CA1279436C - Process for preparing water-absorbing resins - Google Patents
Process for preparing water-absorbing resinsInfo
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- CA1279436C CA1279436C CA000512159A CA512159A CA1279436C CA 1279436 C CA1279436 C CA 1279436C CA 000512159 A CA000512159 A CA 000512159A CA 512159 A CA512159 A CA 512159A CA 1279436 C CA1279436 C CA 1279436C
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Abstract
Abstract of the Disclosure A hot aqueous solution is prepared first which com-prises acrylic acid neutralized 70 to 100 mole percent, a water-miscible or water-soluble polyvinyl monomer, water and, when desired, an organic solvent having a boiling point of 40 to 150° C, and which contains the acrylate monomer and the polyvinyl monomer in a combined concentration of 30 to 80 wt.
%. To achieve the full advantage of the present invention, the acrylate and polyvinyl monomers are present in a combined concentration of less than 70 in weight percent of the monomer solution. In accordance with another important embodiment of the present invention, the combined concentration of the acrylate and polyvinyl monomers is less than 55 weight percent of the monomer solution.
%. To achieve the full advantage of the present invention, the acrylate and polyvinyl monomers are present in a combined concentration of less than 70 in weight percent of the monomer solution. In accordance with another important embodiment of the present invention, the combined concentration of the acrylate and polyvinyl monomers is less than 55 weight percent of the monomer solution.
Description
~9~
-1- 6~267-646 FIELD OF THE INVENTION
The present invention relates to a method of manufacturing polyacrylate resins having improved ~,7ater absorbin~
properties and more particularly to an improved process of preparing cross-linked polymers of acryllc acid and polyvinyl monomers.
BACKGROUND OF THE INVENTION
Wa~er absorbing resins have found wide use in sanitary goods, hygenic goods, wa~er re~aining agents, dehydrating agents, sludge coagulants, thickening agents, condensation preventing - agents and release control agents for various chemicals. ~7ater absorbing resins heretofore known include hydrolysis products of starch-acrylonitrlle graft polymers, carboxymethyl-cellulose, cross-linked polyacryla~e products and other resins such as polyvinyl alcohol, polyethylene oxide and polyacrylonitrile resins. Of these water absorbing resins, the hydrolysis products of starch and acrylonitrile graft polymers have comparatlvely high ability to absorb water but require a cumbersome process for production and have the drawbacks of low heat resistance and decaying or decomposing easily due ~o the presence of starch.
One of the processes for polymerizing acrylic acid and acrylates is a~ueous solution polymerization. The polymer obtained by this process is soluble in water andr therefore, is cross-linked to modify the polymer into a useful water absorbing resin. However, even if the modification is effected by reacting a cross-linking agent concurrently wi~h or after aqueous solution polymerization, the resulting reaction product is in the form of a ,~ ''' ~
~ ~794;~;
-la- 6~267-646 hiyhly viscous aqueous solution or a gel containing absorbed water which is difficult to handle. Thus, the aqueous solution or gel mu~ be dehydrated (dried) to obtaln a water absorbing resin in the desired solid or powder form. It is nevertheless difficult to dry the reaction product.
~, 4;~
efficlently by ~he usual rotary drum roller method or spray drying method because care must be taken to avoid excessive cross-linking which results from over-heating during drying and insufficient drying results in reduced cross-linking density. Extreme difficulties are therefore encountered in preparing a product oE a desired low water content and good water absorbing ability~
SU~RY OF THE INVENTION
An object of the present invention is to provide a process for prepariny a water absorbing cross~linked acrylate resin of low water content by aqueous solution polymerization without any additional dehydrating or drying step.
Another object of the present invention is to provide a process for preparing a cross-linked polyacrylate resin by polymerization of acrylic acid neutralized 70-100 mole percent, and a water-miscible to water soluble polyvinyl monomer in a combined con-centration of 30 to 80 wt. % in water and initiating polymerization without external heating~
Another object of the present invention is to provide a process for preparing a cross-linked polyacrylate resin by co-polymerization of acrylic acid neutralized 70-100 mole percent, with acrylamide and a polyvinyl monomer in proportions of 0 to 30 mole percent acrylamide and 70-100 mole percent neu-tralized acrylic acidO
Another object of the present invention is to provide a process for producing a polyacrylate resin cross-linked with .2 weight percent to .6 weight percent based on the weight of monomers, of a water miscible or water soluble polyvinyl monomer cross-linking agent to achieve a "dry feel" to the resin after significant water absorption.
In brief, the present invention is directed to a process for preparing water absorbing, cross-3L~7~4~
-~- 64~67-64~
linked acrylate resins by aqueous polymeriza~ion of ~A) acrylic acid neutralized 70 to 100 mole percent for examplé with ammonia, and~or caustic alkali and/or an amine; with (B) acrylamide in a mole ratio of 70 to 100 mole percent (A) ~o 30:0 mole percent (B);
and (C~ a water mlscible or a water soluble polyvinyl monomer in an amount of .001 to 0.3 weight percent based on the total weight of (A) and (B). To achieve the full advantage of the present invention the monomer concentration is at least 50 wt. % of ~he aqueous solution. A "dry feel" is obtained at a polyvinyl monomer concen~ration of at least .2 wt. percent of ~he aqueous solution.
In accordance wlth ~he present invention, a heated aqueous solution comprislng (a) acrylic acid neutralized 70 to 100 mole percent for example with ammonia, and/or caustic alkali and/or an amine; and (B) a water-miscible to water-soluble polyvinyl monomer, water and, when desired, an organic solvent having a boiling point of 40 to 150C, and having a combined monomer concentration of (A) plu~ (B) of 30 ~o 80 wt. % i.s subjected to polymerization in the presence of a polymerization initiator without external heating while allowing water to evaporate of~.
Thus, according to one aspect, the invention provides a process for preparing a solid water absorbing resin comprising mixing a monomer solution of (A) acrylic acid neutralized 70-100 mole percen~, wherein the neutralizing agent comprises a potassium alkali; and (B) a water-miscible to water-soluble polyvinyl monomer in a combined concentration of 30 wt. % to less than 55 wt. %; with water to iorm a mixed monomer solution wherein the 1~
~7~
-3a- 54267-646 monomers of the mixed monomer solution consist essentially of (A) and (B~ and initia~ing polymerization of monomers (A) and (B) such that during polymerization, the exothermic heat of reactlon is substantially the only heat energy used to accomplish polymerization, cross-linking and to drlve off sufficient water to obtain a ~olid cross-linked re in haviny a water content o~ 15 percent by weiyht or less.
According to another aspect, the invention provides a process for preparing a solid, water absorbing cross-linked resin comprising.
combining a monomer mixture of (A) potassium acrylate; and (B) a polyvinyl monomer, with water in an amount of at least 30 to less than 55 wt. ~ comhined weight percent of (A) plus ~B) based on the total weight of (A) plus ~B) plus water to form a monomer mixture wherein the monomers of the monomer mixture consist essentially of (A) and (B);
adding a polymerization initiator to said monomer mixture capable of initiating, and in an amount sufficient to initiate polymerization of said monomer mixture;
polymerizing said monomer mixture while utilizing the exothermic heat of reaction as substankially the only non-ambient energy ~ource to drive water away from said polyacrylate resin to form said cross-linked resin haviny a water content sufficiently low to be powdered without an intermediate drying step.
DETAILED DES~CRIPTION OF~THE INVENTION
In accordance with the present invention a ~ross-llnked polyacrylate resin is prepared ~y aqueous solution polymerization i '~
~7~4~
-3b- 64267-6~6 while dehydrating or drying the reaction product during polymerization by utilizing the exothermlc heat from the polymerization and cross-linking reactions ~or drying.
It has been found that acrylic acid neutralized in the range of 70 to 100 mole percent wlll polymerlze and cro~g-linX
rapldly wlth a polyvinyl monomer cross-linklng agent to drive away exeess water leavlng a solid water absorbing resin having a desired degree of polymerization as well as new and unexpected ~, ~7~
water absorbing capacity. One or more polymerization catalyst~ or initiators can be added to th~ aqueous monomer mixture to aid in polymerization.
According to the present invention, a hot aqueous solution is prepared first which comprises acrylic acid neutralized 70 to 100 mole percent, a water-miscible or water-soluble polyvinyl monomer, water and, when desired, an organic solvent having a boiling point of 40 to 150 C, and which contains the acrylate monomer and the polyvinyl monomer in a sombined concentration of 30 to 80 wt. %. To achieve the full advantage of th~ present inven~ion, the acrylate and polyvinyl monomers are present in a combined concen-tration of less than 70 in weight percent of the monomer solution. In accordance with another important embodi-ment of the present invention, the combined concentra-tion of the acrylate and polyvinyl monomers is less than 55 weight percent of the monomer solution. The concentration of the monomers is deliberately de~er-mined considering the state of the solution (iOe. asto whether or not the monomers can be completely dis-solved in water), ease of the reaction of the monomers, escape of the monomers due to the scattering during the reaction, etc. The aqueous solution can be prepared easily usually by placing acrylic acid, a strong alkali such as potassium hydroxide and/or ammonium hydroxide or a basic amine for neutralizing the acid and the polyvinyl monomer into water in such amounts that the resulting solution has the above-mentioned monomer concentration. To dissolve the monomers thoroughly, the mixture can be heated to an elevated temperature.
Any strongly basic alkali metal compound can be used for neutralization of the acrylic acid, such as potassium hydroxide, sodium hydroxide, lithium hy-droxide, cesium hydroxide, potassium carbonate orsodium carbonate. Although it is desirable to use the neutralizing agent usually in an amount sufficient ~ ~ 7~3~ ~ ~
to neutralize acrylic acid 100 mole %, there is no particular need to neutralize the acid 100~ insofar a~ the neutralizing agent, e.g., hydroxide, i5 used in such an amount as to achieve not less than about 70~
neutralization. Accordingly the aqueous solutioh may contain up to about 30~ of free acrylic acid. However, a large quantity of free acrylic acid, if present in the aqueous solution, is likely to partly ~plash out of the system to result in a loss during the reaction, leading to a reduced degree of polymerization. Use of an excessive amount of the neutralizing agent will not raise any particular problem~ but the excess does not participate in the polymerization reaction and is therefore useless.
We have also found that when the aqueous solution further contains an organic solvent having a boiling point of 40 to 150 C, th~ temperature of the aqueous solution is controllable with great ease and the resulting cross-linked resin has remarkably im-proved ability to absorb water at an initial rate.
When incorporating an organic solvent accord-ing to the invention, the aqueous monomer solution has a solidifying point which is about 10 to about 20 C lower than otherwise. This increases the allow-able range of temperature control at least about 3 times. The organic solvent used is vigorously eva-porated along with water by the heat of polymeriza-tion of the monomer. Since the latent heat of the evaporation is considerably smaller than that of water, ~he organic solven~ functions as a blowing agent in the polymerization reaction system, consequently ren-dering the resulting resin porous~ The resin exhibits about ~ to about 5 times higher initial rate of water absorption than the one obtained without using the organic solvent while possessing high water absorbing ability.
~;~7~4~
Thus, the organic solvent, when added to the aqueous monomer solution, produces improved effects without in any way impairing the advantages resulting from the use of the monomer solution.
Examples of organic solvents to be used in the invention when desired and having a boiling point of 40 to 150 C are methanol, ethanol, propanol and like alcohol solvents, acetone, methyl ethyl ketone and like detone solvents, cyclohexane, n-hexane, n-heptane and like hydrocarbon solvents, benzene, toluene and like aromatic hydrocarbon solvents, and tetrahydro-furan and like furan solvents. These 501vent5 may be used singly or in admixture. The solvent is used in an a~ount of 0.5 to 15 wt. %, preferably 1 to 10 wt. %, based on the combined amount of the monomers. With less than 0.5 wt. % of the solvent present, a suffi-cient blowing action will not take place, while the solidifying point of the monomer solution will not lower greatly,. Co~versely if more than lS wt. % of the solvent iCU~ the resulting resin is likely to exhibit reduced water absorbing ability although achieving a high initial rate of water absorption.
Moreover the monomers are likely to separate out, hence objectionable. Because the monomer solutiuon is heated prior to polymerization and further because the organic solvent evaporates along with water, the boiling point of the solvent is more preferably in ~he range of 55 to 120 c.
In accordance with the present invention, acrylic acid neutralized 70-100 mole percent is mixed with a water-miscible or water-soluble polyvinyl monomer in an aqueous solution at a temperature of about 20 to 100 C. The solution is subjected to a polymeriza-tion reaction and a cross-linking reaction by the addition of a polymerization initiator. The polymeriza-tion reaction proceeds sufficiently within a very short period of time and if the monomer concentration 4;~
is at least 30 percent by weight of the aqueous monomer mixture, the heat of the polymerization and cross-linking reactions will evaporate water rapidly from the reaction system to form a dry solid (less than 15 percent by weight water) water absorbing resin without the need for any subsequent drying step. The solid can be easily pulverized into a powder suitable for any desired use.
According to the process of the invention, l~ a hot, i.e. at least 25 C., aqueous solution is pre-pared first including acrylic acid neutralized 70 to 100 mole percent, optionally acrylamide, a water-miscible or water-soluble polyvinyl monomer, and water.
The aqueous solution can be prepared easily by placing lS (A) acrylic acid, and an amine, and/or a caustic alkali and/or ammonia for neutralizing the acid; (B~ acryla-mide (0-30 mole percent); and ~C) a polyvinyl monomer into water to form a mixed monomer solution. To dis-solve the monomers thoroughly, the mixtur~ can be 2~ heated to an elevated temperature up to the boiling point of water i.e. 100 C.
The polyvinyl monomer to be used in both embodiments of the invention should be miscible with or soluble in water so that the monomer will be uni-formly dissolved or dispersed in the aqueous solutionof the monomer mixture. Examples of such polyvinyl monomers include bisacrylamides such as N,N'-methylene-bisacrylamide and N,N'-methylenebismethacrylamide;
polyacrylic (or polymethacrylic~ acid esters repre-sented by the following formula II): and diacrylamidesrepresented by the following formula (II). Among these, especially preferably are N,N'-methylenebis-acrylamide, N,N~-methylenebismethacrylamide and like bisacrylamides.
Frmula (I) CH2 = CH ¦ HC = CH
O - C - O - X O - C = O
)~
~94;~
wh~rein X i5 ethylene, propylene, trimethylene, hexa-methylene, 2-hydroxypropylene, (CH2CH2O)nCH2CH2 - or ~ CH2-CH-O)mCH2-C~- , n and m are each an integer of from 5 to 40, and k is 1 or 2.
The compounds of the formula (I) are prepared by reacting polyols, such as ethylene glycol, propylene glycol, trimethylolpropane, 1,6-hexanediol, glycerin, pentaerythritol, polyethylene glycol and polypropylene glycol, with acrylic acid or methacrylic acid.
Formula (II):
CH2 = C~ HC = CH~
0 = C - NH(CH~CH2NHLC = O
wherein 1 is 2 or 3.
The compounds of the formula (II) are ob-tained by reacting polyalkylenepolyamines, such as die~hylenetriamine and triethylenetetramine, with acrylic acid.
The polyvinyl monomer is used in an amount of about 0.001 to 0.3 wt. % of the amount of acrylic monomers in the aqueous monomer mixture. In accordance with an important embodiment of the present invention, the polyvinyl monomer should be present in the aqueous solu~ion in an amount of at least .2 wt. ~ based on the total weight of monomers to provide a resin suf ficiently cross-linked ~o have a "dry ~eeln after significant water absorption. If the polyvinyl monomer is included in the aqueous solution in an amount of .2 to .6 weight percent based on the weight of neu~ralized acrylic acid and polyvinyl monomers, the resulting polymer will have an exceedingly "dry feel" on absorption of water.
The aqueous mixed monomer solution is heated and thereafter subjected to polymeriza~ion and cross-linking reac~ions with the addition of a polymeriza-~7q~
tion initiator. Although the temperature of the aqueousmixed monomer solution is not particularly limited since the mixed monomer solution is initiated into polymerization by the addition of the initiator, the temperature is usually about 50 to about 85 C, prefer-ably abou~ 60 to about 75 C. Various polymerization initiators are usable which are known for use in pre-par ing polyacrylates. Examples of useful initiators are redox initiators comprising a reducing agent, such a a sulfite or bisulfite of an alkali metal, ammonium sulfite or ammonium bisulfite, and an initia-torp such as a persulfate of an alkali metal or ammonium persulfate, in combination with the reducing agent;
azo initiators including azobis-isobutyronitrile, 4-t~-butylazo-4'-cyanovaleric acid, 4,4'-azobis(4-cyanovaleric acid) and 2,2'-a~obis(2-amidinopropane)-hydrochloric acid salt; trimethylolpropane triacrylate, and the like. These initiators can be used singly or in a suitable combination. Of these, especially pre-2~ ferable are a redox initiator compo,s~d of ammonium hl~d roaen s ~ ~ f / f e persulfate and sodium~'~y~ eo~ e, and azo initia-tors such a azobisisobutyronitrile and 2,2'-azobis(2-amidinopropane)-hydrochloric acid. These initiators are advantageously used usually in the form of an aqueous solution but can be used as diluted with a suitable solvent. The initiator is used in a usual amoùnt, iOe. in an amount, calculated as solids, of about 0.1 to about 10%, preferably about 0.5 to about 5%, o~ the combined weight of the monomers, namely acrylate (and free acrylic acid~, acrylamide, and polyvinyl monomer Depending on the amount and kind of the initiator, the initiator is usable together with isopropyl alcohol, alkylmercaptan or other chain transfer agents to control the mol2cular weight of the polyacrylate to be obtained.
By the addition of the polymerization ini-tiator, the mixed monomer solution is subjected to 1~C794;~
polymerization with evaporation of water withou~ heat-ing the system from outside. More advantageously, the reaction is carried out by admixing a predetermin-ed amount of the initiator or an aqueous solution thereof with the mixed monomer sslution and causing the resulting mixture to flow down onto and spread over a traveling conveyor belt. The initiator ~an be added to the mixed monomer solution as it is poured onto the conveyor belt.
The polymerization proceeds rapidly after admixing the initiator with the mixed monomer solu-tion and i5 completed within a short period of time, usually in about 30 seconds to about 10 minu~es. The reaction is exothermic, so that the reaction system is rapidly heated to about 100 to about 130 C by the heat of polymerization. Consequently, particularly where the monomer concentration in the mixed solution is at least 50 percent by weight, the water evaporates from the system rapidly to give a relatively dry, solid polymer of low water content without resorting to any external heating. The water content of the polymer is usually up to about 15~, and generally about 8 to 12% by weight as recovered. Subsequently, the dry solid polymer can be made into the desired powder easily by a usual method, for example by pulveri-zation, without a drying step~
In accordance with another important feature of the present invention, polystyrene and/or methyl-cellulose can be added to the mixed monomer snlution in an amount of 0.5 to about 10 percent based on the total ~eight of monomers in the mixed monomer solution ~o increase the porosity and water absorbing capacity of the polymers. It has been found, quite surprisingly, the polys~yrene and methylcellulose will substantially incr~ase the water absorbing capacity of the resin described herein. To achieve the fùll advantage of the present invPntion, the polystyrene and methylcel-~.~7~4~
1ulose should be added in an average grain ~ize of less than or equal to 5 micrometers.
The powder thus obtained has outstandingwater absorbing ability and is useful for sanitary goods, paper diaper, disposable diaper and like hygenic goods, agricultural or horticultural water retaining agents, industrial dehydrating agent~, sludge coagu-lants, thickening agents, conden~ation preventing agents for building materials, release control agents for chemicalc and various other applications.
The present invention will be described in greater detail with reference ~o the following ~xamples.
ExamPle 1 To deionized water are added, wherein percents are weight percents based on the total weigh~
of the monomer solution formed, 58.81% acrylic acid first, then 11.76% potassium hydroxide and 11.76%
ammonium carbonate and 14.70% ammonium hydroxide serving as neutralizing agents. Thereafter .03~ of N,N-methylenebisacrylamide as a polyvinyl monomer is added to prepare an aqueous solution of potassium acrylate and ammonium acrylate in 2.79~ of water having a neutralization degree of about 90% and a combine~
monomer concentration of 58084 wt.%.
The aqueous solution is maintained at 70 C, and with the solution are admixed 0.15% of 2,2-azobis-(2-amidino-propane)hydrochloric acid. The final solu~ion is ac follows:
CHBMICALS
ACRYLIC ACID 58.81%
POTASSIUM HYDROXID~ 11.76%
AMMONIUM CA~BONATE 11.76%
N,N-METHYLENEBISACRYLAMIDE 0.03%
POLYMÆRIZATION INITIATOR 0.15 AMMONIUM HYDROXIDE 14.70%
H20 2.79 TOTAL100.00 The mixture i5 poured onto a traveling endless belt and ~pread thereover in the form of a layer about 10 mm in thickness~ About 30 seconds thereafter, the mixture starts to polymerize, and the reaction is completed in about 1 minute. The maximum temperature of the mixture during the reaction is about 120 C.
The polymer i5 allowed ~o complete curing for about 30 minutes at ambient temperature to give a dry solid strip of cross-linked potassium polyacrylate product having a water content of 11% and a re~idual monomer concentration of 1200 ppm. The strip is made into a powder by a pulverizer.
Exa~E1~
Polymers are prepared in the same manner as in Example 1 with the exception of varying, at least one of the combined concentration of monomers, the amount of polyvinyl monomer (N,N-methyle~ebisacrylamide), the kind and amount (degree of neutralization~ of neutralizing agent, and the amounts, based on the combined amount of the monomers, of azo polymerization initiator. The following compositions were polymerized:
ACRYLIC ACID 56.80%
POTASSIUM HYDROXIDE 14.77~
AMMONIUM CARBONATE 11.36%
N,N-METHYLENEBISACRYLAMIDE0.03%
~0 ~,a~/y~ `z~z~ot~ /n; fia7Lor 0.14%
AMMONIUM HYDROXIDE 14.20%
~20 2.70%
TOTAL 100.00%
ACRYLIC ACID 57.13%
POTASSIUM HYDROXIDE 14.28%
AMMONIUM CARBONATE .11.43%
N,N-METHYLENEBISACRYLAMIDE O.03 AZO POLYMERIZATION INITIATOR 0.14 AMMONIUM HYDROXIDE 14.28~
H20 2.71%
TOTAL 100.00 EX~4PLE 4 ACRYLIC ACID 54.66%
POTASSIUM HYDROXIDE 10.93%
AMMONIUM CA~BONATE
N, M~METHYLENEBISACRYL~MIDE O 11~
~4~ ~o/yf~er/~or~ ~Jf~2 ~ v 0 41%
AMMONIUM HYDROXIDE 30.61%
H20 3.27 TOTAL 100.00~
The amount of polyvin~l monomer listed as 2~ expressed in % by weight based on the combined amount of potassium acrylate, free acrylic acid and the poly-vinyl monomer, and the concentration of initiator is expressed in ~ by weight based on the combined amount by weight (calculated as solids) of the monomers and the initiator, the same as hereinbefore.
To 22.2 g of deionized water are added 72.1 y of acrylic acid first, then 49.5 g of potassium hydxoxide having a purity of 85% and serving as a neutralizing agent, and thereafter 0.01 g of N,N-methylenebisacrylamide as a polyvinyl monomer to prepare an aqueous solution of potassium acrylate having a neutralization degree of 75% and a combined monomer concentration of 70 wt.%~
The aqueous solution is maintained at 70 C, and with the solution are admixed 2.9 9 of 18~
aqueous solution of ammonium persulfate (0.5 w~. %
based on the combined weight of the potas~ium asrylate, free acrylic acid and N,N-methylenebisacrylamide, the same as hereinafter). The mixture i5 poured onto a traveling endles belt and spread thereover in the form o~ a layer about 10 mm in thickness. About 30 ~ec~n oee~ thereafter, the mixture starts to polymerize, and the reaction is completed in about 1 minute. The maximum temperature of the mixture during the reaction is about 120 C.
The reaction give~ a dry solid strip of cro~s-linked pota~ium polyacrylate product having a water content of 11% and a residual monomer conc~ntra-tion of 1200 ppm. The s~rip is made into a powder by a pulverizer. The powder has water absorbing ability of 450 as measured with use of deionized water or 60 as measured with 1% saline.
~3~Y~L_~5 ~ 9 Polymers are prepared in the same manner as in Example 5 with the exception of changing at lPast one of the amount of N,N-methylenebisacrylamide and the kind and amount of the polymerization initiator as listed in Table 1 below. Table 4 also shows the water content and water absorbing ability of each polymer obtained.
Table 1 Ex. Initiator Amt. Water Water Absorbing of Poly- _ Ability vinyl Deionized 1%
No. Kind Conc. Monomer Content Water Saline 2,2'-azobis-(2-amidino-propane)hydro-chloric acid 6 0.5 0.01 1~ 520 58 7 " 0.5 0.02 12 610 65 8 " 1.0 0.01 10 550 62 9 1.0 0.02 11 580 63 1~794;~i ExarnPle3 lo to 17 Polymers are prepared in the same manner as in Example 1 except that the compounds listed in Table 2 below are used as polyvinyl monomers in the listed amounts. Table 2 also shows the water content and water absorbing ability of each polymer obtained.
Table 2 Ex. Polyvinyl Monomer Water Deionized Water No. Kind Amount Content Absorbinq AbilitY
Ethylene 0.01 12 480 glycol diallyl ester 11 n 0.0213 430 12 Deithylenetri-0.01 12 510 amine-diacryl-amid 13 " 0.0212 450 14 N,N-methylene-0.01 9 5~0 bismethacryl-amid 15 " 0,0511 3~0 16 Polyethylene0.01 10 500 glycol diacrylate~
17 " 0.0511 430 *Poly~e~hylene glycol diacrylate used in Examples 2~r and ~ is represented by the following formula:
CH2 = CIH CH = CH2 = C~ - (OCH2CH2~0 0 - C = O
3a ~ 0 ~I
Acrylic acid (72.1 9), 18.0 9 of deionized water, 40.9 9 of solid potassium hydroxide (water content 4~) and 5.2 g of one of the solvents (5 wt. %
based on the monomers) listed in Table 3 are mixed together, and the mixture is maintained at 75 C.
With the mixture is further admixed 4.0 9 of 10%
~ ~ 7 aqueous solution of 2,2'-azobis(2-amidinopropane)-hydrochloric acid salt. The resulting mixture is immediately poured onto a traveling endless belt and spread thereover to a thickness of 5 mm. About 15 seconds later, the mixture starts to polymerize, and the polymerization is completed in about 30 seconds.
The maximum temperature of the mixture during the reaction i3 130 to 135 C.
The reaction gives a dry strip of cross-linked potassium polyacrylate product, which i5 pul-verized to a powder 20 to 100 mesh in particle size.
The same procedure as above is repeated with use of the other solvents. All the powders ob- -tained have a water content of 4 to 6%.
A 0.1 9 quantity of each of the powders is accurately measured out and the water absorbing abili~y of the powder is measured a~ter immersing the powder in deionized water or 1% saline for 10 seconds, 30 seconds or 15 minutes. Table 6 shows the results.
Example 22 An aqueous monomer solution is prepared in the same manner as in examples 17 to 21 with the ex-ception of not using any organic solvent and using 23.2 9 of deionized water. The solution is thereafter subjected to polymerization in the same manner as in these examples to obtain a powder of dry solid. Table 3 also shows the test results obtained with this pow-der.
-1- 6~267-646 FIELD OF THE INVENTION
The present invention relates to a method of manufacturing polyacrylate resins having improved ~,7ater absorbin~
properties and more particularly to an improved process of preparing cross-linked polymers of acryllc acid and polyvinyl monomers.
BACKGROUND OF THE INVENTION
Wa~er absorbing resins have found wide use in sanitary goods, hygenic goods, wa~er re~aining agents, dehydrating agents, sludge coagulants, thickening agents, condensation preventing - agents and release control agents for various chemicals. ~7ater absorbing resins heretofore known include hydrolysis products of starch-acrylonitrlle graft polymers, carboxymethyl-cellulose, cross-linked polyacryla~e products and other resins such as polyvinyl alcohol, polyethylene oxide and polyacrylonitrile resins. Of these water absorbing resins, the hydrolysis products of starch and acrylonitrile graft polymers have comparatlvely high ability to absorb water but require a cumbersome process for production and have the drawbacks of low heat resistance and decaying or decomposing easily due ~o the presence of starch.
One of the processes for polymerizing acrylic acid and acrylates is a~ueous solution polymerization. The polymer obtained by this process is soluble in water andr therefore, is cross-linked to modify the polymer into a useful water absorbing resin. However, even if the modification is effected by reacting a cross-linking agent concurrently wi~h or after aqueous solution polymerization, the resulting reaction product is in the form of a ,~ ''' ~
~ ~794;~;
-la- 6~267-646 hiyhly viscous aqueous solution or a gel containing absorbed water which is difficult to handle. Thus, the aqueous solution or gel mu~ be dehydrated (dried) to obtaln a water absorbing resin in the desired solid or powder form. It is nevertheless difficult to dry the reaction product.
~, 4;~
efficlently by ~he usual rotary drum roller method or spray drying method because care must be taken to avoid excessive cross-linking which results from over-heating during drying and insufficient drying results in reduced cross-linking density. Extreme difficulties are therefore encountered in preparing a product oE a desired low water content and good water absorbing ability~
SU~RY OF THE INVENTION
An object of the present invention is to provide a process for prepariny a water absorbing cross~linked acrylate resin of low water content by aqueous solution polymerization without any additional dehydrating or drying step.
Another object of the present invention is to provide a process for preparing a cross-linked polyacrylate resin by polymerization of acrylic acid neutralized 70-100 mole percent, and a water-miscible to water soluble polyvinyl monomer in a combined con-centration of 30 to 80 wt. % in water and initiating polymerization without external heating~
Another object of the present invention is to provide a process for preparing a cross-linked polyacrylate resin by co-polymerization of acrylic acid neutralized 70-100 mole percent, with acrylamide and a polyvinyl monomer in proportions of 0 to 30 mole percent acrylamide and 70-100 mole percent neu-tralized acrylic acidO
Another object of the present invention is to provide a process for producing a polyacrylate resin cross-linked with .2 weight percent to .6 weight percent based on the weight of monomers, of a water miscible or water soluble polyvinyl monomer cross-linking agent to achieve a "dry feel" to the resin after significant water absorption.
In brief, the present invention is directed to a process for preparing water absorbing, cross-3L~7~4~
-~- 64~67-64~
linked acrylate resins by aqueous polymeriza~ion of ~A) acrylic acid neutralized 70 to 100 mole percent for examplé with ammonia, and~or caustic alkali and/or an amine; with (B) acrylamide in a mole ratio of 70 to 100 mole percent (A) ~o 30:0 mole percent (B);
and (C~ a water mlscible or a water soluble polyvinyl monomer in an amount of .001 to 0.3 weight percent based on the total weight of (A) and (B). To achieve the full advantage of the present invention the monomer concentration is at least 50 wt. % of ~he aqueous solution. A "dry feel" is obtained at a polyvinyl monomer concen~ration of at least .2 wt. percent of ~he aqueous solution.
In accordance wlth ~he present invention, a heated aqueous solution comprislng (a) acrylic acid neutralized 70 to 100 mole percent for example with ammonia, and/or caustic alkali and/or an amine; and (B) a water-miscible to water-soluble polyvinyl monomer, water and, when desired, an organic solvent having a boiling point of 40 to 150C, and having a combined monomer concentration of (A) plu~ (B) of 30 ~o 80 wt. % i.s subjected to polymerization in the presence of a polymerization initiator without external heating while allowing water to evaporate of~.
Thus, according to one aspect, the invention provides a process for preparing a solid water absorbing resin comprising mixing a monomer solution of (A) acrylic acid neutralized 70-100 mole percen~, wherein the neutralizing agent comprises a potassium alkali; and (B) a water-miscible to water-soluble polyvinyl monomer in a combined concentration of 30 wt. % to less than 55 wt. %; with water to iorm a mixed monomer solution wherein the 1~
~7~
-3a- 54267-646 monomers of the mixed monomer solution consist essentially of (A) and (B~ and initia~ing polymerization of monomers (A) and (B) such that during polymerization, the exothermic heat of reactlon is substantially the only heat energy used to accomplish polymerization, cross-linking and to drlve off sufficient water to obtain a ~olid cross-linked re in haviny a water content o~ 15 percent by weiyht or less.
According to another aspect, the invention provides a process for preparing a solid, water absorbing cross-linked resin comprising.
combining a monomer mixture of (A) potassium acrylate; and (B) a polyvinyl monomer, with water in an amount of at least 30 to less than 55 wt. ~ comhined weight percent of (A) plus ~B) based on the total weight of (A) plus ~B) plus water to form a monomer mixture wherein the monomers of the monomer mixture consist essentially of (A) and (B);
adding a polymerization initiator to said monomer mixture capable of initiating, and in an amount sufficient to initiate polymerization of said monomer mixture;
polymerizing said monomer mixture while utilizing the exothermic heat of reaction as substankially the only non-ambient energy ~ource to drive water away from said polyacrylate resin to form said cross-linked resin haviny a water content sufficiently low to be powdered without an intermediate drying step.
DETAILED DES~CRIPTION OF~THE INVENTION
In accordance with the present invention a ~ross-llnked polyacrylate resin is prepared ~y aqueous solution polymerization i '~
~7~4~
-3b- 64267-6~6 while dehydrating or drying the reaction product during polymerization by utilizing the exothermlc heat from the polymerization and cross-linking reactions ~or drying.
It has been found that acrylic acid neutralized in the range of 70 to 100 mole percent wlll polymerlze and cro~g-linX
rapldly wlth a polyvinyl monomer cross-linklng agent to drive away exeess water leavlng a solid water absorbing resin having a desired degree of polymerization as well as new and unexpected ~, ~7~
water absorbing capacity. One or more polymerization catalyst~ or initiators can be added to th~ aqueous monomer mixture to aid in polymerization.
According to the present invention, a hot aqueous solution is prepared first which comprises acrylic acid neutralized 70 to 100 mole percent, a water-miscible or water-soluble polyvinyl monomer, water and, when desired, an organic solvent having a boiling point of 40 to 150 C, and which contains the acrylate monomer and the polyvinyl monomer in a sombined concentration of 30 to 80 wt. %. To achieve the full advantage of th~ present inven~ion, the acrylate and polyvinyl monomers are present in a combined concen-tration of less than 70 in weight percent of the monomer solution. In accordance with another important embodi-ment of the present invention, the combined concentra-tion of the acrylate and polyvinyl monomers is less than 55 weight percent of the monomer solution. The concentration of the monomers is deliberately de~er-mined considering the state of the solution (iOe. asto whether or not the monomers can be completely dis-solved in water), ease of the reaction of the monomers, escape of the monomers due to the scattering during the reaction, etc. The aqueous solution can be prepared easily usually by placing acrylic acid, a strong alkali such as potassium hydroxide and/or ammonium hydroxide or a basic amine for neutralizing the acid and the polyvinyl monomer into water in such amounts that the resulting solution has the above-mentioned monomer concentration. To dissolve the monomers thoroughly, the mixture can be heated to an elevated temperature.
Any strongly basic alkali metal compound can be used for neutralization of the acrylic acid, such as potassium hydroxide, sodium hydroxide, lithium hy-droxide, cesium hydroxide, potassium carbonate orsodium carbonate. Although it is desirable to use the neutralizing agent usually in an amount sufficient ~ ~ 7~3~ ~ ~
to neutralize acrylic acid 100 mole %, there is no particular need to neutralize the acid 100~ insofar a~ the neutralizing agent, e.g., hydroxide, i5 used in such an amount as to achieve not less than about 70~
neutralization. Accordingly the aqueous solutioh may contain up to about 30~ of free acrylic acid. However, a large quantity of free acrylic acid, if present in the aqueous solution, is likely to partly ~plash out of the system to result in a loss during the reaction, leading to a reduced degree of polymerization. Use of an excessive amount of the neutralizing agent will not raise any particular problem~ but the excess does not participate in the polymerization reaction and is therefore useless.
We have also found that when the aqueous solution further contains an organic solvent having a boiling point of 40 to 150 C, th~ temperature of the aqueous solution is controllable with great ease and the resulting cross-linked resin has remarkably im-proved ability to absorb water at an initial rate.
When incorporating an organic solvent accord-ing to the invention, the aqueous monomer solution has a solidifying point which is about 10 to about 20 C lower than otherwise. This increases the allow-able range of temperature control at least about 3 times. The organic solvent used is vigorously eva-porated along with water by the heat of polymeriza-tion of the monomer. Since the latent heat of the evaporation is considerably smaller than that of water, ~he organic solven~ functions as a blowing agent in the polymerization reaction system, consequently ren-dering the resulting resin porous~ The resin exhibits about ~ to about 5 times higher initial rate of water absorption than the one obtained without using the organic solvent while possessing high water absorbing ability.
~;~7~4~
Thus, the organic solvent, when added to the aqueous monomer solution, produces improved effects without in any way impairing the advantages resulting from the use of the monomer solution.
Examples of organic solvents to be used in the invention when desired and having a boiling point of 40 to 150 C are methanol, ethanol, propanol and like alcohol solvents, acetone, methyl ethyl ketone and like detone solvents, cyclohexane, n-hexane, n-heptane and like hydrocarbon solvents, benzene, toluene and like aromatic hydrocarbon solvents, and tetrahydro-furan and like furan solvents. These 501vent5 may be used singly or in admixture. The solvent is used in an a~ount of 0.5 to 15 wt. %, preferably 1 to 10 wt. %, based on the combined amount of the monomers. With less than 0.5 wt. % of the solvent present, a suffi-cient blowing action will not take place, while the solidifying point of the monomer solution will not lower greatly,. Co~versely if more than lS wt. % of the solvent iCU~ the resulting resin is likely to exhibit reduced water absorbing ability although achieving a high initial rate of water absorption.
Moreover the monomers are likely to separate out, hence objectionable. Because the monomer solutiuon is heated prior to polymerization and further because the organic solvent evaporates along with water, the boiling point of the solvent is more preferably in ~he range of 55 to 120 c.
In accordance with the present invention, acrylic acid neutralized 70-100 mole percent is mixed with a water-miscible or water-soluble polyvinyl monomer in an aqueous solution at a temperature of about 20 to 100 C. The solution is subjected to a polymeriza-tion reaction and a cross-linking reaction by the addition of a polymerization initiator. The polymeriza-tion reaction proceeds sufficiently within a very short period of time and if the monomer concentration 4;~
is at least 30 percent by weight of the aqueous monomer mixture, the heat of the polymerization and cross-linking reactions will evaporate water rapidly from the reaction system to form a dry solid (less than 15 percent by weight water) water absorbing resin without the need for any subsequent drying step. The solid can be easily pulverized into a powder suitable for any desired use.
According to the process of the invention, l~ a hot, i.e. at least 25 C., aqueous solution is pre-pared first including acrylic acid neutralized 70 to 100 mole percent, optionally acrylamide, a water-miscible or water-soluble polyvinyl monomer, and water.
The aqueous solution can be prepared easily by placing lS (A) acrylic acid, and an amine, and/or a caustic alkali and/or ammonia for neutralizing the acid; (B~ acryla-mide (0-30 mole percent); and ~C) a polyvinyl monomer into water to form a mixed monomer solution. To dis-solve the monomers thoroughly, the mixtur~ can be 2~ heated to an elevated temperature up to the boiling point of water i.e. 100 C.
The polyvinyl monomer to be used in both embodiments of the invention should be miscible with or soluble in water so that the monomer will be uni-formly dissolved or dispersed in the aqueous solutionof the monomer mixture. Examples of such polyvinyl monomers include bisacrylamides such as N,N'-methylene-bisacrylamide and N,N'-methylenebismethacrylamide;
polyacrylic (or polymethacrylic~ acid esters repre-sented by the following formula II): and diacrylamidesrepresented by the following formula (II). Among these, especially preferably are N,N'-methylenebis-acrylamide, N,N~-methylenebismethacrylamide and like bisacrylamides.
Frmula (I) CH2 = CH ¦ HC = CH
O - C - O - X O - C = O
)~
~94;~
wh~rein X i5 ethylene, propylene, trimethylene, hexa-methylene, 2-hydroxypropylene, (CH2CH2O)nCH2CH2 - or ~ CH2-CH-O)mCH2-C~- , n and m are each an integer of from 5 to 40, and k is 1 or 2.
The compounds of the formula (I) are prepared by reacting polyols, such as ethylene glycol, propylene glycol, trimethylolpropane, 1,6-hexanediol, glycerin, pentaerythritol, polyethylene glycol and polypropylene glycol, with acrylic acid or methacrylic acid.
Formula (II):
CH2 = C~ HC = CH~
0 = C - NH(CH~CH2NHLC = O
wherein 1 is 2 or 3.
The compounds of the formula (II) are ob-tained by reacting polyalkylenepolyamines, such as die~hylenetriamine and triethylenetetramine, with acrylic acid.
The polyvinyl monomer is used in an amount of about 0.001 to 0.3 wt. % of the amount of acrylic monomers in the aqueous monomer mixture. In accordance with an important embodiment of the present invention, the polyvinyl monomer should be present in the aqueous solu~ion in an amount of at least .2 wt. ~ based on the total weight of monomers to provide a resin suf ficiently cross-linked ~o have a "dry ~eeln after significant water absorption. If the polyvinyl monomer is included in the aqueous solution in an amount of .2 to .6 weight percent based on the weight of neu~ralized acrylic acid and polyvinyl monomers, the resulting polymer will have an exceedingly "dry feel" on absorption of water.
The aqueous mixed monomer solution is heated and thereafter subjected to polymeriza~ion and cross-linking reac~ions with the addition of a polymeriza-~7q~
tion initiator. Although the temperature of the aqueousmixed monomer solution is not particularly limited since the mixed monomer solution is initiated into polymerization by the addition of the initiator, the temperature is usually about 50 to about 85 C, prefer-ably abou~ 60 to about 75 C. Various polymerization initiators are usable which are known for use in pre-par ing polyacrylates. Examples of useful initiators are redox initiators comprising a reducing agent, such a a sulfite or bisulfite of an alkali metal, ammonium sulfite or ammonium bisulfite, and an initia-torp such as a persulfate of an alkali metal or ammonium persulfate, in combination with the reducing agent;
azo initiators including azobis-isobutyronitrile, 4-t~-butylazo-4'-cyanovaleric acid, 4,4'-azobis(4-cyanovaleric acid) and 2,2'-a~obis(2-amidinopropane)-hydrochloric acid salt; trimethylolpropane triacrylate, and the like. These initiators can be used singly or in a suitable combination. Of these, especially pre-2~ ferable are a redox initiator compo,s~d of ammonium hl~d roaen s ~ ~ f / f e persulfate and sodium~'~y~ eo~ e, and azo initia-tors such a azobisisobutyronitrile and 2,2'-azobis(2-amidinopropane)-hydrochloric acid. These initiators are advantageously used usually in the form of an aqueous solution but can be used as diluted with a suitable solvent. The initiator is used in a usual amoùnt, iOe. in an amount, calculated as solids, of about 0.1 to about 10%, preferably about 0.5 to about 5%, o~ the combined weight of the monomers, namely acrylate (and free acrylic acid~, acrylamide, and polyvinyl monomer Depending on the amount and kind of the initiator, the initiator is usable together with isopropyl alcohol, alkylmercaptan or other chain transfer agents to control the mol2cular weight of the polyacrylate to be obtained.
By the addition of the polymerization ini-tiator, the mixed monomer solution is subjected to 1~C794;~
polymerization with evaporation of water withou~ heat-ing the system from outside. More advantageously, the reaction is carried out by admixing a predetermin-ed amount of the initiator or an aqueous solution thereof with the mixed monomer sslution and causing the resulting mixture to flow down onto and spread over a traveling conveyor belt. The initiator ~an be added to the mixed monomer solution as it is poured onto the conveyor belt.
The polymerization proceeds rapidly after admixing the initiator with the mixed monomer solu-tion and i5 completed within a short period of time, usually in about 30 seconds to about 10 minu~es. The reaction is exothermic, so that the reaction system is rapidly heated to about 100 to about 130 C by the heat of polymerization. Consequently, particularly where the monomer concentration in the mixed solution is at least 50 percent by weight, the water evaporates from the system rapidly to give a relatively dry, solid polymer of low water content without resorting to any external heating. The water content of the polymer is usually up to about 15~, and generally about 8 to 12% by weight as recovered. Subsequently, the dry solid polymer can be made into the desired powder easily by a usual method, for example by pulveri-zation, without a drying step~
In accordance with another important feature of the present invention, polystyrene and/or methyl-cellulose can be added to the mixed monomer snlution in an amount of 0.5 to about 10 percent based on the total ~eight of monomers in the mixed monomer solution ~o increase the porosity and water absorbing capacity of the polymers. It has been found, quite surprisingly, the polys~yrene and methylcellulose will substantially incr~ase the water absorbing capacity of the resin described herein. To achieve the fùll advantage of the present invPntion, the polystyrene and methylcel-~.~7~4~
1ulose should be added in an average grain ~ize of less than or equal to 5 micrometers.
The powder thus obtained has outstandingwater absorbing ability and is useful for sanitary goods, paper diaper, disposable diaper and like hygenic goods, agricultural or horticultural water retaining agents, industrial dehydrating agent~, sludge coagu-lants, thickening agents, conden~ation preventing agents for building materials, release control agents for chemicalc and various other applications.
The present invention will be described in greater detail with reference ~o the following ~xamples.
ExamPle 1 To deionized water are added, wherein percents are weight percents based on the total weigh~
of the monomer solution formed, 58.81% acrylic acid first, then 11.76% potassium hydroxide and 11.76%
ammonium carbonate and 14.70% ammonium hydroxide serving as neutralizing agents. Thereafter .03~ of N,N-methylenebisacrylamide as a polyvinyl monomer is added to prepare an aqueous solution of potassium acrylate and ammonium acrylate in 2.79~ of water having a neutralization degree of about 90% and a combine~
monomer concentration of 58084 wt.%.
The aqueous solution is maintained at 70 C, and with the solution are admixed 0.15% of 2,2-azobis-(2-amidino-propane)hydrochloric acid. The final solu~ion is ac follows:
CHBMICALS
ACRYLIC ACID 58.81%
POTASSIUM HYDROXID~ 11.76%
AMMONIUM CA~BONATE 11.76%
N,N-METHYLENEBISACRYLAMIDE 0.03%
POLYMÆRIZATION INITIATOR 0.15 AMMONIUM HYDROXIDE 14.70%
H20 2.79 TOTAL100.00 The mixture i5 poured onto a traveling endless belt and ~pread thereover in the form of a layer about 10 mm in thickness~ About 30 seconds thereafter, the mixture starts to polymerize, and the reaction is completed in about 1 minute. The maximum temperature of the mixture during the reaction is about 120 C.
The polymer i5 allowed ~o complete curing for about 30 minutes at ambient temperature to give a dry solid strip of cross-linked potassium polyacrylate product having a water content of 11% and a re~idual monomer concentration of 1200 ppm. The strip is made into a powder by a pulverizer.
Exa~E1~
Polymers are prepared in the same manner as in Example 1 with the exception of varying, at least one of the combined concentration of monomers, the amount of polyvinyl monomer (N,N-methyle~ebisacrylamide), the kind and amount (degree of neutralization~ of neutralizing agent, and the amounts, based on the combined amount of the monomers, of azo polymerization initiator. The following compositions were polymerized:
ACRYLIC ACID 56.80%
POTASSIUM HYDROXIDE 14.77~
AMMONIUM CARBONATE 11.36%
N,N-METHYLENEBISACRYLAMIDE0.03%
~0 ~,a~/y~ `z~z~ot~ /n; fia7Lor 0.14%
AMMONIUM HYDROXIDE 14.20%
~20 2.70%
TOTAL 100.00%
ACRYLIC ACID 57.13%
POTASSIUM HYDROXIDE 14.28%
AMMONIUM CARBONATE .11.43%
N,N-METHYLENEBISACRYLAMIDE O.03 AZO POLYMERIZATION INITIATOR 0.14 AMMONIUM HYDROXIDE 14.28~
H20 2.71%
TOTAL 100.00 EX~4PLE 4 ACRYLIC ACID 54.66%
POTASSIUM HYDROXIDE 10.93%
AMMONIUM CA~BONATE
N, M~METHYLENEBISACRYL~MIDE O 11~
~4~ ~o/yf~er/~or~ ~Jf~2 ~ v 0 41%
AMMONIUM HYDROXIDE 30.61%
H20 3.27 TOTAL 100.00~
The amount of polyvin~l monomer listed as 2~ expressed in % by weight based on the combined amount of potassium acrylate, free acrylic acid and the poly-vinyl monomer, and the concentration of initiator is expressed in ~ by weight based on the combined amount by weight (calculated as solids) of the monomers and the initiator, the same as hereinbefore.
To 22.2 g of deionized water are added 72.1 y of acrylic acid first, then 49.5 g of potassium hydxoxide having a purity of 85% and serving as a neutralizing agent, and thereafter 0.01 g of N,N-methylenebisacrylamide as a polyvinyl monomer to prepare an aqueous solution of potassium acrylate having a neutralization degree of 75% and a combined monomer concentration of 70 wt.%~
The aqueous solution is maintained at 70 C, and with the solution are admixed 2.9 9 of 18~
aqueous solution of ammonium persulfate (0.5 w~. %
based on the combined weight of the potas~ium asrylate, free acrylic acid and N,N-methylenebisacrylamide, the same as hereinafter). The mixture i5 poured onto a traveling endles belt and spread thereover in the form o~ a layer about 10 mm in thickness. About 30 ~ec~n oee~ thereafter, the mixture starts to polymerize, and the reaction is completed in about 1 minute. The maximum temperature of the mixture during the reaction is about 120 C.
The reaction give~ a dry solid strip of cro~s-linked pota~ium polyacrylate product having a water content of 11% and a residual monomer conc~ntra-tion of 1200 ppm. The s~rip is made into a powder by a pulverizer. The powder has water absorbing ability of 450 as measured with use of deionized water or 60 as measured with 1% saline.
~3~Y~L_~5 ~ 9 Polymers are prepared in the same manner as in Example 5 with the exception of changing at lPast one of the amount of N,N-methylenebisacrylamide and the kind and amount of the polymerization initiator as listed in Table 1 below. Table 4 also shows the water content and water absorbing ability of each polymer obtained.
Table 1 Ex. Initiator Amt. Water Water Absorbing of Poly- _ Ability vinyl Deionized 1%
No. Kind Conc. Monomer Content Water Saline 2,2'-azobis-(2-amidino-propane)hydro-chloric acid 6 0.5 0.01 1~ 520 58 7 " 0.5 0.02 12 610 65 8 " 1.0 0.01 10 550 62 9 1.0 0.02 11 580 63 1~794;~i ExarnPle3 lo to 17 Polymers are prepared in the same manner as in Example 1 except that the compounds listed in Table 2 below are used as polyvinyl monomers in the listed amounts. Table 2 also shows the water content and water absorbing ability of each polymer obtained.
Table 2 Ex. Polyvinyl Monomer Water Deionized Water No. Kind Amount Content Absorbinq AbilitY
Ethylene 0.01 12 480 glycol diallyl ester 11 n 0.0213 430 12 Deithylenetri-0.01 12 510 amine-diacryl-amid 13 " 0.0212 450 14 N,N-methylene-0.01 9 5~0 bismethacryl-amid 15 " 0,0511 3~0 16 Polyethylene0.01 10 500 glycol diacrylate~
17 " 0.0511 430 *Poly~e~hylene glycol diacrylate used in Examples 2~r and ~ is represented by the following formula:
CH2 = CIH CH = CH2 = C~ - (OCH2CH2~0 0 - C = O
3a ~ 0 ~I
Acrylic acid (72.1 9), 18.0 9 of deionized water, 40.9 9 of solid potassium hydroxide (water content 4~) and 5.2 g of one of the solvents (5 wt. %
based on the monomers) listed in Table 3 are mixed together, and the mixture is maintained at 75 C.
With the mixture is further admixed 4.0 9 of 10%
~ ~ 7 aqueous solution of 2,2'-azobis(2-amidinopropane)-hydrochloric acid salt. The resulting mixture is immediately poured onto a traveling endless belt and spread thereover to a thickness of 5 mm. About 15 seconds later, the mixture starts to polymerize, and the polymerization is completed in about 30 seconds.
The maximum temperature of the mixture during the reaction i3 130 to 135 C.
The reaction gives a dry strip of cross-linked potassium polyacrylate product, which i5 pul-verized to a powder 20 to 100 mesh in particle size.
The same procedure as above is repeated with use of the other solvents. All the powders ob- -tained have a water content of 4 to 6%.
A 0.1 9 quantity of each of the powders is accurately measured out and the water absorbing abili~y of the powder is measured a~ter immersing the powder in deionized water or 1% saline for 10 seconds, 30 seconds or 15 minutes. Table 6 shows the results.
Example 22 An aqueous monomer solution is prepared in the same manner as in examples 17 to 21 with the ex-ception of not using any organic solvent and using 23.2 9 of deionized water. The solution is thereafter subjected to polymerization in the same manner as in these examples to obtain a powder of dry solid. Table 3 also shows the test results obtained with this pow-der.
4~i Table 3 Example No.18 19 20 21 22 OrganicAcetone Ethanol Benzene Tetra- (Water Solventhydro- only) furan ~ . . _ .
5 Water absorbing ability (times) 1% Saline 10 Sec. 73 68 7a 76 54 30 Sec. 83 82 85 85 75 15 Min. ~7 93 94 96 96 Deionized water 10 Sec. 620 690 600 690 300 30 Sec. 900 910 880 ~20 750 15 Min. 960 980 900 980 920 Examples 23 to 25 Water absorbing resin solids are prepared in the same manner as in Example 18 with the exception of using 3, 5 or 10 wt. %, based on the monomers, of 2~ methanol in place of 5.2 9 of acetone and varying the amount of deionized water 50 that the combined amount of the water and the methanol is 23.2 g. Each of the solids is tested for water content and also for water absorbing ability by immersion in 1% saline and deionized water for specified periods of time. The results are given in Table 4, which also shows the of similar tests conducted with use of the solid of E~ample 22.
Table 4 Example No. 19 20 21 22 ~mount of organic solvent (based on monomers, %) 3 5 10 0 ~ater content of resin 7.2 6.0 2.1 10.2 Water absorbing ability (times) 1% Saline 5 Sec~ 50 58 65 32 10 Sec. 64 71 75 54 15 Min. 71 77 79 61 20 Sec. 75 80 82 67 40 Sec. 85 87 88 80 60 Sec. 90 90 91 88 15 Min. 97 93 94 96 L5 Deioni2ed water 5 Sec. 250 420 570 140 10 Sec. 420 650 760 300 15 Sec. 590 740 830 410 20 Sec. 660 790 850 560 40 Sec. 880 900 890 850 60 Sec. 920 910 890 900 15 Min. 930 910 890 920 2~ ~9~Eæ~
281. gr. of acrylic acid and 11.9 gr. of acrylamide were dissolved in 179.1 gr. of distilled water and then 10.9 gr. of NaOH was added for 70 mole percent partial neutralization of acrylic acid; 0.003 gr. of N,N'-methylenebisacrylamide was then ad~ed as the polyvinyl monomer. In this case, 0.04 gr. of 2,2'-azobis(2-amidinopropane~hydrochloride was added as the polymerization initiator and the initial tempera-ture of the mixed monomer solution was 50 C.
Example 27 48.1 gr. of acrylic acid and 11.9 gr. of acrylamide were dissolved in 159 gr. of distilled water and then 22.7 gr.of NaOH was added for partial neutralization of acrylic acid in an amount of 85 mole percent. 0.006 gr. of N,N'-me~hylenebisacrylamide was then added as the polyvinyl monomer. In addition, 0.048 gr. of ammonium persulfa~e and 0.048 gr. of 4~
sodium hydrogen-sulfite were added as the polymeriza-~ion ini~iators. In tbis case, the initial tempera-ture of the mixed monomer solution was 40 C.
Example 28 90.1 gr.of acrylic acid and 9.9 gr. of acrylamide were dissolved in 118.8 gr. of distilled water and 52.6 gr. of KOH wa~ added for 75 mole per- -cent partial neutralization of acrylic acid. 0.018 gr. of N,N'-methylenebisacrylamide was added as the polyvinyl monomer, and 0.08 gr. of ammonium persulfate and 0.08 gr. of sodium hydrogen sulfite were added as the polymerization initiators. The initial temperature o the mixed monomer solution was 30 C.
48.1 gr. of acrylic acid and 11.9 gr. of acrylamide were dissolved in 252.1 gr. of distLlled wa~er and 27.4 gr. of aqueous ammonia was added for 70 mole percent partial neutralization of acrylic acid. In this case, the concentration of the ammonia 2~ is 29 weight percent. In addition, 0.006 gr. of N,N'-methylenebisacrylamide was added as the polyvinyl monomer. The polymerization was performed with the addition of 0.048 gr. of ammonium persulfate and 0.048 gr. of sodium hydrogen-sulfite for initiation. In this case, the initial temperature of the mixed monomer solution was 30 C.
ExamPle 30 52.7 gr. of acrylic acid and 17.3 gr. of acrylamide were dissolved in 25 gr. of distilled water and they w~re partially neutralized 80 mole percent with the addition of 32.8 gr. of KOH. 0.007 gr. of N,N'-methylenebisacrylamide was added as to the poly-vinyl monomer. For the polymerization catalyst 0.7 gr. of 272'-azobisisobutyronitrile dissolved in 10 cc. of acetone was~added. This solution was kept at 80 C. in a TEFLO ~coated, glass fiber reaction chamber until completion of polymeri2ation and cross-linking reactions yielding a white, solid resin.
~ rr~ ~k Example 31 17.3 gr~ of acrylamide was di5solved in 52.7 gr. of acrylic acid and partial (70 mole percent) neutralization of acrylic acid was accomplished by the addition of 30 gr. of agueous ammonia having a concentration of 29 weight percent. In this case, for the polyvinyl monomer, 0.007 gr. of N,N'-methylene-bisacrylamide was added and, as the catalyst, 0.7 gr.
of 2,2'-azobis(2-amidinopropane)hydrochloride dissolved L0 in 8 gr. of distilled water was added. The polymeriza-tion was started at 80 C. yielding a white, solid resin.
Exame~Le 32 21 kg. of acrylic acid and 7 kg. of acrylamide wexe dissolved in 9.5 kg. of distilled water and the acrylic acid was partially neutralized with 12 kg. of KOH. 0.036 kg. of methylenebisacrylamide as a polyvinyl monomer was added to provide an aqueous mixed monomer solution. The mixed monomer solution was mixed with 0.28 kg. of 2,2'-azobisisobutyronitrile, dissolved in 2 kg. of aceton~ as a polymerization initiator.
This mixture at a temperature of 60 C. was transferred on an endless belt (600-700 mm. in width, and 7 m. in length) at a thickness of about 1 cm. The polymeriza-tion was initiated promptly on the belt resulting in a white, solid resin.
Example 33 The polymers of Examples 26-2g, were dehydrated with acetone, dried and pulverized into powders. The polymers of Examples 30-32, were pulverized without any drying into highly water absorb-able powders. The products of Examples 26-32, were compared to commercial prior art products. The testing method was as follows:
1 gr. of sample was added to 1 liter of distilled water with agitation. After one hour of settling for water absorptionf the water-polymer was ~794;~
fil~ered through a 100 mesh sieve and the amount of water absorbed determined by measuring the volume of filtrate recovered. In addition, parallelly, 5 gr.
of the polymers of Examples 26-32, were added to 1 liter of 1 percent NaCl solution, and testing was conducted the same as in the case of distilled water.
The results of the testing are shown in Table 5. Water absorbability is shown as amount of absorbed water/weight of resin.
Table 5 Examples 26-32 Distilled Water 1% NaCl Solution Example 26650 times 68 times Example 27670 times 70 times Example 28680 times 72 times Example 29620 times 65 times Example 30540 times 57 times Example 31520 times 54 times Example 32540 times 56 times Commercial product (1)520 times 49 times Commercial product (2)504 times 47 times Example 33 52.7 gr. of acrylic acid and 17O3 gr. of acrylamide were dissolved in 20 gr. of distilled water.
32.8 gr. of KOH was added for 80 mole percent partial neutralization of acrylic acid. Then 0.007 gr. of N,N'-methylenebisacrylamide polyvinyl monomer was added with 2.5 gr. of methylcellulose. The aqueous monomer mixture was homogenized with agitation. Next, 3S as an initiator, 0.7 gr. of 2,2'-azobisisobutyronitrile dissolved in 10 cc of acetone was added. This mixed solution was kept at 80 C. in a water bath surrounding the reaction chamber. Polymerization was initiated a3 the temperature of the mixture increased as a result of the surrounding water bath, resulting in a white, solid porous resin.
Exam~le 34 20.8 gr. of acrylamide was dis~olved in 49.2 gr. of acrylic acid and 28.0 gr. of aqueous ammonia (29~ concentration) was added for 70 mole percent neutralization of the acrylic acid. Next, 0.01 gr.
of N,N' methylenebisacrylamide and 5 gr. of methyl-cellulose were added and stirred to homogenize. As an initiator, 0.7 gr. of 2,2'~azobi~(2-amidinopropane)-hydrochloride dissolved in 5 yr. of distilled water, was added. The polymerization was initiated in a TEFLON coa~ed glass reaction chamber kept at 80 C., as in Example 8 yielding a white, solid porous resi~
having a water content of about 10% by weight.
Exame~e 35 70 gr. of acrylic acid was dissolved in 20 grO of distilled water. 40.8 gr of KOH was added to neutralize 75 mole percent of the acrylic acid. Next, 0.007 grO of N,N'-methylenebisacrylamide and 2.0 grO
of methylcellulose were added, and the mixture homo-genized with agitation. Then, as an initiator, 0.7 gr. of 2,2'-azobisisobutyronitrile dissolved in 10 cc. of acetone was added. This solution was trans-ferred to the reaction chamber kept at 80 C. and polymerization was initaited with a rise in temperature of the mixture resulting in a white, solid porous resin of low water content.
Same as Example No. 33, but having no methyl-cellulose, Same as Example No. 34, but having no methyl-cellulose.
7 ~
Example 38 $ame as Example No. 35, but having no methyl-cellulose.
Example 39 The water absorbable resins of Example 33-38 were pulverized directly ints powder without any drying process.
The water absorbing capacity of the resins of Examples 33-38 was tested as follow~:
1 gr. of ~he resin powders (20-40 mesh) of Examples 33-38 were each added to 2 liters of dis-tileld water with agitation. After set ling for 1 hour, the water-polymers were filtered through a 100 mesh sieve and the vvlume of filtrate mea~ured to give the amoun~ of water absorbed in the resin. In adition, 5 gr. of the resins of ~xamples 33-38 were each added to 1 liter of 1% NaCl solution, and ~he -testing was conducted the same as the case of distilled water. The results are shown in Table 6. Water 2~ absorbability is shown as amount of absorbed water/weight of resin Table 6 ExamPles 33-38 Distilled Water 1% NaCl Solution Example 331,300 times 98 times Example 341,160 times 84 times Example 35l,360 times 102 times Example 36540 times 56 times Example 37470 times 50 times Example 38590 times 60 times Example 39 52.7 gr. of acrylic acid and 17.3 gr.of acrylamide were dissolved in 20 gr. of dis~illed water.
32 . 8 gr . of potassium hydroxide was added to neutralize ~ ;~7~4~i 80 mole percent of the acrylic acid. Next, 0.007 gr.
of N,NI-methylenebisacrylamide and 5 gr. of a poly-styrene emulsion were added and homogenized under stirring. The polystyrene emulsion had a csncentra-tion of 50 weight percent and a polystyrene grainsize of about 0.5 micro meters. Then, as the initiator, 0.7 gr. of 2,2'-azobi~isobutyronitrile dissolved in 10 cc. of acetone solution was added. The mixed monomer solution was kept at 80 C. in the reaction chamber immersed in a water bath. With the increasing tempera-ture of the mixed monomer solution polymeriæation was initiated resulting in a white, solid, porous resin.
Example 40 20.8 gr. of acrylamide was dissolved in 49.2 gr. of acrylic acid. 28.0 gr. of aqueous ammonia (29~ concentration) was added to neutralize 70 mole percent of the acrylic acid. Then 0.01 gr. of N,N'- -methylenebisacrylamide was added. 3 gr. of the poly-styrene emulsion of Example 39, but having a 1 micro meter average grain size, was added and the mixed solution was homogenized with agitation. Next, as the initiator, 0.7 gr. of 2,2'-azobis(2-amidinopropane)-hydrochloride dissolved in 5 gr. of distilled water was added. The solution was kept at 80~ C. as in Example 39 and polymerization was initiated with increased temperature resulting in a white, solid, porous resin.
Example 41 70 gr. of acrylic acid was dissolved in 20 grO of distilled water and 40.8 gr. of KOH was added to neutralize 75 mole % of the acrylic acid. Next, 0.007 gr. of N,N'-methylenebisacrylamide was added.
2 gr. of the polystyrene emulsion o Example 14 (but having an average grain size of S micro meters), was added and the mixture homogenized. Next, as the ini~iator; 0.7 gr. of 2,2'-azobisisobu~yronitrile dis~olved in 10 cc of acetone was added. The mixed ~.~7~43~
solution was kept at 80 C. in the wa~er bath to initiate the polymerization resulting in a white, solid, porous reæin.
Example 42 Same as Example 39, but having no polysty-rene.
Exame~e 43 Same as Example 40, but having no polystyrene.
ExamPle 44 Same as Example 41, but having no polystyrene.
The polymers of Examples 39-44 were made into powdery resins without any drying step.
The following tests were performed on the resins of Examples 39-44 to determine water absorbing capacity:
1 gr. of the resins of Examples 39-44 (20- ~
40 mesh) were each added into 2 liter of distilled water with agitation and settling for one hour. After 2~ settling, a 100 mesh sieve was employed for filtration and the amount of absorbed water was calculated from ,the amount of filtrate. Their water absorption rate (absorbed water/weight of polymer) is shown in the following Table 7.
Table 7 Exam~les 39-44 Distilled Water 1% NaCl Solution Example 39 1,010 times 83 times Example 40 360 times 76 times Example 41 1,120 times 90 times Example 42 540 times 56 times Example 43 470 times 50 times Example 44 590 times 60 times We claim:
.,
Table 4 Example No. 19 20 21 22 ~mount of organic solvent (based on monomers, %) 3 5 10 0 ~ater content of resin 7.2 6.0 2.1 10.2 Water absorbing ability (times) 1% Saline 5 Sec~ 50 58 65 32 10 Sec. 64 71 75 54 15 Min. 71 77 79 61 20 Sec. 75 80 82 67 40 Sec. 85 87 88 80 60 Sec. 90 90 91 88 15 Min. 97 93 94 96 L5 Deioni2ed water 5 Sec. 250 420 570 140 10 Sec. 420 650 760 300 15 Sec. 590 740 830 410 20 Sec. 660 790 850 560 40 Sec. 880 900 890 850 60 Sec. 920 910 890 900 15 Min. 930 910 890 920 2~ ~9~Eæ~
281. gr. of acrylic acid and 11.9 gr. of acrylamide were dissolved in 179.1 gr. of distilled water and then 10.9 gr. of NaOH was added for 70 mole percent partial neutralization of acrylic acid; 0.003 gr. of N,N'-methylenebisacrylamide was then ad~ed as the polyvinyl monomer. In this case, 0.04 gr. of 2,2'-azobis(2-amidinopropane~hydrochloride was added as the polymerization initiator and the initial tempera-ture of the mixed monomer solution was 50 C.
Example 27 48.1 gr. of acrylic acid and 11.9 gr. of acrylamide were dissolved in 159 gr. of distilled water and then 22.7 gr.of NaOH was added for partial neutralization of acrylic acid in an amount of 85 mole percent. 0.006 gr. of N,N'-me~hylenebisacrylamide was then added as the polyvinyl monomer. In addition, 0.048 gr. of ammonium persulfa~e and 0.048 gr. of 4~
sodium hydrogen-sulfite were added as the polymeriza-~ion ini~iators. In tbis case, the initial tempera-ture of the mixed monomer solution was 40 C.
Example 28 90.1 gr.of acrylic acid and 9.9 gr. of acrylamide were dissolved in 118.8 gr. of distilled water and 52.6 gr. of KOH wa~ added for 75 mole per- -cent partial neutralization of acrylic acid. 0.018 gr. of N,N'-methylenebisacrylamide was added as the polyvinyl monomer, and 0.08 gr. of ammonium persulfate and 0.08 gr. of sodium hydrogen sulfite were added as the polymerization initiators. The initial temperature o the mixed monomer solution was 30 C.
48.1 gr. of acrylic acid and 11.9 gr. of acrylamide were dissolved in 252.1 gr. of distLlled wa~er and 27.4 gr. of aqueous ammonia was added for 70 mole percent partial neutralization of acrylic acid. In this case, the concentration of the ammonia 2~ is 29 weight percent. In addition, 0.006 gr. of N,N'-methylenebisacrylamide was added as the polyvinyl monomer. The polymerization was performed with the addition of 0.048 gr. of ammonium persulfate and 0.048 gr. of sodium hydrogen-sulfite for initiation. In this case, the initial temperature of the mixed monomer solution was 30 C.
ExamPle 30 52.7 gr. of acrylic acid and 17.3 gr. of acrylamide were dissolved in 25 gr. of distilled water and they w~re partially neutralized 80 mole percent with the addition of 32.8 gr. of KOH. 0.007 gr. of N,N'-methylenebisacrylamide was added as to the poly-vinyl monomer. For the polymerization catalyst 0.7 gr. of 272'-azobisisobutyronitrile dissolved in 10 cc. of acetone was~added. This solution was kept at 80 C. in a TEFLO ~coated, glass fiber reaction chamber until completion of polymeri2ation and cross-linking reactions yielding a white, solid resin.
~ rr~ ~k Example 31 17.3 gr~ of acrylamide was di5solved in 52.7 gr. of acrylic acid and partial (70 mole percent) neutralization of acrylic acid was accomplished by the addition of 30 gr. of agueous ammonia having a concentration of 29 weight percent. In this case, for the polyvinyl monomer, 0.007 gr. of N,N'-methylene-bisacrylamide was added and, as the catalyst, 0.7 gr.
of 2,2'-azobis(2-amidinopropane)hydrochloride dissolved L0 in 8 gr. of distilled water was added. The polymeriza-tion was started at 80 C. yielding a white, solid resin.
Exame~Le 32 21 kg. of acrylic acid and 7 kg. of acrylamide wexe dissolved in 9.5 kg. of distilled water and the acrylic acid was partially neutralized with 12 kg. of KOH. 0.036 kg. of methylenebisacrylamide as a polyvinyl monomer was added to provide an aqueous mixed monomer solution. The mixed monomer solution was mixed with 0.28 kg. of 2,2'-azobisisobutyronitrile, dissolved in 2 kg. of aceton~ as a polymerization initiator.
This mixture at a temperature of 60 C. was transferred on an endless belt (600-700 mm. in width, and 7 m. in length) at a thickness of about 1 cm. The polymeriza-tion was initiated promptly on the belt resulting in a white, solid resin.
Example 33 The polymers of Examples 26-2g, were dehydrated with acetone, dried and pulverized into powders. The polymers of Examples 30-32, were pulverized without any drying into highly water absorb-able powders. The products of Examples 26-32, were compared to commercial prior art products. The testing method was as follows:
1 gr. of sample was added to 1 liter of distilled water with agitation. After one hour of settling for water absorptionf the water-polymer was ~794;~
fil~ered through a 100 mesh sieve and the amount of water absorbed determined by measuring the volume of filtrate recovered. In addition, parallelly, 5 gr.
of the polymers of Examples 26-32, were added to 1 liter of 1 percent NaCl solution, and testing was conducted the same as in the case of distilled water.
The results of the testing are shown in Table 5. Water absorbability is shown as amount of absorbed water/weight of resin.
Table 5 Examples 26-32 Distilled Water 1% NaCl Solution Example 26650 times 68 times Example 27670 times 70 times Example 28680 times 72 times Example 29620 times 65 times Example 30540 times 57 times Example 31520 times 54 times Example 32540 times 56 times Commercial product (1)520 times 49 times Commercial product (2)504 times 47 times Example 33 52.7 gr. of acrylic acid and 17O3 gr. of acrylamide were dissolved in 20 gr. of distilled water.
32.8 gr. of KOH was added for 80 mole percent partial neutralization of acrylic acid. Then 0.007 gr. of N,N'-methylenebisacrylamide polyvinyl monomer was added with 2.5 gr. of methylcellulose. The aqueous monomer mixture was homogenized with agitation. Next, 3S as an initiator, 0.7 gr. of 2,2'-azobisisobutyronitrile dissolved in 10 cc of acetone was added. This mixed solution was kept at 80 C. in a water bath surrounding the reaction chamber. Polymerization was initiated a3 the temperature of the mixture increased as a result of the surrounding water bath, resulting in a white, solid porous resin.
Exam~le 34 20.8 gr. of acrylamide was dis~olved in 49.2 gr. of acrylic acid and 28.0 gr. of aqueous ammonia (29~ concentration) was added for 70 mole percent neutralization of the acrylic acid. Next, 0.01 gr.
of N,N' methylenebisacrylamide and 5 gr. of methyl-cellulose were added and stirred to homogenize. As an initiator, 0.7 gr. of 2,2'~azobi~(2-amidinopropane)-hydrochloride dissolved in 5 yr. of distilled water, was added. The polymerization was initiated in a TEFLON coa~ed glass reaction chamber kept at 80 C., as in Example 8 yielding a white, solid porous resi~
having a water content of about 10% by weight.
Exame~e 35 70 gr. of acrylic acid was dissolved in 20 grO of distilled water. 40.8 gr of KOH was added to neutralize 75 mole percent of the acrylic acid. Next, 0.007 grO of N,N'-methylenebisacrylamide and 2.0 grO
of methylcellulose were added, and the mixture homo-genized with agitation. Then, as an initiator, 0.7 gr. of 2,2'-azobisisobutyronitrile dissolved in 10 cc. of acetone was added. This solution was trans-ferred to the reaction chamber kept at 80 C. and polymerization was initaited with a rise in temperature of the mixture resulting in a white, solid porous resin of low water content.
Same as Example No. 33, but having no methyl-cellulose, Same as Example No. 34, but having no methyl-cellulose.
7 ~
Example 38 $ame as Example No. 35, but having no methyl-cellulose.
Example 39 The water absorbable resins of Example 33-38 were pulverized directly ints powder without any drying process.
The water absorbing capacity of the resins of Examples 33-38 was tested as follow~:
1 gr. of ~he resin powders (20-40 mesh) of Examples 33-38 were each added to 2 liters of dis-tileld water with agitation. After set ling for 1 hour, the water-polymers were filtered through a 100 mesh sieve and the vvlume of filtrate mea~ured to give the amoun~ of water absorbed in the resin. In adition, 5 gr. of the resins of ~xamples 33-38 were each added to 1 liter of 1% NaCl solution, and ~he -testing was conducted the same as the case of distilled water. The results are shown in Table 6. Water 2~ absorbability is shown as amount of absorbed water/weight of resin Table 6 ExamPles 33-38 Distilled Water 1% NaCl Solution Example 331,300 times 98 times Example 341,160 times 84 times Example 35l,360 times 102 times Example 36540 times 56 times Example 37470 times 50 times Example 38590 times 60 times Example 39 52.7 gr. of acrylic acid and 17.3 gr.of acrylamide were dissolved in 20 gr. of dis~illed water.
32 . 8 gr . of potassium hydroxide was added to neutralize ~ ;~7~4~i 80 mole percent of the acrylic acid. Next, 0.007 gr.
of N,NI-methylenebisacrylamide and 5 gr. of a poly-styrene emulsion were added and homogenized under stirring. The polystyrene emulsion had a csncentra-tion of 50 weight percent and a polystyrene grainsize of about 0.5 micro meters. Then, as the initiator, 0.7 gr. of 2,2'-azobi~isobutyronitrile dissolved in 10 cc. of acetone solution was added. The mixed monomer solution was kept at 80 C. in the reaction chamber immersed in a water bath. With the increasing tempera-ture of the mixed monomer solution polymeriæation was initiated resulting in a white, solid, porous resin.
Example 40 20.8 gr. of acrylamide was dissolved in 49.2 gr. of acrylic acid. 28.0 gr. of aqueous ammonia (29~ concentration) was added to neutralize 70 mole percent of the acrylic acid. Then 0.01 gr. of N,N'- -methylenebisacrylamide was added. 3 gr. of the poly-styrene emulsion of Example 39, but having a 1 micro meter average grain size, was added and the mixed solution was homogenized with agitation. Next, as the initiator, 0.7 gr. of 2,2'-azobis(2-amidinopropane)-hydrochloride dissolved in 5 gr. of distilled water was added. The solution was kept at 80~ C. as in Example 39 and polymerization was initiated with increased temperature resulting in a white, solid, porous resin.
Example 41 70 gr. of acrylic acid was dissolved in 20 grO of distilled water and 40.8 gr. of KOH was added to neutralize 75 mole % of the acrylic acid. Next, 0.007 gr. of N,N'-methylenebisacrylamide was added.
2 gr. of the polystyrene emulsion o Example 14 (but having an average grain size of S micro meters), was added and the mixture homogenized. Next, as the ini~iator; 0.7 gr. of 2,2'-azobisisobu~yronitrile dis~olved in 10 cc of acetone was added. The mixed ~.~7~43~
solution was kept at 80 C. in the wa~er bath to initiate the polymerization resulting in a white, solid, porous reæin.
Example 42 Same as Example 39, but having no polysty-rene.
Exame~e 43 Same as Example 40, but having no polystyrene.
ExamPle 44 Same as Example 41, but having no polystyrene.
The polymers of Examples 39-44 were made into powdery resins without any drying step.
The following tests were performed on the resins of Examples 39-44 to determine water absorbing capacity:
1 gr. of the resins of Examples 39-44 (20- ~
40 mesh) were each added into 2 liter of distilled water with agitation and settling for one hour. After 2~ settling, a 100 mesh sieve was employed for filtration and the amount of absorbed water was calculated from ,the amount of filtrate. Their water absorption rate (absorbed water/weight of polymer) is shown in the following Table 7.
Table 7 Exam~les 39-44 Distilled Water 1% NaCl Solution Example 39 1,010 times 83 times Example 40 360 times 76 times Example 41 1,120 times 90 times Example 42 540 times 56 times Example 43 470 times 50 times Example 44 590 times 60 times We claim:
.,
Claims (13)
1. A process for preparing a solid water absorbing resin comprising mixing a monomer solution of (A) acrylic acid neutralized 70-100 mole percent, wherein the neutralizing agent comprises a potassium alkali; and (8) a water-miscible to water-soluble polyvinyl monomer in a combined concentration of 30 wt. %
to less than 55 wt. %; with water to form a mixed monomer solution wherein the monomers of the mixed monomer solution consist essentially of (A) and (B) and initiating polymerization of monomers (A) and (B) such that during polymerization, the exothermic heat of reaction is substantially the only heat energy used to accomplish polymerization, cross-linking and to drive off sufficient water to obtain a solid cross-linked resin having a water content of 15 percent by weight or less.
to less than 55 wt. %; with water to form a mixed monomer solution wherein the monomers of the mixed monomer solution consist essentially of (A) and (B) and initiating polymerization of monomers (A) and (B) such that during polymerization, the exothermic heat of reaction is substantially the only heat energy used to accomplish polymerization, cross-linking and to drive off sufficient water to obtain a solid cross-linked resin having a water content of 15 percent by weight or less.
2. A process as defined in claim l wherein the mixed monomer solution has a temperature of 50 to 85°C prior to polymerization.
3. A process as defined in claim l wherein monomer (B) is selected from the group consisting of N,N-methylenebisacrylamide and N,N-methylenebismethacrylamide.
4. A process as defined in claim 1 wherein the mixed monomer solution contains 1 to 10 wt. % of an organic solvent based on the weight of monomers (A) and (B).
5. A process as defined in claim 1 wherein the mixed monomer solution further contains an organic solvent having a boiling point of 40 to 150° C.
6. A process for preparing a solid, water absorbing, cross-linked resin comprising:
combining a monomer mixture of (A) potassium acrylate; and (B) a polyvinyl monomer, with water in an amount of at least 30 to less than 55 wt. % combined weight percent of (A) plus (B) based on the total weight of (A) plus (B) plus water to form a monomer mixture wherein the monomers of the monomer mixture con-sist essentially of (A) and (B);
adding a polymerization initiator to said monomer mixture capable of initiating, and in an amount sufficient to initiate polymerization of said monomer mixture;
polymerizing said monomer mixture while utilizing the exothermic heat of reaction as substantially the only non-ambient energy source to drive water away from said polyacrylate resin to form said cross-linked resin having a water content sufficiently low to be powdered without an intermediate drying step.
combining a monomer mixture of (A) potassium acrylate; and (B) a polyvinyl monomer, with water in an amount of at least 30 to less than 55 wt. % combined weight percent of (A) plus (B) based on the total weight of (A) plus (B) plus water to form a monomer mixture wherein the monomers of the monomer mixture con-sist essentially of (A) and (B);
adding a polymerization initiator to said monomer mixture capable of initiating, and in an amount sufficient to initiate polymerization of said monomer mixture;
polymerizing said monomer mixture while utilizing the exothermic heat of reaction as substantially the only non-ambient energy source to drive water away from said polyacrylate resin to form said cross-linked resin having a water content sufficiently low to be powdered without an intermediate drying step.
7. The process of claim 6 further including the step of adjusting the temperature of the monomer mixture to a temperature of 50 to 85° C prior to adding said polymerization initiator to said monomer mixture.
8. The process of claim 6 wherein said polymerization initiator is added in an amount of at least 0.5% total by weight of monomers (A) and (B).
9 . The process of claim 6 wherein the water content of said cross-linked resin is not greater than about 10% by weight as recovered from the polymerized mixture, without an additional drying step.
10. The process of claim 6 further including combining a non-aqueous solvent having a boiling point of 40-150° C with said monomers (A) and (B) to form a porous resin.
11. The process of claim 6 including the step of pulveriz-ing said cross-linked resin to form a powder.
12. The method of claim 1 including depositing said monomer mixture including said initiator onto a support surface in sheet form for polymerization and cross-linking.
13. The method of claim 6 including depositing said monomer mixture including said initiator onto a support surface in sheet form for polymerization and cross-linking.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US74852885A | 1985-06-25 | 1985-06-25 | |
| US748,528 | 1985-06-25 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1279436C true CA1279436C (en) | 1991-01-22 |
Family
ID=25009839
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000512159A Expired - Fee Related CA1279436C (en) | 1985-06-25 | 1986-06-23 | Process for preparing water-absorbing resins |
Country Status (2)
| Country | Link |
|---|---|
| CA (1) | CA1279436C (en) |
| MX (1) | MX168202B (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN112592425A (en) * | 2020-12-21 | 2021-04-02 | 合肥艾普拉斯环保科技有限公司 | Preparation method of novel thickener polyacrylate |
-
1986
- 1986-06-23 CA CA000512159A patent/CA1279436C/en not_active Expired - Fee Related
- 1986-06-25 MX MX292886A patent/MX168202B/en unknown
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN112592425A (en) * | 2020-12-21 | 2021-04-02 | 合肥艾普拉斯环保科技有限公司 | Preparation method of novel thickener polyacrylate |
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| Publication number | Publication date |
|---|---|
| MX168202B (en) | 1993-05-12 |
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