WO1982000147A1

WO1982000147A1 - Hydrophilic interpolymers of acrylic acid and an acrylate

Info

Publication number: WO1982000147A1
Application number: PCT/US1981/000764
Authority: WO
Inventors: Co B F Goodrich; P George
Original assignee: Co B F Goodrich
Priority date: 1980-07-08
Filing date: 1981-06-08
Publication date: 1982-01-21
Also published as: ES8300804A1; EP0055728A4; EP0055728A1; IT8122628A0; MX160466A; IT1137264B; GR75718B; DK160259C; BE889553A; JPS57500930A; DK98082A; DK160259B; CA1209524A; BR8108674A; KR830006364A; ES503685A0

Abstract

Highly water absorbent polymers are obtained by polymerizing 65 to 95 weight percent of acrylic acid and 5 to 35 weight percent of a comonomer selected from an alkyl or a cyclohexyl methacrylate, phenyl acrylate, phenoxyalkyl acrylate and dialkylaminoalkyl acrylate or methacrylate. The polymerization can be carried out in the presence of a free radical catalyst in which case the polymer is then preferably neutralized with a base. Alternatively, carboxylic groups are neutralized first and then polymerized by subjecting the monomer mixture either to radiation or to UV light.

Description

HYDROPHILIC INTERPOLYMERS OF ACRYLIC ACID AND AN ACRYIATE

BACKGROUND OF THE INVENTION A variety of hydrophilic polymers which are useful in the manufacture of water absorbent films and fibers have been reported in the prior art. U.S. Patent 3,915,921 discloses copolymers of unsaturatad carboxylic acid monomers with alkyl acryiate esters wherein the alkyl group contains 10 to 30 carbon atoms. However, because of the high Tg of these polymeric materials, it is difficult to extrude them in fiber or film form. Furthermore, films pressed from the powders require high temperatures, the films are brittle and fragile, and have a reduced initial rate of water absorption.

U.S. Patent 4,062,817 discloses polymers of unsaturatad copolymerizable carhoxylic acids, at least one alkyl acryiate or methacrylata wherein the alkyl group has 10 to 30 carbon atoms and another alkyl acryiate or methacrylate wherein the alkyl group has 1 to 8 carbons. This composition alleviated many of the deficiencies of the earlier compositions. Further improvements in the hydrophiiic properties were obtained by compositions disclosed in U.S. Patent 4,066,583. This patent discloses a composition comprising (1) a copolymer of the type disclosed in the '817 patent, except that after copolymerizatiαn 30 t'o 90 percent of the carboxylic groups were neutralized with an alkali metal or ammonia and (2) an aliphatic glycol, a plasticizer which is important in facilitating extrusion of the polymer.

Most recently, U.S. Patent 4,167,464 discloses highly water absorbent polymers obtained by photopolymerizing an alkaline metal salt of acrylic acid, a long chain alkyl acryiate or methacrylate and a short chain alkyl acryiate or methacrylate in the presence of a photoinitiator.

SUMMARY OF TEST INVENTION A highly water absorbent interpolymer is obtained from a monomer mixture of 65 to 95 weight percent of acrylic acid, 60 to 100% of the carboxylic groups of said acid having been neutralized prior to polymerization with an alkaline metal hydroxide or ammonia and 5 to 35 weight percent of an alkyl methacrylate wherein the alkyl group has 1 to 30 carbon atoms or a certain phenyl containing acryiate or a dialkylaminoalkyl acryiate or methacrylate. The monomer mixture can be either spread to the desired thickness or spun into a fiber and then polymerized upon exposure to a UV light or radiation sources. If photopoiymerized, a photoinitiator must be employed. Alternatively, the monomer mixture, where the acrylic acid had not been previously neutralized, is polymerized in the presence of a free radical peroxygen catalyst.

DETAILED DISCLOSURE This invention is directed to an interpolymer which has outstanding absorption and retention properties of water and ionic solutions such as urine or blood. The interpolymer is prepared from a monomer mixture comprising a) 65 to 95 weight percent of acrylic acid, 70 to 100 percent, and most preferably 80 to 100 percent of the carboxylic groups having been neutralized with an alkali metal hydroxide or ammonia base prior to polymerization and b) 5 to 35 weight percent of a comonomer selected from the group consisting of an aikvl or a cyclohexyi methacrylate where the alkyl group has 1 to 30 carbon atoms and the cycloalkyl group is unsubstitute or substituted with 1 to 4 alkyl groups each having 1 to 4 carbon atoms, phenyl acryiate, phenoxyalkyl acryiat where the alkyl has 2 to 6 carbon atoms and dialkyl aminoalkyl acryiate or methacrylate where each alkyl of the dialkyl has 1 to 8 carbons and the other alkyl has 2 to 6 carbons.

If the monomer mixture is photopolymerized, 0.01 to 5 weight percent of a photoinitiator is also employed.

Useful alkyl methacrylates are those where the alkyl group has 1 to 30 carbon atoms and preferably 4 to 18 carbon atoms. Representative examples of such methacrylates are methyl methacrylate, ethyl methacry late, n-butyl methacrylate, n-hexyl methacrylate, n-octyl methacrylate, n-decyl methacrylate, i-decyl methacrylate, lauryl methacrylate, stearyl methacrylate, eicosyl methacrylate, octaeicosyl methacrylate and the like. Examples of cycloalkyl methacrylates are cyclohexyi methacrylate, which is preferred, 1-methylcyciohexyl methacrylate, 1, 3-dimethylcyclohexyl methacrylate, 1,3, 5-trimethylcyclohexyl methacrylate, 1-ethylcyclohexyl methacrylate, l-butylcyclohexyl methacrylate, 1,3,5-triethylcycIohexyl methacrylate, 1,3, 5-tributyicyclohexyi methacrylate and the like. Illustrative examples of useful acrylates are phenyl acryiate; phenoxyalkyl acrylates such as phenoxyethyl acryiate, which is preferred, phenoxybutyl acryiate, phenoxypropyl acryiate, phenoxyhexyl acryiate. Examples of dialkylaminoalkyl acrylates and methacrylates are dimethylaminoethyl acryiate, which is preferred, dimethylaminobutyl acryiate, dimethylaminohexyl acryiate, diethylaminoethyl acryiate, diethyiaminobutyl acryiate, dipropylaminohexyl acryiate, dipropylaminopropyl acryiate, dibutylaminoethyl acryiate, dibutylaminobutyl acryiate, dibutylaminohexyl acryiate, di-n-hexylaminoethyl acryiate, di-n-octylaminoethyl acryiate, di-n-octylaminobutyl acryiate, dimethylaminoethyl methacrylate, dimethylaminobutyl methacrylate, dimethylaminohexyl methacryiate, diethylaminoethyl methacrylate, diethylaminobutyl methacrylate, di-n-octylaminohexyl methacrylate and the like.

In addition to the above discussed monomers from which the copolymers of this invention are prepared, minor amounts, that is less than 5 weight percent, of additional monomers may also be used. Whether these additional monomers are employed will depend on the end use and the physical properties required, that is , the speed and decree of absorption and the tear strength needed for the film or fabric. Such additional monomers are discussed below.

One type of such additional monomers are α,β-olefinically unsaturated nitriles, preferably the mono-olefinically unsaturated nitriles, having from 3 to 10 carbon atoms such as acrylonitrile, methacrylonitrile, ethacrylonitrile, and the like. Most preferred nitriles are acrylonitriles and methacrylonitrile.

Another useful class of additional monomers which may be incorporated in the interpolymers of this invention is monoethylenically unsaturated amides which have at least one hydrogen on the amide nitrogen and the olefinic unsaturation is alpha beta to the carbonyl group.

The preferred amides have the structure

wherein R₃ is a member of the group consisting of hydrogen and an alkyl group having from 1 to 4 carbon atoms and R₄ is a member of the group consisting of hydrogen and an alkyl group having from 1 to 6 carbon atciss. Representative amides include acrylamide, methacryla mide, N-methyl acrylamide, N-t-butyl acrylamide, N- cyclohexyl acrylamide, N-ethyl acrylamide and others. Of the amides most preferred are acrylamide and meth acrylamide.

Other acrylic amides include N-alkylol amides of alpha,beta-olefinically unsaturated carboxylic acids including those having from 4 to 10 carbon atoms such as N-methylol acrylamide, N-ethanol acrylamide, N-pro panql acrylamide, and the like. The preferred monomers of the N-alkylol amide type are the N-alkylol amides of alpha beta-monoolefinically unsaturated monocarboxylic acids and the most preferred is N-methylol acrylamide. Also useful are N-alkoxymethyl acrylamides which have the structure

wherein R₅ is selected from the group consisting of hydrogen and methyl, and R₆ is an alkyl group having from 1 to 8 carbon atoms. It is thus intended that where references are made herein regarding the essential N-substituted alkoxymethyl amides, the term "acrylamide" includes "methacrylamide" within its meaning. The preferred alkoxymethyl acrylamides are those wherein R₆ is an alkyl group containing from 2 to 5 carbon atoms, and especially useful is N-butoxymethyl acrylamide.

The above discussed monomers can be copolymerized by subjecting the monomer mixture to UV light. If a film is desired the monomer can be spread on a surface to the desired thickness, e.g. 1 mil to 25 mil, and then subjected to UV light for a short time, e.g. one second to several minutes. The actual length of irradiation will depend on a number of factors, such as the thickness of the monomer film, the distance from and the intensity of the source of irradiation, the specific monomers employed and the ratio of such monomers to each other, the presence or absence of additiona comonomers and the nature and the amount of the photoinitiator employed. The type of photoinitiator employed will depend at least in part on the type of UV irradiation employed (particularly its wave length) since various photoinitiators may be decomposed by UV light of different wavelengths. If it is desired that the material be in the form of fibers , the monomer mixture can be thickened and then spun into fibers which, upon exposure to UV light, are polymerized.

In order to effect quick and efficient polymerization under UV light, 0.01 to 5 weight percent of a photoinitiator, preferably 0.1 to 5 percent and more preferably 0.3 to 1.0 weight percent, must be incorporated into the monomer mixture. Any compound which dissociates into free. radicals when exposed to UV radiation can be employed. There are many known photoinitiators or photosensitizers such as acetophenone, propiophenone, benzophenone, xanthone, fluorenone, benzaldehyde, fluorene, anthraquinone, triphenyiamine, carbazole, 3- or 4-methylacetophenαne, 3- cr 4-penrylacetophenone, 3- or 4-methoxyacetcphenone, 3- or 4-bromoacetophenone, 3- or 4-allylacetophenone, p-diacetyIbenzene, 3- or 4-methoxybenzophenone, 3- or 4-methylbenzophenone, 3- or 4-chlofobenzophenone, 4,4-dimethoxybenzophenone, 4-chIoro-4' -benzylbenzophenone, 3-chloroxanthone, 3 ,9-dichloroxanthone, 3-'chlcro-3-nonyI-xanthone, 3-methoxyxanthone, 3-iodo-7-methoxyxanthone, 2, 2-dimethoxyacetophenone, 2,2-dimethoxy-2-phenylacetophenone, 2, 2-diethoxyacetophenone, 2,2-dibutoxyacetophenone, 2 , 2-dihexoxyacetophencne, 2,2-di (2-ethylhexoxy) acetophenone, 2 ,2-diphenoxyace-oρhen one, benzoin, methyl benzoin ether, ethyl bezoin ether, isopropyl benzoin ether, butyl benzoin ether, isobutyl benzoin ether, benzoin acetate, benzoin phenyl carbamat α , α-diethoxy acetophenone, α , α-diethoxy-a-phenyl-aceto phenone, α,α -dimethoxy-a-pheny lacetophenone, 4 ,4 - dicarboethoxy benzoin ethyl ether, α-chloroacetophenone, a-broraoacetophenone, benzoin phenyl ether, α-methylben zoin ethyl ether, benzoin acryiate, α-methylolbenzoin methyl ether, α , α , α-trichloroacetophenone, o-bromoaceto phenone, 4-(benzoylphenylmethoxycarbonylimino) -2- (acrylyloxyethoxycarbony 1 imino ) -1-methy lbenzene, cumene hydroperoxide , benzoyl peroxide, dicumyl peroxide, tert butyl perbenzoate, α,α-azobisisobutyronitrile, phenyl disulfide, chloromethylbenzanthrone, chlαromethylanthra quinine, chloromethylnaphthalene, bromomethylbenzan throne, bromomethylanthraquinone, bromomethyinaphthalen and the like, and mixtures thereof.

In addition to the photo initiator it may be advantageous to employ also from 0.3 to 5.0 percent of a activator. Illustrative examples of such activators are mercaptoacetic acid, mercaptoethanol, or organic amines such as methylamine, decylamine, diisopropylamine , tributylamine, tri-2-chloroethylamine, ethanolamine, triethanolamine, methyldiethanoiamine, 2-aminoe-hylethanolamine, aliylamine, cyclohexylamine, cyclopentadienylamine, diphenylamine, ditolylamine, trixylyiamine, tribenzyiamine, N-cyclohexylethyleneimine, piper idine, 2- methylpiperidine, N-ethylpiper idine, 1,2,3, 4- tetrahydropyridine, 2- or 3- or 4-picolina, morpholine, N-methylmo pholine, piperazine, N-methylpiperazine, 2 ,2-dimethyI-1,3-bis- [3-(N-morpholinyl.) propionyloxy] -propane, 1, 5-bis [3-(N-morpholinyl)proρionyIoxy] di-ethyl ether, and the like.

The monomer mixtures are prepared as aqueous dispersions which eliminates the need for organic sol removal of organic solvents or the cost associated with the removal of the pollutants. In order to obtain a stable homogeneous dispersion of the monomers, it is preferred that the aqueous dispersions contain 0.01 to 5%, and preferably 0.1 to 1%, of a surface active agent such as an anionic, amphoteric, or nonionic dispersing agent or a mixture of dispersants. Useful anionic dispersing agents include alkali metal or ammonium salts of the sulfates of alcohols having from 8 to 18 carbon atoms such as sodium lauryl sulfata; ethanolamine lauryl sulfata, ethylamine lauryl sulfata; alkali metal and ammonium salts of sulfonated petroleum and paraffin oils; sodium salts of aromatic sulfonic acids such as dodecane-1-sulfonic acid and octadecane-1-sulfonic acid; aralkyl sulfonates such as sodium isopropyl benzene sulfonate, sodium dodecyl benzene sulfonate and sodium isobutyl naphthalene sulfonate; alkali metal and ammonium salts of sulfonated dicarboxylic acid esters such as sodium dioctyl sulfosuccinate, disodium-n-octadecyl sulfosuccinate; alkali metal or ammonium salts of free acid of complex organic mono-and diphosphate esters, sulfosuecinic acid derivatives (AEROSOL dispersants), organic phosphate esters (GAFAC dispersants) and the like. Nonionic dispersants such as octyi-or nonylphenyl polyethoxyethanol as well as the PLURONIC and the TRITON dispersants may also be used. Also useful are amphoteric dispersants such as dicarboxylic coconut derivatives (MIRANOL) . Further examples of useful dispersants are those disclosed beginning on page 102 in J. Van Alphen's "Rubber Chemicals" ,Elsevier Publishing Co.,1956. The monomer mixture can also be polymerized without first neutralizing the carboxylic groups . The polymerization can be carried out in an inert diluent having some solubiliziήg action on one or more of the monomeric ingredients but substantially none on the resultant polymer. Polymerization in mass ma be em lo ed but is not preferred because of the difficulty in working up the solid polymeric masses obtained. Polymerization in an aqueous medium containing a water-soluble free radical catalyst peroxygen is useful. Polymerization in an organic liquid which is a solvent for the monomers but a non-solvent for the polymer, or in a mixture of such solvents, in the presence of a solvent-soluble catalyst is more preferred because the product is usually obtaine as a very fine friable and often fluffy precipitate which, after solvent removal, seldom requires grinding or other treatment before use. The polymerizations preferably are conducted in the presence of a haloethane or halomethane containing at least four halogen atoms. Representative materials include for example, a fluoro ethane, fluoromethane, chlorofluoromethane, bromofluoro ethane, or preferably a chlorofluoroethane or chloro fluoromethane containing at least four halogen atoms.

Polymers obtained from free radical polymerizations generally do not attain their maximum properties until converted to a partial alkali, ammonium or amine salt. The neutralizing agent is preferably a monovalent alkali such as sodium, potassium, lithium or ammonium hydroxide or the carbonates and bicarbonates thereof, or mixtures of the same, and also amine bases having not more than one primary or secondary amino group. Such amines include, for example, triethanolamine, ethanolamine, isopropanolamine, triethylamine, trimethylamine, and the like.

The procedures to be employed in free radical polymerizations of such monomers, neutralization of the resulting polymers and their work up is disclosed in greater detail in U.S. Patent 4,062,817, which disclosure is incorporated herein by reference.

Although cross-linking agents are not required to obtain useful, highly absorbent composi tions of this invention, it may be desirable to incorporate a cross-linking agent since films prepared from compositions containing a cross-linking agent tend to have greater gel strength and an improved ability for the copolymers to swell under a confining pressure. Cross-linking agents may be used in the concentration of about 0.01 to about 50% by weight based on the total weight of the monomers, and preferably about 0.1 to about 5%. Useful cross-linking monomers are polyalkenyl poiyethers having more than one alkenyl ether grouping per molecule or monomers which contain two to six ethylenically unsaturated groups such as allyl, acryiate or vinyl groups. The most useful possess alkenyl groups in which an olefinic double bond is attached to a terminal methylene group, Other cross-

linking monomers include, for example diallyl esters or ethers, allyl or methallyl acrylates and acrylamides άiacrylates and dimethacrylates, divinyl compounds and the like. Illustrative examples of polyfunctional cross-linking agents are polyethyleneglycol diacrylata and dimethacrylate, ethylene glycol dimethacrylata, tatraethyleneglycol diacrylate, 1,3-butyleneglycol dimethacrylate, diethyieneglycol divinyl ether, trimethylolpropane diallyl ether, divinyl benzene, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, triallyl cyanurate, pentaerythritol triacrylate, diallyl itaconate, methylene bis (acrylamide), allyl pentaerithritαl, allyl sucrose, 1, 6-hexanedioi diacrylate, tetramethylene glycol diacrylate and dimethacrylata, ethylene glycol diacrylate and dimethacrylate, triethylene glycol dimethacrylate, triallyl cyanurate, triallyl isocyanurate, diallyl itaconates and the like. As discussed above, the interpolymers of this invention can be photopclymerized. Additionally, these interpolymers can be obtained by radiation polymerization by subjecting said monomers to electron beam radiation of sufficient intensity to cause said monomers to polymerize substantially completely. The amount and the intensity of radiation required will depend on the thickness of the film, the specific monomers employed, and the speed and the degree of polymerization desired. Generally, for the applications for which the resulting polymers are especially useful films, sheets or fibers in the range from 0.5 to 5 mils are most desirable. Therefore, relatively low intensity electron, beam sources, generally less than 200 KV, would be sufficient to effect polymerization. Generally for the type of monomer systems employed in this invention from 1 to 15 M rads of radiation is required. However, it should be pointed out that the amount and intensity of radiation must be optimized far each system taking all variables into consideration, i.e., the monomers employed, the thickness of the film, the desired speed of polymerization, the desired degree of polymerization and the rate of radiation.

When employing photopolymerization or radiation polymerization methods, the polymers of this invention can be polymerized in a film or a fiber form. The resulting film or fiber is an elastic, flexible material that has an appreciable degree of strength. If a fine, flaky form is desired, the film can be converted to such a form by drying and then pulverizing or grinding it in standard equipment. As water absorbent materials these polymers find many uses in film, fiber, fabric and similar forms. They are of particular utility in the disposable non-woven industry where there is need for polymers which will absorb and retain water and ionic physiological fluids. An important feature of these polymers is their enhanced thickening property even in the presence of a salt. Specific applications include disposable diapers, medical-surgical supplies and personal care products. Such applications require a polymer which must imbibe the liquid to be absorbed rapidly and be a polymer that will not dissolve. Further, the fluid must be immobilized or congealed in some way to be retained. The materials may also be used as suitable additives to greatly increase the absorptive power of conventional absorbents such as cotton, wood pulp and other cellulosic absorbents used in applications such as wiping cloths, surgical sponges, catamenial devices, and the like. In a specific application, for example, a disposable diaper, there is an inner layer of a soft absorbent nonwoven material that absorbs and passes urine to an inner layer of fluffy fibrous absorbentmaterial, wherein during the construction of this non-woven fiber agglomerates or fibers of the polymers of this invention may be included and an additional impervious plastic layer, as polyethylene. A film of the copolymers of this invention may be used between the outer plastic layer and the inner fluffy absorbent layer. Use of the polymers of this invention can result in reduction in the bulk size of many disposable non-wovens.

The instant copolymers can also be used as flocculants in water treatment, in metallurgical processes, in ore beneficiation and flotation, in agricultural applications such as in soil treatment or seed coating or in any applications where the inherent properties of the polymer are desirable, such as its thickening property in an aqueous medium.

To prepare the cured copolymers of this invention, the monomers, a dispersant and a photoinitiator, if used, are mixed in a vessel. Then either a film or fibers are produced from the monomer mixture which, upon exposure to UV light or radiation, are rapidly polymerized. The various steps in the procedure are described in greater detail below. Monomer Mixture Preparation: The monomer mixture can be prepared by following one of two simple procedures. One method is to dissolve a previously prepared and dried alkali metal or ammonium salt of acrylic acid in water to which is then added a disper sant. To the aqueous solution is then added the acryiate or the methacrylate ester which already contains a photoinitiator if one is employed. Another method is to prepare the acrylic acid salt in situ by adding acrylic acid to the proper amount of cold aqueous base (e.g. KOH, NaOH or NH₄OH) with cooling. To the aqueous solution is then added a mixture of the acryiate or the methacrylate. ester to which, if required, a photo initiator was previously added; the dispersant is added last. Film Preparation: The aqueous monomer dispersion is spread to a desired thickness (e.g. by the use of Boston-Bradley adjustable blade, by spraying or other known means) on a suitable substrate (e.g. Mylar, polyethylene, paper, etc.). The liquid film is then exposed to a UV or radiation source which polymerizes the monomer mixture into a soft, pliable form. If desired, this film can be dried in an oven at about 50ºC for 1 to 15 min. After drying the film may still retain some flexibility or become brittle and flaky, depending on the length of drying.

Fiber Preparation: The aqueous monomer dispersion is thickened to the desired degree with a non-reactive thickening agent such as a cellulose derivative as, for example, hydroxypropyl cellulose, high molecular weight polyvinyl pyrrolicone and the like; natural gums such as guar gum, locust bean gum, gum tragacanth; agar, naturally occuring hydrocolloids such as alginates and the like. Fibers are then spun from a spinneret in a regular manner and immediately exposed to a UV or radiation source.

To further illustrate the present invention the following examples are presented. The copolymers and the films were prepared according to the procedures described above. The copolymers of Examples 1 to 9, presented in Table I, have been photopolymerized using QC 1202 Processor manufactured by Radiation Polymer Co. (with belt speed of 0 to 1000 ft/min-304.3 m/min) having 2 medium pressure quartz mercury vapor lamps at 200 watts/lineal inch (watts/lineal 2.54 cm.) . The distance from the lamps to the film was 15 cm. and the exposure time was 20 sec. at belt speed of 20 ft/min. (6 m/min.).

Comonomers employed in the Examples and identified in Table I by capital l≤tters A to I, are identified below: A - Methyl methacrylate

B - 2-Hydroxyethyl methacrylate C - Lauryl methacrylate D - Stearyl methacrylate S - Phenoxyethyl acryiate F - Dimethylaminoethyl acryiate

G - Mixture of 17.0 g. DMAEA + 1.9 g. trimethylolpropane triacrylate H - Phenyl acryiate I - n-Hexyl methacrylate

Copolymers having substantially the same properties are obtained when in some of the above compositions potassium hydroxide was employed in place of sodium or ammonium hydroxide, 2,2-diethyoxyaceto phenone in place of IRGACURE 651 and an oligomeric surfactant POLYWET KX-3 (from Uniroyal) or TRITON N-lll (maonophenoxy polyethoxy ethanol) in place of AEROSOL A102.

A number of tests are available to determine the absorbency of a material. Following are descriptions of the two test procedures which were employed in evaluating absorbency of the interpolymers of this invention.

Static Test (ST) - A weighed film sample is immersed in a test liquid for 10 minutes. It. is then removed from the liquid, the excess liquid drained for a few seconds and then shaken lightly several times. The swelled sample is weighed again to determine the weight of liquid absorbed by the polymer. Demand Wettability Test (DWT) - A test diaper is constructed from a 4 inch diameter pad (10.16 cm.) using materials from a commercial diaper. A film prepared from a polymer to be tested for absorbency is placed in the center of the test diaper between two layers of fluff (wood pulp) . A diaper without the polymer film is used as a blank. The demand-wettability apparatus is a burette filled with the test fluid and firmly stoppered at the top, with an air bleed on the side, and a delivery orifice on the bottom connected by a flexible tube to the sample holder. The sample holder has an opening in the center which is connected to the flexible tube that leads to the delivery orifice of the burette. The sample holder is level with the air bleed opening in the burette. With this closed-system arrangement the fluid in the flexible tube that comes uo to the opening in the sample holder is at zero pressure. Thus when the test diaper is placed on the sample holder over the opening it will absorb the fluid on its own through wicking action. The sample's own absorbent powder will determine the rate and amount of fluid that will be withdrawn from the burette. The amount of fluid withdrawn at any given time can be easily read from the burette calibration. An additional feature is that absorbency can be measured against a range of pressures that can be obtained by placing various weights on top of the test diaper. Such pressures are intended to simulate the pressures applied on a diaper in actual use.

This test is described in greater detail by Lichstein, "Demand Wettability, a New Method for Measuring Absorbency Characteristics of Fabrics", Symposium Papers-INDA Technical Symposium, 1974, pp. 129-142.

Compression Test (CT) - This test is a follow-up test to the Demand-wettability Test (DWT) . After the sample has absorbed the liquid against a lower pressure in a DWTest, it is removed from the DWT apparatus and placed atop a porous filter funnel. The sample is then subjected to 1.5 psi (0.105 kg/cm ) of pressure for 1 minute and the amount of liquid that is squeezed from the sample is measured. Said pressure corresponds to the maximum pressure that is exerted on portions of a diaper when a toddler is picked up or held. This is 10 to 15 times the pressure that the diaper normally would experience.

The sample is then weighed to determine the amount of fluid in grams retained per one gram of polymer.

In Table II below is presented data comparing the absorbency properties of the cσpoiymer of this invention with two other polymers. The polymer number in the Table corresponds to the example describing the preparation of that specific polymer.

Claims

1. An interpolymer of

(a) 65 to 95 weight percent of acrylic acid and (b) 5 to 35 weight percent of a comonomer selected from the group consisting of an alkyl or a cyclohexyi methacrylate where the alkyl group has 1 to 30 carbon atoms and the cycloalkyl group is unsubstituted or substituted with 1 to 4 alkyl groups each having 1 to 4 carbon atoms, phenyl acryiate, phenoxyalkyl acryiate where the alkyl has 2 to 6 carbon atoms and dialkylaminoalkyl acryiate or methacrylate where each alkyl of the dialkyl has 1 to 8 carbons and the other alkyl has 2 to 6 carbon atoms, or a mixture thereof.

2. An interpolymer of Claim 1, wherein 70 to 100 percent of carboxylic groups of acrylic acid are neutralized with an alkali metal hydroxide or ammonia prior to polymerization.

3. An interpolymer of Claim 2 wherein 80 to

100 percent of carboxylic groups are neutralized.

4. An interpolymer of Claim 3 wherein the comonomer is selected from the group consisting essentially of alkyl methacrylate wherein the alkyl group has 1 to 18 carbons, cyclohexyi methacrylate, phenyl acryiate, phenoxyethyl acryiate and dimethylaminoethyl acryiate.

5. An interpolymer of Claim 3 obtained from photopolymerization of said monomers which additionally contain from 0.01 to 5 weight percent of a photoinitiator.

6. An interpolymer of Claim 5 , wherein the photoinitiator is used in the amount of from 0.1 to 5.0 weight percent.

7. An interpolymer of Claim 4 prepared by photopolymerizing said monomers which additionally contain from 0.1 to 5.0 weight percent of a photo initiator.

8. An interpolymer of Claim 7 wherein the comonomer is lauryl methacrylate.

9. An interpolymer of Claim 7 wherein the comonomer is 2-hydroxyethyl methacrylate.

10. An interpolymer of Claim 7 wherein the comonomer is phenoxyethyl acryiate.

11. An interpolymer of Claim 3 obtained from radiation polymerization by subjecting said monomers to electron beam radiation of sufficient intensity and quantity to cause said monomers to polymerize substantially completely.

12. An article of manufacture designed for absorbing body fluids comprising an absorbent cellulose material, and a polymer of Claim 1 in the form of a fiber or fibers.