FEDERALLY SPONSORED RESEARCH STATEMENT
REFERENCE TO MICROFICHE APPENDIX
FIELD OF THE INVENTION
This present invention describes absorbent compositions comprising sulfonated substantially random interpolymers. The sulfonated substantially random interpolymers can be used either alone or as blends with other polymers, and can be in either the sulfonic acid form, or as a neutralized or partially neutralized sulfonate salt. Another feature of the present invention is a process to prepare the sulfonated substantially random interpolymers, comprising the use of a hydrocarbon swelling agent, prior to or coincident with, exposure to the sulfonating agent. The sulfonated substantially random interpolymers or blends therefrom can be used to prepare structures such as pellets, film, ribbon, sheet, strand or fiber, or closed and open cell foams, and fabricated articles therefrom.
BACKGROUND OF THE INVENTION
The generic class of substantially random α-olefin/vinyl or vinylidene aromatic monomer interpolymers, and their preparation, are known in the art, such as described in EP 416 815 A2, the entire contents of which are herein incorporated by reference. These materials offer a wide range of material structures and properties, which makes them useful for varied applications.
The structure, thermal transitions and mechanical properties of substantially random interpolymers of ethylene and styrene containing up to 50 mole percent styrene have been described (see Y. W. Cheung, M. J. Guest; Proc. Antec '96 pages 1634-1637). These polymers were found to have glass transitions in the range −20° C. to +35° C., and show crystallinity below 25 mole percent styrene incorporation, and no measurable crystallinity above 25 mole percent styrene incorporation, that is, they are essentially amorphous. This ability to tailor the properties of the substantially random interpolymers by varying the relative amount of alpha olefin and vinyl or vinylidene aromatic monomer content provides a great deal of flexibility in tailoring their properties for a particular end use application. For example, copending U.S. application Ser. No. 09/317,389 filed on May 24, 1999 and PCT Publication WO 99/64500 (the entire contents of both of which are herein incorporated by reference) describes the use of substantially random interpolymers in formable membranes. Also, copending U.S. application Ser. No. 08/991,036 filed on Dec. 16 1997, and PCT Publication WO 99/31176 (the entire contents of both of which are herein incorporated by reference) describes the use of substantially random interpolymers in the form of barrier membranes for retarding gas migration.
Although of utility in their own right, Industry is constantly seeking to improve the applicability of these interpolymers. There are a number of applications where the ability to absorb or transport water or ions such as protons, would be highly advantageous if combined with the flexibility of being able to tailor the product properties of the substantially random interpolymers.
In order to facilitate water migration (for water absorbent applications) or proton transfer (for electrochemical applications), polystyrene and styrenic block copolymers are often sulfonated at the aromatic ring. U.S. Pat. Nos. 5,468,574 5,468,574 and 5,679,482 (the entire contents of both of which are incorporated herein by reference) disclose ion-conducting membranes prepared from polymers composed of sulfonated hydrogenated block copolymers of styrene and butadiene.
For certain applications, it would be preferable if the sulfonated aromatic rings be randomly dispersed throughout the polymer chains and, in order to precisely tailor the resulting product properties, that the sulfonation be done in a controlled fashion such that all degrees of sulfonation can be attained including surface sulfonation, bulk sulfonation or anything in between. In contrast, quite the opposite is desirable for ionomer applications. These require both low sulfonation conversion, (i.e. <approximately 10 percent approximately 10 percent) and localized sulfonation resulting in ionic domains called clusters, which propagate physical crosslinks at low levels.
This degree of control of the amount of sulfonation, the location (surface or bulk) and control over the dispersion cannot be accomplished using block or graft styrene copolymers. Such copolymers have the aromatic rings in discrete regions or domains within the polymer chains, or as in random styrenic copolymers, a random placement of the aromatic rings which is difficult to control. In high conversion sulfonation of polystyrene (or blocky styrenic copolymers), once a phenyl group is sulfonated, it acts as a polar director toward nearest neighbor phenyl group sulfonation. This results in blocky sulfonated segments early in sulfonation and can also result in higher melt viscosities, thus slowing the overall rate of sulfonation.
The majority of such sulfonated styrenic compositions to date have been prepared either in (a) a single phase system (uncrosslinked polymer in solution) or (b) a two phase system (crosslinked beads, fiber, etc). The most common solvents/swelling agents are the halogenated hydrocarbons such as methylene chloride, ethylene dichloride, and chlorobenzene.
PCT Publication WO 99/20691 (the entire contents of which are herein incorporated by reference) discloses surface sulfonated substantially random interpolymers and articles therefrom as in the form of sheet or film, and that films and sheets made from such polymers can be used to “improve the barrier properties of articles to gases”. The sulfonation of any particular phenyl group in such substantially random interpolymers has minimal directing effect on the sulfonation of other phenyl group in the interpolymer.
For substantially random interpolymers, which are uncrosslinked, we have surprisingly found that simple C3-C20 aliphatic and cycloaliphatic hydrocarbons such as hexanes, heptane, octane, cyclohexane and the like, provide rapid swelling capability without dissolution over a wide range of swelling rates. This allows for the use of sulfonation processes, which have a wide variation in residence times and thus can be either batch or continuous processes. Thus by judicious choice of process residence time and/or swelling agent one can control the degree of sulfonation of the substantially random interpolymers in a polymer (or fabricated article therefrom) such that one can achieve everything from simple surface sulfonation to almost complete bulk sulfonation.
In addition, use of the materials and processes of the present invention allows for the preparation of absorbent articles that exhibit an improved balance of wicking and absorption kinetics. This is provided by variation of both the nature of the substantially random interpolymer-based starting material (crystalline or amorphous, ionomeric or not, and degree of gel domains) as well as control of the process conditions and degree of sulfonation. Thus both variables can then be optimized to yield improvements in polymer performance and economics.
In one preferred embodiment of the present invention, such processes are applied to the manufacture of absorbent fibers comprising the sulfonated substantially random interpolymers. Existing technology for the preparation of absorbent fibers typically involves dry spinning (where a solution of polymer is spun and the solvent is evaporated is more costly). In addition, existing technology is limited to simple process control for variation in wicking/absorbent performance and the polymer composition typically has limited variability. The use of the sulfonated substantially random interpolymer-based materials for absorbent and/or superabsorbent applications represents a simple, low cost process in comparison to existing technology.
Thus the absorbent fibers of the present invention can be initially formed comprising the substantially random polymers which fibers can then be subsequently sulfonated to the required degree. Alternatively the fibers can be directly fabricated from the sulfonated substantially random interpolymers.
Similarly in the preparation of fabricated articles from the absorbent materials of the present invention, it is possible to either prepare the fabricated article from one or more sulfonated substantially random interpolymers (or blend therefrom). It is also possible to prepare the fabricated article from one or more substantially random interpolymers (or blend therefrom) with subsequent sulfonation.
In an especially preferred embodiment, the use of the materials and processes of the present invention allows the design of bicomponent/biconstituent materials comprising the sulfonated substantially random interpolymers for performance and cost optimization.
SUMMARY OF THE INVENTION
The present invention pertains to an absorbent polymer composition comprising
A) one or more sulfonated substantially random interpolymers comprising repeating units derived from;
a) ethylene and/or one or more alpha olefins;
b) one or more sulfonated vinyl or vinylidene aromatic monomers;
c) one or more vinyl or vinylidene aromatic monomers, or a combination of one or more vinyl or vinylidene aromatic monomers and one or more sterically hindered aliphatic or cycloaliphatic vinyl or vinylidene monomers; and optionally
B) one or more polymers other than said sulfonated substantially random interpolymer.
Uses of the compositions include the preparation of absorbent foams, fibers films and membranes as well as the preparation of absorbent fabricated articles for personal hygiene. These include diapers, sanitary napkins, adult incontinence pads, and highly absorbent wipes, and dust pickups.
BRIEF DESCRIPTION OF THE DRAWINGS
DETAILED DESCRIPTION OF THE INVENTION
All references herein to elements or metals belonging to a certain Group refer to the Periodic Table of the Elements published and copyrighted by CRC Press, Inc., 1989. Also any reference to the Group or Groups shall be to the Group or Groups as reflected in this Periodic Table of the Elements using the IUPAC system for numbering groups.
Any numerical values recited herein include all values from the lower value to the upper value in increments of one unit provided that there is a separation of at least 2 units between any lower value and any higher value. As an example, if it is stated that the amount of a component or a value of a process variable such as, for example, temperature, pressure, time and the like is, for example, from 1 to 90, preferably from 20 to 80, more preferably from 30 to 70, it is intended that values such as 15 to 85, 22 to 68, 43 to 51, 30 to 32 etc. are expressly enumerated in this specification. For values which are less than one, one unit is considered to be 0.0001, 0.001, 0.01 or 0.1 as appropriate. These are only examples of what is specifically intended and all possible combinations of numerical values between the lowest value and the highest value enumerated are to be considered to be expressly stated in this application in a similar manner.
The term “hydrocarbyl” as employed herein means any aliphatic, cycloaliphatic, aromatic, aryl substituted aliphatic, aryl substituted cycloaliphatic, aliphatic substituted aromatic, or aliphatic substituted cycloaliphatic groups.
The term “hydrocarbyloxy” means a hydrocarbyl group having an oxygen linkage between it and the carbon atom to which it is attached.
The term “interpolymer” is used herein to indicate a polymer wherein at least two different monomers are polymerized to make the interpolymer. This includes copolymers, terpolymers, etc.
The term “absorbent polymer composition” is used herein to indicate a polymer or blend of polymers able to take up at least 5, preferably at least 50, more preferably at least 100 percent of its own weight when placed in water.
The term “superabsorbent polymer” is used herein in the conventional sense in reference to polymeric materials that imbibe fluid and thereby form a swollen hydrogel. That is, a superabsorbent polymer is a hydrogel-forming polymeric gelling agent. In particular, the polymeric gelling agent comprises a substantially water-insoluble, partially neutralized, hydrogel-forming polymer material that is typically prepared from polymerizable, unsaturated, acid-containing monomers and often grafted onto other types of polymer moieties and then slightly crosslinked with agents such as, for example, triallyl amine. See, for example, U.S. Pat. No. 5,061,259 and U.S. Pat. No. 4,654,039, the disclosures of which are incorporated herein by reference, for additional description pertaining to superabsorbent polymers. Superabsorbent polymer is referenced herein by the acronym “SAP”.
The term “absorbent fabricated article” “is used herein to indicate an article such as a foam, fiber, film, membrane, or any article prepared therefrom which in turn comprises the absorbent polymer compositions of the present invention. More specifically, the term refers to devices that are placed against or in proximity to the body of the wearer to absorb and contain the various exudates discharged from the body. These exudates include, but are not limited to urine, menses, vaginal discharge, sweat and feces. The devices include, but are not limited to absorbent articles for personal hygiene such as diapers, sanitary napkins and adult incontinence pads,
The term “substantially random” (in the substantially random interpolymer comprising polymer units derived from ethylene and one or more α-olefin monomers with one or more vinyl or vinylidene aromatic monomers and/or sterically hindered aliphatic or cycloaliphatic vinyl or vinylidene monomers) as used herein means that the distribution of the monomers of said interpolymer can be described by the Bernoulli statistical model or by a first or second order Markovian statistical model, as described by J. C. Randall in Polymer Sequence Determination, Carbon-13 NMR Method, Academic Press New York, 1977, pp. 71-78. Preferably, substantially random interpolymers do not contain more than 15 percent of the total amount of vinyl aromatic monomer in blocks of vinyl aromatic monomer of more than 3 units. More preferably, the interpolymer is not characterized by a high degree of either isotacticity or syndiotacticity. This means that in the carbon-13 NMR spectrum of the substantially random interpolymer the peak areas corresponding to the main chain methylene and methine carbons representing either meso diad sequences or racemic diad sequences should not exceed 75 percent of the total peak area of the main chain methylene and methine carbons.
The term “degree of sulfonation” or “percent conversion” are used interchangeably and as used herein refer to the percentage of the aromatic content of the aromatic groups in the unsulfonated substantially random interpolymer which are converted to sulfonated aromatic groups on sulfonation (on a scale of 0 to 100). It is calculated from the percent weight gain of the interpolymer on sulfonation using the following formula:
Conversion=[(percent weight gain)(MW va)]/[(MW svas −MW va)(VA f)] where;
MWvas=vinyl aromatic sulfonic acid or sulfonate salt molecular weight
MWva=vinyl aromatic molecular weight
VAf=weight fraction of vinyl aromatic in starting substantially random interpolymer.
Thus for a substantially random interpolymer of ethylene and styrene containing 75 wt percent styrene and converted into the sodium sulfonate derivative, the calculation becomes:
% Conversion=[(% weight gain)(104)]/[(206−104)(0.75)]=(% weight gain)(1.36)×100/1
The term “homofil” as used herein refers to fiber which has a single polymer region or domain and does not have any other distinct polymer regions (as do bicomponent fibers), even though the polymer itself may have a plurality of phases or microphases.
The term “meltblown” is used herein in the conventional sense to refer to fibers formed by extruding the molten elastic composition through a plurality of fine, usually circular, die capillaries as molten threads or filaments into converging high velocity gas streams (e.g. air) which function to attenuate the threads or filaments to reduced diameters. Thereafter, the filaments or threads are carried by the high velocity gas streams and deposited on a collecting surface to form a web of randomly dispersed fibers with average diameters generally smaller than 10 microns.
The term “spunbond” is used herein in the conventional sense to refer to fibers formed by extruding the molten elastic composition as filaments through a plurality of fine, usually circular, die capillaries of a spinneret with the diameter of the extruded filaments then being rapidly reduced and thereafter depositing the filaments onto a collecting surface to form a web of randomly dispersed spunbond fibers with average diameters generally between about 7 and about 30 microns.
The term “nonwoven” as used herein and in the conventional sense means a web or fabric having a structure of individual fibers or threads which are randomly interlaid, but not in an identifiable manner as is the case for a knitted fabric.
The term “conjugated” refers to fibers which have been formed from at least two polymers extruded from separate extruders but meltblown or spun together to form one fiber.
The Substantially Random Interpolymers
The interpolymers used in the present invention include the substantially random interpolymers, which are then sulfonated either prior to or after fabrication. The substantially random interpolymers are prepared by polymerizing i) ethylene and/or one or more α-olefin monomers and ii) one or more vinyl or vinylidene aromatic monomers and/or one or more sterically hindered aliphatic or cycloaliphatic vinyl or vinylidene monomers, and optionally iii) other polymerizable ethylenically unsaturated monomer(s). Suitable α-olefins include for example, α-olefins containing from 3 to about 20, preferably from 3 to about 12, more preferably from 3 to about 8 carbon atoms. Particularly suitable are ethylene, propylene, butene-1,4-methyl-1-pentene, hexene-1 or octene-1 or ethylene in combination with one or more of propylene, butene-1,4-methyl-1-pentene, hexene-1 or octene-1. These α-olefins do not contain an aromatic moiety.
Suitable vinyl or vinylidene aromatic monomers, which can be employed to prepare the interpolymers, include, for example, those represented by the following formula:
wherein R1 is selected from the group of radicals consisting of hydrogen and alkyl radicals containing from 1 to about 4 carbon atoms, preferably hydrogen or methyl; each R2 is independently selected from the group of radicals consisting of hydrogen and alkyl radicals containing from 1 to about 4 carbon atoms, preferably hydrogen or methyl; Ar is a phenyl group or a phenyl group substituted with from 1 to 5 substituents selected from the group consisting of halo, C1-4-alkyl, and C1-4-haloalkyl; and n has a value from zero to about 4, preferably from zero to 2, most preferably zero. Exemplary vinyl or vinylidene aromatic monomers include styrene, vinyl toluene, α-methylstyrene, t-butyl styrene, chlorostyrene, including all isomers of these compounds, and the like. Particularly suitable such monomers include styrene and lower alkyl- or halogen-substituted derivatives thereof. Preferred monomers include styrene, α-methyl styrene, the lower alkyl-(C1-C4) or phenyl-ring substituted derivatives of styrene, such as for example, ortho-, meta-, and para-methylstyrene, the ring halogenated styrenes, para-vinyl toluene or mixtures thereof, and the like. A more preferred aromatic vinyl monomer is styrene.
By the term “sterically hindered aliphatic or cycloaliphatic vinyl or vinylidene compounds”, it is meant addition polymerizable vinyl or vinylidene monomers corresponding to the formula:
wherein A1 is a sterically bulky, aliphatic or cycloaliphatic substituent of up to 20 carbons, R1 is selected from the group of radicals consisting of hydrogen and alkyl radicals containing from 1 to about 4 carbon atoms, preferably hydrogen or methyl; each R2 is independently selected from the group of radicals consisting of hydrogen and alkyl radicals containing from 1 to about 4 carbon atoms, preferably hydrogen or methyl; or alternatively R1 and A1 together form a ring system. Preferred aliphatic or cycloaliphatic vinyl or vinylidene compounds are monomers in which one of the carbon atoms bearing ethylenic unsaturation is tertiary or quaternary substituted. Examples of such substituents include cyclic aliphatic groups such as cyclohexyl, cyclohexenyl, cyclooctenyl, or ring alkyl or aryl substituted derivatives thereof, tert-butyl, norbornyl, and the like. Most preferred aliphatic or cycloaliphatic vinyl or vinylidene compounds are the various isomeric vinyl-ring substituted derivatives of cyclohexene and substituted cyclohexenes, and 5-ethylidene-2-norbornene. Especially suitable are 1-, 3-, and 4-vinylcyclohexene and 5-ethylidene-2-norbornene. Simple linear non-branched α-olefins including for example, α-olefins containing from 3 to about 20 carbon atoms such as propylene, butene-1,4-methyl-1-pentene, hexene-1 or octene-1 are not examples of sterically hindered aliphatic or cycloaliphatic vinyl or vinylidene compounds.
Other optional polymerizable ethylenically unsaturated monomer(s) include norbornene and C1-10 alkyl or C6-10 aryl substituted norbornenes, with an exemplary interpolymer being ethylene/styrene/norbornene.
The most preferred substantially random interpolymers are the ethylene/styrene, ethylene/propylene/styrene, ethylene/styrene/norbornene, and ethylene/propylene/styrene/norbornene interpolymers.
The substantially random interpolymers include the pseudo-random interpolymers as described in EP-A-0,416,815 by James C. Stevens et al. and U.S. Pat. No. 5,703,187 by Francis J. Timmers, both of which are incorporated herein by reference in their entirety. The substantially random interpolymers can be prepared by polymerizing a mixture of polymerizable monomers in the presence of one or more metallocene or constrained geometry catalysts in combination with various cocatalysts. Preferred operating conditions for such polymerization reactions are pressures from atmospheric up to 3000 atmospheres and temperatures from −30° C. to 200° C. Polymerizations and unreacted monomer removal at temperatures above the autopolymerization temperature of the respective monomers may result in formation of some amounts of homopolymer polymerization products resulting from free radical polymerization.
Examples of suitable catalysts and methods for preparing the substantially random interpolymers are disclosed in U.S. application Ser. No. 702,475, filed May 20, 1991 (EP-A-514,828); as well as U.S. Pat. Nos. 5,055,438; 5,057,475; 5,096,867; 5,064,802; 5,132,380; 5,189,192; 5,321,106; 5,347,024; 5,350,723; 5,374,696; 5,399,635; 5,470,993; 5,703,187; and 5,721,185 all of which patents and applications are incorporated herein by reference.
The substantially random α-olefin/vinyl aromatic interpolymers can also be prepared by the methods described in JP 07/278230 employing compounds shown by the general formula
where Cp1 and Cp2 are cyclopentadienyl groups, indenyl groups, fluorenyl groups, or substituents of these, independently of each other; R1 and R2 are hydrogen atoms, halogen atoms, hydrocarbon groups with carbon numbers of 1-12, alkoxyl groups, or aryloxyl groups, independently of each other; M is a group IV metal, preferably Zr or Hf; most preferably Zr; and R3 is an alkylene group or silanediyl group used to cross-link Cp1 and Cp2.
The substantially random α-olefin/vinyl aromatic interpolymers can also be prepared by the methods described by John G. Bradfute et al. (W. R. Grace & Co.) in WO 95/32095; by R. B. Pannell (Exxon Chemical Patents, Inc.) in WO 94/00500; and in Plastics Technology, p. 25 (September 1992), all of which are incorporated herein by reference in their entirety.
Also suitable are the substantially random interpolymers which comprise at least one α-olefin/vinyl aromatic/vinyl aromatic/α-olefin tetrad disclosed in U.S. application Ser. No. 08/708,869 filed Sep. 4, 1996 and WO 98/09999 both by Francis J. Timmers et al., the entire contents of both of which are herein incorporated by reference. These interpolymers contain additional signals in their carbon-13 NMR spectra with intensities greater than three times the peak to peak noise. These signals appear in the chemical shift range 43.70-44.25 ppm and 38.0-38.5 ppm. Specifically, major peaks are observed at 44.1, 43.9, and 38.2 ppm. A proton test NMR experiment indicates that the signals in the chemical shift region 43.70-44.25 ppm are methine carbons and the signals in the region 38.0-38.5 ppm are methylene carbons.
Further preparative methods for the interpolymers used in the present invention have been described in the literature. Longo and Grassi (Makromol. Chem., Volume 191, pages 2387 to 2396 ) and D'Anniello et al. (Journal of Applied Polymer Science, Volume 58, pages 1701-1706 ) reported the use of a catalytic system based on methylalumoxane (MAO) and cyclopentadienyltitanium trichloride (CpTiCl3) to prepare an ethylene-styrene copolymer. Xu and Lin (Polymer Preprints, Am. Chem. Soc., Div. Polym. Chem.) Volume 35, pages 686,687 ) have reported copolymerization using a MgCl2/TiCl4/NdCl3/Al(iBu)3 catalyst to give random copolymers of styrene and propylene. Lu et al (Journal of Applied Polymer Science, Volume 53, pages 1453 to 1460 ) have described the copolymerization of ethylene and styrene using a TiCl4/NdCl3/MgCl2/Al(Et)3 catalyst. Sernetz and Mulhaupt, (Macromol. Chem. Phys., v. 197, pp. 1071-1083, 1997) have described the influence of polymerization conditions on the copolymerization of styrene with ethylene using Me2Si(Me4Cp)(N-tert-butyl)TiCl2/methylaluminoxane Ziegler-Natta catalysts. Copolymers of ethylene and styrene produced by bridged metallocene catalysts have been described by Arai, Toshiaki and Suzuki (Polymer Preprints, Am. Chem. Soc., Div. Polym. Chem.) Volume 38, pages 349, 350 ) and in U.S. Pat. No. 5,652,315, issued to Mitsui Toatsu Chemicals, Inc. The manufacture of α-olefin/vinyl aromatic monomer interpolymers such as propylene/styrene and butene/styrene are described in U.S. Pat. No. 5,244,996, issued to Mitsui Petrochemical Industries Ltd or U.S. Pat. No. 5,652,315 also issued to Mitsui Petrochemical Industries Ltd or as disclosed in DE 197 11 339 A1 and U.S. Pat. No. 5,883,213 to Denki Kagaku Kogyo KK. All the above methods disclosed for preparing the interpolymer component are incorporated herein by reference. Also, although of high isotacticity and therefore not “substantially random”, the random copolymers of ethylene and styrene as disclosed in Polymer Preprints, Vol. 39, No. 1, March 1998 by Toru Aria et al. can also be employed as blend components for the foams of the present invention.
While preparing the substantially random interpolymer, an amount of atactic vinyl aromatic homopolymer may be formed due to homopolymerization of the vinyl aromatic monomer at elevated temperatures. The presence of vinyl aromatic homopolymer is in general not detrimental for the purposes of the present invention and can be tolerated. The vinyl aromatic homopolymer may be separated from the interpolymer, if desired, by extraction techniques such as selective precipitation from solution with a non solvent for either the interpolymer or the vinyl aromatic homopolymer. For the purpose of the present invention it is preferred that no more than 30 weight percent, preferably less than 20 weight percent based on the total weight of the interpolymers of atactic vinyl aromatic homopolymer is present.
The Sulfonated Substantially Random Interpolymers
The substantially random interpolymers can be sulfonated by any suitable means known in the art for sulfonating aromatic ring compounds including using so called “wet” (sulfuric acid, oleum, chlorosulphonic acid, SO3 complexes) or gaseous (air sulfonation, SO3 vapor phase sulfonation) reagents.
A preferred method involves contacting the substantially random interpolymer with a fluid phase of sulfur trioxide, present as minor composition (less than 50 percent by weight) in another carrier gas such as nitrogen or air at a temperature of from about 20° C. to about 200° C., preferably from about 50° C. to about 150° C., more preferably from about 80° C. to about 150° C. Optionally, a C1-C20, preferably C1-C10, more preferably C1-C6 hydrocarbon swelling agent (including but not exclusively ethane, propane, butane, pentane, hexane, and cyclohexane) can be incorporated with the carrier gas or, alternatively the interpolymer can be exposed to the swelling agent prior to sulfonation.
The substantially random interpolymer can also be sulfonated by contacting with a liquid phase of oleum (5-60 percent sulfur trioxide dissolved in sulfuric acid), at a temperature of from about −20° C. to about 100° C., preferably from about 0° C. to about 80° C., more preferably from about 0° C. to about 50° C. Optionally, the polymer can be exposed to a a C1-C20, preferably C1-C10, more preferably C1-C6 hydrocarbon swelling agent (including, but not exclusively, pentane, hexane, and cyclohexane) either prior to or concurrently with sulfonation.
Another suitable method is that described by Turbuk in U.S. Pat. No. 3,072,618 which is incorporated herein by reference in its entirety. The substantially random interpolymer is sulfonated by contacting with a sulfonating complex comprising the reaction product of about 2 to about 4 moles of sulfur trioxide and 1 mole of a lower trialkyl phosphate or phosphite at a temperature of from about 25° C. to about 100° C., preferably from about 50° C. to about 83° C., more preferably from about 75° C. to about 83° C. followed by recovering the resultant sulfonated polymer. Sulfur trioxide can also be supplied in the form of chlorosulfonic acid or fuming sulfuric acid. Particularly suitable trialkyl phosphates include trimethyl phosphate, triethyl phosphate, tripropyl phosphate, tributyl phosphate, trimethyl phosphite, triethyl phosphite, tripropyl phosphite, tributyl phosphate, hydrogen phosphate, diethyl hydrogen phosphate, dimethyl hydrogen phosphite, diethyl hydrogen phosphite, methyl dihydrogen phosphate, ethyl dihydrogen phosphate, methyl dihydrogen phosphite, ethyl dihydrogen phosphite, any combination thereof and the like.
Another method of sulfonation is that described by H. S. Makowski, R. D. Lundberg, and G. H. Singhal in U.S. Pat. No. 3,870,841 which is incorporated herein by reference in its entirety. In this method, a mixed anhydride is prepared by mixing sulfuric acid with acetic anhydride at a temperature of from about −70° C. to about 130° C. (preferably between −20 to about 20° C.) followed by adding this mixture to a solution of the interpolymer in a chlorinated solvent such as, for example dichloroethane, methylene chloride, chloroform, tetrachloroethane, trichloroethane or combinations thereof at a temperature of from about −20° C. to about 100° C.
The salts of the sulfonated interpolymers can be prepared by reacting with a neutralizing agent or base (ammonia, alkylamines, ammonium hydroxide, sodium hydroxide, etc.) in a solvent or as a gas phase at temperatures of from about −20° C. to about 100° C., preferably from about 40° C. to about 100° C., more preferably from about 60° C. to about 80° C. for a period of time to convert essentially all of the SO3H groups to the neutralized salt, —SO3Me (where Me is the counterion). This time is usually from about 0.01 to about 240, preferably from about 1 to about 60, more preferably from about 5 to about 30 minutes. Me can include a group 1, 2, 7, 11 or 12 metals of the Periodic Table of Elements. The amount of the neutralizing agent employed is that which is sufficient to convert substantially all of the sulfonate groups to the neutralized salt, usually from about 1 to about 1.5, preferably from about 1 to about 1.1, more preferably about 1 mole of the neutralizing agent per mole of sulfonate group present in the interpolymer. The amount of solvent employed is that amount sufficient to create a substantially homogeneous mixture, which can range from about 5 to about 95, preferably from about 10 to about 80, more preferably from about 15 to about 75 percent by weight based on the combined weight of the mixture.
The sulfonated substantially random interpolymers comprise from about 35 to about 98.5 mol percent of polymer units derived from ethylene and/or said α-olefin which comprises at least one of propylene, 4-methyl-1-pentene, butene-1, hexene-1 or octene-1; and from about 1.5 to about 65 mol percent of polymer units derived from one or more sulfonated vinyl aromatic monomers which are mono substituted with either a sulfonic acid group or a sulfonic acid salt represented by the following formula;
wherein R1 is selected from the group of radicals consisting of hydrogen and alkyl radicals containing from 1 to about 4 carbon atoms, each R2 is independently selected from the group of radicals consisting of hydrogen and alkyl radicals containing from 1 to about 4 carbon atoms, Ar is a phenyl group or a phenyl group substituted with from 1 to 5 substituents selected from the group consisting of halo, C1-4-alkyl, and C1-4-haloalkyl; and n has a value from zero to about 4, and X is hydrogen, a group 1, 2, 7, 11 or 12 metal ion, an ammonium salt NR′4 + where R′ is hydrogen or a C3-C20 alkyl or a combination thereof; Preferably suitable metal salts which can be employed herein include the salts formed from group 1, 2, 7, 11 or 12 metals as well as the ammonium (NH4 +) salts. Particularly suitable metals of group 1, 2, 7, 11, or 12 include Na, K, Li, Co, Cu, Mg, Ca, Mn, or Zn. Also suitable are the hydroxides of such metals. Particularly suitable salts and hydroxides include the hydroxides, acetates, hexanoates, and oxides of Na, Li, K, Ca, Mg, Cu, Co, Zn Al, NH4+, and any combination thereof and the like. Also suitable are the hydrates of the aforementioned salts.
In the case where the sulfonation conversion is less than 100 percent, the sulfonated substantially random interpolymers would thus also comprise polymer units derived from the starting substantially random interpolymer namely ethylene and/or one or more α-olefin monomers and ii) one or more vinyl or vinylidene aromatic monomers and/or one or more sterically hindered aliphatic or cycloaliphatic vinyl or vinylidene monomers, and optionally iii) other polymerizable ethylenically unsaturated monomer(s).
Additional Blend Component(s).
The polymers used to prepare the absorbent compositions of the present invention can also comprise one or more polymers other than the sulfonated substantially random interpolymer. These additional polymers can comprise homogenous α-olefin homopolymer or interpolymers comprising polypropylene, propylene/C4-C20 α-olefin copolymers, polyethylene, and ethylene/C3-C20 α-olefin copolymers, the interpolymers can be either heterogeneous ethylene/α-olefin interpolymers, preferably a heterogeneous ethylene/C3-C8 α-olefin interpolymer, most preferably a heterogeneous ethylene/octene-1 interpolymer or homogeneous ethylene/α-olefin interpolymers, including the substantially linear ethylene/α-olefin interpolymers, preferably a substantially linear ethylene/α-olefin interpolymer, most preferably a substantially linear ethylene/C3-C8 α-olefin interpolymer; or a heterogeneous ethylene/α-olefin interpolymer; or a thermoplastic olefin, preferably an ethylene/propylene rubber (EPM) or ethylene/propylene diene monomer terpolymer (EPDM) or isotactic polypropylene, most preferably isotactic polypropylene; or a styreneic block copolymer, preferably styrene-butadiene (SB), styrene-isoprene(SI), styrene-butadiene-styrene (SBS), styrene-isoprene-styrene (SIS) or styrene-ethylene/butene-styrene (SEBS) block copolymer, most preferably a styrene-butadiene-styrene (SBS) copolymer; or styrenic homopolymers or copolymers, preferably polystyrene, high impact polystyrene, polyvinyl chloride, copolymers of styrene and at least one of acrylonitrile, methacrylonitrile, maleic anhydride, or α-methyl styrene, most preferably polystyrene, or elastomers, preferably polyisoprene, polybutadiene, natural rubbers, ethylene/propylene rubbers, ethylene/propylene diene (EPDM) rubbers, styrene/butadiene rubbers, thermoplastic polyurethanes, most preferably thermoplastic polyurethanes; or engineering thermosplastics, preferably poly(methylmethacrylate) (PMMA), cellulosics, nylons, poly(esters), poly(acetals); poly(amides), the poly(arylate), aromatic polyesters, poly(carbonate), poly(butylene) and polybutylene and polyethylene terephthalates, most preferably poly(methylmethacrylate) (PMMA), and poly(esters).
Especially preferred as the other polymer component is one or more existing water retentive polymers. Such polymers can comprise nonionic polymers like polyacrylamide, polyethylene oxide, polyvinyl alcohol; anoionic polymers and their neutralized salts including polyacrylic acid, graft copolymers including starch-g-polyacrylic acid, poly(vinyl alcohol-g-polyacrylic acid), hydrolyzed starch-g-poly(acrylonitrile), carboxymethylcellulose, alginic acid; cationic polymers including poly(diallyldimethylammonium chloride, polyvinylpyridine, cationic starches, and hydroyzed chitin. These materials can be optionally crosslinked to prevent dissolution into water.
Also included as a potential component of the polymer compositions used in the present invention are various organic and inorganic fillers, the identity of which depends upon the type of application for which the composition is to be utilized. The fillers can also be included in the sulfonated substantially random interpolymer, component, the other polymer component and/or the overall blend compositions employed in the present invention. Representative examples of such fillers include organic and inorganic fibers such as those made from asbestos, boron, graphite, ceramic, glass, metals (such as stainless steel) or polymers (such as aramid fibers) talc, carbon black, carbon fibers, calcium carbonate, alumina trihydrate, glass fibers, marble dust, cement dust, clay, feldspar, silica or glass, fumed silica, alumina, magnesium oxide, magnesium hydroxide, antimony oxide, zinc oxide, barium sulfate, aluminum silicate, magnesium aluminum silicate, calcium silicate, titanium dioxide, titanates, aluminum nitride, B2O3, nickel powder or chalk.
Other representative organic or inorganic, fiber or mineral, fillers include carbonates such as barium, calcium or magnesium carbonate; fluorides such as calcium or sodium aluminum fluoride; hydroxides such as aluminum hydroxide; metals such as aluminum, bronze, lead or zinc; oxides such as aluminum, antimony, magnesium or zinc oxide, or silicon or titanium dioxide; silicates such as asbestos, mica, clay (kaolin or calcined kaolin), feldspar, glass (ground or flaked glass or hollow glass spheres or microspheres or beads, whiskers or filaments), nepheline, perlite, pyrophyllite, talc or wollastonite; sulfates such as barium or calcium sulfate; metal sulfides; cellulose, in forms such as wood or shell flour; calcium terephthalate; and liquid crystals. Also included are the various classes of fillers that act as anti-microbial agents. Mixtures of more than one such filler may be used as well.
Additives such as antioxidants (e.g., hindered phenols such as, for example, Irganox™ 1010), phosphites (e.g., Irgafos™ 168) both trademarks of, and commercially available from, Ciba Geigy Corporation), U.V. stabilizers, cling additives (e.g., polyisobutylene), antiblock additives, colorants, pigments, and the like are optionally also included in in the sulfonated substantially random interpolymer, component, the other polymer component and/or the overall blend compositions employed in the present invention, to the extent that they do not interfere with the enhanced properties discovered by Applicants.
Processing aids, which are also referred to herein as plasticizers, can also be included in the sulfonated substantially random interpolymer, component, the other polymer component and/or the overall blend compositions employed in the present invention. These include the phthalates, such as dioctyl phthalate and diisobutyl phthalate, natural oils such as lanolin, and paraffin, naphthenic and aromatic oils obtained from petroleum refining, and liquid resins from rosin or petroleum feedstocks. Exemplary classes of oils useful as processing aids include white mineral oil (such as Kaydol™ oil (available from and a registered trademark of Witco), and Shellflex™ 371 naphthenic oil (available from and a registered trademark of Shell Oil Company). Another suitable oil is Tuflo™ oil (available from and a registered trademark of Lyondell).
Tackifiers, can also be included in the sulfonated substantially random interpolymer, component, the other polymer component and/or the overall blend compositions employed in the present invention, to alter the processing performance of a polymer and thus extend the available application temperature window of the application. A suitable tackifier may be selected on the basis of the criteria outlined by Hercules in J. Simons, Adhesives Age, “The HMDA Concept: A New Method for Selection of Resins”, November 1996. This reference discusses the importance of the polarity and molecular weight of the resin in determining compatibility with the polymer. In the case of substantially random interpolymers of at least one α-olefin and a vinyl aromatic monomer, preferred tackifiers will have some degree of aromatic character to promote compatibility, particularly in the case of substantially random interpolymers having a high content of the vinyl aromatic monomer.
Tackifying resins can be obtained by the polymerization of petroleum and terpene feedstreams and from the derivatization of wood, gum, and tall oil rosin. Several classes of tackifiers include wood rosin, tall oil and tall oil derivatives, and cyclopentadiene derivatives, such as are described in United Kingdom patent application GB 2,032,439A. Other classes of tackifiers include aliphatic C5 resins, polyterpene resins, hydrogenated resins, mixed aliphatic-aromatic resins, rosin esters, natural and synthetic terpenes, terpene-phenolics, and hydrogenated rosin esters.
The additives are advantageously employed in functionally equivalent amounts known to those skilled in the art. For example, the amount of antioxidant employed is that amount which prevents the polymer or polymer blend from undergoing oxidation at the temperatures and environment employed during storage and ultimate use of the polymers. Such amount of antioxidants is usually in the range of from 0.01 to 10, preferably from 0.05 to 5, more preferably from 0.1 to 2 percent by weight based upon the weight of the polymer or polymer blend. Similarly, the amounts of any of the other enumerated additives are the functionally equivalent amounts such as the amount to render the polymer or polymer blend antiblocking, to produce the desired amount of filler loading to produce the desired result, to provide the desired color from the colorant or pigment. Such additives are advantageously employed in the range of from 0.05 to 50, preferably from 0.1 to 35, more preferably from 0.2 to 20 percent by weight based upon the weight of the polymer or polymer blend. Fillers, however can be advantageously employed in amounts up to about 90 percent by weight based on the weight of the polymer or polymer blend.
The sulfonated substantially random interpolymers and blends therefrom of the present invention can be available in a wide range of structures including but not limited to, fibers, films, sheet, and foams, and fabricated articles therefrom
Preparation of Fibers Comprising the Sulfonated Substantially Random Interpolymers
In one embodiment of the present invention, the sulfonated substantially random interpolymers are used to prepare absorbent fibers. The fibers can be prepared from the sulfonated substantially random interpolymers using the methods described herein. Alternatively, the fibers can be prepared from the substantially random interpolymers and then the resulting fiber can then be sulfonated either after or during the fiber manufacturing process, using the sulfonation processes described herein. In such a post fiber sulfonation process, the nature and incorporation of the previously described swelling and sulfonation agents and reaction times can then be tailored to the particular fiber preparation.
The main advantages of the sulfonated substantially random interpolymers versus other polymers such as sulfonated polystyrene for use in fibers are the improved physical properties such as flexibility resulting from the occurrence of aromatic and ethylene and/or alpha olefin functionality in the polymer and their relative distributions. Polystyrene and sulfonated polystyrene by itself will be very brittle. In addition, the olefinic groups of the sulfonated substantially random interpolymer component provide improved compatibility with a polyolefin core fiber in bicomponent structures. In addition, the ethylene groups can provide some degree of hydrophobicity to the fiber, keeping it from dissolving even when all the aromatic rings are sulfonated.
The absorbent fibers of the present invention can be prepared using techniques well known in the art including for example, dry lay, wet lay, carding, spin bonding, garnetting, and air laying processes. (See, e.g. U.S. Pat. Nos. 5,108,827, 5,487,943, 4,176,108 and 4,814,226). Nonwoven fabrics and articles can be prepared using binding techniques including, for example, hot roll, hot press, lamination, hot air bonding, calendar, spray, dip and roll transfer processes. (See, e.g., U.S. Pat. Nos. 5,824,610, 5,593,768, 5,169,580 and 5,244,695).
For the absorbent fibers of the present invention, the diameter can be widely varied. Fiber diameter can be measured and reported in a variety of fashions. Generally, fiber diameter is measured in denier per filament. Denier is a textile term that is defined as the grams of the fiber per 9000 meters of that fiber's length. Monofilament generally refers to an extruded strand having a denier per filament greater than 15, usually greater than 30. Fine denier fiber generally refers to fiber having a denier of about 15 or less. Microdenier (aka microfiber) generally refers to fiber having a diameter not greater than about 100 micrometers. The fiber denier can be adjusted to suit the capabilities of the finished article and as such, would preferably be: from about 0.5 to about 30 denier/filament for melt blown; from about 1 to about 30 denier/filament for spunbond; and from about 1 to about 20,000 denier/filament for continuous wound filament. Nonetheless, preferably, the nominal denier is greater than 37, more preferably greater than or equal to 55 and most preferably greater than or equal to 65. These preferences are due to the fact that typically durable apparel employ fibers with deniers greater than or equal to about 40.
Finishing operations can optionally be performed on the fibers of the present invention. For example, the fibers can be texturized by mechanically crimping or forming such as described in Textile Fibers, Dyes, Finishes, and Processes: A Concise Guide, by Howard L. Needles, Noyes Publications, 1986, pp. 17-20.
The interpolymer compositions used to make the fibers of the present invention or the fibers themselves (both prior to or post sulfonation) may also be modified by various cross-linking processes using curing methods at any stage of the fiber preparation including, but not limited to, before during, and after drawing at either elevated or ambient temperatures. Such cross-linking processes include, but are not limited to, peroxide-, silane-, sulfur-, radiation-, or azide-based cure systems. A full description of the various cross-linking technologies is described in copending U.S. patent application Ser. Nos. 08/921,641 and 08/921,642 both filed on Aug. 27, 1997, the entire contents of both of which are herein incorporated by reference.
Dual cure systems, which use a combination of heat, moisture cure, and radiation steps, may be effectively employed. Dual cure systems are disclosed and claimed in U.S. patent application Ser. No. 536,022, filed on Sep. 29, 1995, in the names of K. L. Walton and S. V. Karande, incorporated herein by reference. For instance, it may be desirable to employ peroxide crosslinking agents in conjunction with silane crosslinking agents, peroxide crosslinking agents in conjunction with radiation, sulfur-containing crosslinking agents in conjunction with silane crosslinking agents, etc.
The polymer compositions may also be modified by various cross-linking processes including, but not limited to the incorporation of a diene component as a termonomer in its preparation and subsequent cross linking by the aforementioned methods and further methods including vulcanization via the vinyl group using sulfur for example as the cross linking agent.
The fibers of the present invention may be surface functionalized by methods including, but not limited to, chlorination using chemical treatments for permanent surfaces or incorporating a temporary coating using the various well known spin finishing processes.
The fibers comprising the sulfonated substantially random interpolymers can be essentially in the form of any fibers previously known in the art. This includes the homofil fibers including staple fibers, spunbond fibers or melt blown fibers (using, e.g., systems as disclosed in U.S. Pat. No. 4,340,563 (Appel et al.), U.S. Pat. No. 4,663,220 (Wisneski et al.), U.S. Pat. No. 4,668,566 (Braun), or U.S. Pat. No. 4,322,027 (Reba), all of which are incorporated herein by reference), and gel spun fibers (e.g., the system disclosed in U.S. Pat. No. 4,413,110 (Kavesh et al.), incorporated herein by reference). Staple fibers can be melt spun (i.e., they can be extruded into the final fiber diameter directly without additional drawing), or they can be melt spun into a higher diameter and subsequently hot or cold drawn to the desired diameter using conventional fiber drawing techniques.
The shape of the fiber is not limited. For example, typical fiber has a circular cross-sectional shape, but sometimes fibers have different shapes, such as a trilobal shape, or a flat (i.e., “ribbon” like) shape. The absorbent fibers disclosed herein, are not limited by the shape of the fiber.
The fibers comprising the sulfonated substantially random interpolymers can also be used as bonding fibers, especially where the inventive fibers have a lower melting point than the surrounding matrix fibers. In a bonding fiber application, the bonding fiber is typically blended with other matrix fibers and the entire structure is subjected to heat, where the bonding fiber melts and bonds the surrounding matrix fiber. Typical matrix fibers which benefit from use of the inventive fibers disclosed herein include, but are not limited to, poly(ethylene terephthalate) fibers, cotton fibers, nylon fibers, polypropylene fibers, heterogeneously branched polyethylene fibers, homogeneously branched ethylene polymer fibers, linear polyethylene homopolymer fibers and the like and combinations thereof. The diameter of the matrix fiber can vary depending upon the end use application.
These fibers of the present invention can comprise more than one polymer, including wettable binder fibers (U.S. Pat. No. 5,894,000); hydrophilic fibers, superabsorbent polymer fibers (U.S. Pat. Nos. 5,593,399 and 5,698,480); and the fibers listed in U.S. Pat. No. 4,176,108. The teachings of these patents, and all other patents cited herein, are hereby incorporated by reference in their entirety. Mixtures of fibers can also be employed. Examples of common materials used in the manufacture of fibers available for mixing with the fibers of the present invention include natural and synthetic materials such as, for example, polyethylene terephthalate, polyethylene, polypropylene, polyurethane, nylon, rayon, and cotton and other cellulosic materials.
In an especially preferred embodiment, the absorbent fibers comprising the sulfonated substantially random interpolymers are conjugated or bicomponent or multi-component fibers (as disclosed in U.S. Pat. Nos. 5,843,063; 5,169,580; 4,634,739; 5,921,973; 4,483,976; and 5,403,444 which are hereby incorporated by reference in their entirety). The polymer components are usually different from each other, although conjugated fibers may be mono-component fibers. The polymers are arranged in substantially constantly positioned distinct zones across the cross-section of the conjugated fibers and extend continuously along the length of the conjugated fibers. The configuration of the conjugated fibers of the present invention can be, for example, a sheath/core arrangement (wherein one polymer is surrounded by another), a side by side arrangement, a pie arrangement or an “islands-in-the sea” arrangement. Conjugated fibers are described in U.S Pat. No. 5,108,820 to Kaneko et al.; U.S. Pat. No. 5,336,552 to Strack et al.; and U.S. Pat. No. 5,382,400 to Pike et al., the disclosures of all of which are incorporated herein by reference. The fibers comprising the sulfonated substantially random interpolymers of the present invention can be in a conjugated configuration, for example, as a core or sheath, or both. Different sulfonated substantially random interpolymers can also be used independently as the sheath and the core in the same fiber, especially where the sheath component has a lower melting point than the core component.
Fabrics and Fabricated Articles
Fabrics made from such novel absorbent fibers of the present invention can include both woven and nonwoven fabrics. Nonwoven fabrics can be made variously, including spunlaced (or hydrodynamically entangled) fabrics as disclosed in U.S. Pat. No. 3,485,706 (Evans) and U.S. Pat. No. 4,939,016 (Radwanski et al.), the disclosures of which are incorporated herein by reference; by carding and thermally bonding staple fibers; by spunbonding continuous fibers in one continuous operation; or by melt blowing fibers into fabric and subsequently calandering or thermally bonding the resultant web. These various nonwoven fabric manufacturing techniques are well known to those skilled in the art and the disclosure is not limited to any particular method. Other structures made from such fibers are also included within the scope of the invention, including e.g., blends of these novel fibers with other fibers (e.g., poly(ethylene terephthalate) (PET) or cotton or wool or polyester). For example, nonwoven fabrics of the invention may be used in filtration applications, medical applications, clean room applications, garments, barrier products, sterilization wraps, interlinings, cushioning, CSR wrap, stretchable absorbent materials, and wipes.
The absorbent articles of the present invention can be utilized in disposable products which are capable of absorbing significant quantities of body fluids, such as urine and water in body wastes. Such articles may be prepared in the form of sanitary napkins and other feminine hygiene products, disposable diapers, adult incontinence briefs, adult incontinence pads and the like.
In a preferred embodiment of the present invention the sulfonated substantially random interpolymer fibers are used in the construction of diapers, as part of the distribution, acquisition and/or surge layers and in the core. (See, e.g., U.S. Pat. Nos. 5,108,827, 5,893,063, 5,593,768, 5,646,077, and 5,244,695). Especially preferred absorbent articles of this invention are disposable diapers. Articles in the form of disposable diapers are fully described in Duncan and Baker, U.S. Pat. No. Re. 26,151, Issued Jan. 31, 1967; Duncan, U.S. Pat. No. 3,592,194, Issued Jul. 13, 1971; Duncan and Gellert, U.S. Pat. No. 3,489,148, Issued Jan. 13, 1970; and Buell, U.S. Pat. No. 3,860,003, Issued Jan. 14, 1975; which patents are incorporated herein by reference.
One means for increasing the liquid retention capabilities of such products is through the addition of superabsorbents, which are also referred to as hydrogels and hydrocolloids. This is particularly true in the case of diapers, training pants and incontinence garments. As these products have become more and more sophisticated, the manufacturers of these products have reduced the amount of wood pulp or fluff in the absorbent layers of these materials and replaced the fluff with varying amounts of superabsorbent in the form of particles. As the amount of superabsorbent has increased in these absorbent structures, a problem called gel-blocking has arisen. Early superabsorbents were made in particle form and while being capable of absorbing many times their own weight in liquid such as water and urine, would not hold their particle or generally spherical shape as they absorbed liquid. Instead, they would turn into a mushy gel which would swell, fill the voids between the wood pulp fibers and quickly turned the structure into a gelled mess. This is now referred to as gel blocking. The absorbent fibers of the present invention may be used as the sole superabsorbent core component or may be used in addition to the aforementioned core components of the prior art to facilitate liquid transport and alleviate the problem of gell blocking.
Nonwoven products prepared with the absorbent fibers of the invention may also be useful in specialty applications such as the preparation of hygiene articles having patterned component distribution (see, e.g., U.S. Pat. Nos. 5,843,063, 5,593,399 and 5,941,862) and flushable diapers (see, e.g., U.S. Pat. No. 5,770,528).
Woven fabrics can also be made which comprise the absorbent fibers of the present invention. The various woven fabric-manufacturing techniques are well known to those skilled in the art and the disclosure is not limited to any particular method. Woven fabrics are typically stronger and more heat resistant and are thus used typically in durable, non-disposable applications as for example in the woven blends with polyester and polyester cotton blends. The woven fabrics comprising the absorbent fibers of the present invention can be used in applications including but not limited to, upholstery, athletic apparel, carpet, fabrics, bandages. In addition the fibers of the present invention can be included in the woven fabrics of the prior art (e.g. as staple fibers in existing fabrics) to promote absorbency.
The novel absorbent fibers described herein also can be used in a spunlaced (or hydrodynamically entangled) process to make novel structures. For example, U.S. Pat. No. 4,801,482 (Goggans), the disclosure of which is incorporated herein by reference, discloses a sheet which can now be made with the novel fibers/fabric described herein. Composites that utilize very high molecular weight linear polyethylene or copolymer polyethylene also benefit from the novel fibers disclosed herein. For example, for the novel fibers that have a low melting point, such that in a blend of the novel fibers and very high molecular weight polyethylene fibers (as described in U.S. Pat. No. 4,584,347 by Harpell et al., the disclosure of which is incorporated herein by reference), the lower melting fibers bond the high molecular weight polyethylene fibers without melting the high molecular weight fibers, thus preserving the high strength and integrity of the high molecular weight fiber.
Absorbent and Superabsorbent Foams
Absorbent and superabsorbent foams have attracted considerable attention as candidates for replacing multiple components of an absorbent core. They hold the potential of offering some of the same advantages sought for film or fiber forms; performing the absorbent functions of multiple components of a conventional diaper, not migrating in the product, and not creating dust. Several different approaches to superabsorbent polymer foams have been described in the patent literature. One approach seeks to embed conventional superabsorbent granules in non-superabsorbent foam. A second option is to utilize capillary suction forces, instead of or in addition to osmotic pressure, to create an absorbent material.
The incorporation of a conventional granular superabsorbent polymer into a foam structure is a relatively obvious extension of superabsorbent polymer technology. For any composite structure comprising a foam and a superabsorbent polymer to have enhanced performance, a number of technical challenges must be met. The foam must convey the fluid to the superabsorbent polymer particles rapidly and effectively. As the superabsorbent polymer swells, it must not block the passage of fluid through the foam, nor should it become detached from the foam structure.
While conventional superabsorbent polymers utilize osmotic forces to retain aqueous fluids, most other common absorbents depend on capillary forces, or the tendency of an aqueous fluid to spread and wet a high-energy surface. Paper towels, sponges, and cellulose fluffs are examples of capillary absorbers. Recently there has been a significant amount of activity on microcellular foams as superabsorbent structures, including absorbent materials made using high internal phase-ratio emulsions (HIPEs). An important aspect of these foams is that they are inherently lipophilic, requiring a post-treatment in order to absorb aqueous solutions.
In one embodiment of the present invention, the sulfonated substantially random interpolymers are used to prepare absorbent foams. The foams can be prepared from the sulfonated substantially random interpolymers using the methods described herein. Alternatively, the foams can be prepared from the substantially random interpolymers and then the resulting foams can then be sulfonated either after or during the foam manufacturing process, using the sulfonation processes described herein. In such a post foam sulfonation process, the nature and incorporation of the previously described swelling and sulfonation agents and reaction times can then be tailored to the particular foam preparation.
Foam forming steps of the process are within the skill in the art. For instance as exemplified by the excellent teachings to processes for making ethylenic polymer foam structures and processing them in C. P. Park. “Polyolefin Foam”, Chapter 9, Handbook of Polymer Foams and Technology, edited by D. Klempner and K. C. Frisch, Hanser Publishers, Munich, Vienna, New York, Barcelona (1991), which is incorporated here in by reference.
The absorbent foam structures of the present invention are optionally made by a conventional extrusion foaming process. The structure is advantageously prepared by heating the sulfonated substantially random interpolymer or blend to form a plasticized or melt polymer material, incorporating therein a blowing agent to form a foamable gel, and extruding the gel through a die to form the foam product. Prior to mixing with the blowing agent, the sulfonated substantially random interpolymer is heated to a temperature at or above its glass transition temperature or melting point. The blowing agent is optionally incorporated or mixed into the melt polymer material by any means known in the art such as with an extruder, mixer, blender, or the like. The blowing agent is mixed with the melt polymer material at an elevated pressure sufficient to prevent substantial expansion of the melt polymer material and to advantageously disperse the blowing agent homogeneously therein. Optionally, a nucleator is optionally blended in the melt or dry blended with the sulfonated substantially random interpolymer prior to plasticizing or melting. The foamable gel is typically cooled to a lower temperature to optimize physical characteristics of the foam structure. The gel is then extruded or conveyed through a die of desired shape to a zone of reduced or lower pressure to form the foam structure. The zone of lower pressure is at a pressure lower than that in which the foamable gel is maintained prior to extrusion through the die. The lower pressure is optionally superatmospheric or subatmospheric (vacuum) but is preferably at an atmospheric level.
In another embodiment, the resulting absorbent foam structure is optionally formed in a coalesced strand form by extrusion of the polymer material through a multi-orifice die. The orifices are arranged so that contact between adjacent streams of the molten extrudate occurs during the foaming process and the contacting surfaces adhere to one another with sufficient adhesion to result in a unitary foam structure. The streams of molten extrudate exiting the die take the form of strands or profiles, which desirably foam, coalesce, and adhere to one another to form a unitary structure. Desirably, the coalesced individual strands or profiles should remain adhered in a unitary structure to prevent strand delamination under stresses encountered in preparing, shaping, and using the foam. Apparatuses and method for producing foam structures in coalesced strand form are seen in U.S. Pat. Nos. 3,573,152 and 4,824,720, both of which are incorporated herein by reference.
Alternatively, the resulting absorbent foam structure is conveniently formed by an accumulating extrusion process as described in U.S. Pat. No. 4,323,528, the entire contents of which are incorporated by reference herein. In another embodiment, the resulting foam structure is formed into non-crosslinked foam beads suitable for molding into articles. This process is well taught in U.S. Pat. Nos. 4,379,859 and 4,464,484, which are incorporated herein by reference.
In one modification of the uncrosslinked bead process, styrene monomer is optionally impregnated into the suspended pellets prior to their impregnation with blowing agent to form a graft interpolymer with the sulfonated substantially random interpolymer. Such a process of making such interpolymer beads is described for instance in U.S. Pat. No. 4,168,353, which is incorporated herein by reference.
The foam beads are conveniently then molded by any means within the skill in the art, such as taught for instance in U.S. Pat. Nos. 3,504,068 and 3,953,558. and C. P. Park, supra, p. 191, pp. 197-198, and pp. 227-229, the entire contents of all of which are incorporated herein by reference.
Blowing agents useful in making the absorbent foam structures of the present invention include inorganic agents, organic blowing agents and chemical blowing agents. Suitable inorganic blowing agents include carbon dioxide, nitrogen, argon, water, air, nitrogen, and helium. Organic blowing agents include aliphatic hydrocarbons having 1-6 carbon atoms, aliphatic alcohols having 1-3 carbon atoms, and fully and partially halogenated aliphatic hydrocarbons having 1-4 carbon atoms. Aliphatic hydrocarbons include methane, ethane, propane, n-butane, isobutane, n-pentane, isopentane, neopentane, and the like. Aliphatic alcohols include methanol, ethanol, n-propanol, and isopropanol. Fully and partially halogenated aliphatic hydrocarbons include fluorocarbons, chlorocarbons, and chlorofluorocarbons. Examples of fluorocarbons include methyl fluoride, perfluoromethane, ethyl fluoride, 1,1-difluoroethane (HFC-152a), 1,1,1-trifluoroethane (HFC-143a), 1,1,1-2-tetrafluoro-ethane (HFC-134a), pentafluoroethane, difluoromethane, perfluoroethane, 2,2-difluoropropane, 1,1,1-trifluoropropane, perfluoropropane, dichloropropane, difluoropropane, perfluorobutane, perfluorocyclobutane. Partially halogenated chlorocarbons and chlorofluorocarbons for use in this invention include methyl chloride, methylene chloride, ethyl chloride, 1,1,1-trichloroethane, 1,1-dichloro-1 fluoroethane (HCFC-141b), 1-chloro 1,1-difluoroethane (HCFC-142b), 1-dichloro-2,2,2-trifluoroethane (HCFC-123) and 1-chloro-1,2,2,2-tetrafluoroethane (HCFC-124). Fully halogenated chlorofluorocarbons include trichloromonofluoromethane (CFC-11), dichlorodifluoromethane (CFC-12), trichlorotrifluoroethane (CFC-113), 1,1,1-trifluoroethane, pentafluoroethane, dichlorotetrafluoroethane (CFC-114), chloroheptafluoropropane, and dichlorohexafluoropropane. Chemical blowing agents include azodicarbonamide, azodiisobutyro-nitrile, barium azodicarboxylate, N,N′-dimethyl-N,N′-dinitrosoterephthalamide, and benzenesulfonhydrazide, 4,4-oxybenzene sulfonyl semicarbazide, and p-toluene sulfonyl semicarbazide trihydrazino triazine. Preferred blowing agents include isobutane, HFC-152a, and mixtures of the foregoing.
The absorbent foams are optionally perforated to enhance or accelerate permeation of blowing agent from the foam and air into the foam. Such perforation is within the skill in the art, for instance as taught in U.S. Pat. Nos. 5,424,016 and 5,585,058, which are incorporated herein by reference.
Various additives are optionally incorporated in the resulting foam structure such as stability control agents, nucleating agents, inorganic fillers, pigments, antioxidants, acid scavengers, ultraviolet absorbers, flame retardants, processing aids, extrusion aids, and the like.
A stability control agent is optionally added to the present foam to enhance dimensional stability. Preferred agents include amides and esters of C10-24 fatty acids. Such agents are seen in U.S. Pat. Nos. 3,644,230 and 4,214,054, which are incorporated herein by reference.
In addition, a nucleating agent is optionally added in order to control the size of foam cells. Preferred nucleating agents include inorganic substances such as calcium carbonate, talc, clay, titanium oxide, silica, barium sulfate, diatomaceous earth, mixtures of citric acid and sodium bicarbonate, and the like. The amount of nucleating agent employed may range from about 0.01 to about 5 parts by weight per hundred parts by weight of a polymer resin.
The resulting foam structure is optionally closed-celled or open-celled. The open cell content will range from 0 to 100 volume percent as measured according to ASTM D2856-A.
The resulting absorbent foam structure is substantially noncrosslinked or uncrosslinked, and is optionally is in any physical configuration within the skill in the art, such as extruded sheet, rod, plank, and profiles.
Compositions of the Absorbent Polymers of the Present Invention
The starting material substantially random interpolymer prior to sulfonation comprise from about 0.5 to about 65, preferably from about 5 to about 65, more preferably from about 10 to about 65 mole percent of at least one vinyl or vinylidene aromatic monomer and/or aliphatic or cycloaliphatic vinyl or vinylidene monomer and from about 35 to about 99.5, preferably from about 35 to about 95, more preferably from about 35 to about 90 mole percent of ethylene and/or at least one aliphatic α-olefin having from 3 to about 20 carbon atoms.
The melt index (I2) of the starting material substantially random interpolymer prior to sulfonation is from about 0.01 to about 1000, preferably of from about 0.3 to about 30, more preferably of from about 0.5 to about 10 g/10 min.
The molecular weight distribution (Mw/Mn) of the starting material substantially random interpolymer prior to sulfonation is from about 1.5 to about 20, preferably of from about 1.8 to about 10, more preferably of from about 2 to about 5.
The density of the starting material substantially random interpolymer prior to sulfonation is greater than about 0.930, preferably from about 0.930 to about 1.045, more preferably of from about 0.930 to about 1.040, most preferably of from about 0.930 to about 1.030 g/cm3.
The degree of sulfonation of the starting material substantially random interpolymer is from about 1.5 to about 100, preferably from about 15 to about 100, more preferably from about 30 to 100 mol percent (based on the total number of aromatic rings in the initial substantially random interpolymer) of mono substituted aromatic rings substituted with a sulfonic acid group or a sulfonic acid salt.
The absorbent polymers compositions of the present invention comprise from about 10 to 100, preferably from about 20 to 100, more preferably from about 50 to 100 wt percent, (based on the combined weights of this component and the polymer component other than the sulfonated substantially random interpolymer) of one or more sulfonated substantially random interpolymers of ethylene and/or one or more α-olefins and one or more vinyl or vinylidene aromatic monomers and/or one or more sterically hindered aliphatic or cycloaliphatic vinyl or vinylidene monomers.
The sulfonated substantially random interpolymers comprise from about 35 to about 98.5, preferably from about 35 to about 85, more preferably from about 35 to about 70 mol percent of repeating units derived from ethylene and/or said ox-olefin which comprises at least one of propylene, 4-methyl-1-pentene, butene-1, hexene-1 or octene-1.
The sulfonated substantially random interpolymers comprise from about 1.5 to about 65 preferably from about 15 to about 65, more preferably from about 30 to about 65 mol percent of repeating units derived from said sulfonated vinyl or vinylidene aromatic monomers.
The sulfonated substantially random interpolymers comprise from 0 to about 63.5, preferably from 0 to about 50, more preferably from 0 to about 35 mol percent of repeating units derived from vinyl or vinylidene aromatic monomers.
The sulfonated substantially random interpolymers comprise from 0 to about 63.5, preferably from 0 to about 50, more preferably from 0 to about 35 mol percent of repeating units derived from said sterically hindered aliphatic or cycloaliphatic vinyl or vinylidene monomers.
The sulfonated substantially random interpolymers comprise from 0 to about 20 preferably, more preferably mol percent of norbornene, or a C1-10 alkyl or C6-10 aryl substituted norbornene.
The absorbent polymers compositions of the present invention can also comprise from 0 to about 90, preferably from 0 to about 80, more preferably from 0 to about 50 wt percent of at least one polymer other than said sulfonated substantially random interpolymer (based on the combined weights of this component and the substantially random interpolymer).
Applications for the materials of the present invention include the various applications for membranes as described in “Membrane Technology” in The Encyclopedia of Chemical Technology, Vol 16, ppgs 135-193, (4th ed, 1995, J. Wiley and Sons Inc., NY) the entire contents of which are herein incorporated by reference.
Other applications include modification of petroleum and hydrocarbon-based materials such as oils, asphalts and bitumenous products, in which the sulfonation improves the compatibility of the polymer. Also included are reinforcement of cementitious products by the sulfonated fibers of the present invention. Films and multilayer films for food packaging, and medical applications such as medicine bags, bandages, tapes, casts and the like, as well as delivery systems for agricultural products such as herbicides, pesticicdes and fertiliers as well as pharmaceutical products or other pharmaceutical applications. Also included are the use of the compositions of the present invention as binders for the recovery of coal and refractory fines. Also included are applications using the materials of the present invention as solid acid catalysts including shape selective and optically active catalytic transformations. Others uses include packaging (absorbent fiber used in packaging in case of spills), food packaging, cable wrap (water block tape in cables), medical applications (bandages, surgical drapes, spill clean up), apparel (absorbent fiber for improved comfort), controlled release fiber (imbibe absorbent fiber with antimicrobial, perfume, antibiotics etc.), absorbent articles for meat trays, absorbent articles for personal hygiene such as diapers, sanitary napkins adult incontinence pads, wipes (highly absorbent wipes, dust pickup), softener (sulfonated fiber holds on to fabric softeners and slowly releases them), towels with superabsorbing power (staple fibers to be combined in cotton yarns and improved water absorption capacity of towels, even in presence of fabric softeners), and disposable high absorbing towels (staple fibers to be combined with paper/non wovens towels for disposable applications such as towels for gym clubs, hospitals, etc.)
The following examples are to illustrate this invention and do not limit it.