Superabsorbent polymer and method of making the same
阅读说明：本技术 超吸收性聚合物及其制备方法 (Superabsorbent polymer and method of making the same ) 是由 崔用锡 洪连祐 申恩智 安泰彬 于 2019-11-07 设计创作，主要内容包括：提供了制备超吸收性聚合物的方法。更特别地,提供了制备超吸收性聚合物的方法,所述方法能够制备在表现出改善的吸收速率的同时保持优异的基本吸收性能例如离心保留容量等的超吸收性聚合物。(Methods of preparing superabsorbent polymers are provided. More particularly, a method of preparing a superabsorbent polymer is provided that is capable of preparing a superabsorbent polymer that exhibits improved absorption rates while maintaining excellent basic absorption properties such as centrifuge retention capacity and the like.)
1. A method of making a superabsorbent polymer, the method comprising the steps of:
a) mixing a water-soluble ethylenically unsaturated monomer, an internal crosslinking agent, and a polymerization initiator to prepare a monomer composition;
b) polymerizing the monomer composition to produce an aqueous gel polymer;
c) chopping the aqueous gel polymer;
d) adding one or more of fluff pulp and synthetic polymer fibers to the chopped aqueous gel polymer and mixing them with each other to prepare a mixture;
e) chopping the mixture;
f) drying the mixture; and
g) the mixture is pulverized.
2. The method of preparing a superabsorbent polymer of claim 1 wherein the fiber is included in an amount of 1 to 18 parts by weight with respect to 100 parts by weight of the aqueous gel polymer.
3. The method of preparing superabsorbent polymer of claim 1 wherein the length of the fibers is from 1mm to 20 mm.
4. The method of preparing superabsorbent polymer of claim 1 wherein the width of the fibers is from 1 μ ι η to 100 μ ι η.
5. The method of preparing superabsorbent polymer of claim 1, wherein further water is added in one or more of the steps c) to e).
6. The method of preparing a superabsorbent polymer of claim 5 wherein the water is added in an amount of 1 to 20 parts by weight relative to 100 parts by weight of the aqueous gel polymer.
7. The method of preparing a superabsorbent polymer of claim 1 wherein the monomer composition further comprises a blowing agent.
8. The method of making superabsorbent polymer of claim 7 wherein the monomer composition further comprises one or more foam stabilizers selected from the group consisting of: alkyl sulfates, alkyl sulfonates, alkyl phosphates, alkyl carbonates, polyethylene glycol alkyl esters, polypropylene glycol alkyl esters, glucoside alkyl esters, glycerol alkyl esters, and block copolymers of polyethylene glycol and polypropylene glycol.
9. The method of preparing superabsorbent polymer of claim 1, further comprising, after said step g),
h) adding a surface cross-linking agent to the mixture obtained in step g); and
i) a surface crosslinking reaction is carried out.
10. The method of preparing superabsorbent polymer of claim 9 wherein the surface cross-linking agent is one or more selected from the group consisting ofAnd (3) multiple: a polyol compound; an epoxy compound; a polyamine compound; a halogenated epoxy compound; condensation products of halogenated epoxy compounds;
11. The method of preparing a superabsorbent polymer of claim 9 wherein the surface cross-linking agent is added in an amount of 0.001 to 5 parts by weight relative to 100 parts by weight of the mixture.
12. A superabsorbent polymer prepared by the preparation method according to any one of claims 1 to 11.
13. A superabsorbent polymer comprising: base polymer particles comprising a crosslinked polymer obtained by crosslinking-polymerizing a water-soluble ethylenically unsaturated monomer in the presence of an internal crosslinking agent, and one or more fibers of fluff pulp and synthetic polymer fibers; and
a surface cross-linked layer formed on the surface of the base polymer particles and obtained by additionally cross-linking the cross-linked polymer via a surface cross-linking agent,
wherein at least a portion of the fibers are incorporated into the interior of the base polymer particles.
14. The superabsorbent polymer of claim 13 wherein the superabsorbent polymer has a Centrifuge Retention Capacity (CRC) as measured according to EDANA method WSP 241.3 of from 25g/g to 45 g/g.
15. The superabsorbent polymer of claim 13 wherein the superabsorbent polymer has an Absorbency Under Load (AUL) under 0.3psi of 25g/g to 40g/g as measured according to EDANA method WSP 242.3.
16. A superabsorbent polymer composition comprising:
superabsorbent polymer particles; and
one or more fibers of fluff pulp and synthetic polymer fibers,
wherein at least a portion of the fibers are incorporated into the interior of the superabsorbent polymer particles.
Technical Field
Cross Reference to Related Applications
The present application is based on and claims priority from korean patent application nos. 10-2018-0158919 and 10-2019-0139625, filed on 11.12.2018 and on 4.11.2019, respectively, the disclosures of which are hereby incorporated by reference in their entireties.
The present invention relates to superabsorbent polymers and methods of making the same. More particularly, the present invention relates to a method of preparing superabsorbent polymers having excellent basic absorption properties while having improved absorption rates.
Background
Superabsorbent polymer (SAP) is a synthetic polymeric material that is capable of absorbing 500 to 1000 times its own weight of moisture. Since such a super absorbent polymer has come into practical use in sanitary products, it has now been widely used not only in sanitary products such as disposable diapers for children and the like, but also in water-retaining soil products for horticulture, water-stopping materials for civil engineering and construction, sheets for raising seedlings, freshness retaining agents for the field of food distribution, materials for cataplasm and the like.
In most cases, these superabsorbent polymers have been widely used in the field of hygiene materials such as diapers, sanitary pads, and the like. For these applications, superabsorbent polymers are required to exhibit high absorbency for water and the like and to have excellent absorption characteristics, for example, not to release absorbed water even under external pressure. Further, in recent years, an absorption rate for more rapidly absorbing and storing a target solution such as moisture or the like is more demanded. Basically, the absorption of aqueous solutions by superabsorbent polymers takes place on their surface. Therefore, in order to improve the absorption rate, a method of enlarging the surface area of the superabsorbent polymer may be considered. In this regard, as a method for increasing the absorption rate, a method of reducing the particle size of the superabsorbent polymer or a method of forming a porous structure has been considered.
For example, methods of preparing superabsorbent polymers by adding a foaming agent to form a porous structure in the superabsorbent polymer have been proposed. However, when the content of the foaming agent is higher, the absorption rate is improved to a certain level, but there are problems in that the amount of fine powder of the superabsorbent polymer is increased due to excessive foaming and the gel strength is decreased. In addition, as the particle size of the superabsorbent polymer decreases, its basic absorption characteristics tend to decrease. Therefore, the known methods have a limitation in improving the absorption rate while maintaining the basic absorbency.
BRIEF SUMMARY OF THE PRESENT DISCLOSURE
Technical problem
In order to solve the problems of the prior art described above, the present invention provides a method of preparing a superabsorbent polymer exhibiting excellent basic absorption properties such as water retention capacity (CRC) while exhibiting an improved initial absorption rate.
Technical scheme
To achieve the above object, the present invention provides a method of preparing a superabsorbent polymer, the method comprising the steps of:
a) mixing a water-soluble ethylenically unsaturated monomer, an internal crosslinking agent, and a polymerization initiator to prepare a monomer composition;
b) polymerizing the monomer composition to produce an aqueous gel polymer;
c) chopping the aqueous gel polymer;
d) adding one or more of fluff pulp and synthetic polymer fibers to the chopped aqueous gel polymer and mixing them with each other to prepare a mixture;
e) chopping the mixture;
f) drying the mixture; and
g) the mixture is pulverized.
The fiber may be included in an amount of 1 to 18 parts by weight with respect to 100 parts by weight of the aqueous gel polymer.
The length of the fibers may be 1mm to 20 mm.
The width of the fibers may be 1 μm to 100 μm.
In one embodiment, water may also be added in one or more of steps c) to e). In this regard, water may be added in an amount of 1 to 20 parts by weight with respect to 100 parts by weight of the aqueous gel polymer.
In one embodiment, the monomer composition may further comprise a blowing agent. In this regard, the monomer composition may further comprise one or more foam stabilizers selected from the group consisting of: alkyl sulfates, alkyl sulfonates, alkyl phosphates, alkyl carbonates, polyethylene glycol alkyl esters, polypropylene glycol alkyl esters, glucoside alkyl esters, glycerol alkyl esters, and block copolymers of polyethylene glycol and polypropylene glycol.
In one embodiment, the method may further comprise the following step after step g):
h) adding a surface cross-linking agent to the mixture obtained in step g); and
i) a surface crosslinking reaction is carried out.
In this regard, the surface cross-linking agent may be one or more selected from the group consisting of: a polyol compound; an epoxy compound; a polyamine compound; a halogenated epoxy compound; condensation products of halogenated epoxy compounds;
The surface cross-linking agent may be added in an amount of 0.001 to 5 parts by weight, relative to 100 parts by weight of the mixture.
Meanwhile, the present invention provides a superabsorbent polymer prepared by the above preparation method.
In particular, the present invention provides a superabsorbent polymer comprising: base polymer particles comprising a crosslinked polymer obtained by crosslinking-polymerizing a water-soluble ethylenically unsaturated monomer in the presence of an internal crosslinking agent, and one or more fibers of fluff pulp and synthetic polymer fibers; and
a surface cross-linked layer formed on the surface of the base polymer particle and obtained by additionally cross-linking the cross-linked polymer via a surface cross-linking agent,
wherein at least a portion of the fibers may be incorporated into the interior of the base polymer particles.
The superabsorbent polymer may have a Centrifuge Retention Capacity (CRC) of from 25g/g to 45g/g as measured according to EDANA method WSP 241.3.
The superabsorbent polymer can have an Absorbency Under Load (AUL) at 0.3psi of from 25g/g to 40g/g as measured according to EDANA method WSP 242.3.
Further, according to one embodiment of the present invention, there is provided a superabsorbent polymer composition comprising: superabsorbent polymer particles; and
one or more fibers of fluff pulp and synthetic polymer fibers,
wherein at least a portion of the fibers can be incorporated into the interior of the superabsorbent polymer particles.
Advantageous effects
The method of preparing a superabsorbent polymer according to the present invention can provide a high-quality superabsorbent polymer having excellent basic absorption properties such as centrifuge retention capacity, etc. while exhibiting an improved absorption rate.
In addition, the method of preparing a superabsorbent polymer according to the present invention has high efficiency due to relatively simple process steps, and thus, a superabsorbent polymer having a high absorption rate can be obtained.
Drawings
FIG. 1 is a Scanning Electron Microscope (SEM) image of a superabsorbent polymer prepared in example 1; and
FIG. 2 is an SEM image of a superabsorbent polymer prepared in comparative example 2.
Detailed Description
The terms used in the present specification are used only for illustrating exemplary embodiments and are not intended to limit the present invention. Unless the context differently expresses, a singular expression may include a plural expression. It must be understood that the terms "comprises," "comprising," or "having" in this specification are used merely to specify the presence of stated features, steps, components, or combinations thereof, but do not preclude the presence or addition of one or more other features, steps, components, or combinations thereof.
The present invention may be modified and embodied in various forms, and specific examples thereof are explained in the specification. However, it is not intended to limit the present invention to the specific examples, and it must be understood that the present invention includes various modifications, equivalents, or alternatives included within the spirit and technical scope of the present invention.
Hereinafter, the superabsorbent polymer and the method of preparing the same will be described in more detail according to embodiments of the present invention.
The method of preparing a superabsorbent polymer according to one embodiment of the present invention may include the steps of:
a) mixing a water-soluble ethylenically unsaturated monomer, an internal crosslinking agent, and a polymerization initiator to prepare a monomer composition;
b) polymerizing the monomer composition to produce an aqueous gel polymer;
c) chopping the aqueous gel polymer;
d) adding one or more of fluff pulp and synthetic polymer fibers to the chopped aqueous gel polymer and mixing them with each other to prepare a mixture;
e) chopping the mixture;
f) drying the mixture; and
g) the mixture is pulverized.
In the present invention, in order to achieve an excellent absorption rate while maintaining the basic absorption properties of the superabsorbent polymer, one or more fibers of fluff pulp and synthetic polymer fibers are added in the step of chopping the aqueous gel polymer. On the surface of the superabsorbent polymer thus prepared, fibers having excellent absorbency are absorbed, and thus, an improved absorption rate can be obtained as compared with the existing superabsorbent polymer. Therefore, the superabsorbent polymer prepared according to the present invention can exhibit more improved absorption rate while maintaining basic absorption characteristics such as water retention capacity.
First, a) a water-soluble ethylenically unsaturated monomer, an internal crosslinking agent, and a polymerization initiator are mixed to prepare a monomer composition.
As the water-soluble ethylenically unsaturated monomer, any monomer generally used for preparing a superabsorbent polymer may be used without particular limitation. Here, any one or more monomers selected from the following may be used: anionic monomers and salts thereof, nonionic hydrophilic monomers, and amino group-containing unsaturated monomers and quaternization products thereof.
In particular, one or more selected from the following may be used: anionic monomers such as (meth) acrylic acid, maleic anhydride, fumaric acid, crotonic acid, itaconic acid, 2-acryloylethanesulfonic acid, 2-methacryloylethanesulfonic acid, 2- (meth) acryloylpropanesulfonic acid, or 2- (meth) acrylamide-2-methylpropanesulfonic acid, and salts thereof; nonionic hydrophilic monomers such as (meth) acrylamide, N-substituted (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, methoxypolyethylene glycol (meth) acrylate or polyethylene glycol (meth) acrylate; and amino group-containing unsaturated monomers such as (N, N) -dimethylaminoethyl (meth) acrylate or (N, N) -dimethylaminopropyl (meth) acrylamide, and quaternized products thereof.
More preferably, acrylic acid or a salt thereof, such as acrylic acid or an alkali metal salt thereof, for example a sodium salt thereof, may be used. When these monomers are used, a superabsorbent polymer having more excellent physical properties can be prepared. When an alkali metal salt of acrylic acid is used as a monomer, acrylic acid may be used after neutralization with an alkaline compound such as caustic soda (NaOH).
The concentration of the water-soluble ethylenically unsaturated monomer may be about 20% by weight to about 60% by weight, preferably about 40% by weight to about 50% by weight, relative to the monomer composition including the raw material of the superabsorbent polymer and the solvent, and the concentration may be appropriately controlled by considering polymerization time, reaction conditions, and the like. If the concentration of the monomer is too low, the yield of the superabsorbent polymer may become low and there may be a problem in terms of economic efficiency. Conversely, if the concentration of the monomer is too high, the following process problems exist: a part of the monomer precipitates or the pulverization efficiency is reduced when the polymerized aqueous gel polymer is pulverized, and the physical properties of the superabsorbent polymer may be reduced.
As the polymerization initiator used during the polymerization in the method of preparing a superabsorbent polymer of the present invention, a polymerization initiator generally used for preparing a superabsorbent polymer may be used without particular limitation.
Specifically, the polymerization initiator may be a thermal polymerization initiator or a photopolymerization initiator by UV irradiation, depending on the polymerization method. However, even in the case of using a photopolymerization method, since a certain amount of heat is generated by ultraviolet irradiation or the like and a certain degree of heat is generated as the exothermic polymerization reaction proceeds, a thermal polymerization initiator may be additionally included.
The photopolymerization initiator may be used without any limitation as long as it is a compound capable of forming radicals by light (e.g., UV rays).
The photopolymerization initiator may include, for example, one or more initiators selected from the group consisting of: benzoin ethers, dialkyl acetophenones, hydroxy alkyl ketones, phenyl glyoxylates, benzyl dimethyl ketals, acyl phosphines and alpha-amino ketones. Meanwhile, specific examples of the acylphosphine may include commercially available lucirin TPO, i.e., 2,4, 6-trimethyl-benzoyl-trimethylphosphine oxide. Further different photopolymerization initiators are well disclosed on page 115 of "UV Coatings: bases, recountdevelopments and New Application (Elsevier, 2007)" written by Reinhold Schwalm, however, the photopolymerization initiators are not limited to the above examples.
The photopolymerization initiator may be included at a concentration of about 0.01 wt% to about 1.0 wt% with respect to the monomer composition. When the concentration of the photopolymerization initiator is too low, the polymerization rate may become slow, and when the concentration of the photopolymerization initiator is too high, the molecular weight of the superabsorbent polymer becomes small and the physical properties thereof may become non-uniform.
Further, as the thermal polymerization initiator, one or more initiators selected from the group consisting of: persulfate-based initiators, azo-based initiators, hydrogen peroxide, and ascorbic acid. Specific examples of the persulfate-based initiator may include sodium persulfate (Na)2S2O8) Potassium persulfate (K)2S2O8) Ammonium persulfate ((NH)4)2S2O8) Etc., and examples of the azo-based initiator may include 2, 2-azobis (2-amidinopropane) dihydrochloride, 2-azobis- (N, N-dimethylene) isobutyramidine dihydrochloride, 2- (carbamoylazo) isobutyronitrile, 2-azobis [2- (2-imidazolin-2-yl) propane ] dihydrochloride]Dihydrochloride, 4-azoAzobis- (4-cyanovaleric acid), and the like. More various thermal Polymerization initiators are well disclosed in "principles of Polymerization (Wiley, 1981)" page 203 written by Odian, however, the thermal Polymerization initiators are not limited to the above examples.
The thermal polymerization initiator may be included at a concentration of about 0.001 wt% to about 0.5 wt% with respect to the monomer composition. When the concentration of the thermal polymerization initiator is too low, additional thermal polymerization hardly occurs, and thus the effect caused by the addition of the thermal polymerization initiator may not be significant, and when the concentration of the thermal polymerization initiator is too high, the molecular weight of the superabsorbent polymer becomes small and the physical properties may become uneven.
As the internal crosslinking agent, a crosslinking agent having one or more functional groups reactive with the water-soluble substituent group of the water-soluble ethylenically unsaturated monomer and having one or more water-soluble ethylenically unsaturated groups; or a crosslinking agent having two or more functional groups reactive with the water-soluble substituents of the monomers and/or the water-soluble substituents formed by hydrolysis of the monomers.
Specific examples of the internal crosslinking agent may include one or more selected from the group consisting of: bisacrylamide having 8 to 12 carbon atoms, bismethacrylamide, poly (meth) acrylate esters of polyols having 2 to 10 carbon atoms, or poly (meth) allyl ethers of polyols having 2 to 10 carbon atoms. More specific examples thereof may include: n, N' -methylenebis (meth) acrylate, ethyleneoxy (meth) acrylate, polyethyleneoxy (meth) acrylate, propyleneoxy (meth) acrylate, glycerol diacrylate, glycerol triacrylate, trimethyloltriacrylate, triallylamine, triarylcyanurate, triallylisocyanate, polyethylene glycol, diethylene glycol, and propylene glycol.
Further, as the internal crosslinking agent, an epoxy compound having one or more epoxy groups may be used. In this regard, the epoxy compound may include one or more functional groups reactive with the water-soluble ethylenically unsaturated monomer in addition to the epoxy group. Specific examples may include: polyepoxides, such as ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerol polyglycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, and the like.
The internal crosslinking agent may be used in combination of two or more thereof, and may be included at a concentration of about 0.01 wt% to about 0.5 wt% with respect to the monomer composition, thereby crosslinking the polymerized polymer.
Meanwhile, in the production method of the present invention, the monomer composition may further contain additives such as a foaming agent, a foam stabilizer, a thickener, a plasticizer, a preservation stabilizer, an antioxidant, and the like, if necessary.
As the foaming agent, inorganic foaming agents and encapsulated foaming agents generally used in the art may be used without limitation.
As inorganic blowing agents, one or more selected from the following may be used: calcium carbonate (CaCO)3) Sodium bicarbonate (NaHCO)3) Ammonium hydrogen carbonate (NH)4HCO3) Ammonium carbonate ((NH)4)2CO3) Ammonium Nitrite (NH)4NO2) Sodium borohydride (NaBH)4) And sodium carbonate (Na)2CO3) But is not limited thereto.
The encapsulated blowing agent may be present in an encapsulated state during polymerization of the monomer composition and may be foamed by heat applied during the drying process described below. Accordingly, pores having an appropriate size are generated between the polymer structures of the superabsorbent polymer, and thus the superabsorbent polymer sheet may exhibit an open pore channel structure. Therefore, when the encapsulated blowing agent is contained in the monomer composition, the absorption rate of the superabsorbent polymer can be further improved, which is preferable.
The encapsulated blowing agent may have a structure including a core containing a hydrocarbon and a shell surrounding the core and formed using a thermoplastic resin. Such encapsulated blowing agents may have expansion characteristics that may vary depending on the components that make up the core and shell, the weight of each component, its particle size. By adjusting these factors, it is possible to expand the pores to a desired size and control the porosity of the superabsorbent polymer sheet.
Meanwhile, in order to check whether or not a cell having a desired size is generated, it is necessary to check the expansion characteristics of the encapsulated blowing agent. However, the foaming shape of the enclosed foaming agent inside the superabsorbent polymer is difficult to be defined as one shape because it may vary according to the preparation conditions of the superabsorbent polymer. Thus, the encapsulated blowing agent is first foamed in air and then its expansion rate and size are examined to determine if it is suitable for forming the desired cells.
In detail, the encapsulated foaming agent was applied on a glass petri dish, which was then heated in air at 150 ℃ for 10 minutes to expand the encapsulated foaming agent. In this regard, when the encapsulated foaming agent exhibits a maximum expansion ratio in air of 3 times to 15 times, 5 times to 15 times, or 8.5 times to 10 times, it may be determined to be suitable for forming an appropriate open cell structure in the method of preparing a superabsorbent polymer sheet of the present invention.
The average diameter of the encapsulated blowing agent can be from 5 μm to 50 μm, or from 5 μm to 30 μm, or from 5 μm to 20 μm, or from 7 μm to 17 μm. When the encapsulated blowing agent exhibits the above average diameter, it may be determined to be suitable for achieving an appropriate porosity.
Further, when the encapsulated blowing agent exhibits a maximum expansion diameter in air of 20 μm to 190 μm, or 50 μm to 190 μm, or 70 μm to 190 μm, or 75 μm to 190 μm, it may be determined to be suitable for forming a suitable open pore structure in the method of preparing a superabsorbent polymer sheet of the present invention.
The maximum expansion ratio and the maximum expansion diameter of the encapsulated blowing agent in air will be described in more detail in the following preparation examples.
The hydrocarbon constituting the core of the encapsulated blowing agent may be one or more selected from the group consisting of: n-propane, n-butane, isobutane, cyclobutane, n-pentane, isopentane, cyclopentane, n-hexane, isohexane, cyclohexane, n-heptane, isoheptane, cycloheptane, n-octane, isooctane, and cyclooctane. Among them, hydrocarbons having 3 to 5 carbon atoms (n-propane, n-butane, isobutane, cyclobutane, n-pentane, isopentane, cyclopentane) may be suitable for forming the pores having the above-mentioned size, and isobutane may be most suitable.
The thermoplastic resin constituting the shell of the encapsulated blowing agent may be a polymer formed from one or more monomers selected from the group consisting of (meth) acrylates, (meth) acrylonitrile, aromatic vinyl, vinyl acetate, vinyl halide, and vinylidene halide. Among them, a copolymer of (meth) acrylate and (meth) acrylonitrile may be most suitable for forming pores having the above-mentioned size.
The encapsulated blowing agent can comprise a hydrocarbon in an amount from 10 wt% to 30 wt%, relative to the total weight of the encapsulated blowing agent. This range may be most suitable for forming an open pore structure.
An encapsulated blowing agent prepared directly may be used, or a commercially available blowing agent satisfying the above conditions may be used.
Further, the encapsulated blowing agent may be used in an amount of 0.001 to 10 parts by weight, preferably 0.01 to 5 parts by weight, and more preferably 0.1 to 1 part by weight, relative to 100 parts by weight of the water-soluble ethylenically unsaturated monomer. If the content of the encapsulated blowing agent is too low, there is a problem in that an open cell structure may not be properly formed. If the level of encapsulated blowing agent is too high, the porosity may be too high and, as a result, the strength of the superabsorbent polymer may be weakened. In this regard, the encapsulated blowing agent may be preferably used in the above content range.
When an encapsulated blowing agent is used, a foam stabilizer may also be included in the monomer composition to initiate stable foaming.
As the foam stabilizer, alkyl sulfate, alkyl sulfonate, alkyl phosphate, alkyl carbonate, polyethylene glycol alkyl ester, polypropylene glycol alkyl ester, glucoside alkyl ester, glycerin alkyl ester, block copolymer of polyethylene glycol and polypropylene glycol, or a mixture thereof may be used. In this regard, the alkyl group may include, but is not particularly limited to, linear, branched, and cyclic alkyl groups having 1 to 30 carbon atoms, and the like. Such foam stabilizers may be included at a concentration of about 0.0001 to 0.1% by weight or about 0.001 to 0.1% by weight, based on 100% by weight of the monomer composition, to improve the foaming efficiency of the foaming agent, thereby forming a crosslinked polymer having an appropriate cell structure.
Raw materials such as the above-mentioned water-soluble ethylenically unsaturated monomer, photopolymerization initiator, thermal polymerization initiator, internal crosslinking agent and additives may be prepared in the form of a solution in which the monomer composition is dissolved in a solvent.
As applicable solvents, any solvent may be used without limitation in the constitution as long as it can dissolve the above components, for example, one or more selected from the following may be used in combination: water, ethanol, ethylene glycol, diethylene glycol, triethylene glycol, 1, 4-butanediol, propylene glycol, ethylene glycol monobutyl ether, propylene glycol monomethyl ether acetate, methyl ethyl ketone, acetone, methyl amyl ketone, cyclohexanone, cyclopentanone, diethylene glycol monomethyl ether, diethylene glycol diethyl ether, toluene, xylene, butyrolactone, carbitol, methyl cellosolve acetate, and N, N-dimethylacetamide.
The solvent may be included in a residual amount excluding the above components from the total weight of the monomer composition.
Next, b) the aqueous gel polymer may be prepared by thermal polymerization or photopolymerization of the monomer composition.
The thermal polymerization or photopolymerization of the monomer composition is not particularly limited in terms of the constitution as long as it is a commonly used polymerization method.
Specifically, polymerization methods are roughly classified into thermal polymerization and photopolymerization according to the polymerization energy source. Thermal polymerization can be generally carried out in a reactor equipped with an agitating shaft, such as a kneader, while photopolymerization can be carried out in a reactor equipped with a movable conveyor belt. The above polymerization method is only an example, and the present invention is not limited to the above polymerization method.
For example, an aqueous gel polymer can be obtained by: the thermal polymerization is carried out while supplying hot air to the above-mentioned reactor equipped with a stirring shaft such as a kneader or heating the reactor. When the aqueous gel polymer is discharged from the outlet of the reactor, the aqueous gel polymer may have a size of several centimeters or several millimeters depending on the type of the stirring shaft provided in the reactor. Specifically, the size of the obtained aqueous gel polymer may vary depending on the concentration of the monomer composition fed thereto, the feeding speed, and the like, and generally an aqueous gel polymer having a weight average particle size of 2mm to 50mm may be obtained.
Further, as described above, when photopolymerization is performed in a reactor equipped with a movable conveyor belt, the obtained water-containing gel polymer may be generally a sheet-like water-containing gel polymer having a width of the belt. In this case, the thickness of the polymer sheet may vary depending on the concentration of the monomer composition fed thereto and the feeding speed. Generally, it is preferable to supply the monomer composition so that a sheet-like polymer having a thickness of about 0.5cm to about 5cm can be obtained. When the monomer composition is supplied to such an extent that the thickness of the sheet-like polymer becomes too thin, it is undesirable due to low production efficiency, and when the thickness of the sheet-like polymer is more than 5cm, the polymerization reaction may not occur uniformly throughout the thickness due to an excessively large thickness.
The water content of the aqueous gel polymer obtained by the above method may be 40 to 80% by weight. Meanwhile, "water content" as used herein means a weight occupied by water with respect to the total weight of the aqueous gel polymer, which may be a value obtained by subtracting the weight of the dried polymer from the weight of the aqueous gel polymer. Specifically, the water content may be defined as a value calculated by measuring a weight loss due to evaporation of water in the polymer during a drying process in which the temperature of the polymer is increased by infrared heating. At this time, the water content was measured under the dry condition determined as follows: the drying temperature was increased from room temperature to about 180 ℃, then the temperature was maintained at 180 ℃, and the total drying time was set to 20 minutes, including 5 minutes for the warming step.
Next, c) a step of chopping the prepared aqueous gel polymer is performed.
In this regard, the pulverizer used herein is not limited by its configuration, and specifically, it may include any one selected from the group consisting of: vertical mills, turbo cutters, turbo mills, rotary shredders (rotary mill), shredders (cutter mill), disc mills (disc mill), chip breakers, crushers, shredders (chopper), and disc cutters, but are not limited to the above examples.
In this regard, step (c) may be performed such that the particle size of the aqueous gel polymer becomes about 2mm to about 20 mm.
Due to the high water content of the aqueous gel polymer, it is technically not easy to coarsely pulverize it to a particle size of less than 2mm, and agglomeration between pulverized particles may occur. Meanwhile, if the polymer is pulverized to a particle size of more than 20mm, the effect of improving efficiency in a subsequent drying step may not be significant.
Next, step d) is performed of adding one or more of fluff pulp and synthetic polymer fibers to the minced aqueous gel polymer and mixing them with each other to prepare a mixture, and step e) is performed of mincing the mixture again.
When the fibers are added in the step of chopping the aqueous gel polymer, the fibers adsorbed on the surface of the aqueous gel polymer particles can be incorporated into the inside of the particles by the chopper. Thus, at least a portion of the fibers may be incorporated into the interior of the base polymer particles, and the fibers may be distributed in both the exterior and interior of the base polymer particles. As described above, the fibers distributed in both the interior and exterior of the base polymer rapidly absorb ambient moisture by capillary action and transfer the moisture to the polymer. Thus, the superabsorbent polymer prepared according to the present invention may exhibit an improved initial absorption rate. In addition, since such fibers are easy to apply to the method and are inexpensive and harmless to the human body, a superabsorbent polymer that is friendly to the human body and has excellent absorbency can be prepared in a simple and economical manner according to the present invention.
Fluff pulp is cellulosic fluff pulp and can be, but is not limited to, wood fluff pulp, such as softwood kraft pulp and hardwood kraft pulp. Fluff pulp used in absorbent articles can be used without limitation.
The synthetic polymer fibers may be one or more selected from the group consisting of: nylon, polypropylene, polyethylene, polyester, polyacrylonitrile, polyvinyl chloride, polyvinyl alcohol, polyacrylate, and acetate. Since the synthetic polymer fiber has excellent moisture absorption characteristics and the width or length of the fiber can be easily controlled, the physical properties of the superabsorbent polymer can be easily controlled.
The length of the fibers may preferably be 1mm to 20 mm. Further, the width of the fiber may preferably be 1 μm to 100 μm. If the length of the fiber is too long or the width of the fiber is too wide to exceed the above range, a load may be generated during the process of chopping the aqueous gel polymer together with the fiber, and the fiber is hardly adsorbed on the inside and outside of the base polymer particle. Thus, it may be difficult to uniformly distribute the fibers in the superabsorbent polymer. Further, if the length of the fiber is too short or the width of the fiber is too narrow, the effect of improving the physical properties of the superabsorbent polymer may not be significant, and thus it is preferable to satisfy the above range.
Meanwhile, when the length and width of the fiber are increased within the range satisfying the above length and width, more fibers may be adsorbed onto the relatively large hydrogel polymer particles. In this case, in the subsequent surface crosslinking step, the surface crosslinking solution can be applied more uniformly regardless of the change in the particle size of the base polymer particles, thereby further improving the surface crosslinking efficiency.
In other words, when the size of the base polymer particles is smaller, the absorption rate of the liquid, i.e., the surface crosslinking solution, is faster. Accordingly, the degree of crosslinking may vary according to the particle size of the base polymer particles, and thus, a change in absorption characteristics between the superabsorbent polymer particles may occur. As described above, when more fibers are adsorbed onto relatively large water-containing gel polymer particles, the variation in the absorption rate between large particles and small particles may be reduced due to the adsorbed fibers. Therefore, the coating degree of the surface cross-linking solution becomes uniform regardless of the particle size of the base polymer, and the variation in the cross-linking degree is reduced, thereby improving the overall physical balance of the superabsorbent polymer to be produced.
To ensure these effects, the length of the fibers may be 2mm or more, or 3mm or more and 15mm or less, or 10mm or less. For example, a fiber having an average length of 3mm to 10mm in which the length of the individual fiber satisfies the range of 1mm to 20mm may be preferably used. Here, the average length of the fibers can be obtained by randomly selecting 100 fibers, measuring the length of the individual fibers and calculating the average value thereof.
Further, the width of the fibers may be 10 μm or more, 15 μm or more, 30 μm or more, or 50 μm or more and 90 μm or less, or 80 μm or less.
The content of the fiber may be 1 part by weight or more, 3 parts by weight or more, or 5 parts by weight or more and 18 parts by weight or less, 15 parts by weight or less, or 10 parts by weight or less with respect to 100 parts by weight of the aqueous gel polymer. If the content is less than 1 part by weight with respect to 100 parts by weight of the water-containing gel polymer fiber, the effect of improving the absorption rate due to the fiber may not be secured. If the content is more than 18 parts by weight with respect to 100 parts by weight of the aqueous gel polymer fiber, the basic absorption properties (e.g., Centrifuge Retention Capacity (CRC), Absorbency Under Load (AUL), etc.) and absorption rate of the superabsorbent polymer to be prepared may be reduced. And in the step of chopping the aqueous gel polymer, the mechanical load may be increased.
In this regard, steps d) and e) may be repeated two to five times. When steps d) and e) are repeated two or more times, the incorporation of the fibers and the aqueous gel polymer can be further improved, and the absorption rate of the resulting superabsorbent polymer can be further improved.
If steps d) and e) are repeated two or more times, the same amount of fiber may be added in each repetition period to facilitate mixing, but preferably, the total amount of fiber to be added is within the above range.
Furthermore, in one or more of steps c) to e), water may also be added. When an appropriate amount of water is added in the step of chopping the aqueous gel polymer, the load on the crusher can be reduced, and the aqueous gel polymer can be more uniformly chopped. Therefore, the particle size of the aqueous gel polymer can be easily controlled. The water may be distilled water. The amount of water added in each step is not particularly limited, but may be, for example, 1 part by weight to 20 parts by weight with respect to 100 parts by weight of the aqueous gel polymer.
The particle size of the aqueous gel polymer comprising fibres finally prepared in step e) may preferably be in the range of 1mm to 15 mm. Within this particle size range, the efficiency of the drying step can be increased.
Next, f) drying the mixture.
In this regard, the drying temperature of the drying step may be about 150 ℃ to about 200 ℃. If the drying temperature is less than 150 ℃, the drying time becomes too long and the physical properties of the final superabsorbent polymer may deteriorate. If the drying temperature is higher than 200 ℃, only the polymer surface is excessively dried, and thus fine powder may be generated during a subsequent pulverizing process and physical properties of the finally formed superabsorbent polymer may be deteriorated. More preferably, the drying may be performed at a temperature of 150 ℃ to 200 ℃, and more preferably at a temperature of 160 ℃ to 180 ℃.
Meanwhile, the drying step may be performed for 20 minutes to 1 hour in consideration of process efficiency, but is not limited thereto.
In the drying step, any drying method may be selected and used without limitation in composition as long as it is generally used in the process of drying the aqueous gel polymer. Specifically, the drying step may be performed by a method such as hot air supply, infrared irradiation, microwave irradiation, or ultraviolet irradiation. When the drying step is completed as above, the water content of the polymer may be from about 0.1% to about 10% by weight.
Next, g) pulverizing the dried mixture obtained by the drying step.
The particle size of the polymer powder obtained by the pulverization step may be about 150 μm to about 850 μm. Specific examples of the pulverizer that can be used to achieve the above particle size may include a pin mill, a hammer mill, a screw mill, a roll mill, a disc mill, a jog mill, and the like, but the present invention is not limited thereto.
In order to manage the physical properties of the superabsorbent polymer powder finally commercialized after the pulverization step, the polymer powder obtained after the pulverization is generally classified according to the particle size. Preferably, the polymer powder is classified into a polymer having a particle size of less than about 150 μm, a polymer having a particle size of about 150 μm to about 850 μm, and a polymer having a particle size of greater than about 850 μm.
Meanwhile, the method of preparing the superabsorbent polymer of the present invention may further comprise: step h) adding a surface cross-linking agent to the mixture obtained after step g); and step i) carrying out a surface cross-linking reaction.
The surface crosslinking step is a step of forming a superabsorbent polymer having more improved physical properties by initiating a crosslinking reaction on the surface of the mixture, i.e., the surface of the polymer comprising fibers on the surface thereof, in the presence of a surface crosslinking agent. By this surface crosslinking, a surface crosslinked layer (surface modified layer) is formed on the surface of the pulverized polymer particles.
Generally, because the surface cross-linking agent is applied on the surface of the superabsorbent polymer particles, a surface cross-linking reaction occurs on the surface of the superabsorbent polymer particles, resulting in improved cross-linkability on the surface of the particles while not substantially affecting the interior of the particles. Thus, surface-crosslinked superabsorbent polymer particles have a higher degree of crosslinking near their surface than inside them.
As the surface cross-linking agent, a surface cross-linking agent used in the preparation of the superabsorbent polymer may be used without particular limitation. More specific examples thereof may include: one member selected from the group consisting of ethylene glycol, propylene glycol, 1, 3-propanediol, 1, 4-butanediol, 1, 6-hexanediol, 1, 2-hexanediol, 1, 3-hexanediol, 2-methyl-1, 3-propanediol, 2, 5-hexanediol, 2-methyl-1, 3-pentanediol, 2-methyl-2, 4-pentanediol, tripropylene glycol and glycerolOne or more polyols; one or more carbonate-based compounds selected from the group consisting of ethylene carbonate and propylene carbonate; epoxy compounds such as ethylene glycol diglycidyl ether;azoline compounds, e.g.
Such surface cross-linking agents may be used in an amount of about 0.01 to about 5 parts by weight, relative to 100 parts by weight of the mixture obtained in step g). The amount of the surface cross-linking agent is controlled within the above range, thereby providing a superabsorbent polymer having excellent absorption characteristics.
The surface-crosslinking agent can be dry-mixed with the mixture obtained in step g) or added in the form of a surface-crosslinking solution. As the solvent of the surface crosslinking solution, water, methanol, ethanol, propylene glycol, and a combination thereof may be used, but is not limited thereto.
Meanwhile, in the surface crosslinking step, in addition to the above-mentioned surface crosslinking agent, a polyvalent metal salt, an inorganic filler, a thickener, and the like may be contained as necessary. These additives may be dry-mixed with the mixture obtained in step g) or mixed in the form of additions to the surface-crosslinking solution.
The multivalent metal salt may also include, for example, an aluminum salt, more specifically, one or more selected from the group consisting of: sulfates, potassium, ammonium, sodium, and hydrochloride salts of aluminum.
When the polyvalent metal salt is further used, the liquid permeability of the superabsorbent polymer prepared by the method of one embodiment may be further improved. The polyvalent metal salt may be added to the surface crosslinking solution together with the surface crosslinking agent, and may be used in an amount of 0.01 to 4 parts by weight with respect to 100 parts by weight of the base polymer.
The inorganic filler may include silica, alumina, or silicate. The inorganic filler may be included in an amount of 0.01 to 0.5 parts by weight, based on 100 parts by weight of the base polymer powder. Such inorganic fillers may act as lubricants to improve the coating efficiency of the surface crosslinking solution on the surface of the superabsorbent polymer, and further improve the liquid permeability of the superabsorbent polymer prepared.
A thickener may also be included in the surface crosslinking step. By further crosslinking the surface of the base polymer powder in the presence of the thickener, deterioration of physical properties can be minimized even after pulverization. Specifically, one or more selected from polysaccharides and hydroxyl group-containing polymers may be used as the thickener. As the polysaccharide, a gum-based thickener and a cellulose-based thickener can be used. Specific examples of the gum-based thickener may include xanthan gum, gum arabic, karaya gum, tragacanth gum, ghatti gum (ghatti gum), guar gum, locust bean gum, psyllium seed gum, and the like, and specific examples of the cellulose-based thickener may include hydroxypropylmethylcellulose, carboxymethylcellulose, methylcellulose, hydroxymethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, hydroxyethylmethylcellulose, hydroxymethylpropylcellulose, hydroxyethylhydroxypropylcellulose, ethylhydroxyethylcellulose, methylhydroxypropylcellulose, and the like. Meanwhile, specific examples of the hydroxyl group-containing polymer may include polyethylene glycol, polyvinyl alcohol, and the like.
The surface crosslinking reaction may be performed by heating a mixture of the pulverized aqueous gel polymer, the surface crosslinking agent and the fiber.
The surface crosslinking step may be carried out by heating at a temperature of 185 ℃ or higher, preferably 185 ℃ to about 230 ℃ for about 10 minutes to about 90 minutes, preferably about 20 minutes to about 70 minutes. If the crosslinking reaction temperature is less than 185 ℃ or the reaction time is too short, there is a problem that the surface crosslinking agent does not sufficiently react with the aqueous gel polymer. If the crosslinking reaction temperature is higher than 230 ℃ or the reaction time is too long, the aqueous gel polymer may be degraded to cause a problem of deterioration of physical properties.
Means for raising the temperature of the surface crosslinking reaction is not particularly limited. Heating may be performed by providing a heating medium or by directly providing a heat source. In this regard, the kind of the heating medium that can be applied may be a hot fluid such as steam, hot air, hot oil, etc., but the present invention is not limited thereto. The temperature of the heating medium to be supplied may be appropriately controlled in consideration of the means of heating the medium, the heating rate, and the target temperature. Meanwhile, as the heat source to be directly provided, an electric heater or a gas heater may be used, but the present invention is not limited to these examples.
Through the above surface crosslinking reaction step, a surface modification layer may be formed on the surface of the polymer.
The superabsorbent polymer prepared according to the preparation method of the present invention may include one or more fibers of fluff pulp and synthetic polymer fibers, thereby exhibiting improved absorption rate.
Thus, according to one embodiment of the present invention, there is provided a superabsorbent polymer comprising: base polymer particles comprising a crosslinked polymer obtained by crosslinking-polymerizing a water-soluble ethylenically unsaturated monomer in the presence of an internal crosslinking agent, and one or more fibers of fluff pulp and synthetic polymer fibers; and a surface cross-linked layer formed on the surface of the base polymer particle and obtained by additionally cross-linking the cross-linked polymer via a surface cross-linking agent, wherein at least a part of the fiber may be incorporated into the inside of the base polymer particle.
The superabsorbent polymer of the present invention may comprise fibers having excellent moisture absorption characteristics in a process of chopping the aqueous gel polymer during the preparation of the base polymer, and thus, the fibers may be uniformly distributed inside and outside the particulate base polymer. Therefore, the superabsorbent polymer of the present invention can exhibit excellent basic absorption properties such as water retention capacity and absorption yield under load while having improved absorption rate and liquid permeability.
Specifically, the water retention capacity (CRC) of the superabsorbent polymer can be in a range of about 25g/g or more, 28g/g or more, or about 30g/g or more, and about 45g/g or less, 40g/g or less, or about 35g/g or less, as measured according to EDANA method WSP 241.3.
Further, the superabsorbent polymer can have an Absorbency Under Load (AUL) at 0.3psi of 25g/g or greater, or 27g/g or greater, and 40g/g or less, or 30g/g or less, as measured according to EDANA method WSP 242.3.
Further, the absorption rate (vortex time) of the superabsorbent polymer may be 50 seconds or less, or 45 seconds or less, as measured by stirring a magnetic bar (8 mm in diameter and 31.8mm in length) at 600rpm and measuring the time (seconds) taken for vortex loss after adding 2g of the superabsorbent polymer to 50mL of physiological saline at 23 ℃ to 24 ℃. A lower absorption rate means that the superabsorbent polymer is more excellent. Therefore, the lower limit is not limited, but is, for example, 10 seconds or more or 20 seconds or more.
Meanwhile, according to one embodiment of the present invention, there is provided a superabsorbent polymer composition including: superabsorbent polymer particles; and one or more fibers of fluff pulp and synthetic polymer fibers, wherein at least a portion of the fibers can be incorporated into the interior of the superabsorbent polymer particles.
In other words, in the superabsorbent polymer composition, a portion of the fibers may be present outside of the superabsorbent polymer particles and a portion of the fibers may be incorporated into the superabsorbent polymer particles. Therefore, the superabsorbent polymer composition of the present invention can exhibit an improved absorption rate as compared to a composition in which a superabsorbent polymer and absorbent fibers are simply mixed with each other.
Hereinafter, the present invention will be described in more detail with reference to examples. However, the following examples are only for illustrating the present invention, and the contents of the present invention are not limited to the following examples. In addition, "%" and "part(s)" representing the contents in the following examples and comparative examples are "% by weight" and "part(s) by weight", respectively, unless otherwise specified.
< example >
Preparation of superabsorbent polymers
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