WO2005111088A1

WO2005111088A1 - Method for production of water-swellable polymeric particles

Info

Publication number: WO2005111088A1
Application number: PCT/EP2005/005156
Authority: WO
Inventors: Klaus-Dieter Hungenberg; Dennis LÖSCH; Volker Seidl; Marco KRÜGER; Hans-Ulrich Moritz
Original assignee: Basf Aktiengesellschaft
Priority date: 2004-05-14
Filing date: 2005-05-12
Publication date: 2005-11-24
Also published as: DE102004024437A1

Abstract

The invention relates to a method for production of water-swellable polymeric particles, by means of spray polymerisation with use of an initiator with a 10 hour half-life temperature of at most 55 °C, the water-swellable polymeric particles and use thereof for the absorption of liquids, in particular, for the thickening of aqueous wastes.

Description

Process for the production of water-swellable, polymeric particles

The present invention relates to a method for producing water-swellable, polymeric particles by spray polymerization, the water-swellable, polymeric particles and their use for the absorption of liquids.

Water-swellable polymers, so-called superabsorbents (SAP), are in particular polymers of (co) polymerized hydrophilic monomers, graft (co) polymers of one or more hydrophilic monomers on a suitable graft base, crosslinked cellulose or starch ethers, crosslinked carboxy methyl cellulose, partially cross-linked polyalkylene oxide or natural products swellable in aqueous liquids, such as guar derivatives. Such polymers are used as products which absorb aqueous solutions for the production of diapers, tampons, sanitary napkins and other hygiene articles, but also as water-retaining agents in agricultural horticulture or for thickening all types of waste, in particular medical waste.

To improve the application properties, water-swellable polymers are usually surface or gel post-crosslinked.

This postcrosslinking is known per se to the person skilled in the art and is preferably carried out in the aqueous gel phase or as surface postcrosslinking of the ground and sieved polymer particles.

Waste, in particular medical waste and any type of waste that is contaminated with toxic, contagious or hazardous to humans and the environment, must be handled and transported safely. A superabsorbent can immobilize most dangerous substances by absorbing the liquid waste.

Medical waste, especially hospital waste from operating rooms, mainly consists of blood, body fluids and physiological saline, which is used as a flushing solution.

The rapid solidification allows faster and safer handling of this waste, for example during transport and storage.

An advantageous behavior for the absorption of medical waste is when the added superabsorbent floats on the liquid surface after the addition to the solution. As a result, the surface of the liquid is immediately covered with superabsorbers and it is difficult for substances such as viruses or bacteria to escape, in particular the liquid is prevented from splashing. Patent application WO-A-95/17455 describes a porous superabsorbent that can float on water even when swollen. The process requires large amounts of expensive azo compounds as blowing agents.

The object of the present invention was to provide an improved process for the production of floatable, water-swellable polymers.

Patent application EP-A-0348 180 describes a process for the spray polymerization of water-absorbent resins. For this purpose, an aqueous solution of partially neutralized acrylic acid, crosslinker and initiator is sprayed into a gas stream and polymerized. The application teaches that the relative humidity in the gas stream must be at least 30%. At lower relative humidities, the water contained in the drops evaporates too quickly and in the drops separates monomer that can no longer polymerize, the monomer conversion remains incomplete.

US 5,269,980 describes a process for the production of polymer particles. Aerosols are generated from polymer solutions, solutions of prepolymerized monomers or monomer solutions and these aerosol particles are dried or polymerized at temperatures above 150 ° C.

According to patent application WO-A-96/40427, the spray polymerization is carried out in such a way that monomer solutions are sprayed into a heated, essentially static atmosphere. The particles obtained in the application examples had a diameter of 50 to 100 μm. At reduced pressure, the water content in the polymer balls produced is significantly reduced, but the polymer particles have a rough surface. At elevated pressure, smooth polymer balls are obtained.

It has now been found that by spray polymerizing a monomer solution containing

a) at least one ethylenically unsaturated monomer bearing acid groups, the acid groups being neutralized to at least 65%, b) optionally at least one crosslinking agent, c) at least one initiator, d) optionally one or more ethylenically unsaturated monomers copolymerizable with a), e) optionally one or more water-soluble polymers and f) water, In the presence of an inert carrier gas, the 10-hour half-life temperature of the at least one initiator c) being at most 55 ° C., preferably at most 50 ° C., particularly preferably at most 45 ° C., water-swellable polymer particles are obtained. These polymers are characterized by good buoyancy.

The 10-hour half-life temperature is the temperature at which half of the initiator has decomposed thermally after 10 hours.

The concentration of the at least one monomer a) in the monomer solution is at least 50% of the saturation concentration.

The reaction temperature is usually between 110 to 300 ° C, preferably 110 to 180 ° C, particularly preferably 120 to 160 ° C.

The reaction temperature and initiator are selected such that the half-life of the initiator is, for example, less than 5 seconds, preferably less than 1 second, preferably less than 0.2 seconds.

The inert carrier gas is preferably nitrogen. The oxygen content of the inert carrier gas is advantageously below 5% by volume, preferably below 1% by volume, particularly preferably below 0.1% by volume.

The inert carrier gas is preferably passed in cocurrent to the free-falling drops of the monomer solution through the reaction space.

Ethylenically unsaturated monomers a) bearing acid groups are, for example, ethylenically unsaturated C ₃ -C ₆ carboxylic acids. These compounds are, for example, acrylic acid, methacrylic acid, ethacrylic acid, α-chloroacrylic acid, crotonic acid, maleic acid, maleic anhydride, itaconic acid, citraconic acid, mesaconic acid, glutaconic acid, aconitic acid and fumaric acid and the alkali metal or ammonium salts of these acids.

Further radically polymerizable monomers a) are acrylamidopropanesulfonic acid, vinylphosphonic acid and / or alkali metal or ammonium salts of vinylsulfonic acid. The other acids can also be used in the polymerization either in non-neutralized form or in partially or up to 100% neutralized form.

Other monoethylenically unsaturated sulfonic or phosphonic acids are also suitable, for example allylsulfonic acid, sulfoethyl acrylate, sulfoethyl methacrylate, sulfopropyl acrylate, sulfopropyl methacrylate, 2-hydroxy-3-acryloxypropylsulfonic acid, 2-hydroxy-3-methacryoxypropylsulfonic acid, allylololsulfonic acid, allylololsulfonic acid, allylolsol acid and 2-acrylamido-2-methylpropanesulfonic acid. The monomers a) can be used alone or as a mixture with one another.

Preferred monomers a) are acrylic acid, methacrylic acid and the alkali metal or ammonium salts of these acids or mixtures of these acids, for example mixtures of acrylic acid and methacrylic acid.

Preferred monomers a) are also mixtures of the abovementioned acids with their alkali metal or ammonium salts. For example, mixtures of acrylic acid and its alkali metal salts can be obtained by neutralizing acrylic acid with alkali metal hydroxides and / or alkali metal carbonates. The degree of neutralization is, for example, at least 50%, preferably 65 to 100%, particularly preferably 70 to 80%. For example, in the case of a mixture of acrylic acid and sodium acrylate, a degree of neutralization of 50% means that sodium acrylate and acrylic acid are in a molar ratio of 50:50, and a degree of neutralization of 75% means that sodium acrylate and acrylic acid are in a molar ratio of 75:25.

Very particularly preferred monomers a) are acrylic acid, methacrylic acid, the sodium salts of these acids and mixtures thereof, for example mixtures of acrylic acid and sodium acrylate.

The monomers a) can be polymerized in the presence of a crosslinker b) or a combination of different crosslinkers. The polymerization in the presence of at least one crosslinker is preferred.

An aqueous monomer solution is usually used. The concentration of the monomers a) is chosen to be as high as possible. The concentration of the monomers a) is typically at least 50%, preferably at least 60%, particularly preferably at least 80%, of the saturation concentration. The person skilled in the art can calculate the saturation concentration for a monomer mixture to be used on the basis of the solubility products.

Suitable crosslinkers b) are, for example, (meth) acrylic esters of polyhydric alcohols which can be alkoxylated with up to 100, usually up to 50, ethylene oxide and / or propylene oxide units. Suitable polyhydric alcohols are, in particular, C ₂ -C ₁₀ -alkane polyols having 2 to 6 hydroxyl groups, such as ethylene glycol, glycerol, trimethylolpropane, pentaerythritol or sorbitol. Preferred crosslinkers are polyethylene glycol diacrylate and polyethylene glycol dimethacrylates, which are each derived from polyethylene glycols (which can be regarded as ethoxylated ethylene glycol) with a molecular weight of 200 to 2000. Further crosslinkers b) which can be used are methylene bisacrylamide, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, ethylene glycol diacrylate, propylene glycol diacrylate, butanediol diacrylate, hexanediol diacrylate, hexanediol dimethacrylate or diacrylates and dimethacrylates of block copolymers of ethylene oxide and propylene oxide.

Further crosslinkers b) are diallyl carbonate, allyl carbonates or allyl ethers of polyhydric alcohols, which can be alkoxylated with up to 100, usually up to 50, ethylene oxide and / or propylene oxide units, and allyl esters of polyhydric carboxylic acids.

Allyl carbonates of polyhydric alcohols correspond to the general formula

wherein A stands for the remainder of a polyhydric alcohol, which can be alkoxylated with 0 to 100, usually 0 to 50, ethylene oxide and / or propylene oxide units; and n stands for the valence of the alcohol, for example an integer from 2 to 10, preferably 2 to 5. A particularly preferred example of such a compound is ethylene glycol di (allyl carbonate). Also particularly suitable are polyethylene glycol di (allyl carbonates) which are derived from polyethylene glycols with a molecular weight of 200 to 2000.

The following are preferred examples of allyl ethers: polyethylene glycol diallyl ethers which are derived from polyethylene glycols with a molecular weight of 200 to 2000; Pentraerythritol triallyl ether or trimethylol propane diallyl ether. Reaction products of ethylene glycol diglycidyl ether or polyethylene glycol glycidyl ether with 2 moles of allyl alcohol and / or pentaerythritol triallyl ether are also suitable.

A suitable allyl ester of a polyvalent carboxylic acid is, for example, dialyl phthalate.

The monomers are generally copolymerized with one another in aqueous solution in the presence of polymerization initiators c).

All of the compounds which break down into free radicals under the polymerization conditions can be used as polymerization initiators c), for example peroxides, hydroperoxides, hydrogen peroxide, persulfates, azo compounds and the so-called redox catalysts. The use of water-soluble initiators is preferred. In some cases it is advantageous to use mixtures of different polymerization initiators, for example mixtures of hydrogen peroxide and sodium or potassium peroxodisulfate. Mixtures of hydrogen peroxide and sodium peroxodisulfate can be used in any ratio. Suitable organic peroxides are, for example, acetylacetone peroxide, methyl ethyl ketone peroxide, tert-butyl hydroperoxide, cumene hydroperoxide, tert-amyl perpivalate, tert-butyl perpivalate, tert-butyl perneohexanoate, tert-butyl perisobutyrate, tert-butyl per-2-ethylhexanoate, tert-butyl perisonone, tert-butyl perisonone -Butyl perbenzoate, di- (2-ethyl! Hexyl) peroxydicarbonate, dicyclohexyl peroxydicarbonate, di- (4-tert-butylcyclohexyl) peroxydicarbonate, dimyristilperoxydicarbonate, diacetylperoxydicarbonate, allyl perester, cumylperoxy-neodyl peroxyl-peroxyl-hexyl-oxyl-peroxydonyl-oxyl-peroxydonyl-oxyl-peroxydonyl-xyl-oxo-oxo-5-oxo-3-oxy-oxo-5-oxo , Dilauryl peroxide, dibenzoyl peroxide and tert

Amylperneodekanoat. Preferred polymerization initiators c) are azo starters, for example 2,2'-azobis-isobutyronitrile, 2,2'-azobis (2,4-dimethylvaleronitrile) and 2,2'-azobis (4-methoxy-2,4-dimethylvaleronitrile), in particular water-soluble azo starters, for example 2,2'-azobis {2- [1- (2-hydroxyethyl) -2-imidazolin-2-yl] propane} dihydrochloride, 2,2'-azobis- (2-amidinopropane) dihydrochloride, 2, 2'-azobis [2- (2-imidazolin-2-yl) propane] dihydrochloride and 2,2'-azobis [2- (5-methyl-2-imidazolin-2-yl) propane] dihydrochloride. 2,2'-Azobis [2- (2-imidazolin-2-yl) propane] dihydrochloride and 2,2'-azobis [2- (5-methyl-2-imidazolin-2-yl) propane] are very particularly preferred. dihydrochloride. The polymerization initiators c) mentioned are used in customary amounts, for example in amounts of 0.01 to 5, preferably 0.05 to 2.0% by weight, based on the monomers to be polymerized.

Redox catalysts are also suitable as initiators c). The redox catalysts contain at least one of the above-mentioned per compounds as the oxidizing component and as reducing component, for example, ascorbic acid, glucose, sorbose, ammonium or alkali metal hydrogen sulfite, sulfite, thiosulfate, hyposulfite, pyrosulfite or sulfide, metal salts such as iron (II) ions or silver ions or sodium hydroxymethyl sulfoxylate. Ascorbic acid or sodium pyrosulfite is preferably used as the reducing component of the redox catalyst. Relative to the employed in the polymerization amount of monomers 10 ^"5 uses, for example, 1 x to 1 mol% of the reducing component of the redox catalyst. Instead of the oxidizing component of the redox catalyst it is also possible to use one or more water-soluble azo initiators. Table 1: Azostarter according to the invention

The 10-hour half-life temperatures are usually determined in a suitable solvent. Water is a suitable solvent for water-soluble initiators and toluene is a suitable solvent for water-insoluble initiators.

The monomers used are preferably stabilized with a commercially available polymerization inhibitor, particularly preferably with a polymenation inhibitor which only works together with oxygen, for example hydroquinomonomethyl ether.

Commercially available polymerization inhibitors are polymerization inhibitors which are used as storage stabilizers in the respective monomers for reasons of product safety. Examples of such storage stabilizers are hydroquinone, hydroquinone monomethyl ether, 2,5-di-tert-butylhydroquinone and 2,6-di-tert-butyl-4-methylphenol.

Ethylene-unsaturated monomers copolymerizable with the monomers a) are, for example, acrylamide, methacrylamide, crotonic acid amide, dimethylaminoethyl methacrylate, dimethylaminoethyl acrylate, dimethylaminopropylacrylate, diethylaminopropyl acrylate, dimethylaminobutyl acrylate, dimethylaminoethyl methacrylate methacrylate, diethyl methacrylate Polyvinyl alcohol, polyvinyl pyrrolidone, starch, starch derivatives, polyglycols or polyacrylic acids, preferably polyvinyl alcohol and starch, can be used as water-soluble polymers e). The water-soluble polymers e) can also serve as a graft base for the monomers a).

The reaction is preferably carried out in apparatus which are also suitable for spray drying. Such reactors are described, for example, in K. Masters, Spray Drying Handbook, 5th Edition, Longman, 1991, pages 23 to 66. The reaction is preferably carried out in apparatuses in which the monomer solution can fall freely in the form of monodisperse drops. Devices are suitable for this purpose, as described, for example, in US Pat. No. 5,269,980, column 3, lines 25 to 32. The droplet diameter which arises during spraying is expediently from 20 to 1400 μm, preferably from 50 to 600 μm.

If a swinging orifice is used to generate droplets, the droplet diameter is approximately 1.9 times the orifice diameter.

A drop caused by laminar jet decay, as in Rev. Sei. Instr., Volume 38 (1966), pages 502 to 506, is also possible.

The reaction can be carried out under positive or negative pressure.

An inert gas, preferably nitrogen, flows through the reactor. The direct current mode of operation is preferred, that is to say the inert gas flows through the reactor from top to bottom. The water vapor content of the inert gas is generally up to 1% by volume, preferably up to 0.5% by volume. The gas velocity is preferably set such that the flow in the reactor is directed, for example there are no convection vortices opposite to the general flow direction, and is for example 0.02 to 1.5 m / s, preferably 0.05 to 0.4 m / s ,

The inert gas is advantageously preheated in front of the reactor to the reaction temperature of 70 to 300 ° C., preferably 90 to 180 ° C., particularly preferably 110 to 160 ° C.

The reaction exhaust gas can, for example, be cooled in a heat exchanger. Water and unreacted acrylic acid condense. The exhaust gas can then be at least partially reheated and returned to the reactor as circulating gas. The exhaust gas is preferably cooled such that the cooled exhaust gas has the desired proportion of water vapor for the reaction. Part of the gases can be discharged and replaced with fresh inert gas, whereby unreacted acrylic acid contained in the exhaust gas can be separated off and recycled.

A heat composite is particularly preferred, that is to say that part of the waste heat when the exhaust gas is cooled is used to warm up the circular gas.

The reactors can be heated. The trace heating is set so that the wall temperature is at least 5 ° C above the inside temperature of the reactor and the condensation on the reactor walls is reliably avoided.

The reaction product can usually be removed from the reactor, preferably at the bottom via a screw conveyor, and optionally dried to the desired residual moisture and the desired residual monomer content.

The process of the invention produces water-swellable, polymeric particles with a shell structure, the ratio of shell thickness and particle diameter being from 0.05 to 0.5, preferably from 0.2 to 0.45, preferably from 0.25 to 0.35 , is obtained, the particles having at least one cavity.

The particle diameter is in the range from 50 to 2000 μm, preferably 150 to 850 μm.

The water-swellable, polymeric particles which can be produced by the process according to the invention are suitable for absorbing blood and / or body fluids, for thickening aqueous solutions and / or suspensions, in particular for thickening medical waste, and as an absorbent in hygiene articles.

It is important in the process according to the invention that the initiators disintegrate rapidly under reaction conditions. This quickly creates a stable outer shell that can no longer be torn apart by evaporating water inside, but can only be inflated. As a result, the particle diameter of the water-swellable, polymeric particles obtainable by the process according to the invention is between 1.4 and 3 times the drop diameter. After the reaction and drying have ended, a cavity (particle type A) usually remains in the particles.

If the course of the reaction is somewhat slower, the hollow spheres are still soft at the end of the fall and are deformed. This creates particles that resemble folded spherical shells (particle type B). Irregular, fibrous structures (type C particles) are generally not desired to be obtained and can be avoided according to the teaching according to the invention. The particles produced by the process according to the invention have a narrow particle size distribution and thus a low proportion of fine dust. Due to their hollow spherical structure, the particles have a low density and are able to float on the liquids to be absorbed and thus cover them.

Examples:

Unless otherwise stated, all quantities are parts by weight.

Examples 1 to 13

An aqueous monomer solution consisting of partially neutralized or neutralized acrylic acid and methylenebisdiacrylamide (crosslinking agent) was mixed with a 1.0% by weight aqueous solution of the initiator or initiator mixture immediately before the reactor.

The amount of crosslinker was 0.3% by weight, based on the monomer used. The amount of initiator was 0.11 mol%, based on the monomer solution used.

A vertically suspended stainless steel tube with a length of 2,600 mm and a diameter of 164 mm was used as the reactor. The temperature could be set using three independent heating circuits. A glass tube with a diameter of 102 mm was inserted into the stainless steel tube from above. A modified SBG-2000 oscillating screen aerosol generator from Palas was placed on the glass tube

GmbH from Karlsruhe set up. The swing aperture had a diameter of 75 microns. 0.4 l / min carrier gas and 1.0 ml / min monomer solution were metered into the reactor via the oscillating-aperture aerosol generator. In addition, 10 l / min of carrier gas preheated to the reaction temperature were metered into the space between the stainless steel tube and the glass tube. The gap was filled with Raschig rings and open to the bottom for the nitrogen. The Raschig rings served as flow straighteners.

The product was collected at the bottom of the reactor, dried (1 h at 125 ° C.) and analyzed. A Philips SEM 515 scanning electron microscope was used to record the water-swellable, polymeric particles. The ratio R of the shell thickness and particle diameter was determined on the basis of the recordings. Table 3: Test results

*) Comparative tests

Initiator A: 2,2'-azobis- (2-amidinopropane) dihydrochloride

Initiator B: 2,2'-azobis [2- (2-imidazolin-2-yl) propane] dihydrochloride Initiator C: 2,2'-azobis [2- (5-methyl-2-imidazolin-2-yl) propane ] dihydrochloride

Claims

claims

1. A process for the preparation of water-swellable, polymeric particles by spray polymerization of a monomer solution comprising a) at least one ethylenically unsaturated, acid-bearing monomer, the acid groups being neutralized to at least 65%, b) optionally at least one crosslinker, c) at least one initiator, d) optionally one or more ethylenically unsaturated monomers copolymerizable with a), e) optionally one or more water-soluble polymers and f) water, at a reaction temperature between 110 to 300 ° C. in the presence of an inert carrier gas, the carrier gas passing the reaction space from the top flows through below, characterized in that the 10-hour half-life temperature of the at least one initiator c) is at most 55 ° C.

2. The method according to claim 1, characterized in that the 10-hour half-life temperature of the at least one initiator c) is at most 50 ° C.

3. The method according to claim 1, characterized in that the 10-hour half-life temperature of the at least one initiator c) is at most 45 ° C.

4. The method according to any one of claims 1 to 3, characterized in that the at least one initiator c) 2,2'-azobis [2- (2-imidazolin-2-yl) propane] dihydrochloride and / or 2,2 '- Azobis [2- (5-methyl-2-imidazolin-2-yl) propane] dihydrochloride.

5. The method according to any one of claims 1 to 4, characterized in that the concentration of the at least one monomer a) in the monomer solution is at least 50% of the saturation concentration.

6. The method according to any one of claims 1 to 5, characterized in that the reaction temperature is between 110 and 180 ° C.

7. The method according to any one of claims 1 to 6, characterized in that the inert atmosphere contains at most 0.1 vol .-% oxygen.

8. The method according to any one of claims 1 to 7, characterized in that the monomer a) is a mixture of acrylic acid and sodium acrylate and / or potassium acrylate.

9. Water-swellable, polymeric particles with a shell structure, the ratio of shell thickness and particle diameter being from 0.2 to 0.45.

10. Particles according to claim 9 with a particle diameter of 50 to 2000 microns.

11. Particles according to claim 9 or 10, wherein the ratio of shell thickness and particle diameter is from 0.25 to 0.35.

12. Use of the particles according to one of claims 9 to 11 for the absorption of blood and / or body fluids or for thickening aqueous solutions and / or suspensions.

13. Use of the particles according to one of claims 9 to 11 for thickening medical waste.

14. Use according to claim 12 in hygiene articles.