, the upper part of the measuring cylinder was sealed with the rubber stopper 14, then the valve 12 and the valve 13 of the measuring cylinder 1 were opened, and then the height of the test table 3 (the center part of which was opened with a hole having a diameter of 2mm) was adjusted so that the tip of the guide tube 2 (having a diameter of 2mm) at the center part of the test table 3 and the air inlet port of the air inlet tube 11 were at the same height.
On the other hand, 0.10g of water-absorbent resin 5 was uniformly spread on nylon mesh cloth 41 of cylinder 40, and weight 42 (1.9 cm in diameter, 119.6g in weight, placed on water-absorbent resin 5, and capable of uniformly applying a load of 4.14 kPa) was placed on water-absorbent resin 5. The measurement unit 4 is placed so that the central portion thereof coincides with the catheter port in the central portion of the measurement table 3.
The amount of decrease in physiological saline (the amount of physiological saline absorbed by the water-absorbent resin 5) wc (mL) in the measuring cylinder 10 was continuously read from the time when the water-absorbent resin 5 started to absorb water. The water absorption capacity of the water-absorbent resin 5 under a load of 4.14kPa after 60 minutes from the start of water absorption was determined by the following equation:
water absorption capacity (mL/g) of physiological saline under load of 4.14 kPa: wc (mL)/mass (g) of water-absorbent resin
(2) Vertical diffusion absorption Capacity (mL/g)
The same measurement apparatus x was used to measure the vertical diffusion water absorption capacity, and the same operation was carried out as that for physiological saline under a load of 4.14kPa except that the amount of the water-absorbent resin 5 used was changed to 1.0g without using the weight 42.
The amount of decrease Wd (mL) in the physiological saline in the measuring cylinder 10 (the amount of physiological saline absorbed by the water-absorbent resin 5) is continuously read from the time when the water-absorbent resin 5 starts absorbing water. The vertical diffusion water absorption capacity of the water-absorbent resin 5 after 60 minutes from the start of water absorption was determined by the following equation: water absorption capacity in vertical diffusion (mL/g) ═ Wd (mL)/mass (g) of water-absorbent resin
(3) Centrifuge water retention (g/g)
0.2g of sample is weighed to the nearest 0.001g and the mass is recorded as m0Pouring all the samples into a tea bag, sealing the tea bag, and soaking until enough 0.9% physiological substance is filledSoaking in a beaker of saline water for 30 min. Then the tea bag containing the sample is lifted out, hung by a clip, and after dripping water for 10min in a static state, the tea bag containing the sample is dehydrated for 3min under the centrifugal force condition of 250G, and then the mass of the tea bag containing the sample is weighed and is recorded as m2. Using the tea bag without the sample to perform blank value measurement, weighing the blank tea bag and recording the mass as m1The centrifugal water retention rate is (m)2-m1-m0)/m0。
(4)1min pure water absorption (g/g)
Adding 0.5g (accurate to 0.001g) of dried SAP sample into a beaker containing 250mL of deionized water (the water temperature is controlled to be 23-25 ℃), starting timing by a stopwatch, stirring the aqueous solution uniformly as soon as 1min, immediately introducing the solution into a filter bag, slightly dripping off free water, weighing the weight of the filter bag when the colloid is added and after the colloid is taken out, wherein the weight is m respectively2And m1Namely: the SAP sample had a pure water absorption (g/g) of 1min ═ m2-m1)/0.5. The two types of fine water-absorbent resin powders used in the following examples were prepared by the following methods, respectively:
aqueous solution polymerization process micropowder A-1:
100 parts of acrylic acid and 70 parts of deionized water are put into a mixing device, 130 parts of a 50% sodium hydroxide aqueous solution by mass concentration are added, after thorough mixing, the temperature is cooled to 60 ℃, and then 0.2 part of polyethylene glycol 400 diacrylate, 0.1 part of ethoxylated trimethylolpropane (n ═ 9) triacrylate, 0.2 part of sodium bicarbonate, 0.02 part of sodium dodecyl sulfate and 0.1 part of sodium persulfate are rapidly added.
Pouring the acrylic acid neutralized solution into a reaction kettle, adding 0.05 part of sodium sulfite, and reacting at 60 ℃ for 20min to obtain the water-absorbent resin hydrogel. Cutting, granulating, drying, grinding and screening the obtained hydrogel to obtain the super absorbent resin with the water content of 1.8 percent, and taking the raw powder with the particle size of below 150 micrometers as micro powder A-1; aqueous solution polymerization process micropowder A-2:
putting 100 parts of acrylic acid and 249 parts of deionized water into a mixing device, adding 0.2 part of pentaerythritol triallyl ether, 0.4 part of polyethylene glycol 400 diacrylate, 0.01 part of hydrogen peroxide and 0.025 part of 2,2' -azobisisobutyramidine hydrochloride (AIBA), fully mixing, introducing nitrogen for 30min, and cooling to 5-10 ℃.
And (2) quickly pouring the acrylic acid aqueous solution into a reaction kettle, adding 0.005 part of ascorbic acid, reacting at 10 ℃ for 30min, raising the temperature to 88 ℃ at the maximum, and then keeping the temperature at 80 ℃ for 8h to obtain the water-absorbent resin hydrogel. The hydrogel obtained was subjected to multistage granulation while mixing with 80 parts of a 50% aqueous sodium hydroxide solution to obtain hydrogel particles. Then drying, grinding and screening to obtain the super absorbent resin with the water content of 1.6 percent, and taking the raw powder with the particle size of less than 150 microns as micro powder A-2;
inverse suspension polymerization process micropowder B-1:
300g of n-heptane was charged into a 1L four-necked round bottom flask equipped with a stirrer, a reflux condenser, a thermometer and a nitrogen inlet tube. To this was added 0.92g of sucrose fatty acid ester (S-370, HLB ═ 3.0), heated to 50 ℃ and uniformly dissolved and dispersed at a stirring speed of 300rpm, and then cooled to 30 ℃.
92g of an aqueous acrylic acid solution was placed in a 500mL Erlenmeyer flask, and 120g of a 32% w.t. aqueous sodium hydroxide solution was added dropwise to the Erlenmeyer flask while cooling. Then, 0.184g of potassium persulfate, 0.02g of ethylene glycol diglycidyl ether, and 86g of deionized water were added thereto to obtain an aqueous acrylic acid monomer solution.
The aqueous acrylic monomer solution was charged into the above four-necked round-bottomed flask, and nitrogen gas was introduced for 30min while stirring. Then the water bath is heated to 80 ℃ and the reaction is carried out for 1 h. After the reaction is finished, the temperature is continuously raised to 120 ℃ for azeotropic dehydration, and 150g of water is removed. Then the residual n-heptane in the system is removed by filtration and distillation reaction, and finally the water-absorbent resin micro powder B is dried for 40min at 150 ℃, and then the single isolated spherical water-absorbent resin micro powder B with the average particle size of 60 microns and the water content of 1.9 percent can be obtained.
Inverse suspension polymerization process micropowder B-2:
300g of cyclohexane was charged to a 1L four necked round bottom flask equipped with a stirrer, reflux condenser, thermometer and nitrogen inlet tube. To this was added 0.92g of a maleic anhydride-modified ethylene-propylene block copolymer (Mitsui chemical Co., Ltd., Hiwax-1105A), heated to 80 ℃ and uniformly dissolved and dispersed at a stirring speed of 300rpm, and then cooled to 50 ℃.
92g of an aqueous acrylic acid solution was placed in a 500mL Erlenmeyer flask, and 120g of a 32% w.t. aqueous sodium hydroxide solution was added dropwise to the Erlenmeyer flask while cooling. Then, 0.184g of potassium persulfate, and 86g of deionized water of 0.015g of ethoxylated trimethylolpropane (n ═ 9) triacrylate were added thereto to obtain an aqueous acrylic monomer solution.
The aqueous acrylic monomer solution was charged into the above four-necked round-bottomed flask, and nitrogen gas was introduced for 30min while stirring. Then the water bath is heated to 75 ℃ and the reaction is carried out for 2 h. After the reaction is finished, the temperature is continuously raised to 100 ℃ for azeotropic dehydration, and 150g of water is removed. Then the residual n-heptane in the system was removed by filtration and distillation reaction, and finally dried at 130 ℃ for 1 hour, at which time a single isolated spherical water-absorbent resin fine powder B-2 having an average particle diameter of 80 μm and a water content of 2.8% was obtained.
Preparation of aqueous epoxy dispersion a (stepwise method):
injecting 800g of PEG6000 subjected to melting and dehydration into a kettle, keeping the temperature in the kettle at 80 ℃, then adding 47g of hexahydrophthalic anhydride into the reaction kettle, heating to 100 ℃, reacting for about 3 hours, sampling to test the acid value to reach a theoretical value of 10mgKOH/g (determined by NaOH back titration, the same below), injecting 210g of liquid epoxy resin E20, uniformly stirring, adding 3.5g of triphenylphosphine catalyst, reacting at the constant temperature of 130 ℃ for 3 hours, testing the acid value to be-0.25 mgKOH/g, and discharging to prepare the active emulsifier. Injecting 450g of molten epoxy resin E20 into a dispersion kettle, maintaining the temperature in the kettle at 100 ℃, then adding 100g of the prepared active emulsifier and 100g of glycol dimethyl ether solvent, and stirring and mixing for 20min at the speed of 800 r/min; then, the temperature is reduced to 75 ℃, the lifting rotation speed is 1200r/min, 400g of deionized water is dripped within 2 hours (initial 1/2 water is dripped slowly), and the system is cooled to 50 ℃ after the water dripping is finished, and then the material is discharged. The dispersion was measured as follows: the dispersion particle size was approximately 830 nm; viscosity 1000 cp; solid content: 58 percent.
Preparation of aqueous epoxy dispersion B (one-shot):
simultaneously adding 56g of polyether amine (PEA, molecular weight of 2000), 3.5g of aminoethanesulfonic acid, 200g of epoxy resin E44 and 80g of propylene glycol dimethyl ether serving as a solvent into a reaction kettle, raising the temperature to 100 ℃, reacting for 2.5h, and stirring and mixing for 20min at the speed of 800 r/min; then cooling to 75 ℃, increasing the rotating speed to 1200r/min, dripping 300g of deionized water (slowly dripping the initial 1/2 water) within 2h, and cooling the system to 50 ℃ after the water dripping is finished, and discharging. The dispersion was measured as follows: the dispersion particle size was about 620 nm; viscosity 630 cp; solid content: 40 percent.
Lignocellulose (shanghai meimengjia chemical science and technology limited): the average fiber length is 200-800 μm, and the bulk density is 20-80 g/L.
Example 1:
respectively mixing micro powder A-170 g and micro powder B-130 g prepared by the two processes with 1.0g of lignocellulose, and adding 100g of deionized water containing 1% of 1, 3-propylene glycol to uniformly swell the mixture and form hydrogel particles. Drying the granulated hydrogel particles at 210 ℃ until the moisture content is lower than 3%. Then, the dried water-absorbent resin particles are ground and sieved to obtain raw powder with the particle size distribution of 150-850 microns. And finally, uniformly spraying an aqueous epoxy dispersion A accounting for 1.0 percent of the total mass of the two micro powders into the obtained raw powder, uniformly dispersing and adsorbing the aqueous epoxy dispersion A, and drying the aqueous epoxy dispersion A at the temperature of 130 ℃ for 1 hour to obtain a finished product with special appearance and performance.
Example 2:
mixing micro powder A-260 g and micro powder B-240 g prepared by the two processes with lignocellulose 1.0g respectively, and adding deionized water 100g containing 2% of 1, 4-butanediol to uniformly swell the mixture and form hydrogel particles. Drying the granulated hydrogel particles at 210 ℃ until the moisture content is lower than 3%. Then, the dried water-absorbent resin particles are ground and sieved to obtain raw powder with the particle size distribution of 150-850 microns. And finally, uniformly spraying an aqueous epoxy dispersion B which accounts for 0.6 percent of the total mass of the two micro powders into the obtained raw powder, uniformly dispersing and adsorbing the aqueous epoxy dispersion B, and drying the mixture for 1 hour at the temperature of 130 ℃ to obtain a finished product with special appearance and performance.
Example 3:
the main difference between this embodiment and embodiment 1 is that: the micro powder prepared by the two processes is 50g of A-2 and 50g of B-1, the addition amount of lignocellulose is 2.0g, and the addition amount of the aqueous epoxy dispersion A is 2.0 percent of the total mass of the two micro powders.
Example 4:
the main difference between this example and example 2 is that the micropowder prepared by the two processes was 80g of A-1 and 20g of B-2, respectively, the amount of lignocellulose added was 0.5g, and the amount of aqueous epoxy dispersion B added was 1.2% of the total mass of the two micropowder.
Example 5:
this example differs from example 3 mainly in that the amount of lignocellulose added was 1.0g, the amount of aqueous epoxy dispersion a added was 1.0% of the total mass of the two fine powders and the amount of aqueous epoxy dispersion B added was 0.5% of the total mass of the two fine powders.
Comparative example 1:
the subsequent operation of example 1 described above was repeated except that the mass of the fine powder a1 was changed to 100g and the mass of the fine powder B was changed to 0 g.
Comparative example 2:
the subsequent operation of the above example 2 was repeated except that the mass of the fine powder A was changed to 0g and the mass of the fine powder B-2 was changed to 100 g.
Comparative example 3:
the subsequent operation of example 1 above was repeated except that no lignocellulose was added.
Comparative example 4:
the subsequent operation of example 2 was repeated except that the aqueous epoxy dispersion B was replaced with a 2% aqueous solution of ethylene glycol diglycidyl ether (mass concentration: 0.5%) and the amount of lignocellulose added was adjusted to 0 g.
Comparative example 5:
the subsequent operation of example 4 described above was repeated except that the aqueous epoxy dispersion B was replaced with a 2% aqueous solution of ethylene glycol diglycidyl ether (mass concentration: 0.5%).
The process and the performance of the obtained product are respectively shown in the following tables 1 and 2, and the structure of the product obtained by mixing and granulating the fine powder A and the fine powder B is shown in the attached figure 2:
TABLE 1 comparison of granulation processes for fine powders in examples and comparative examples
TABLE 2 comparison of product Properties in examples and comparative examples
The embodiment shows that in the process of mixing two kinds of micro powder of different processes for fine powder granulation, when the micro powder A and the micro powder B are blended, a water-absorbent resin product with excellent comprehensive performance can be obtained, the product performance at the time makes up the defects caused by respective single fine powder granulation, and the advantage complementation is effectively formed; the water-based epoxy dispersion is used as the surface crosslinking treatment liquid, so that the water-based epoxy dispersion can be uniformly diffused and permeated with the surface of the powder, the crosslinking reaction is more thorough, and a more effective core-shell structure is formed; and the introduction of lignocellulose with a loose porous structure and good dispersion and conduction effects can ensure that fine powder is granulated and dispersed better, which is beneficial to a drying process and improves the vertical absorption performance of a final product to a certain extent. However, as can be seen from the comparative examples, the fine powder a or the fine powder B is granulated alone or the mixed fine powders a and B are granulated, but when the ratio is not suitable or the addition amount of the conventional surface crosslinking treatment liquid or the aqueous epoxy dispersion is insufficient, the comprehensive properties of the obtained product cannot be well balanced, and a single property defect exists.
The absorbed liquid can be absorbed by the passages formed by the lignocellulose at the moment of contacting the water-absorbent resin particles, and the absorbed liquid is quickly diffused to the surfaces of the particles by virtue of the aqueous epoxy dispersion and the nuclear layer formed on the surfaces of the particles and then absorbed again, so that the absorption rate is improved, the effect of instant dryness is achieved, the diffusion and liquid passing capacities are improved, and the utilization rate of the water-absorbent resin is improved. The improved fine powder granulation method of the water-absorbent resin provides a certain research thought for preparing a water-absorbent resin product with a novel structure and excellent liquid passing, diffusion and conductivity properties.
The above embodiments are only for illustrating the invention and not for limiting the invention, and persons skilled in the art should understand that any modifications, equivalent replacements, fine process adjustment and the like of the invention are within the scope of the invention, and the protection scope of the invention is defined by the claims.
Claims (10)
1. An improved process for the preparation of a water-absorbent resin, characterized in that it comprises the following steps:
a. and (3) fine powder granulation: mixing the water-absorbent resin micro powder prepared by an aqueous solution polymerization method, the water-absorbent resin micro powder prepared by an inverse suspension polymerization method and lignocellulose according to a certain proportion, and adding deionized water and a swelling aid to uniformly swell the mixture and form hydrogel particles;
b. and (3) drying: drying the hydrogel particles prepared in the step a to a moisture content of less than 3%, preferably, the drying temperature is 100-300 ℃, more preferably 180-240 ℃;
c. grinding and screening: grinding and screening the dried particles prepared in the step b to obtain raw powder with the particle size distribution of 150-850 microns;
d. surface crosslinking: and c, uniformly spraying a surface crosslinking treatment solution into the raw powder obtained in the step c, and carrying out heat treatment at 80-180 ℃ for 0.5-2h to obtain a water-absorbent resin finished product.
2. The method of claim 1, wherein: the fine powder in step a means a raw water-absorbent resin powder having a particle size distribution of 150 μm or less, and preferably, the fine powder of the water-absorbent resin produced by the reversed-phase suspension polymerization accounts for 10 to 100%, preferably 10 to 99%, more preferably 20 to 80%, and further preferably 30 to 70% of the total mass of the fine powder.
3. The method according to claim 1 or 2, characterized in that: the addition amount of the lignocellulose in the step a is 0.1-10% of the total mass of the two kinds of micro powder, and the preferable addition amount is 0.5-3%; preferably, the lignocellulose has an average fiber length of 100-1000 μm and a bulk density of 10-100 g/L.
4. A method according to any one of claims 1-3, characterized in that: the swelling aid in the step a is selected from one or more of 1, 3-propylene glycol, 1, 4-butanediol, 1, 2-propylene glycol and glycerol, and the addition amount of the swelling aid is 0.1-10%, preferably 1-5% of the total mass of the two micro powders.
5. The method according to any one of claims 1-4, wherein: the adding amount of the deionized water in the step a is 50-500% of the total mass of the two micro powders, and preferably 100-200%.
6. The method according to any one of claims 1 to 5, wherein: the surface crosslinking treatment fluid in the step d is an aqueous epoxy dispersion, the solid content of the aqueous epoxy dispersion is 30-60%, the viscosity of the aqueous epoxy dispersion is 300-1200cP, and the particle size of the aqueous epoxy dispersion is 500-1000 nm.
7. The method of claim 6, wherein: the aqueous epoxy dispersion comprises: epoxy resin, cosolvent, emulsifier and water;
preferably, the content of each component is 30-60% of epoxy resin, 5-15% of cosolvent, 5-15% of emulsifier and 30-50% of water based on the total weight of the aqueous epoxy dispersion.
8. The method according to claim 6 or 7, characterized in that: the addition amount of the aqueous epoxy dispersion is 0.2-5%, preferably 0.5-2% of the total mass of the two micro powders;
preferably, the epoxy resin is one or more of E-20, E-44 or E-51;
preferably, the emulsifier comprises one or more of modified epoxy resin, polyethylene glycol, polyether amine or conventional anionic surfactant;
preferably, the modified epoxy resin is an epoxy resin containing a hydroxyl group, a carboxyl group or an amino group, and can be prepared by reacting the epoxy resin with a compound containing a hydroxyl group, a carboxyl group or an amino group;
preferably, the cosolvent is one or more of ethylene glycol methyl ether, propylene glycol methyl ether, ethylene glycol dimethyl ether and propylene glycol dimethyl ether.
9. The method according to any one of claims 6-8, wherein: the preparation method of the aqueous epoxy dispersion comprises the steps of adding the emulsifier and the cosolvent into epoxy resin according to a proportion, adding water to disperse the emulsifier and the cosolvent, and performing phase inversion to form an epoxy resin aqueous dispersion;
or mixing the emulsifier, the cosolvent, the compound containing hydroxyl, carboxyl or amino and the epoxy resin, and then adding water for dispersion.
10. A water-absorbent resin prepared by the method according to any one of claims 1 to 9, characterized in that: the obtained product has a centrifuge retention capacity of 29g/g or more, a 1-min pure water absorption capacity of 180g/g or more, a vertical diffusion absorption capacity of 8.0g/ml or more, and an absorption under a load of 4.14kpa of 18g/g or more.
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