RADIATION POLYMERIZED HYDROPHILIC INTERPOLYMERS OF UNSATURATED CARBOXYLIC ACID AND ESTERS

Abstract: A method of preparing highly absorbent interpolymers from an alkaline metal salt of acrylic acid, at least one alkyl acrylate or methacrylate wherein the alkyl group contains 10 to 30 carbon atoms and at least one alkyl acrylate or methacrylate wherein the alkyl group contains 1 to 4 carbon atoms by subjecting the mixture of monomers to an electron beam source causing said monomers to polymerize substantially completely. The resulting interpolymers are particularly useful in the preparation of highly absorbent personal hygiene and care products.

Description: RADIATIOLI ..POLYMERIZED HYDROPHILIC INTERPOLYMERS OF UNSATURATED CARBOXYLIC ACID AND ESTERS 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 unsaturated carboxylic acid monomers with alkyl acrylate 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 unsaturated copolymerizable carboxylic acids, at least one alkyl acrylate or methacrylate wherein the alkyl group has 10 to 30 carbon atoms and another alkyl acry¬ late or methacrylate wherein the alkyl group has 1 to 8 carbons. This composition alleviated many of the de¬ ficiencies of the earlier compositions. Further i - provements in the hydrophilic 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 copolymerization 30 to 90 percent of ^ the carboxylic groups were neutralized with an alkali metal or ammonia and (2) an aliphatic glycol, a plasti- cizer which is important in facilitating extrusion of the polymer. SUMMARY OF THE INVENTION A method for preparing an interpolymer from a mixture of monomers comprising 50 to 90 weight percent of acrylic acid, 60 to 100% of. the carboxylic groups of said acid having been neutralized prior to polymeriza¬ tion with an alkaline metal hydroxide, 2 to 20 weight percent of an alkyl acrylate or methacrylate wherein the alkyl group has 10 to 30 carbon atoms, 5 to 30 weight percent of an alkyl acrylate wherein the alkyl group has 1 to 9 carbon atoms by exposing said mixture to an elec¬ tron beam source of sufficient intensity to cause said monomers to polymerize. The monomers can be polymerized in any desired form, including films and fibers which would be most useful for absorption of water and body fluids, such as urine or blood. DETAILED DISCLOSURE This invention is directed to a method of pro- ducing interpolymers which have outstanding absorption and retention properties of water and ionic solutions such as urine or blood by the use of electron beam radiation. More specifically, the invention deals with a method of producing polymers from a monomer mixture comprising a) 50 to 90 weight percent of acrylic acid, 60 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 poly- merization, b) 2 to 25 weight percent of a higher.acrylic ester monomer of the formula R 1 0 CH 2 =C - C - OR, and wherein R 1 is hydrogen, methyl or ethyl and R is an alkyl group of 10 to 30 carbon atoms, c) 5 to 30 weight percent of a lower acryiic ester monomer of the formula R' O . if CH 2 =C * c " 0R " wherein R" is a lower alkyl group having 1 to 8 carbon atoms, 0 to 50 percent of said lower acrylic ester being replaced by acrylic or methacrylic nitrile or amide; said method comprising subjecting said monomers to elec¬ tron beam radiation of sufficient intensity to cause said monomers to polymerize. The higher acrylic ester monomers are those which have a long chain aliphatic group and may be represented by the formula R' O f II CH 2 =C—C-O-R wherein R is an alkyl group having from 10 to 30 carbon atoms, preferably 10 to 18 carbon atoms and R 1 is hydro¬ gen, methyl or ethyl group. Representative higher alkyl acrylic esters are decyl acrylate, isodecyl acrylate, lauryl acrylate, stearyl acrylate, behenyl acrylate and melissyl acrylate and the corresponding alkacrylates including methacrylates for example. Mixtures of two or three or more long chain acrylic esters may be success¬ fully polymerized with one of the carboxylic monomers to provide useful thickening resins of this invention. Particularly useful are those acrylates and methacrylates where the alkyl group contains 10 to 18 carbon atoms present preferably in amounts of about 5 to 20 weight percent of the total monomers. Outstanding polymers have been made with 15—5 weight percent isodecyl methacrylate, 10—3 weight percent lauryl methacrylate, 7—3 weight percent stearyl methacrylate. The lower acrylic esters can be represented by the formula R! 0 I II CH 2 =C—C-O-R wherein R is an alkyl, alkoxy, haloalkyl, cyanoalkyl, hydroxyalkyl and like groups having from 1to 8 carbon atoms and R' is hydrogen, methyl or ethyl group. Preferably R' is hydrogen or methyl and R is alkyl, most preferably methyl, and the lower ester is present in the amount of from 5 to 20 and most preferably 7 to 17 weight percent. Representative acrylates include methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, butyl acrylate, isobutyl acrylate, methyl methacrylate, methyl ethacrylate, ethyl methacrylate, octyl acrylate, heptyl acrylate, octyl methacrylate, isopropyl methacrylate, 2-ethyl-hexyl acrylate, nonyl acrylate, hexyl acrylate, n-hexyl methacrylate, hydroxy ethyl methacrylate, di ethylamino ethylmethacrylate. 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 degree of absorption and the tear strength needed for the film or fabric. Such additional monomers ae discussed below. One type of such additional monomers are α,β- olefinically unsaturated nitriles pref rably the ono- olefinically unsaturated nitriles having from 3 to 10 carbon atoms such as acrylonitxile, methacrylonitrile, ethacrylonitrile, chloroacrylonitrile, and the like. Most preferred nitriles are acrylonitriles and meth¬ acrylonitrile. 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 0 It CH 2 =C — C-NH-R 4 *3 5 wherein R3 is a member of the group consisting of hydro¬ gen and an alkyl group having from 1 to 4 carbon atoms and R 4 is a member of the group consisting of hydrogen and an alkyl group having from 1 to 6 carbon atoms. Representative amides include acrylamide, methacrylamide, 10 N-methyl acrylamide, N-t-butyl acrylamide, N-cyclohexyl acrylamide, N-ethyl acrylamide and others. Of the amides most preferred are acrylamide and methacrylamide. Other acrylic amides include N-alkylol amides of α,β-olefinically unsaturated carboxylic acids includ- 15 ing those having from 4 to 10 carbon atoms such as N- methylol acrylamide, N-ethanol acrylamide, N-propanol acrylamide, and the like. The preferred monomers of the N-alkylol amide type are the N-alkylol amides of c.,8- monoolefinically unsaturated monocarboxylic acids and 20 the most preferred is N-methylol acrylamide. Also useful are N-alkoxymeth l acrylamides which have the structure 0 H II I wherein R-. is selected from the group consisting of hydrogen and methyl, and R g is an alkyl group having 30 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 pre¬ ferred alkoxymethyl acrylamides are those wherein R g 35 is an alkyl group containing from 2 to 5 carbon atoms, and especially useful is N-butoxymethyl acrylamide. The monomer mixtures are prepared as aqueous dispersions which eliminates the need for organic solvents. This avoids the pollution problems caused by the 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 sul ates of alcohols having from 8 to 18 carbon atoms such as sodium lauryl sulfate; ethanolamine lauryl sulfate, ethylamine lauryl sulfate; 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 ammon¬ ium salts of sulfonated dicarboxyliσ acid esters such as sodium dioctyl sulfosuccinate, disodium-b-octadecyl sulfosuccinate; alkali metal or ammonium salts of free acid of complex organic mono- and diphosphate esters, sulfosuccinic acid derivatives (AEROSOL dispersants) , organic phosphate esters (GAFAC dispersants) and the like. Nonionic dispersants such as octyl- or nonyl- phenyl polyethoxyethanol as well as the PLURONIC and the TRITON dispersants may also be used. Also useful are amphoteric dispersants such as dicarbox lic coconut derivatives (MIRANOL) . Further examples of useful dis¬ persants are those disclosed beginning on page 102 in J. Van Alphen's "Rubber Chemicals", Elsevier Publishing Co., 1956. Although cross-linking agents are not required to obtain useful, highly absorbent compositions 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 to about 15% by weight based on the total weight of the monomers, and preferably about 1 to about 10%. Useful cross-linking monomers are polyalkenyl polyethers having more than one alkenyl ether grouping per molecule. The most useful possess alkenyl groups in which an olefinic double bond is attached to a terminal methylene group, CH_=C< . Other crosslinking monomers include for example, diallyl esters, dimethallyl ethers, allyl or methallyl acrylates and acrylamides, tetraallyl tin, tetravinyl silane, polyalkenyl methanes, diacry- lates and dimethacrylates, divinyl compounds as divinyl benzene, polyallyl phosphate, diallyloxy compounds and phosphite esters and the like. Typical agents are allyl pentaerythritol, allyl sucrose, trimethylolpropane triacrylate, 1,6-hexanediol diacrylate, pentaerythritol triacrylate, tetrameth lene dimethyacrylate, tetra- methylene diacrylate, ethylene diacrylate, ethylene dimethacrylate, triethylene glycol dimethacrylate, triallyl cyanurate, triallyl isocyanurate, diallyl itaconate, polyethylene glycol acrylates and methacrylates and the like. As already stated, polymers from the above discussed monomers are prepared by subjecting said mono¬ mers to electron beam radiation of sufficient intensity to cause said monomers to polymerize substantially com¬ pletely. 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 applica¬ tions 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. General¬ ly for the type of monomer systems employed in this in¬ vention 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 for each system taking all variables into consideration, i.e., the mono¬ mers employed, the thickness of the film, the desired speed of polymerization, the desired degree of polymer¬ ization and the rate of radiation. The copolymers of this invention can be radia¬ tion polymerized in any form, the film form being the most practical one. The resulting film 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 pul¬ verizing 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 nonwoven industry where there is need for polymers which will absorb and retain water and ionic physio¬ logical 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 per- sonal 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 O/'.PI 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 appli- cation, 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 fib¬ rous absorbent material, wherein during the construc¬ tion of this nonwoven fiber agglomerates or fibers of the polymers of this invention may be included and an additional impervious plastic later, 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 dispos¬ able nonwove s. The instant copolymers can also be used as flocculants in water treatment, in metallurgical pro¬ cesses, in ore beneficiation and flotation, in agricul- tural 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 copolymers, the monomers, water and a dispersant are mixed in a vessel. Then either a film or fibers are produced from the monomer mixture which, upon exposure to electron beam 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 acrylate in water to which is then added a dispersant. To the aqueous solution is then added a mixture of acrylate esters. Another method is to prepare the acrylate salt ' OREΛT; in situ by adding acrylic acid to the proper amount of cold aqueous base (e.g. KOH, NaOH or NH.OH) with cooling. To the aqueous solution is then added a mixture of the acrylate esters. The dispersant can be added at any time. Film Preparation: The aqueous monomer dis¬ persion 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 electron beam radiation which polymerizes the monomer mixture into a soft, pliable form. If desired this film can be dried in an oven at about 50 β C 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. The following example will further illustrate the present invention without introducing any limitations thereto. EXAMPLE The monomer mixture was prepared following the above described procedure using the following compon¬ ents: 83 g. acrylic acid 10 g. methyl methacrylate 7 g. . lauryl methacrylate 43 g. sodium hydroxide 152 g. water 1.24 g. AEROSOL A102 (disodium ethoxylated alcohol half-ester of sulfosuccinic acid (a dispersant) . The monomer mixture was 95% neutralized prior to polymerization. The mixture was spread to give a 2 mil film which was exposed to 0.4 M rad of electron beam radiation. The resulting film was soft, elastic and pliable. It absorbed more than 30 times its own weight of simulated urine composition which was estab¬ lished according to Demand Wettability Test described below. Demand Wettability Test (DWT) - A test diaper is con¬ structed 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 up 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 with¬ drawn 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 Measur- ing Absorbency Characteristics of Fabrics", Symposium Papers -INDA Technical Symposium, 1974, pp. 129-142.

Claims: CLAIMS 1. A method of producing an interpolymer from the comonomers comprising a) 50 to 90 weight percent of acrylic acid, 560 to 100% of the carboxylic groups having been neutral¬ ized with an alkali metal or ammonium base prior to polymerization. b) 2 to 25 weight percent of a higher acrylic ester monomer of the formula 10 R' 0 I II CH 2 =C - C - OR wherein R' is hydrogen, methyl or ethyl and R is an alkyl group of 10 to 30 carbon atoms, • j _5 c) 5 to 30 weight percent of a lower acrylic ester monomer of the formula R' O I II CH 2 =C - C - OR", and wherein R' is hydrogen, methyl or ethyl and R" is a 20 lower alkyl group having 1 to 8 carbon atoms, 0 to 50 percent of said lower acrylic ester being replaced by acrylic or methacrylic nitrile or amide; said method comprising subjecting said monomers to electron beam radiation of sufficient intensity and quantity to cause 25 said monomers to polymerize substantially completely. 2. A method of Claim 1 wherein said monomers are subjected to from 1 to 15 M rads of radiation. 3. A method of Claim 1 wherein additionally 0.1 to 5 percent of a dispersant is employed. 30 4. A method of Claim 3, wherein a) acrylic acid is in the amount of from 65 to 85 weight percent, b) the higher acrylic ester is an acrylate or methacrylate wherein R is an alkyl group of 16 to 21 35 carbon atoms, said ester being in the amount of from 5 to 20 percent, c) the lower acrylic ester is an alkyl acryl¬ ate or methacrylate which is in the amount of from 5 to 20 percent, and d) the dispersant is in the amount of from 0.1 to 1 percent. 5. A method of Claim 4 wherein a) the higher acrylic ester is selected from lauryl or stearyl acrylate or methacrylate, and b) the lower acrylic ester is methyl acrylate or methacrylate. 6. A method of Claim 1 or 3 containing additionally up to 15 weight percent of a cross-linking agent.

Inventors: GEORGE P
Applicants: GOODRICH CO B F, BF GOODRICH CO
Application year: 1980
Main classification: C08F2
IPC codes: A61L15, C08F2, C08F20, C08F220