FIELD OF THE INVENTION
This invention is directed to the field of fabric finishes, and more particularly to polymeric fabric finishes that impart hydrophilicity and other properties to fibers, yarns, textiles, or other fibrous substrates.
BACKGROUND OF THE INVENTION
Synthetic textile materials, such as nylon and polyester, are uncomfortable to wear due to their poor permeability to water. In hot weather, sweat cannot easily penetrate (or wick) through these fabrics and evaporate. The poor wicking and permeability are due to the natural hydrophobicity of nylon and polyester polymers; water does not readily spread out over surfaces composed of these materials. Nylon and polyester also often exhibit static cling and stain retention due to their hydrophobicity.
A method for imparting durable hydrophilic properties to nylon, polyester, and other synthetic materials would thus be desirable. This may be achieved by attaching hydrophilic materials to the hydrophobic fibers. Imparting hydrophilic properties to the hydrophobic substrate will also diminish or eliminate static cling and enable the release of stains during laundering.
U.S. Pat. No. 3,377,249 to Marco discloses the application of a stain-releasing finish to fabrics made of polyester, cotton, and polyester/cotton blends. The formulations comprise an acrylate copolymer (composed of at least 20% acrylic acid monomer) emulsion, an aminoplast resin, and a resin catalyst. The fabrics thus treated show stain-releasing properties durable to between five and ten home launderings.
Michielsen and Tobiesen have reported a method of grafting poly(acrylic acid) (or PAA) onto nylon 6,6 films (Tobiesen, F. A., Michielsen, S.; J. Poly. Sci. A; 40, 719-728 (2002)). In this method, nylon 6,6 films were dipped in aqueous solutions containing PAA, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) and N-hydroxysuccinimide (NHS). It is reported that the carboxylates of the PAA are activated by reaction with EDC; some of the activated carboxylates then react with amine groups on the chain ends of the nylon polymers while the rest are hydrolyzed back to carboxylate form. The NHS is believed to aid in slowing the rate of hydrolysis. After incubating the film in the solutions for times ranging from 0.5 to 18 hours, and at temperatures ranging from 0 to 60° C., the treated films were removed and rinsed at least six times with deionized water. The authors report that a drop of water placed on untreated nylon 6,6 film spreads slowly over the surface, whereas a drop placed on a treated film immediately spreads to cover the surface. Disadvantages to this method are that large amounts of the expensive reagents EDC and NHS, in greater-than-stoichiometric amounts relative to the number of carboxyl groups, are required for grafting.
Herein is disclosed the invention of a treatment for polyester, nylon, and other synthetic, hydrophobic materials that renders the treated material hydrophilic. The treatment durably attaches hydrophilic material directly to a hydrophobic substrate, rendering the substrate hydrophilic without altering the other properties of the material.
SUMMARY OF THE INVENTION
This invention is directed to fabric finishes or treatment preparations for nylon, polyester, and other synthetic or hydrophobic textile materials that will render them hydrophilic.
The finishes of the invention are comprised primarily of polymers that contain carboxyl groups, salts of carboxyl groups, or moieties that can be converted to carboxyl groups by a chemical reaction (referred to herein as “carboxyl precursors”). Fibrous substrates, such as textiles or webs, are exposed to these carboxyl-containing polymers, then dried and cured. By this process, the fibers of the treated substrates are directly bonded to the hydrophilic carboxyl-containing polymers without the use of “activating reagents”. The treated textiles or webs are thus endowed with hydrophilic characteristics, including improved water-wicking and breathability, in comparison to untreated textiles of the same fiber type.
This invention is further directed to synthetic or hydrophobic fibers, and yarns, fabrics, textiles, finished goods, or non-woven goods (encompassed herein under the terms “fibrous substrates”, “textiles” or “webs”), which are treated with the hydrophilic treatment preparations of the invention. The treated fibers and fibrous substrates exhibit hydrophilic characteristics in comparison to untreated fibers and fibrous substrates of the same fiber type.
DETAILED DISCUSSION OF THE INVENTION
According to the present invention, a fibrous substrate is exposed to a solution that contains a polymer or oligomer that contains carboxyl, carboxylate, or carboxyl precursor groups (all of which polymers or oligomers are encompassed herein and in the claims under the terms “carboxyl-containing polymer” or “polycarboxylate”). The treated web is then dried and cured to durably fix the hydrophilic agent to the fiber. Cross-linking agents may be used to enhance fixation of the carboxyl-containing polymer. Wetting agents may be used to facilitate application of the polymer to the web, and a catalyst, such as sodium hypophosphite, may be added. By “durably fix” or “durable” is meant that the hydrophilic properties provided to the treated substrates by the treatment finish of the invention remain for at least about 10 home launderings, preferably for at least about 35 home launderings, and more preferably for at least about 50 home launderings. In a preferred embodiment, the treatment is permanent; that is, the hydrophilic characteristics are present for the life of the treated fibrous substrate.
The carboxyl-containing polymers, according to the invention, can be obtained through polymerization or copolymerization of one or more monomers that contain a carboxyl group, a carboxylate, or a group that can become a carboxyl or carboxylate group through a chemical reaction (a carboxyl precursor group). Non-limiting examples of such monomers include: acrylic acid, methacrylic acid, aspartic acid, glutamic acid, β-carboxyethyl acrylate, maleic acid, monoesters of maleic acid [ROC(O)CH═CHC(O)OH, where R represents a chemical group that is not hydrogen], maleic anhydride, fumaric acid, monoesters of fumaric acid [ROC(O)CH═CHC(O)OH, where R represents a chemical group that is not hydrogen], acrylic anhydride, crotonic acid, cinnamic acid, itaconic acid, itaconic anhydride, monoesters of itaconic acid [ROC(O)CH2(═CH2)C(O)OH, where R represents a chemical group that is not hydrogen], saccharides with carboxyl (e.g. alginic acid), carboxylate, or carboxyl precursor groups, and macromonomers that contain carboxyl, carboxylate, or carboxyl precursor groups. Carboxyl precursors include, but are not limited to, acid chlorides, N-hydroxysuccinimidyl esters, amides, esters, nitriles, and anhydrides. Examples of monomers with carboxyl precursor groups include (meth)acrylate chloride, (meth)acrylamide, N-hydroxysuccinimide (meth)acrylate, (meth)acrylonitrile, asparigine, and glutamine. Herein the designation “(meth)acryl” indicates both the acryl- and methacryl-versions of the monomer. Preferred carboxylate cations include aluminum, barium, chromium, copper, iron, lead, nickel, silver, strontium, zinc, zirconium, and phosphonium (R4P+). More preferred cations include hydrogen, lithium, sodium, potassium, rubidium, ammonium, calcium, and magnesium. The polymers may be linear or branched. In a presently preferred embodiment, the polymers are branched, and more preferably they have between about 0.001% and about 10% branching, inclusive. Preferred monomers are acrylic acid, methacrylic acid and β-carboxyethyl acrylate.
Acrylate polymers containing carboxyl groups are commercially available. In particular, poly(acrylic acid) is in wide production worldwide for use as a “super-absorbent” in disposable diapers and as a thickener in printing pastes. Poly(acrylic acid) can be obtained from, among other sources, Polycryl AG, Bohler, Postfach, CH-6221 Rickenbach, Switzerland (trade name: Polycryl); Stockhausen, 2401 Doyle Street, Greensboro, N.C., 27406-2911; and B F Goodrich, Four Coliseum Centre, 2730 West Tyvola Rd., Charlotte, N.C. 28217-4578 (trade name: Carbopol). The presently preferred polycarboxylate is poly(acrylic acid) (PAA).
The present invention is further directed to synthetic or hydrophobic yarns, fibers, fabrics, finished goods, or other textiles (encompassed herein under the terms “fibrous substrates”, “textiles” and “webs”) that are treated with the hydrophilic fabric finishes of the invention. These treated textiles or webs will display characteristics usually associated with hydrophilic textiles (e.g. cotton), such as improved wettability and moisture breathability, while retaining the traditional advantages of synthetic textiles, such as strength and durability. In addition, optical and other properties of the fiber may also be modified so as to, for example, reduce the shininess and improve the hand of synthetic fibers and fabrics. Anti-static and stain release characteristics may also be imparted by treatment according to the invention.
These treated fibrous substrates can be used in a variety of ways including, but not limited to the following: clothing, upholstery and other interior furnishings, hospital and other medical uses, and industrial uses. The Wellington Sears Handbook of Industrial Textiles (Ed. S. Adanur, Technomic Publishing Co., Lancaster, Pa., 1995, p. 8-11) lists a number of potential uses.
The hydrophilic fibrous substrates of the invention comprise (1) polymer chains that contain carboxyl groups, which have been cured and affixed onto (2) synthetic or hydrophobic fibers formed into a fibrous substrate. Optionally, a cross-linking agent and a catalyst may be added with the polymer to enhance the fixation of the polymer to the fiber. The fibrous substrates of the present invention are intended to include fibers, fabrics and textiles, and may be sheet-like structures (woven, knitted, tufted, stitch-bonded, or non-woven) comprised of fibers or structural elements. Included with the fibers can be non-fibrous elements, such as particulate fillers, binders, and sizes. The hydrophobic textiles or webs include fibers, woven and non-woven fabrics derived from natural or synthetic fibers or blends of such fibers. They can comprise hydrophobic fibers in the form of continuous or discontinuous monofilaments, multifilaments, staple fibers, and yarns containing such filaments and/or fibers, which fibers can be of any desired composition. Mixtures of natural fibers and synthetic fibers may also be used. Examples of natural fibers include cotton, wool, silk, jute, and linen. Examples of man-made fibers include regenerated cellulose rayon, cellulose acetate, and regenerated proteins. Examples of synthetic fibers include, but are not limited to, polyesters (including polyethyleneterephthalate and polypropyleneterephthalate), polyamides (including nylon), acrylics, olefins, aramids, azlons, modacrylics, novoloids, nytrils, aramids, spandex, vinyl polymers and copolymers, vinal, vinyon, vinylon, Nomex® (DuPont) and Kevlar® (DuPont).
To prepare the fibrous substrates of the invention, a synthetic or hydrophobic fiber, yarn, fabric, textile, finished good, or non-woven good (the “fibrous substrate” or “web”) is exposed to a solution or suspension of the carboxyl-containing polymer or polycarboxylate by methods known in the art, including soaking, spraying, dipping, fluid-flow, and padding. The solution or suspension may optionally include a cross-linking agent, cross-linking catalysts and/or wetting agents. The solvent may be water, an organic liquid, or a supercritical fluid. The treated web is then removed from exposure, dried, and cured. The resulting web exhibits hydrophilic characteristics that are not present in the untreated web.
Without being bound by theory, it is believed that the mechanism of fixation of the polycarboxylate to the fiber surface is the formation of covalent bonds between the two. In the case of polyester fiber, there are hydroxyl-terminated chain ends that form ester bonds with the polycarboxylate, whereas the amine-terminated chain ends of nylon form amide bonds with the polycarboxylate; these bonds are believed to form during the curing process. While ester and amide bonds are reasonably strong, they can still be subject to hydrolysis during laundering procedures. It is believed that the durability of the finish corresponds to the number of covalent bonds between the polycarboxylate and the fiber surface; as a result, it is preferable to form as many bonds as possible to maximize the durability of the hydrophilic finish. However, the “density” of reactive groups over a given area of synthetic fiber surface is expected to be quite small. Michielsen reports that Nylon 6,6 has only one reactive amine group per 90 nm2 (Michielsen, S.; J. Appl. Polym. Sci. 1999, 73, 129-136). As comparison, 5-kD poly(acrylic acid) has a radius of gyration, RG, of less than 5 nm, so on average only one amide bond could be formed between each polymer chain and the surface. As the density of reactive groups of the fiber surface cannot be increased without damaging the fibers, the only available method to maximize the number of fiber-polycarboxylate bonds is to use high molecular weight polycarboxylates so that surface coverage is maximized. Such polycarboxylates may be prepared by cross-linking lower molecular weight polycarboxylates either previous to or concurrently with the curing process. Cross-linked polycarboxylates of high molecular weight are commercially available from sources cited herein.
The polycarboxylate polymers can be cross-linked together by including a cross-linking agent, a molecule that contains two or more carboxyl-reactive groups, in the treatment bath. Non-limiting examples of carboxyl-reactive groups include alcohols, amines, thiols, aminoplasts (e.g. condensation products of ureas and aldehydes), and oxazolines. It is desirable that the cross-linking agent be non-volatile at or below the curing temperature; to this end, polymeric or high molecular weight cross-linking agents are of value. It is further desirable that the cross-linking agent be soluble or readily suspended in the bath liquor. Examples of alcohol cross-linking agents include glycerol and other non-polymeric polyols (including α,ω-diols such as 1,5-pentanediol), poly(ethylene glycol), poly(vinyl alcohol) and poly(saccharides). The poly(saccharides) may be either found in nature or derivatized from natural sources and may include celluloses, agars, pectins, xanthan gums and guar gums. Examples of amine cross-linkers include polyamines, poly(vinyl amine) and poly(ethylene imine). Examples of aminoplast cross-linkers include dimethyloldihydroxyurea (DMDHEU) and related ureaaldehyde condensation products as well as polymers containing aminoplast reactive groups. Examples of oxazoline cross-linkers include the Epocros product line from Nippon Shokubai (2651 Riverport Rd. Chattanooga, Tenn. 37406).
If polymers that contain carboxyl precursor groups are used as the carboxyl-containing polymer, the precursors must be hydrolyzed to form carboxyl groups either during or after application of the finish to the textile. Conditions for hydrolysis depend on the nature of the precursors. Preferably, the hydrolysis occurs at the pH and temperature conditions at which the fibrous substrate is treated, so as to facilitate formation of the carboxyl groups as the polymer is being applied to the textile or web. Preferred precursor groups are acid chlorides and anhydrides. Less preferred precursor groups may require acidic or basic aqueous conditions and elevated temperatures for hydrolysis; such groups include esters and amides.
A preferred molecular weight of the carboxyl-containing polymer useful in the present invention is between about 90 and about 4,000 kilodaltons; a more preferred molecular weight is between about 125 and about 3,000 kilodaltons, and a most preferred molecular weight is between about 750 and about 1,250 kilodaltons. It is preferred that the polycarboxylate be cross-linked between about 0.001% and about 10%, more preferably between about 0.01% and about 1%. The molecular weight and degree of cross-linking can be obtained either prior to making the finish formulation or during the course of curing the finish onto the web.
The amount of carboxyl-containing polymer and other substituents in the treatment solution will depend on factors such as the particular polymer(s) used, the degree of hydrophilicity desired, and the like. Generally, the carboxyl-containing polymer is present in the treatment solution in an amount of from about 0.001 wt. % to about 25 wt. %, preferably from about 0.005 wt. % to about 5 wt. %, more preferably from about 0.01 wt. % to about 2 wt. %. The cross-linking agent is present in an amount from 0 wt. % to about 10 wt. %, preferably from about 0 wt. % to about 1 wt. %, more preferably from about 0 wt. % to about 0.5 wt. %. The catalyst is present in an amount from 0 wt. % to about 4 wt. %, preferably from about 0 wt. % to about 2 wt. %, more preferably from about 0 wt. % to about 1.5 wt. %. The wetting agent is present in an amount from 0 wt. % to about 5 wt. %, preferably from about 0.01 wt. % to about 1 wt. %, more preferably from about 0.05 wt. % to about 0.5 wt. %.
In applying the hydrophilic carboxyl-containing polymers of the invention to a fiber or fibrous substrate, the process temperature can vary widely, depending on the reactivity of the reactants. However, the temperature should not be so high as to decompose the reactants or so low as to cause inhibition of the reaction or freezing of the solvent. Unless specified to the contrary, the textile is exposed to the polymer at atmospheric pressure over a temperature range between 5° C. and 110° C., more preferably between 15° C. and 60° C., and most preferably at room temperature, approximately 20° C. The pH at which the carboxyl-containing polymer is applied may be between pH 0 to pH 7, preferably between pH 1 to pH 5, and more preferably between pH 2 to pH 4.5. The time required for the processes herein will depend to a large extent on the temperature being used and the relative reactivities of the starting materials. Unless otherwise specified, the process times and conditions are intended to be approximate. Curing conditions may range from 5° C. to 250° C., preferably between 150° C. and 200° C.