CN113527598B

CN113527598B - Super water-absorbing polymer and preparation method thereof

Info

Publication number: CN113527598B
Application number: CN202010318717.6A
Authority: CN
Inventors: 王晓; 纪学顺; 刘懿平; 丁明强; 王刚; 赵帅; 赵镇; 田云; 马磊; 贾海东; 孙家宽
Original assignee: Wanhua Chemical Group Co Ltd
Current assignee: Wanhua Chemical Group Co Ltd
Priority date: 2020-04-21
Filing date: 2020-04-21
Publication date: 2022-08-02
Anticipated expiration: 2040-04-21
Also published as: CN113527598A

Abstract

The invention relates to a super absorbent polymer, in particular to a super absorbent polymer and a preparation method thereof, wherein the preparation method comprises the following steps: at the temperature of less than or equal to 20 ℃, the ethylenically unsaturated monomer containing carboxyl and/or the salt thereof, the oxidant, the reducing agent and the internal crosslinking agent are contacted to initiate polymerization reaction, so that hydrogel is obtained; crushing and extruding the hydrogel, and then contacting the hydrogel with a neutralizer to perform neutralization reaction to prepare colloidal particles; drying, grinding and screening the colloidal particles, and then contacting with a surface cross-linking agent to carry out surface cross-linking treatment to obtain super water-absorbent polymer resin; wherein the internal crosslinking agent at least comprises gallic acid epoxy resin. The method of the invention can improve the local internal crosslinking density of the super absorbent polymer resin and has strong supporting effect, thereby effectively improving the liquid permeability and the pressurization performance and ensuring the good water retention of the SAP resin.

Description

Super water-absorbing polymer and preparation method thereof

Technical Field

The invention relates to a super absorbent polymer, in particular to a super absorbent polymer with improved performance and a preparation method thereof.

Background

The water-absorbing polymer is a crosslinked, partially neutralized polymer, including crosslinked polyacrylic acid or crosslinked starch-acrylic acid graft polymers. According to its general definition, superabsorbent polymers are capable of absorbing large amounts of aqueous liquids and body fluids under swelling and the formation of hydrogels, as well as of retaining aqueous liquids under a certain pressure. Superabsorbent Polymers (SAP) can be formed into particles, commonly referred to as particulate Superabsorbent Polymers, wherein the particulate Superabsorbent Polymers can be post-treated with surface crosslinking, surface treatment, and other treatments to form the particulate Superabsorbent Polymers. The main use of superabsorbent polymers and particulate superabsorbent polymers is in hygiene articles, such as baby diapers, incontinence products or sanitary napkins.

Superabsorbent polymers used as absorbents in absorbent articles (e.g., disposable diapers) must have sufficiently high absorbent capacity as well as sufficiently high liquid permeability. The absorbent capacity needs to be high enough to enable the superabsorbent polymers to absorb large amounts of aqueous body fluids encountered during use of the absorbent article. The liquid permeability determines the diffusivity of liquid in the middle of the super absorbent polymer, increases the effective use ratio of the super absorbent polymer in the absorbent product and reduces the occurrence of gel blocking. Once gel blocking occurs, this can hinder fluid distribution to drier areas or portions of the absorbent article, and leakage from the absorbent article can occur before the particulate superabsorbent polymer within the absorbent article is fully saturated or before the fluid can diffuse or wick past the "blocking" particles into the remainder of the absorbent article.

For improving the liquid permeability and anti-caking property of super absorbent polymers, a common method is to add silica or metal oxides such as alumina and titanium oxide to polymer particles. Although the liquid permeability of the absorbent product can be improved well by adding the inorganic particles, the liquid absorption capacity, particularly under pressure, is also lowered, thereby affecting the liquid absorption capacity and the action effect of the super absorbent polymer during actual use.

Aiming at the aqueous solution polymerization process for preparing the super absorbent polymer, secondary surface crosslinking or inorganic particle addition and other means can be selected to improve the liquid permeability; for example, patent documents of Noel (publication Nos. CN 106987075A and CN 102702656A) disclose a method for preparing a water-absorbent resin which is polymerized at a low temperature and subjected to surface cross-linking multiple times, and which can prepare a water-absorbent resin having excellent liquid permeability and gel strength. Patent document CN 107406595 a discloses a method for preparing SAP particles by two surface cross-linking, and the cross-linking agent used for the two surface cross-linking is different. The inventors aimed to achieve a multiple shell structure by two cross-linking to improve the problem of resin blocking.

For example, patent document CN 107428948A discloses a method for preparing SAP particles by surface crosslinking through different methods, and surface crosslinking treatment can be performed using three methods using a polyhydric alcohol, a polyvalent metal salt, and a polyglycidyl ether; because the used surface cross-linking agents all have EO chain segment structures, the molecular chains are soft, and the degradation may occur in the high-temperature baking reaction stage, so that the comprehensive performance of the SAP particles is reduced.

In the above prior patent documents, the liquid permeability of the SAP particles is improved by means of multiple surface cross-linking, but the process is more complicated and the efficiency is lower.

In summary, SAP resins for hygiene articles require a low monomer residue, low long-term reverse osmosis, low extractables and other properties, such as a combination of water retention, pressure, and liquid permeability. The process recipe in the polymerization process plays a crucial role for the whole resin structure, and thus, intensive research into the process recipe is required.

Disclosure of Invention

The present invention has been made in view of the problem that the conventional improvement of super absorbent polymer cannot be achieved at the same time in terms of pressure performance, water retention and liquid permeability, and an object of the present invention is to provide a super absorbent polymer and a method for producing the same, which can increase the local internal crosslink density of the super absorbent polymer resin obtained and have a strong supporting effect, and can effectively improve the liquid permeability and pressure performance thereof while ensuring a high water retention rate of SAP resin.

In order to achieve the purpose, the technical scheme provided by the invention is as follows:

in one aspect, a superabsorbent polymer is provided having a polymerization feed comprising the following components:

a) a carboxyl group-containing ethylenically unsaturated monomer and/or a salt thereof in an aqueous polymerization solution at a concentration of 20 wt% or more and 35 wt% or less (e.g., 32 wt%, 25 wt%, 22 wt%), preferably 20 wt% or more and 30 wt% or less;

b) an internal crosslinking agent at least comprising gallic acid epoxy resin; the gallic acid epoxy resin is used in an amount of 0.01 wt% to 2 wt% (e.g., 0.015 wt%, 0.02 wt%, 0.04 wt%, 0.08 wt%, 0.1 wt%, 0.5 wt%, 0.8 wt%, 1.2 wt%, 1.8 wt%), preferably 0.05 wt% to 1 wt%, based on the weight of component a);

c) oxidizing agent in an amount of 0.005 wt% to 5 wt% (e.g., 0.008 wt%, 0.02 wt%, 0.05 wt%, 0.1 wt%, 0.4 wt%, 1.0 wt%, 3.0 wt%), preferably 0.01 wt% to 0.5 wt%, based on the weight of component a);

d) reducing agents in an amount of 0.005 wt% to 5 wt% (e.g., 0.008 wt%, 0.02 wt%, 0.05 wt%, 0.1 wt%, 0.4 wt%, 1.0 wt%, 3.0 wt%), preferably 0.01 wt% to 0.5 wt%, based on the weight of component a);

wherein, after the hydrogel obtained from the polymerization reaction is neutralized, the degree of neutralization of the carboxylic acid of the polymer in the obtained colloidal particles is 50 to 80 mol% (e.g., 55 mol%, 60 mol%, 70 mol%); the colloidal particles are converted into polymer particles, and the proportion of the polymer particles with the particle size of 150-700 microns (for example, 155 microns, 200 microns, 400 microns and 600 microns) is more than or equal to 92 wt% (for example, 94 wt%, 96 wt% and 98 wt%);

and, the surface of the polymer particles is treated with:

e) surface crosslinking is performed by 0.5 wt% to 5 wt% (e.g., 0.8 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt%) of a surface crosslinking agent applied to the surface of the dried polymer particles, based on the dried polymer particles, and, optionally

f) 0-2 wt% (e.g., 0.05 wt%, 0.1 wt%, 0.3 wt%, 0.5 wt%, 1.5 wt%) of an insoluble inorganic powder is added after surface crosslinking based on the dried polymer particles.

In the present invention, the carboxyl group-containing ethylenically unsaturated monomer and/or a salt thereof means a carboxyl group-containing ethylenically unsaturated monomer and/or a salt of a carboxyl group-containing ethylenically unsaturated monomer. The salt here may be an alkali metal salt (for example, sodium salt or potassium salt) of an ethylenically unsaturated monomer having a carboxyl group.

According to the superabsorbent polymer provided herein, in some examples, the ethylenically unsaturated monomer having a carboxyl group is selected from one or more of acrylic acid, methacrylic acid, ethacrylic acid, α -chloroacrylic acid, α -cyanoacrylic acid, β -methylacrylic acid (crotonic acid), α -phenylacrylic acid, β -acryloxypropionic acid, sorbic acid, α -chlorosorbic acid, 2' -methylisojac acid, cinnamic acid, p-chlorocinnamic acid, β -stearic acid, itaconic acid, citraconic acid, mesaconic acid, glutaconic acid, aconitic acid, maleic acid, fumaric acid, tricarboxyethylene, and maleic anhydride, preferably selected from acrylic acid and/or methacrylic acid, more preferably acrylic acid.

In some examples, the oxidizing agent is a peroxide, preferably selected from one or more of sodium persulfate, hydrogen peroxide, potassium persulfate, and ammonium persulfate, more preferably hydrogen peroxide.

In some examples, the reducing agent is selected from one or more of ascorbic acid, ammonium bisulfite, ammonium thiosulfate, ammonium dithionite, ammonium sulfide, and sodium hydroxymethylsulfoxylate, preferably ascorbic acid.

In some examples, the insoluble inorganic powder is selected from one or more of silicon dioxide, silica, titanium dioxide, alumina, magnesia, zinc oxide, talc, calcium phosphate, clay, diatomaceous earth, zeolite, bentonite, kaolin, hydrotalcite, and activated clay, preferably silicon dioxide (e.g., fumed silica and/or precipitated silica).

In some examples, the surface cross-linking agent is selected from one or more of a polyol compound, an epoxy compound, an amine compound, and a metal inorganic salt. The polyalcohol compound is preferably selected from ethylene glycol, propylene glycol, glycerol, 1, 4-butanediol or pentaerythritol; the epoxy compound is preferably selected from (poly) ethylene glycol diglycidyl ether, 1, 4-butanediol diglycidyl ether, ethylene carbonate or propylene carbonate; the amine compound is preferably selected from tris (hydroxymethyl) aminomethane or carbodiimide; the metal inorganic salt is preferably selected from an inorganic salt of calcium, magnesium, aluminum, iron, copper or zinc.

In some examples, the internal crosslinking agent further includes an internal crosslinking agent containing a double bond compound; the internal crosslinking agent containing a double bond compound is used in an amount of 0 to 4 wt% (e.g., 0.03 wt%, 0.08 wt%, 0.1 wt%, 0.5 wt%, 1.0 wt%, 1.5 wt%, 3.0 wt%), preferably 1 wt% to 2 wt%, based on the weight of component a).

In some examples, the internal crosslinking agent of the double bond-containing compound is selected from one or more of ethylene glycol diacrylate, propylene glycol diacrylate, N' -methylene bisacrylamide, polyethylene glycol diacrylate, polypropylene glycol diacrylate, pentaerythritol triallyl ether, ethoxylated glycerol triacrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate, triallylamine, pentaerythritol tetraacrylate, and dipentaerythritol hexaacrylate.

In some examples, the polymerization feedstock further comprises: g) at least one thermal initiator.

In some examples, the thermal initiator is an azo-based initiator, preferably selected from one or more of azobisisobutyronitrile, azobiscyanovaleric acid, azobisdimethylvaleronitrile, 2 '-azobis (2-amidinopropane) dihydrochloride, azobisamidinopropane dihydrochloride, 2' -azobis (N, N-dimethyleneisobutyramidine) dihydrochloride, 2- (carbamoylazo) isobutyronitrile, and 4, 4-azobis (4-cyanovaleric acid).

In some examples, the thermal initiator is used in an amount of 0.005 wt% to 1 wt% (e.g., 0.008 wt%, 0.015 wt%, 0.02 wt%, 0.05 wt%, 0.1 wt%, 0.5 wt%, 0.8 wt%), preferably 0.01 wt% to 0.2 wt%, based on the weight of component a).

In some examples, the superabsorbent polymer has a liquid absorption capacity of 60 to 70g/g, a centrifuge retention capacity of 35 to 40g/g, a 0.7psi press absorption capacity of 20 to 27g/g, a liquid absorption rate of 30 to 45s, a liquid flow rate (GBP) of 30Darcy or higher, a residual monomer content of 350ppm or less, and an extractable content of 4.5 wt% or less.

In another aspect, there is provided a method for preparing a super absorbent polymer, comprising the steps of:

contacting an ethylenically unsaturated monomer having a carboxyl group and/or a salt thereof, an oxidizing agent, a reducing agent and an internal crosslinking agent at 20 ℃ or less (e.g., 0 ℃,2 ℃, 5 ℃, 10 ℃, 15 ℃) to initiate polymerization, thereby obtaining a hydrogel; crushing and extruding the hydrogel, and then contacting the hydrogel with a neutralizer to perform neutralization reaction to prepare colloidal particles; drying, grinding and screening the colloidal particles, and then contacting with a surface cross-linking agent to carry out surface cross-linking treatment to obtain super water-absorbent polymer resin;

wherein the internal crosslinking agent at least comprises gallic acid epoxy resin.

According to the production method provided by the present invention, in some examples, the polymerization reaction is an aqueous solution polymerization. The initial temperature of the aqueous solution polymerization reaction does not exceed 20 ℃. After the initial temperature of the system is more than 25 ℃, the branching and chain transfer reactions are more frequent, which may lead to an increase in extractables content in the polymerization. In some examples, the system is pre-deoxygenated with nitrogen prior to the start of the reaction, which facilitates initiation of the monomer.

In the preparation process, it is possible that the carboxyl group-containing ethylenically unsaturated monomer and/or the salt of the carboxyl group-containing ethylenically unsaturated monomer participate in the polymerization reaction. When the salt of the carboxyl group-containing ethylenically unsaturated monomer participates in the polymerization reaction, it is necessary to perform a neutralization reaction (which may be referred to as a pre-neutralization reaction) of the carboxyl group-containing ethylenically unsaturated monomer with an alkaline substance before the polymerization reaction to obtain a salt of the carboxyl group-containing ethylenically unsaturated monomer, and then perform the polymerization reaction. The basic substance may be the same as the neutralizing agent used for the neutralization treatment (which may be referred to as a post-neutralization reaction) of the hydrogel, and examples thereof include sodium hydroxide and potassium hydroxide.

The concentration of the carboxyl group-containing ethylenically unsaturated monomer and/or its salt in the aqueous polymerization solution during the polymerization reaction can be suitably controlled, and is generally from 20 to 35% by weight. When the concentration continues to decrease, the heat of reaction is insufficient and the temperature of the system is not significantly raised, which may cause insufficient reaction and may result in higher residual monomers. When the concentration of the monomer participating in the polymerization in the system is too high, the temperature rises during the polymerization and may exceed the boiling point of water, which is disadvantageous for the control of the polymerization reaction. In some examples, the concentration of the carboxyl group-containing ethylenically unsaturated monomer and/or its salt in the aqueous polymerization solution is 20 wt% or more and 35 wt% or less (e.g., 32 wt%, 25 wt%, 22 wt%), preferably 20 wt% or more and 30 wt% or less.

In some examples, the gallic acid epoxy resin is used in an amount of 0.01 wt% to 2 wt% (e.g., 0.015 wt%, 0.02 wt%, 0.04 wt%, 0.08 wt%, 0.1 wt%, 0.5 wt%, 0.8 wt%, 1.2 wt%, 1.8 wt%), preferably 0.05 wt% to 1 wt%, based on the weight of the carboxyl group containing ethylenically unsaturated monomer and/or salt thereof.

In the polymerization system, in addition to the monomers participating in the polymerization, a redox initiator is included. In some examples, the oxidizing agent is used in an amount of 0.005 wt% to 5 wt% (e.g., 0.008 wt%, 0.02 wt%, 0.05 wt%, 0.1 wt%, 0.4 wt%, 1.0 wt%, 3.0 wt%), preferably 0.01 wt% to 0.5 wt%, based on the weight of the carboxyl group-containing ethylenically unsaturated monomer and/or salt thereof.

In some examples, the reducing agent is used in an amount of 0.005 wt% to 5 wt% (e.g., 0.008 wt%, 0.02 wt%, 0.05 wt%, 0.1 wt%, 0.4 wt%, 1.0 wt%, 3.0 wt%), preferably 0.01 wt% to 0.5 wt%, based on the weight of the carboxyl group-containing ethylenically unsaturated monomer and/or salt thereof.

In the preparation process, the polymerization reaction is understood to be: the initial phase was maintained by an ice bath and the temperature of the system rose after the induction phase was over, at which point polymerization began and the temperature did not exceed 20 ℃. The subsequent polymerization reaction is exothermic and the temperature of the system is raised to 70-90 ℃ and the reaction is continued for several hours at this temperature.

Considering that the reaction efficiency of epoxy groups and carboxyl groups in the gallic acid epoxy resin is relatively low, besides the optional addition of the alkaline catalyst, the hydrogel obtained by polymerization can be continuously cured and kept warm for a period of time after the polymerization temperature rise is finished. In some examples, the temperature of the curing heat-preservation is 85-95 ℃, and the time of the curing heat-preservation is 4-8 hours.

After the polymerization reaction is finished, the obtained hydrogel needs to be subjected to neutralization treatment so that the degree of neutralization of the carboxylic acid of the polymer can be controlled within a suitable range. The neutralization degree of the carboxylic acid of the polymer is too low, so that the obtained colloid is sticky and is not beneficial to subsequent treatment; too high a degree of neutralization of the carboxylic acid of the polymer may cause the pH of the SAP resin to be high, which may cause safety problems for human skin when used. In some examples, after subjecting the hydrogel to a neutralization reaction, the resulting colloidal particles have a degree of carboxylic acid neutralization of the polymer of 50 to 80 mol% (e.g., 55 mol%, 60 mol%, 70 mol%).

Drying, grinding and screening the colloidal particles to obtain Super Absorbent Polymer (SAP) particles; then the surface of the film is subjected to surface cross-linking treatment. In some examples, the surface cross-linking agent is applied to the surface of the dried superabsorbent polymer particles in an amount of 0.5 wt% to 5 wt% (e.g., 0.8 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt%) based on the dried superabsorbent polymer particles.

In some examples, the ethylenically unsaturated monomer having a carboxyl group is selected from one or more of acrylic acid, methacrylic acid, ethacrylic acid, α -chloroacrylic acid, α -cyanoacrylic acid, β -methacrylic acid, α -phenylacrylic acid, β -acryloxypropionic acid, sorbic acid, α -chlorosorbic acid, 2' -methylisonicacid, cinnamic acid, p-chlorocinnamic acid, β -stearic acid, itaconic acid, citraconic acid, mesaconic acid, glutaconic acid, aconitic acid, maleic acid, fumaric acid, tricarboxyethylene and maleic anhydride, preferably from acrylic acid and/or methacrylic acid, more preferably acrylic acid.

In some examples, the neutralizing agent is an aqueous solution of a basic compound having a concentration of 30 to 60 wt%, preferably 40 to 50 wt%. The basic compound is preferably selected from one or more of sodium hydroxide, potassium hydroxide, sodium carbonate and potassium carbonate, more preferably sodium hydroxide.

In some examples, a basic catalyst is also added during the polymerization reaction.

In some examples, the content of the basic catalyst in the aqueous polymerization solution is 10 to 1000ppm, preferably 50 to 300ppm, in the case of aqueous polymerization.

Preferably, the basic catalyst is selected from tertiary amines (e.g. triethylamine) and/or triphenylphosphine, more preferably triphenylphosphine.

Besides the gallic acid epoxy resin, other internal cross-linking agents can be optionally added. In some examples, the internal crosslinking agent further includes an internal crosslinking agent containing a double bond compound. The internal crosslinking agent containing a double bond compound is used in an amount of 0 to 4 wt% (e.g., 0.03 wt%, 0.08 wt%, 0.1 wt%, 0.5 wt%, 1.0 wt%, 1.5 wt%, 3.0 wt%), preferably 1 wt% to 2 wt%, based on the weight of the carboxyl group-containing ethylenically unsaturated monomer and/or its salt.

The colloid particles obtained after neutralization can obtain small-size colloidal particles after granulation, extrusion and crushing, and the colloidal particles need to be further dried before the small-size colloidal particles because the water content of the colloidal particles is higher. According to the preparation method provided by the present invention, in some examples, the drying temperature of the colloidal particles is 100 ℃ to 240 ℃ (e.g., 150 ℃, 180 ℃, 200 ℃, 220 ℃). The drying process may be carried out using apparatus well known in the art, for example, by forced air drying through an oven.

The size of the resulting SAP particles can be controlled by further grinding and sieving the dried colloidal particles. The size here is to be understood as the particle size of the particles.

During screening, a screen with the required size is selected for screening, and the proportion of oversize particles and undersize particles is controlled. For example, screening with particle sizes of 150 μm and 700 μm can achieve a majority of SAP particle sizes in the range of 150-700 microns; wherein the proportion of superabsorbent polymer (SAP) particles having a size of < 150 μm is not more than 3 wt.%, and the proportion of superabsorbent polymer (SAP) particles having a size of > 700 μm is not more than 5 wt.%. In some examples, after the colloidal particles are dried, the colloidal particles are further ground and sieved to control the size of the superabsorbent polymer particles; wherein the proportion of the superabsorbent polymer particles having a particle size of 150-700 [ mu ] m (e.g., 155 [ mu ] m, 200 [ mu ] m, 400 [ mu ] m, 600 [ mu ] m) is 92 wt% (e.g., 94 wt%, 96 wt%, 98 wt%).

The SAP particles obtained after sieving may be referred to herein as polymer raw powder. Further, the surface of the Super Absorbent Polymer (SAP) particles obtained by sieving may be subjected to a surface cross-linking treatment. In some examples, the process conditions of the surface cross-linking treatment include: the reaction temperature is 50-150 ℃, preferably 80-130 ℃; the reaction time is 0.5h-3h, preferably 1h-2 h.

In order to improve the flowability of superabsorbent polymers, some water-insoluble inorganic powders are generally added to prevent blocking on a large scale. Alternatively, 0 to 2 wt% (e.g., 0.05 wt%, 0.1 wt%, 0.5 wt%, 1 wt%, 1.5 wt%) of an insoluble inorganic powder is added after the surface cross-linking treatment, based on the dried superabsorbent polymer particles. In some examples, the insoluble inorganic powder is selected from one or more of silicon dioxide, silica, titanium dioxide, alumina, magnesia, zinc oxide, talc, calcium phosphate, clay, diatomaceous earth, zeolite, bentonite, kaolin, hydrotalcite, and activated clay, preferably silicon dioxide (e.g., fumed silica and/or precipitated silica).

In order to further reduce the residual monomers in the SAP resin, a thermal initiator may also be used in conjunction with the polymerization process. The thermal initiator is added into the system, so that the residual monomer in the system can be continuously consumed in the later stage of polymerization temperature rise. In some examples, at least one thermal initiator is added during the polymerization reaction.

In some examples, the thermal initiator is used in an amount of 0.005 wt% to 1 wt% (e.g., 0.008 wt%, 0.015 wt%, 0.02 wt%, 0.05 wt%, 0.1 wt%, 0.5 wt%, 0.8 wt%), preferably 0.01 wt% to 0.2 wt%, based on the weight of the carboxyl group-containing ethylenically unsaturated monomer and/or salt thereof.

The internal crosslinking reaction during the preparation of superabsorbent polymers places a particular emphasis on improving the water retention properties of the SAP, i.e., the state and capacity of absorbing saturated water. The key point of the invention is that gallic acid epoxy resin is introduced as an internal crosslinking agent in SAP resin polymerization, and a plurality of epoxy groups contained in the gallic acid epoxy resin are utilized to react with carboxyl.

The gallic acid epoxy resin used herein can be prepared by the method disclosed in patent document CN 102276788A. The chemical structure of the compound is shown in the following formula I.

It should be noted that the reaction efficiency of gallic acid epoxy resin as internal cross-linking agent is low, and in order to ensure the internal cross-linking effect of the polymer, a proper basic catalyst can be added into the polymer system to improve the internal cross-linking efficiency.

The alkaline catalyst is added to improve the internal crosslinking efficiency of the gallic acid epoxy resin, and the main purpose is to catalyze the reaction of carboxyl and epoxy group. In the polymerization reaction using gallic acid epoxy resin as internal crosslinking agent, in order to make the SAP resin have low extractable content (small molecular weight fraction), the initial polymerization temperature is usually selected to be low, at which the reaction of carboxyl group and epoxy group is slow, and the addition of alkaline catalyst can promote the generation of internal crosslinking.

The reaction of carboxyl and epoxy group is a nucleophilic addition reaction, and the basic catalyst can be selected from tertiary amine (such as triethylamine), triphenylphosphine and the like.

Other types of internal crosslinking agents, generally those containing bifunctionality and being aliphatic flexible chains, are commonly used. Since the degree of internal crosslinking is low during polymerization of such an internal crosslinking agent, gel collapse is caused to easily cause clogging in the absorption process, and the liquid permeability of the SAP resin is deteriorated. Liquid permeability can only be improved unless excessive internal crosslinking is employed, which can compromise the liquid absorption rate and water retention properties of the SAP resin.

The SAP resin particles prepared by the method have obvious performance improvement effect, namely, the SAP resin has high water retention rate, high pressure liquid absorption rate and high liquid passing rate on the premise of lower content of residual monomers and low content of extracts. In addition, SAP resins have high absorbency under pressure, partly because SAP resins prepared in a kettle process have a high molecular weight, and higher molecular weights are more likely to form high absorbency under pressure products.

Compared with the prior art, the technical scheme of the invention has the beneficial effects that:

by introducing gallic acid epoxy resin as an internal crosslinking agent in the polymerization reaction process, the local internal crosslinking density of the polymer can be high due to the addition of a small amount of gallic acid epoxy resin, and the gallic acid epoxy resin contains benzene rings, so that the strength of internal crosslinking points is improved, the core structure pore canal of the obtained SAP particles has a good retention effect, the liquid penetration depth and penetration retention can be facilitated, and the SAP particles have high water retention rate and liquid absorption rate while the high pressurization liquid absorption rate and liquid passing rate of the SAP particles are ensured.

Detailed Description

In order that the technical features and contents of the present invention can be understood in detail, preferred embodiments of the present invention will be described in more detail below. While the preferred embodiments of the present invention have been described in the examples, it should be understood that the present invention may be embodied in various forms and should not be limited by the embodiments set forth herein.

< sources of raw materials >

Acrylic acid, purchased from watson chemical, with a purity of over 99.5%;

gallic acid epoxy resin, self-made, preparation method refer to patent document CN 102276788A (e.g., example 1);

hydrogen peroxide (H) ₂ O ₂ Aqueous solution) purchased from Chinese medicine, aqueous solution with concentration of 30 wt%;

ascorbic acid, available from sigma, with a purity of over 99%;

caustic soda aqueous solutions with concentrations of 32 wt% and 50 wt%, respectively, purchased from watson chemical;

pentaerythritol triallyl ether purchased from Japan, with a purity of more than 80%;

polyethylene glycol diacrylate purchased from Changxing materials, with the purity of more than 95%;

other reagents used in the embodiments of the present invention are conventional in the art, and the purchase information thereof is not described herein again.

< test methods >

a) Liquid absorption rate

Weighing 0.2g of test sample to be accurate to 0.001g, recording the mass as m, pouring all the test samples into a tea bag, sealing the tea bag, soaking into a beaker filled with enough physiological saline with the concentration of 0.9 percent, and soaking for 30 min. Then, the tea bag containing the test specimen was lifted out, hung with a clip, and after dripping water for 10min in a static state, the mass of the tea bag containing the test specimen was weighed and recorded as m 1). Then, a blank value measurement was performed using a tea bag without the test sample, and the mass of the blank test tea bag was weighed and recorded as m 2. The liquid-absorbing capacity is (m1-m 2)/m.

b) Centrifugal water retention

The tea bag with the test sample having the above-mentioned test absorbency was dehydrated under a centrifugal force condition of 250G for 3min, and then the mass of the tea bag with the test sample was weighed and designated as m 3. The blank value measurement was performed using a tea bag without a test sample, and the mass of the blank tea bag was weighed and recorded as m 4. The centrifuge retention rate was (m3-m 4)/m.

c)0.7psi pressure imbibition factor

The equipment used for the test was: (1) the inner diameter of the plastic cylinder with openings at two ends is 60mm, and a nylon net with 200 meshes is fixed at one end of the plastic cylinder; (2) the outer diameter of the plastic piston is slightly smaller than 59mm, and the plastic piston can be tightly connected with the plastic cylinder and can freely move up and down; (3) a round weight of 1340 g; (4) the glass dish is internally provided with a porous plate, so that the plastic cylinder can be placed on the porous plate, does not contact the bottom of the glass dish and can freely absorb moisture.

The test method comprises the following steps: the glass dish was placed on the platform and then 0.9% physiological saline was poured in. 0.9g of the test specimen was weighed, uniformly sprinkled into the bottom of the plastic cylinder, and then a plastic piston with a weight added thereto was added to the plastic cylinder, and the mass thereof was measured and designated as m 5. The plastic cylinder with the added sample is placed on the perforated plate of a glass dish, and after 60min the plastic cylinder is lifted out of the glass dish and after the water drops have been cleaned the mass of the plastic cylinder is tested and marked m 6. Then, the liquid absorption capacity under pressure at 0.7psi is (m6-m 5)/0.9.

d) Imbibition rate (vortex method)

50g of physiological saline at 23 ℃ was weighed in a 100ml beaker, and then a magnetic rod was added to the beaker, and the beaker was stirred on a magnetic stirrer at a revolution number of 600 rpm. 2.0g of the test specimen was accurately weighed and poured all at once into a vortex. The timing was started after the input, and the middle vortex was gradually reduced in the process of the test sample absorbing the physiological saline. And stopping timing until the vortex disappearance cut liquid level reaches the level, wherein the measured time is the liquid absorption rate of the test sample.

e) Liquid throughput rate (GBP)

Weighing 0.9g of test sample, and putting the test sample into an organic glass cylinder with the inner diameter of 60 mm; the plexiglass cylinder containing the test sample is placed in 0.9% saline and allowed to freely swell for 30 min. The plexiglass cylinder is taken out of the physiological saline, the cylinder cover is closed, the weight is placed, the height of the gel layer is read and marked as H. And (3) placing the organic glass cylinder on testing equipment, enabling the liquid level in the cylinder to reach a 4cm scale mark, maintaining the liquid level unchanged, starting timing after the liquid stably flows out, measuring the amount of the liquid flowing through the gel layer, and calculating the flow Q of the liquid passing through the gel layer.

The formula for calculating GBP is:

wherein Q is the liquid flow rate and the unit is g/s;

h is the height of the gel layer, and the unit is cm;

mu is liquid viscosity in unit of P, and the viscosity of physiological saline is 1cP (0.01P);

a is the area of the gel layer in cm ² The inner diameter of the plexiglass cylinder is 6cm, and the area of the gel layer is 28.27cm ² ；

P is hydrostatic pressure in dyne/cm ² And P is rho gh, h is the liquid level height of 4cm, the hydrostatic pressure is 3924dyne/cm ² ；

Rho is the density of the liquid in g/cm ³ The density of the normal saline is 1g/cm ³ And (6) counting.

f) Content of extractable matter

Measuring 200ml of 0.9% NaCl solution in a 250ml beaker by using a measuring cylinder, weighing 1.0g of test sample to be accurate to 0.005g, adding the test sample into the solution, sealing the opening of the beaker by using a sealing film, placing the beaker on a magnetic stirrer and stirring the beaker at the rotating speed of 500 +/-50 rpm for 16 hours; stopping stirring, allowing the colloid in the beaker to settle to the bottom, filtering the supernatant in the beaker by using a Buchner funnel and filter paper, collecting more than 50ml of filtrate, and measuring 50ml of filtrate to perform a titration test.

Simultaneously preparing a blank sample (200ml of a 0.9% NaCl solution), carrying out titration on the blank solution (100ml of a 0.9% NaCl aqueous solution), and carrying out titration by using a 0.1mol/l NaOH solution until the pH value is 10; then, titration was carried out using a 0.1mol/l hydrochloric acid solution until the pH was 2.7. The blank titration amounts were [ bNaOH ], [ bHCL ] (mL), respectively.

A0.9% NaCl solution was added to 50mL of the filtrate, and the same titration as above was carried out to obtain the amounts of [ NaOH ], [ HCl ] (mL) in the titrated amounts.

The calculation formula of the neutralization degree is as follows:

DN(％)＝100-(([NaOH]-[bNaOH])×c(NaOH)*100)/(([HCl]-[bHCl])×c(HCl))；

average molecular weight Mw is 72.06x (1-DN/100) +94.04 xDN/100;

the extractable content Ex (wt%) (([ HCl ] - [ bHCl ]) xc (HCl) x Mwx 2)/5.

g) Residual monomer content (ppm)

Weighing 1.000 g of test sample to 0.005g, putting the sample into a clean 250ml beaker, and measuring 200ml of 0.9% NaCl solution by using a measuring cylinder and adding the solution into the beaker; a magnetic stirrer was added, the beaker was sealed with a sealing film, and the solution was stirred on a magnetic stirrer at 500. + -. 50rpm for 60 minutes. Stopping stirring, standing for 5 min, collecting the upper layer solution 1-2ml, filtering with 0.45 μm filter, placing in a liquid phase special sample bottle, marking, and analyzing by HPLC.

And opening the automatic sample injector, filling the numbered sample bottles into corresponding positions, aligning the positions, and closing the door. Selecting a sequence in software, opening a sequence table, editing the sequence table and clicking application. And clicking a green general start button in a menu bar, autonomously inputting the name of the sample group, and clicking 'running', so that the test is started. The change in the intensity of the sample signal over time is visible. And (4) waiting for the instrument to be stable, and enabling the temperature and the degassing pressure of the column incubator of the host machine and the temperature and the energy of the detector to reach set values, and then automatically starting the test.

After the sample is tested, the LC1260 (offline) software is opened, the data analysis is selected, the folder is opened, and the analysis result needing to be opened is found. And selecting a sample to be processed, opening a spectrogram, selecting 'integral current chromatogram', and reading a peak area. The residual monomer content of the test samples was calculated in the EXCEL table using the calibration curve.

Example 1

Preparation process of SAP resin particles:

mixing 550g of prepared acrylic acid aqueous solution with the concentration of 60 wt%, 640g of deionized water, 0.85g of gallic acid epoxy resin and 1.6g of polyethylene glycol diacrylate in a 2L polymerization kettle, cooling to 5 ℃ in an ice bath, deoxidizing for 10min by using nitrogen, adding 2g H into the polymerization kettle ₂ O ₂ Aqueous solution (diluted to a concentration of 2 wt.%), 2g of 2, 2' -azobis (N, N-dimethyleneisobutyramidine) dihydrochlorideAnd (3) mixing the solution (diluted to the concentration of 4 wt%), 0.1g of triphenylphosphine and 2.5g of 2 wt% ascorbic acid aqueous solution (in the polymerization aqueous solution, the concentration of the monomer is 27.5 wt%), after the induction period is finished, starting the polymerization reaction when the temperature starts to obviously rise, reacting for about 1.5h, and keeping the temperature for curing for 5h to obtain the hydrogel polymer.

Crushing and extruding the hydrogel polymer by using a granulating auger machine, adding 270g of NaOH aqueous solution with the concentration of 50 wt% for post-neutralization, and neutralizing about 74 mol% of carboxyl in the polymer of the obtained colloidal particles into sodium carboxylate; drying by using a forced air drying oven (purchased from high-speed railway company), setting the temperature at 180 ℃, carrying out forced air drying on the neutralized colloid particles, wherein the drying time lasts for 40min, crushing the dried colloid by using a crusher or a wall breaking machine (purchased from American company), and sieving by using a screen until the particle size is within the range of 150-700 microns to obtain the SAP resin particles. The SAP resin particles that are not surface-crosslinked are defined as polymer raw powder a.

Performing surface crosslinking treatment on SAP resin particles:

100g of polymer raw powder a was weighed, a mixture of 0.1g of ethylene glycol diglycidyl ether, 1.4g of 1, 2-propanediol and 6g of deionized water was atomized, uniformly sprayed on the surfaces of the polymer raw powder a particles, and the polymer particles were fluidized in the air and continuously mixed. And then placing the mixed polymer particles into a high-temperature air blast oven, and heating for 1.5h at 110 ℃ to perform surface crosslinking treatment. The polymer particles after surface cross-linking treatment were cooled to below 40 ℃, and 2g of an aqueous solution of aluminum sulfate having a concentration of 20 wt% was atomized and sprayed onto the surface cross-linked polymer particles, while the polymer particles were fluidized in air and continuously mixed. The mixed polymer particles were sieved using a standard mesh of the desired mesh size to obtain the target product having a particle size distribution of 150-700 microns.

Example 2

The preparation process was carried out according to the procedure of example 1, except that:

during the polymerization stage, a mass of 550g of deionized water was added (the concentration of the monomer in the aqueous polymerization solution was 29.7 wt%).

In the surface crosslinking treatment stage, 1g of ethylene glycol diglycidyl ether was added.

Example 3

The preparation process refers to the operating procedure of example 1, with the difference that:

in the polymerization stage, the amount of gallic acid epoxy resin added was 6.5g (gallic acid epoxy content: 1.97% by mass), and the amount of 50 wt% NaOH aqueous solution added was changed to 294g (degree of neutralization of carboxylic acid: 80 mol%).

Example 4

in the polymerization stage, the mass of the added gallic acid epoxy is 0.05g (the mass of the gallic acid epoxy accounts for 0.01 percent), and 1.6g of the added polyethylene glycol diacrylate is replaced by 1.8g of pentaerythritol triallyl ether.

In the polymerization stage, 50g of NaOH aqueous solution with the concentration of 50 wt% and acrylic acid aqueous solution are added to carry out preneutralization reaction, the temperature is reduced, and the generated acrylate is subjected to polymerization reaction; after the polymerization, the hydrogel obtained was post-neutralized by adding 220g of a 50% strength by weight aqueous NaOH solution.

Example 5

during the polymerization stage, the temperature is reduced to 12 ℃ in an ice bath, and H is added simultaneously ₂ O ₂ The mass of the aqueous solution (diluted to a concentration of 2% by weight) was replaced with 1.5 g;

and in the surface crosslinking treatment stage, the temperature of surface crosslinking is increased to 130 ℃, and the time of surface crosslinking is shortened to 1 h.

Example 6

after the surface cross-linking treatment was completed, 2g fumed silica HDK N20D (Watt grams) was added, the SAP particles were fluidized and continuously mixed in air, and the mixed polymer particles were then sieved using a standard mesh of the desired mesh number to obtain the target product with a particle size distribution of 150-700 microns.

COMPARATIVE EXAMPLE 1 (epoxy resin without Gallic acid)

in the polymerization stage, no gallic acid epoxy resin is added into the system as an internal crosslinking agent.

COMPARATIVE EXAMPLE 2 (addition of excess Gallic acid epoxy resin)

in the polymerization stage, the mass of the epoxy resin added with gallic acid is replaced by 12 g.

COMPARATIVE EXAMPLE 3 (replacement of Gallic acid epoxy resin by other internal crosslinking Agents)

in the polymerization stage, 0.85g of gallic acid epoxy resin added is replaced by adding 0.85g of pentaerythritol triallyl ether.

The polymer products produced in each of the examples and comparative examples were tested using the test methods described above. Unless otherwise indicated, the test should be conducted at ambient temperature 23. + -. 2 ℃ and relative air humidity 50. + -. 10% and the absorbent polymer mixed as uniformly as possible before the test. The results of testing the properties of the products obtained in the respective examples and comparative examples are shown in Table 1 below:

TABLE 1 test results of product Properties

As can be seen from a comparison of the test results in table 1,

in comparative example 1, when no gallic acid epoxy resin was added as an internal crosslinking agent for internal crosslinking, the centrifugal water retention and the liquid absorption rate of the obtained SAP resin were adversely affected, and the liquid absorption rate under pressure and the liquid flow rate were also much lower than those of the obtained SAP resin using gallic acid epoxy resin.

In comparative example 2, when the amount of gallic acid epoxy resin was too large, the crosslinking degree of the inner core of the entire SAP resin particle was too high, and the strength of gallic acid epoxy resin itself was high, so that the centrifugal water retention of the obtained SAP resin was greatly reduced, and the liquid-absorbing rate became slow, which was not favorable for the use of the SAP resin in practical applications.

In comparative example 3, when the internal crosslinking agent containing a bifunctional and being an aliphatic flexible chain was used for internal crosslinking, the liquid permeability became poor and the centrifuge retention rate and the pressure liquid absorption rate were low because the internal crosslinking degree was low and the gel was likely to collapse to cause clogging in the absorption process.

The various embodiments can achieve a balanced and superior level of SAP resin performance by adding gallic acid epoxy resin and selecting the appropriate amount during the polymerization process.

Having described embodiments of the present invention, the foregoing description is intended to be exemplary, not exhaustive, and not limited to the embodiments disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the spirit of the invention.

Claims

1. A super absorbent polymer is characterized in that the raw materials for polymerization reaction comprise the following components:

a) a carboxyl group-containing ethylenically unsaturated monomer and/or a salt thereof at a concentration of 20 wt% or more and 35 wt% or less in the aqueous polymerization solution;

b) an internal crosslinking agent at least comprising gallic acid epoxy resin; the dosage of the gallic acid epoxy resin is 0.01 wt% -2 wt% of the weight of the component a);

c) an oxidizing agent in an amount of 0.005 to 5 wt% based on the weight of component a);

d) a reducing agent in an amount of 0.005 to 5 wt% based on the weight of component a);

wherein, after the hydrogel obtained by the polymerization reaction is neutralized, the neutralization degree of carboxylic acid of the polymer in the obtained colloidal particles is 50-80 mol%; the colloidal particles are converted into polymer particles, and the polymer particles with the particle size of 150-700 microns account for more than or equal to 92 wt%;

and, the surface of the polymer particles is treated with:

e) surface crosslinking by 0.5 wt% to 5 wt%, based on the dried polymer particles, of a surface crosslinking agent applied to the surface of the dried polymer particles, and, optionally

f) Adding 0-2 wt% of insoluble inorganic powder after surface cross-linking, based on the dried polymer particles;

the chemical structure of the gallic acid epoxy resin is shown in the following formula I:

2. the superabsorbent polymer of claim 1, wherein the carboxyl group-containing ethylenically unsaturated monomer and/or its salt has a concentration of 20 wt% or more and 30 wt% or less in the aqueous polymerization solution;

the dosage of the gallic acid epoxy resin is 0.05 wt% -1 wt% of the weight of the component a);

the amount of the oxidant is 0.01 wt% -0.5 wt% of the weight of the component a);

the reducing agent is used in an amount of 0.01 wt% to 0.5 wt% based on the weight of component a).

3. Superabsorbent polymer according to claim 1, characterized in that the ethylenically unsaturated monomers containing carboxyl groups are selected from one or more of acrylic acid, methacrylic acid, ethacrylic acid, a-chloroacrylic acid, a-cyanoacrylic acid, β -methacrylic acid, a-phenylacrylic acid, β -acryloxypropionic acid, sorbic acid, a-chlorosorbic acid, 2' -methylisonicacid, cinnamic acid, p-chlorocinnamic acid, β -stearic acid, itaconic acid, citraconic acid, mesaconic acid, glutaconic acid, aconitic acid, maleic acid, fumaric acid, tricarboxyethylene and maleic anhydride; and/or

The oxidant is peroxide and is selected from one or more of sodium persulfate, hydrogen peroxide, potassium persulfate and ammonium persulfate; and/or

The reducing agent is selected from one or more of ascorbic acid, ammonium bisulfite, ammonium thiosulfate, ammonium dithionite, ammonium sulfide and sodium hydroxymethylsulfoxylate; and/or

The insoluble inorganic powder is selected from one or more of silicon dioxide, silica, titanium dioxide, alumina, magnesia, zinc oxide, talc, calcium phosphate, clay, diatomaceous earth, zeolite, bentonite, kaolin, hydrotalcite and activated clay; and/or

The surface cross-linking agent is selected from one or more of polyalcohol compounds, epoxy compounds, amine compounds and metal inorganic salts; the polyalcohol compound is selected from ethylene glycol, propylene glycol, glycerol, 1, 4-butanediol or pentaerythritol; the epoxy compound is selected from ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, 1, 4-butanediol diglycidyl ether, ethylene carbonate or propylene carbonate; the amine compound is selected from trihydroxymethyl aminomethane or carbodiimide; the metal inorganic salt is selected from inorganic salts of calcium, magnesium, aluminum, iron, copper or zinc.

4. Superabsorbent polymer according to claim 3, characterized in that the ethylenically unsaturated monomers containing carboxyl groups are selected from acrylic acid and/or methacrylic acid; and/or

The oxidant is hydrogen peroxide; and/or

The reducing agent is ascorbic acid; and/or

The insoluble inorganic powder is silicon dioxide.

5. Superabsorbent polymer according to claim 4, characterized in that the ethylenically unsaturated monomer containing carboxyl groups is acrylic acid.

6. The superabsorbent polymer of claim 1, wherein the internal crosslinking agent further comprises an internal crosslinking agent containing a double bond compound in an amount of 0 to 4 wt% based on the weight of component a);

the internal crosslinking agent of the double-bond-containing compound is selected from one or more of ethylene glycol diacrylate, propylene glycol diacrylate, N' -methylene bisacrylamide, polyethylene glycol diacrylate, polypropylene glycol diacrylate, pentaerythritol triallyl ether, ethoxylated glycerol triacrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate, triallylamine, pentaerythritol tetraacrylate and dipentaerythritol hexaacrylate.

7. The superabsorbent polymer of claim 6, wherein the internal crosslinking agent containing a double bond compound is used in an amount of 1 wt% to 2 wt% based on the weight of component a).

8. Superabsorbent polymer according to any of claims 1 to 7, characterized in that the starting materials of the polymerization reaction further comprise: g) at least one thermal initiator, wherein the thermal initiator is an azo initiator.

9. Superabsorbent polymer according to claim 8, characterized in that the azo initiators are selected from one or more of azobisisobutyronitrile, azobiscyanovaleric acid, azobisdimethylvaleronitrile, 2 '-azobis (2-amidinopropane) dihydrochloride, azobisamidinopropane dihydrochloride, 2' -azobis (N, N-dimethyleneisobutyramidine) dihydrochloride, 2- (carbamoylazo) isobutyronitrile and 4, 4-azobis (4-cyanovaleric acid).

10. Superabsorbent polymer according to claim 8, characterized in that the thermal initiator is used in an amount of 0.005% to 1% by weight based on the weight of component a).

11. Superabsorbent polymer according to claim 10, characterized in that the thermal initiator is used in an amount of 0.01% to 0.2% by weight of component a).

12. The superabsorbent polymer of any one of claims 1 to 7 and 9 to 11, wherein the superabsorbent polymer has a liquid absorption capacity of 60 to 70g/g, a centrifuge retention capacity of 35 to 40g/g, a 0.7psi press absorption capacity of 20 to 27g/g, a liquid absorption rate of 30 to 45s, a liquid feed rate GBP of 30Darcy or more, a residual monomer content of 350ppm or less, and an extractable content of 4.5 wt% or less.

13. A method for preparing super absorbent polymer is characterized by comprising the following steps:

at the temperature of less than or equal to 20 ℃, the ethylenically unsaturated monomer containing carboxyl and/or the salt thereof, the oxidant, the reducing agent and the internal crosslinking agent are contacted to initiate polymerization reaction, so that hydrogel is obtained; crushing and extruding the hydrogel, and then contacting the hydrogel with a neutralizer to perform neutralization reaction to prepare colloidal particles; drying, grinding and screening the colloidal particles, and then contacting with a surface cross-linking agent to carry out surface cross-linking treatment to obtain super water-absorbent polymer resin;

wherein the internal crosslinking agent at least comprises gallic acid epoxy resin, and the chemical structure of the gallic acid epoxy resin is shown in the following formula I:

the polymerization reaction is aqueous solution polymerization; the concentration of the carboxyl group-containing ethylenically unsaturated monomer and/or salt thereof in the aqueous polymerization solution is 20 wt% or more and 35 wt% or less;

the gallic acid epoxy resin is used in an amount of 0.01 wt% to 2 wt% based on the weight of the carboxyl group containing ethylenically unsaturated monomer and/or salt thereof;

the oxidizing agent is used in an amount of 0.005 to 5 wt% based on the weight of the carboxyl group-containing ethylenically unsaturated monomer and/or salt thereof;

the reducing agent is used in an amount of 0.005 to 5 wt% based on the weight of the carboxyl group-containing ethylenically unsaturated monomer and/or its salt.

14. The production method according to claim 13, wherein the concentration of the carboxyl group-containing ethylenically unsaturated monomer and/or salt thereof in the aqueous polymerization solution is 20 wt% or more and 30 wt% or less; and/or

The gallic acid epoxy resin is used in an amount of 0.05 wt% to 1 wt% based on the weight of the carboxyl group containing ethylenically unsaturated monomer and/or salt thereof; and/or

The oxidizing agent is used in an amount of 0.01 to 0.5 wt% based on the weight of the carboxyl group-containing ethylenically unsaturated monomer and/or its salt; and/or

The reducing agent is used in an amount of 0.01 to 0.5 wt% based on the weight of the carboxyl group-containing ethylenically unsaturated monomer and/or its salt; and/or

After the hydrogel is subjected to neutralization reaction, the neutralization degree of carboxylic acid of the polymer in the obtained colloidal particles is 50-80 mol%; and/or

The amount of surface cross-linking agent applied to the surface of the dried superabsorbent polymer particles is from 0.5% to 5% by weight, based on the dried superabsorbent polymer particles.

15. The production method according to claim 13, characterized in that the ethylenically unsaturated monomer having a carboxyl group is selected from one or more of acrylic acid, methacrylic acid, ethacrylic acid, α -chloroacrylic acid, α -cyanoacrylic acid, β -methacrylic acid, α -phenylacrylic acid, β -acryloxypropionic acid, sorbic acid, α -chlorosorbic acid, 2' -methylisonicacid, cinnamic acid, p-chlorocinnamic acid, β -stearic acid, itaconic acid, citraconic acid, mesaconic acid, glutaconic acid, aconitic acid, maleic acid, fumaric acid, tricarboxyethylene and maleic anhydride; and/or

The neutralizing agent is an aqueous solution of an alkaline compound, and the concentration of the aqueous solution is 30-60 wt%; the alkaline compound is selected from one or more of sodium hydroxide, potassium hydroxide, sodium carbonate and potassium carbonate; and/or

16. The process according to claim 15, wherein the ethylenically unsaturated monomer containing a carboxyl group is selected from acrylic acid and/or methacrylic acid; and/or

The oxidant is hydrogen peroxide; and/or

The reducing agent is ascorbic acid; and/or

The concentration of the aqueous solution of the alkaline compound is 40-50 wt%; the alkaline compound is sodium hydroxide.

17. The method according to claim 16, wherein the ethylenically unsaturated monomer having a carboxyl group is acrylic acid.

18. The method of claim 13, wherein during the polymerization reaction, a basic catalyst is further added;

the content of the alkaline catalyst in the aqueous polymerization solution is 10-1000 ppm;

the basic catalyst is selected from tertiary amine and/or triphenylphosphine.

19. The production method according to claim 18, wherein the content of the basic catalyst in the aqueous polymerization solution is 50 to 300 ppm;

the basic catalyst is triphenylphosphine.

20. The production method according to claim 13, wherein the internal crosslinking agent further comprises an internal crosslinking agent containing a double bond compound; the amount is from 0 to 4% by weight, based on the weight of the carboxyl group-containing ethylenically unsaturated monomer and/or salt thereof.

21. The method according to claim 20, wherein the internal crosslinking agent containing the double bond compound is used in an amount of 1 to 2 wt% based on the weight of the carboxyl group-containing ethylenically unsaturated monomer and/or its salt.

22. The method according to claim 20, wherein the internal crosslinking agent of the double bond-containing compound is one or more selected from the group consisting of ethylene glycol diacrylate, propylene glycol diacrylate, N' -methylene bisacrylamide, polyethylene glycol diacrylate, polypropylene glycol diacrylate, pentaerythritol triallyl ether, ethoxylated glycerol triacrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate, triallylamine, pentaerythritol tetraacrylate, and dipentaerythritol hexaacrylate.

23. The method as set forth in any one of claims 13 to 22, wherein the drying temperature of the colloidal particles is 100 ℃ to 240 ℃.

24. The production method according to any one of claims 13 to 22,

after the colloidal particles are dried, the colloidal particles are further ground and sieved to control the size of the superabsorbent polymer particles; wherein the proportion of the super absorbent polymer particles with the particle diameter of 150-700 microns is more than or equal to 92wt percent.

25. The production method according to any one of claims 13 to 22, wherein the process conditions of the surface cross-linking treatment include: the reaction temperature is 50-150 ℃; the reaction time is 0.5h-3 h;

optionally, 0-2 wt% of an insoluble inorganic powder is added after the surface cross-linking treatment, based on the dried superabsorbent polymer particles;

the insoluble inorganic powder is selected from one or more of silicon dioxide, silica, titanium dioxide, alumina, magnesia, zinc oxide, talc, calcium phosphate, clay, diatomaceous earth, zeolite, bentonite, kaolin, hydrotalcite and activated clay.

26. The method for preparing a composite material according to claim 25, wherein the process conditions of the surface cross-linking treatment include: the reaction temperature is 80-130 ℃; the reaction time is 1h-2 h.

27. The method of claim 25, wherein the insoluble inorganic powder is silica.

28. The method according to any one of claims 13 to 22 and 26 to 27, wherein at least one thermal initiator is added during the polymerization reaction, and the thermal initiator is an azo-type initiator;

the thermal initiator is used in an amount of 0.005 to 1% by weight based on the weight of the carboxyl group-containing ethylenically unsaturated monomer and/or salt thereof.

29. The method according to claim 28, wherein the azo initiator is selected from one or more of azobisisobutyronitrile, azobiscyanovaleric acid, azobisdimethylvaleronitrile, 2 '-azobis (2-amidinopropane) dihydrochloride, azobisamidinopropane dihydrochloride, 2' -azobis (N, N-dimethyleneisobutyramidine) dihydrochloride, 2- (carbamoylazo) isobutyronitrile, and 4, 4-azobis (4-cyanovaleric acid).

30. The method according to claim 28, wherein the thermal initiator is used in an amount of 0.01 to 0.2 wt% based on the weight of the carboxyl group-containing ethylenically unsaturated monomer and/or salt thereof.