CN111393684A

CN111393684A - Super water-absorbing polymer and preparation method thereof

Info

Publication number: CN111393684A
Application number: CN202010318702.XA
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: 2020-07-10

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 olefinic unsaturated monomer containing carboxyl and/or salt thereof, the reduced transition metal salt containing d orbits, an oxidant, a reducing agent and an internal cross-linking agent containing a double-bond compound 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; the colloidal particles are dried and ground, and then are contacted with a surface cross-linking agent for surface cross-linking treatment, so that Super Absorbent Polymer (SAP) resin is obtained. The method of the invention can change the main chain structure of the super absorbent polymer, effectively improve the pressure performance and the water retention of the SAP resin and improve the liquid permeability 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, and of retaining aqueous liquids under a certain pressure. Superabsorbent Polymers (SAP) can form particles, commonly referred to as particulate Superabsorbent Polymers. The particulate polymer raw powder can be subjected to surface crosslinking, surface treatment and other post-treatments to form a particulate superabsorbent polymer having a more balanced and excellent property profile. The main use of superabsorbent polymers and particulate superabsorbent polymers is in sanitary articles, such as baby diapers, incontinence products or sanitary napkins.

In absorbent articles (e.g., disposable diapers), superabsorbent polymers used as absorbents must have sufficiently high absorption capacity as well as sufficiently high compression. 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 water absorbent polymer in the absorbent product, and reduces the occurrence of gel blocking. Once gel blocking occurs, fluid distribution to drier areas or portions of the absorbent article may be hindered, and leakage from the absorbent article may occur before the particulate superabsorbent polymer within the absorbent article is fully saturated or before the fluid may diffuse or wick past the "blocking" particles into the remainder of the absorbent article.

In order to improve the liquid permeability and the anti-blocking property of the water-absorbent polymer, it is common practice to add silica, or metal oxides such as alumina and titanium oxide, to the water-absorbent polymer particles. Although the liquid permeability of the super absorbent polymer product can be improved well by adding the inorganic particles, the liquid absorption capacity, particularly the absorption capacity under pressure, is also reduced, thereby affecting the liquid absorption capacity and the action effect of the super absorbent polymer in the actual use process.

In the aqueous solution polymerization process of the super absorbent polymer, the liquid permeability can be improved by selecting means such as secondary surface crosslinking or addition of inorganic particles. For example, patent documents by Norbiol (publication Nos. CN 106987075A and CN 102702656A) disclose a method for producing a water-absorbent resin which is polymerized at a low temperature and subjected to surface crosslinking for a plurality of times and can produce 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 combination of low monomer residue, low long-term permeability, low extractables content, and other properties, such as water retention, absorbency under pressure, and liquid passage rate. 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 polymers cannot be achieved by combining the pressure-applying property, water-retention property 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 change the main chain structure of the super absorbent polymer and effectively improve the pressure-applying liquid-absorbing capacity and water-retention rate of an SAP resin and the liquid permeability thereof.

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) the content of the reduced transition metal salt having d-orbitals in the aqueous polymerization solution is 5 to 1000ppm (e.g., 10ppm, 20ppm, 50ppm, 100ppm, 300ppm, 800ppm), preferably 10 to 500 ppm;

c) internal crosslinking agents containing double bond compounds in an amount of 0.01 to 4 wt.% (e.g., 0.03, 0.08, 0.1, 0.5, 1.0, 1.5, 3.0 wt.%), preferably 0.05 to 2 wt.%;

d) 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);

e) 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 polymer particles with the particle size of 150-700 microns (for example, 155 microns, 200 microns, 400 microns and 600 microns) account for more than or equal to 92wt percent;

and, the surface of the polymer particles (i.e., polymer raw powder) is treated with:

f) surface crosslinking is performed by 0.5-5 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

g) 0-2 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 surface crosslinking based on the dried polymer particles.

In a preferred embodiment, the reduced transition metal salt having d-orbitals contains a cation selected from the group consisting of Fe²⁺、Cu⁺、Cr³⁺、Mn²⁺、Co²⁺、Nb²⁺、V²⁺、Rh²⁺、Ni²⁺、Pd²⁺、Ru²⁺、Zr²⁺、Ti²⁺、Pa³⁺And Mo²⁺Contains an anion selected from one or more of halide, nitrate, sulfate, sulfite, carbonate, bicarbonate, phosphate, chlorate and permanganate.

According to the super absorbent polymer provided by the present invention, in some examples, the reduced transition metal salt containing d-orbitals is selected from FeSO₄、CuCl、MnCl₂、FeCl₂、Co(NO₃)₂、PdCl₂And MnSO₄Preferably selected from FeSO₄、FeCl₂、Co(NO₃)₂And PdCl₂More preferably selected from FeSO₄And/or Co (NO)₃)₂。

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 thereof. 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.

In some examples, the ethylenically unsaturated monomer containing 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 (crotonic 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 internal crosslinking agent 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 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.

In a preferred embodiment, the polyol compound is selected from ethylene glycol, propylene glycol, glycerol, 1, 4-butanediol or pentaerythritol.

In a preferred embodiment, the epoxy compound is selected from (poly) ethylene glycol diglycidyl ether, 1, 4-butanediol diglycidyl ether, ethylene carbonate or propylene carbonate.

In a preferred embodiment, the amine compound is selected from tris or carbodiimide.

In a preferred embodiment, the metal inorganic salt is selected from an inorganic salt of calcium, magnesium, aluminum, iron, copper or zinc.

According to the super absorbent polymer provided by the present invention, in some examples, the raw materials for the polymerization reaction further include: h) at least one thermal initiator, wherein the thermal initiator is an azo initiator.

In a preferred embodiment, the thermal 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).

In some examples, the thermal initiator is used in an amount of 0.005 wt% to 1 wt% (e.g., 0.008 wt%, 0.02 wt%, 0.05 wt%, 0.1 wt%, 0.4 wt%, 0.8 wt%), preferably 0.01 wt% to 0.2 wt%, based on the weight of component a).

According to the super absorbent polymer provided by the invention, in some examples, the super absorbent polymer has a liquid absorption capacity of 60-70g/g, a centrifugal water retention rate of 35-40g/g, a 0.7psi pressure liquid absorption capacity of 20-26g/g, a liquid absorption rate of 25-40s, a liquid passing rate (GBP) of 30Darcy or more, a residual monomer content of 400ppm or less, and an extractable content of 5 wt% or less.

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

at 20 ℃ or less (e.g., 0 ℃, 1 ℃, 5 ℃, 8 ℃, 10 ℃, 15 ℃), contacting the carboxyl-containing ethylenically unsaturated monomer and/or salt thereof, the d-orbital-containing reduced transition metal salt, the oxidizing agent, the reducing agent, and the double bond-containing compound with an internal crosslinking agent to initiate polymerization reaction, thereby obtaining hydrogel; crushing and extruding the hydrogel, and then contacting the hydrogel with a neutralizer to perform neutralization reaction to prepare colloidal particles; the colloidal particles are dried, ground and screened, and then are subjected to surface cross-linking treatment by contacting with a surface cross-linking agent to obtain a Super Absorbent Polymer (SAP) resin.

In a preferred embodiment, the reduced transition metal salt having d-orbitals contains a cation selected from the group consisting of Fe²⁺、Cu⁺、Cr³⁺、Mn²⁺、Co²⁺、Nb²⁺、V²⁺、Rh²⁺、Ni²⁺、Pd²⁺、Ru²⁺、Zr²⁺、Ti²⁺、Pa³⁺And Mo²⁺Contains an anion selected from one or more of halide ions (e.g., chloride, bromide), nitrate, sulfate, sulfite, carbonate, bicarbonate, phosphate, chlorate, and permanganate.

In some examples, the reduced transition metal salt containing a d-orbital is selected from FeSO₄、CuCl、MnCl₂、FeCl₂、Co(NO₃)₂、PdCl₂And MnSO₄Preferably selected from FeSO₄、FeCl₂、Co(NO₃)₂And PdCl₂More preferably selected from FeSO₄And/or Co (NO)₃)₂。

In the preparation method, the reduced transition metal salt containing the d-orbit has certain reducibility, namely, the metal ions have valence-changing property and are in a low valence state.

The key points of the invention are as follows: the transition metal salt containing d orbitals is added in the polymerization stage, and the metal salt is in a low valence state of the valence state, namely the metal salt has certain reducibility. From the data of the experimental results, the inventors speculate that the polymer structure in the system is changed as shown in fig. 1:

that is, the addition of a small amount of reduced transition metal salt in the polymerization stage may cause the polymer in the system to form more branched structures, and more neutralizing ions are contained in the SAP particles to form more favorable osmotic pressure and hydration environment, so that a higher pressurization rate and a better water retention rate of the SAP particles can be ensured, and a very high liquid passing rate is achieved.

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 reduced transition metal salt having d orbitals is present in the aqueous polymerization solution in an amount of 5 to 1000ppm (e.g., 10ppm, 20ppm, 50ppm, 100ppm, 300ppm, 800ppm), preferably 10 to 500 ppm.

In some examples, the internal crosslinking agent containing a double bond compound is used in an amount of 0.01 wt% 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 0.05 wt% to 2 wt%, based on the weight of the carboxyl group-containing ethylenically unsaturated monomer and/or its salt.

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.

In order to ensure that the polymer hydrogel obtained by the polymerization reaction has low residual monomer, the polymerized hydrogel can be continuously aged and kept warm for a period of time after the temperature rise in the polymerization process 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 polymer in the colloidal particles has a degree of carboxylic acid neutralization 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 material is subjected to surface crosslinking treatment. In some examples, the surface cross-linking agent is applied to the surface of the dried superabsorbent polymer (SAP) particles in an amount of 0.5 to 5 wt% (e.g., 0.8 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt%) based on the dried superabsorbent polymer (SAP) particles.

According to the preparation method provided by the present invention, 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 (crotonic acid), α -phenylacrylic acid, β -acryloxypropionic acid, sorbic acid, α -chlorosorbic acid, 2' -methylisothiacrylic 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. In a preferred embodiment, the oxidizing agent is selected from one or more of sodium persulfate, hydrogen peroxide, potassium persulfate, and ammonium persulfate, more preferably hydrogen peroxide.

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%. In a preferred embodiment, the basic compound is selected from one or more of sodium hydroxide, potassium hydroxide, sodium carbonate and potassium carbonate, more preferably sodium hydroxide.

The colloid particles obtained after neutralization are extruded and crushed to obtain small-sized colloidal particles, and the colloidal particles need to be further dried before the small-sized colloidal particles are crushed due to high water content of the colloidal particles. 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 superabsorbent polymer (SAP) particles; wherein the proportion of the superabsorbent polymer (SAP) particles having a particle size of 150-700 [ mu ] m (e.g., 180 [ mu ] m, 250 [ 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 deg.C (e.g., 70 deg.C, 100 deg.C, 120 deg.C), preferably 80-130 deg.C; the reaction time is 0.5h to 3h (e.g., 0.8h, 1.5h, 2.5h), preferably 1h to 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. In some examples, optionally, 0-2 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 accordance with the preparation methods provided herein, in some examples, at least one thermal initiator is added during the polymerization reaction. 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%, 0.02 wt%, 0.05 wt%, 0.1 wt%, 0.4 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 SAP resin particles prepared by the preparation method have obvious performance improvement effects: the SAP resin particles have high water retention, high pressurized liquid absorption, and improved liquid flow rate with less residual monomer and extractables.

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

by adding a trace amount of reduced transition metal salt in the polymerization stage to react with an oxidation-reduction initiation system, it is speculated that more branched structures may be formed in polymer molecules, so that more neutralizing ions are in the SAP particles, and more favorable osmotic pressure and hydration environments are formed, so that the prepared SAP particles have higher pressurization and water retention and better liquid permeability. In addition, the resulting SAP particles have a low extractables content and a low residual monomer content.

Drawings

FIG. 1 shows a diagram of the presumed change of the structure of the substance in the system before and after addition of a reduced transition metal salt to the polymerization reaction.

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%;

hydrogen peroxide (H)₂O₂Solution) 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 mass concentrations of 32% and 50% were 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%;

ferrous sulfate purchased from Chinese medicines with purity of over 99 percent;

cobalt nitrate purchased from Chinese medicine with purity of more than 99%;

other raw materials are conventional reagents in the field, and the purchase information of the raw materials is not described in detail.

< 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 cm²The inner diameter of the plexiglass cylinder is 6cm, and the area of the gel layer is 28.27cm²；

P is hydrostatic pressure in dyne/cm²And P is rho gh, h is the liquid level height of 4cm, the hydrostatic pressure is 3924dyne/cm²；

Rho is the density of the liquid in g/cm³The density of the normal saline is 1g/cm³And (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.

Meanwhile, a blank sample (200ml of a 0.9% NaCl solution) was prepared, titration of the blank solution (100ml of a 0.9% NaCl aqueous solution) was performed, titration was performed using a 0.1mol/l NaOH solution until the PH became 10, and then titration was performed using a 0.1mol/l hydrochloric acid solution until the PH became 2.7, and blank titration amounts of [ bmoh ], [ bHC L ] (m L) were obtained, respectively.

50ml of the filtrate was weighed and added with 0.9% NaCl solution to 100ml, and the same titration as above was carried out to obtain the titrated amounts of [ NaOH ], [ HCl ] (m L), respectively.

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 extractables content Ex (wt%) (([ HCl ] - [ bHCl ]) xc (HCl) × Mwx 2)/5.

g) Residual monomer content (ppm)

Weighing 1.000 g of test sample to be accurate to 0.005g, putting the test sample into a clean 250ml beaker, measuring 200ml of 0.9% NaCl solution by using a measuring cylinder, adding the NaCl solution into the beaker, adding a magnetic stirrer, sealing the beaker by using a sealing film, putting the beaker on a magnetic stirrer, stirring the solution at the rotating speed of 500 +/-50 rpm for 60 minutes, stopping stirring, standing for 5 minutes, taking 1-2ml of upper solution, filtering the solution by using a 0.45 mu m filter, putting the upper solution into a special liquid-phase sample bottle, marking the sample for HP L C analysis.

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, L C1260 (offline) software is opened, data analysis is selected, a folder is opened, an analysis result needing to be opened is found, a sample to be processed is selected, a spectrogram is opened, an integral current chromatogram is selected, a peak area is read, and the content of residual monomers in the test sample is calculated by using a correction curve in an EXCE L table.

Preparing an ascorbic acid aqueous solution containing a reduced transition metal salt:

(1) 2g of ascorbic acid and 0.5g of ferrous sulfate are weighed, dissolved in 97.5g of deionized water, stirred uniformly in a beaker, and sealed by a preservative film for later use, namely, the ascorbic acid solution A is obtained.

(2) 2g of ascorbic acid and 5g of ferrous sulfate are weighed, dissolved in 93g of deionized water, stirred uniformly in a beaker, and sealed by a preservative film for later use, namely, ascorbic acid solution B.

(3) 2g of ascorbic acid and 0.5g of cobalt nitrate are weighed, dissolved in 97.5g of deionized water, stirred uniformly in a beaker, and sealed by a preservative film for later use, and the solution is called ascorbic acid solution C.

(4) 2g of ascorbic acid and 5g of cobalt nitrate are weighed, dissolved in 93g of deionized water, stirred uniformly in a beaker, and sealed by a preservative film for later use, and the solution is called ascorbic acid solution D.

(5) 2g of ascorbic acid is weighed, dissolved in 98g of deionized water, stirred uniformly in a beaker, and sealed by a preservative film for later use, and the solution is called ascorbic acid solution E.

(6) 2g ascorbic acid, 3g FeCl were weighed₃It is dissolved in 95g of deionized water, stirred uniformly in a beaker, and then sealed by a preservative film for later use, and is called ascorbic acid solution F.

Example 1:

a method for preparing a superabsorbent polymer, comprising the steps of:

mixing 550g of prepared acrylic acid aqueous solution with the concentration of 60 wt%, 640g of deionized water 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 of H into the polymerization kettle₂O₂A solution (diluted to a concentration of 2 wt%), 2g of 2, 2' -azobis (N, N-dimethyleneisobutyramidine) dihydrochloride solution (diluted to a concentration of 4 wt%) and 2.5g of a ferrous sulfate-containing ascorbic acid solution A (in an aqueous polymerization solution, the concentration of the monomer is 27.5%, and the content of the reduced transition metal salt is 10 ppm); after the induction period is finished, the polymerization reaction starts when the temperature starts to obviously rise, the temperature reaches about 85 ℃ after the reaction is carried out for about 1.5h, and then the thermal insulation curing is carried out for 5h at the temperature to obtain the hydrogel polymer.

Crushing and extruding the hydrogel polymer by using a granulating auger machine, and then adding 270g of NaOH aqueous solution with the concentration of 50 wt% for neutralization, so that about 74 mol% of carboxyl in the polymer of the obtained colloidal particles is neutralized into sodium carboxylate; using a forced air drying oven (purchased from high-speed railway company) to carry out forced air drying on the neutralized colloidal particles at the set temperature of 180 ℃, wherein the drying time lasts for 40 min; crushing the dried colloidal particles by a crusher or a wall breaking machine (purchased from American company), and sieving by using a screen until the particle size is in the range of 150-700 microns to obtain SAP particles; SAP particles that have not been surface cross-linked are defined as polymer raw powder (1).

100g of the prepared polymer raw powder (1) is weighed, a mixture prepared from 0.1g of ethylene glycol diglycidyl ether, 1.4g of 1, 2-propylene glycol and 6g of deionized water is atomized, and then uniformly sprayed on the particle surface of the polymer raw powder (1), and then the polymer particles are fluidized in the air and continuously mixed. Then, the mixture was placed in a high-temperature forced air oven and heated at 110 ℃ for 1.5 hours to carry out surface crosslinking treatment. The polymer particles after surface cross-linking treatment were cooled to below 40 ℃, and 2g of a 20% aqueous solution of aluminum sulfate was atomized and sprayed onto the polymer particles after surface cross-linking treatment, while the polymer particles were fluidized in air and continuously mixed. The treated polymer particles were then sieved through a standard mesh of the desired mesh size to obtain the target product having a particle size distribution of 150-710 μm.

Example 2:

a process for the preparation of superabsorbent polymer, operating procedure see example 1, except that:

in the polymerization stage, 550g of deionized water (in the polymerization aqueous solution, the concentration of the monomer is 29.7%, and the content of the reduced transition metal salt is 22ppm) was added, and 5g of the ascorbic acid solution A containing ferrous sulfate was added;

the resulting SAP particles, which were not surface cross-linked, were defined as polymer raw powder (2).

In the surface crosslinking treatment of the polymer raw powder (2), 1g of ethylene glycol diglycidyl ether was added.

Example 3:

in the polymerization stage, acrylic acid aqueous solution and 100g of caustic soda aqueous solution with the concentration of 50 wt% are subjected to pre-neutralization reaction, and then are subjected to polymerization reaction after being cooled to obtain acrylate; after the polymerization reaction, 194g of a 50 wt% aqueous solution of caustic soda was added to the resulting hydrogel to conduct a post-neutralization reaction, so that 80 mol% of the carboxyl groups in the polymer of the resulting colloidal particles were neutralized to carboxylic acid sodium salts.

In the polymerization stage, an ascorbic acid solution B containing ferrous sulfate was added in an amount of 6g (the content of the reduced transition metal salt in the aqueous polymerization solution was 250 ppm);

after the polymerization reaction is finished, keeping the temperature and curing for 4 hours;

the resulting SAP particles, which were not surface cross-linked, were defined as polymer raw powder (3).

The surface crosslinking treatment stage of the polymer raw powder (3) was carried out in accordance with example 1.

Example 4:

in the polymerization stage, an ascorbic acid solution D containing ferrous sulfate was added in an amount of 15g (content of reduced transition metal salt in the aqueous polymerization solution: 620 ppm); 1.6g of polyethylene glycol diacrylate was replaced with 1.6g of pentaerythritol triallyl ether;

in the neutralization treatment, 421g of caustic soda water solution with the concentration of 32 wt% is added;

in the drying treatment, the temperature for drying the colloid was 210 ℃ and the drying time was 1 hour.

The resulting SAP particles, which were not surface crosslinked, were defined as polymer raw powder (4).

The surface crosslinking treatment stage of the polymer raw powder (4) was carried out in accordance with example 1.

Example 5:

in the polymerization stage, an ascorbic acid solution C containing ferrous sulfate was added in an amount of 4g (the content of reduced transition metal salt in the aqueous polymerization solution was 17 ppm); addition of H₂O₂The mass of the solution was 1.5g, and the mass of the solution to which 2, 2' -azobis (N, N-dimethyleneisobutyramidine) dihydrochloride was added was 1 g;

after the polymerization is finished, keeping the temperature and curing for 8 hours;

in the neutralization treatment, 294g of a mass of a 50 wt% strength aqueous solution of caustic soda was added to neutralize 80 mol% of carboxyl groups in the polymer of the resulting colloidal particles to carboxylic acid sodium salts (neutralization degree: 80%).

The resulting SAP particles, which were not surface crosslinked, were defined as polymer raw powder (5).

The surface crosslinking treatment stage of the polymer raw powder (5) was carried out in accordance with example 1.

Example 6:

in the polymerization stage, an ascorbic acid solution B containing ferrous sulfate was added in an amount of 5g (the content of the reduced transition metal salt in the aqueous polymerization solution was 208 ppm); 1.6g of polyethylene glycol diacrylate was replaced by a mixture of 1.2g of pentaerythritol triallyl ether and 1.2g of polyethylene glycol diacrylate;

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

The resulting SAP particles, which were not surface crosslinked, were defined as polymer raw powder (6).

The surface crosslinking treatment stage of the polymer raw powder (6) was carried out in accordance with example 1. And after the surface cross-linking treatment is finished, 0.05g of silicon powder is added and mixed uniformly.

Example 7:

in the polymerization stage, an ascorbic acid solution B containing ferrous sulfate was added in an amount of 24g (the content of reduced transition metal salt in the aqueous polymerization solution was 985 ppm); 1.6g of polyethylene glycol diacrylate was replaced by a mixture of 0.8g of pentaerythritol triallyl ether and 0.7g of polyethylene glycol diacrylate;

the resulting SAP particles, which were not surface crosslinked, were defined as polymer raw powder (7).

In the surface crosslinking treatment stage of the polymer raw powder (7), the time of the surface crosslinking treatment is 1h, and the temperature is 120 ℃.

Comparative example 1:

a process for the preparation of superabsorbent polymer, operating procedure see example 1, except that: in the polymerization stage, an ascorbic acid solution E containing no reduced transition metal salt is added.

Comparative example 2

A process for the preparation of superabsorbent polymer, operating procedure see example 1, except that: in the polymerization stage, 50g of an ascorbic acid solution B containing a reduced transition metal salt was added (the content of the reduced transition metal salt in the aqueous polymerization solution was 2000 ppm).

Comparative example 3

A process for the preparation of superabsorbent polymer, operating procedure see example 1, except that: in the polymerization stage, FeCl-containing solution is added₃The ascorbic acid solution F in an amount of 4g (in the aqueous polymer solution, the content of the oxidized transition metal salt is 100ppm), was not able to initiate polymerization.

The superabsorbent polymers obtained in the examples and comparative examples described above 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 the tests on the properties of the target products are shown in table 1 below:

TABLE 1 test results of target product Properties

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

in each example, when a reduced transition metal salt is added during the polymerization stage, the resulting SAP resin has high absorbency under pressure, centrifuge retention, and flow through rate. The SAP resins obtained in the examples achieved higher water retention and improved liquid permeability compared to the products obtained in the comparative examples.

As can be seen from comparative example 1, when the reduced transition metal salt was not added at the polymerization stage, the resulting product could maintain a high liquid-suction rate, but the centrifuge retention rate, the pressure-liquid-suction rate and the liquid-passing rate were not satisfactory.

As can be seen from comparative example 2, when too much reduced transition metal salt was added to the polymerization system, the initiation efficiency was too high, the molecular chain of the polymer became short, the extractable content thereof was remarkably increased, and the residual monomer content was also increased.

From comparative example 3, it can be seen that the addition of the transition metal salt in an oxidized state at the polymerization stage does not allow the polymerization reaction to take place.

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, preferably 20 wt% or more and 30 wt% or less in the aqueous polymerization solution;

b) the content of the reduced transition metal salt containing the d-orbit in the aqueous polymerization solution is 5-1000ppm, preferably 10-500 ppm;

c) internal crosslinking agents containing double bond compounds in an amount of 0.01% to 4% by weight, preferably 0.05% to 2% by weight, based on the weight of component a);

d) oxidizing agents in amounts of 0.005% to 5%, preferably 0.01% to 0.5%, by weight based on the weight of component a);

e) reducing agents in amounts of 0.005% to 5%, preferably 0.01% to 0.5%, by weight 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:

f) surface crosslinking by 0.5 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

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

preferably, the reduced transition metal salt containing d-orbitals contains cations selected from Fe²⁺、Cu⁺、Cr³⁺、Mn²⁺、Co²⁺、Nb²⁺、V²⁺、Rh²⁺、Ni²⁺、Pd²⁺、Ru²⁺、Zr²⁺、Ti²⁺、Pa³⁺And Mo²⁺Contains an anion selected from one or more of halide, nitrate, sulfate, sulfite, carbonate, bicarbonate, phosphate, chlorate and permanganate.

2. Superabsorbent polymer according to claim 1, characterized in that the reduced transition metal salt containing d orbitals is selected from FeSO₄、CuCl、MnCl₂、FeCl₂、Co(NO₃)₂、PdCl₂And MnSO₄Preferably selected from FeSO₄、FeCl₂、Co(NO₃)₂And PdCl₂More preferably selected from FeSO₄And/or Co (NO)₃)₂。

3. Superabsorbent polymer according to claim 1, characterized in that the ethylenically unsaturated monomer containing 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' -methylisonic 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 from acrylic acid and/or methacrylic acid, more preferably acrylic acid, and/or

The internal crosslinking agent 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; and/or

The oxidant is peroxide, preferably one or more selected from sodium persulfate, hydrogen peroxide, potassium persulfate and ammonium persulfate, and more preferably hydrogen peroxide; 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 is preferably ascorbic acid; 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, preferably silicon dioxide; 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 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.

4. Superabsorbent polymer according to any of claims 1 to 3, characterized in that the starting materials of the polymerization reaction further comprise: h) at least one thermal initiator which is an azo-type 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);

preferably, the thermal initiator is used in an amount of 0.005% to 1% by weight, more preferably 0.01% to 0.2% by weight, based on the weight of component a).

5. The superabsorbent polymer of any one of claims 1 to 4, 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 26g/g, a liquid absorption rate of 25 to 40s, a liquid transport rate (GBP) of 30Darcy or more, a residual monomer content of 400ppm or less, and an extractable content of 5 wt% or less.

6. 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 olefinic unsaturated monomer containing carboxyl and/or salt thereof, the reduced transition metal salt containing d orbits, an oxidant, a reducing agent and an internal cross-linking agent containing a double-bond compound 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;

7. The method according to claim 6, wherein the reduced transition metal salt having d-orbitals is selected from FeSO₄、CuCl、MnCl₂、FeCl₂、Co(NO₃)₂、PdCl₂And MnSO₄Preferably selected from FeSO₄、FeCl₂、Co(NO₃)₂And PdCl₂More preferably selected from FeSO₄And/or Co (NO)₃)₂。

8. The production method according to claim 6 or 7, wherein the polymerization reaction is an aqueous solution polymerization; preferably, 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, more preferably 20 wt% or more and 30 wt% or less; and/or

The content of the reduced transition metal salt containing the d-orbit in the aqueous polymerization solution is 5-1000ppm, preferably 10-500 ppm; and/or

The internal crosslinking agent containing a double bond compound is used in an amount of 0.01 to 4 wt%, preferably 0.05 to 2 wt%, based on the weight of the carboxyl group-containing ethylenically unsaturated monomer and/or its salt; and/or

The oxidizing agent is used in an amount of 0.005 to 5 wt%, preferably 0.01 to 0.5 wt%, based on the weight of the carboxyl group-containing ethylenically unsaturated monomer and/or salt thereof; and/or

The reducing agent is used in an amount of 0.005 to 5 wt%, preferably 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 wt.%, based on the dried superabsorbent polymer particles.

9. The method according to any one of claims 6 to 8, wherein 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' -methylisotaloic 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 from acrylic acid and/or methacrylic acid, more preferably acrylic acid, and/or

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; and/or

The neutralizing agent is an aqueous solution of an alkaline compound, the concentration of which is 30-60 wt%, preferably 40-50 wt%; the alkaline compound is preferably selected from one or more of sodium hydroxide, potassium hydroxide, sodium carbonate and potassium carbonate, more preferably sodium hydroxide; and/or

10. The method as set forth in any one of claims 6 to 9, wherein the drying temperature of the colloidal particles is 100-240 ℃.

11. The production method according to any one of claims 6 to 10,

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.

12. The production method according to any one of claims 6 to 11, wherein 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;

optionally adding 0-2 wt% of insoluble inorganic powder after the surface cross-linking treatment, based on the dried superabsorbent polymer particles; the insoluble inorganic powder is preferably 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 more preferably silicon dioxide.

13. The process according to any one of claims 6 to 12, wherein at least one thermal initiator is added during the polymerization reaction, said thermal initiator being an azo-type 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);

preferably, the thermal initiator is used in an amount of 0.005 to 1 wt%, more preferably 0.01 to 0.2 wt%, based on the weight of the carboxyl group-containing ethylenically unsaturated monomer and/or salt thereof.