WO1997011220A1

WO1997011220A1 - Method of coating a hydrophobic fibrous material with an amphiphilic polyelectrolyte

Info

Publication number: WO1997011220A1
Application number: PCT/US1996/013618
Authority: WO
Inventors: Gunilla Elsa Gillberg-La Force; Kristi Lynn Kiick-Fischer
Original assignee: Kimberly-Clark Worldwide, Inc.
Priority date: 1995-09-22
Filing date: 1996-08-22
Publication date: 1997-03-27
Also published as: MX9801610A; CA2228603A1; AU6857096A

Abstract

A method of coating a hydrophobic fibrous material with an amphiphilic polyelectrolyte which involves coating the hydrophobic fibrous material with a foam under conditions sufficient to substantially uniformly coat the hydrophilic fibrous material with the amphiphilic polyelectrolyte. The foam is generated from a solution of an amphiphilic polyelectrolyte in water. The hydrophobic fibrous material may be a polyolefin, such as polyethylene or polypropylene. The hydrophobic fibrous material also may be a nonwoven web, such as a meltblown or spunbonded nonwoven web. When the hydrophobic fibrous material is a nonwoven web, the web typically is coated with the foam, vacuum extracted, nipped, and dried.

Description

METHOD OF COATING A HYDROPHOBIC FIBROUS MATERIAL WITH AM AMPHIPHILIC POLYELECTROLYTE

Background of the Invention

The present invention relates to a coated fibrous material.

Polymers are used extensively to make a variety of products which include blown and cast films, extruded sheets, injection molded articles, foams, blow molded articles, extruded pipe, monofilaments, and fibrous materials such as nonwoven webs. Some of the polymers, such as polyolefins, have no functionality (i.e., reactive groups) and are naturally hydrophobic, and for many uses these properties are either a positive attribute or at least not a disadvantage.

There are a number of uses for polymers, however, where their hydrophobic/nonfunctional nature either limits their usefulness or requires some effort to modify the surface characteristics of the shaped articles made therefrom. By way of example, polyolefins, such as polyethylene and polypropyl¬ ene, are used to manufacture polymeric fabrics which are employed in the construction of such disposable absorbent articles as diapers, feminine care products, incontinence products, training pants, wipes, and the like. Such polymeric fabrics often are nonwoven webs prepared by, for example, such processes as meltblowing, coforming, and spunbonding. Frequently, such polymeric fabrics need to be wettable by water. Wettability can be obtained by spraying or otherwise coating (i.e., surface treating or topically treating) the fabric with a surfactant solution during or after its formation, and then drying the web.

Some of the more common topically applied surfactants are nonionic surfactants, such as polyethoxylated octylphenols and condensation products of propylene oxide with propylene glycol, by way of illustration only. These surfactants are effective in rendering normally hydrophobic polymeric fabrics wettable. However, the surfactant is readily removed from the fabric, often after only a single exposure to an aqueous liquid.

Polymers also are employed in the preparation of filter media. For example, depth-type filters generally are made from fibrous, porous, or caked media. Fibrous media con¬ stitute a layer, or mat, of numerous fine fibers (e.g. , fiber diameters ranging from 0.5 to 30 micrometers). These fibers are randomly oriented, thereby creating the numerous tortuous passages or pores in which the particles are trapped. Retention efficiency in conventional deep-bed filters is achieved by means of a series of low-efficiency particle captures. Adsorptive surface forces (molecular and electros¬ tatic) can enhance attachment to the medium, which then improves retention within the filter. Such adsorptive surface forces may be achieved by introducing functional or ionic groups on the surfaces of the fibers of the filter media. Commonly used fibrous materials are cellulose, cotton, glass, and synthetics (e.g. rayon, polypropylene) .

Notwithstanding past improvements in rendering a polymeric fibrous material wettable or introducing functional or ionic groups on the surfaces of the fibers of filter media, there still are opportunities for improvements in these areas.

Summary of the invention

The present invention addresses some of the difficulties and problems discussed above by providing a method of coating a hydrophobic fibrous material with an amphiphilic polyelec¬ trolyte. The method involves coating the hydrophobic fibrous material with a foam composed of an amphiphilic polyelectro¬ lyte and water under conditions sufficient to substantially uniformly coat the hydrophobic fibrous material with the amphiphilic polyelectrolyte.

The hydrophobic fibrous material generally is made from a synthetic hydrophobic polymer. Such polymers in general give contact angles with water of at least about 60° and typically have surface free energies of less than about 45 dynes/cm. Examples of such polymers include, by way of illustration only, aromatic polyesters, such as poly(ethyl¬ ene terephthalate) , and polyolefins, such as polyethylene and polypropylene. The hydrophobic fibrous material also may be a nonwoven web. By way of example, the nonwoven web may a meltblown nonwoven web. As another example, the nonwoven web may be a spunbonded nonwoven web. As a further example, the nonwoven web may be a coformed nonwoven web.

The amphiphilic polyelectrolyte may be any material having both a plurality of polar, water-soluble groups and a plurality of nonpolar, water-insoluble groups. For example, the amphiphilic polyelectrolyte may be a surfactant/polyelec- trolyte complex. As another example, the amphiphilic polyelectrolyte may be a polymeric surfactant. As still another example, the amphiphilic polyelectrolyte may be a hydrophobized polyelectrolyte.

To substantially uniformly coat the hydrophilic fibrous material with the amphiphilic polyelectrolyte, a relatively unstable foam is desired. That is, it is desired that the foam collapse upon coating the hydrophobic fibrous material with the foam. In this case, the method involves: preparing an aqueous solution of an amphiphilic polyelec¬ trolyte; generating a foam from the aqueous solution; and coating the hydrophobic fibrous material with the foam under conditions sufficient to substantially uniformly coat the hydrophilic fibrous material with the amphiphilic polyelectrolyte.

When the hydrophobic fibrous material is a nonwoven web, the conditions sufficient to substantially uniformly coat the hydrophilic fibrous material with the amphiphilic polyelectro¬ lyte typically include: coating the nonwoven with the foam described above; vacuum extracting the coated nonwoven web; nipping the vacuum-extracted coated nonwoven web; and drying the nipped nonwoven web. The method of the present invention converts normally hydrophobic surfaces to hydrophilic or wettable surfaces. In addition, such method permits further surface modifications to be carried out, if desired. For example, compounds which aid or promote skin wellness and having the appropriate functional groups may be associated with the surfaces of fibrous materials adapted to be used in such disposable absorbent products as diapers, feminine care products, and incontinent products. Without wishing to be bound by theory, it is believed that the following advantages accrue from the method of the present invention in contrast with the use of amphiphilic polyelectrolyte solutions:

(a) using air as a diluent instead of water allows a more even distribution of a low level of add-on of the amphiphilic polyelectrolyte and reduces the amount of water to be removed by drying, with a concomitant decrease in drying costs; and

(b) a desired outward orientation of the hydrophobic groups of the amphiphilic polyelectrolyte is obtained in a foam since the hydrophobic groups are oriented towards air and, as a consequence, can directly interact with a hydrophobic polymer surface, whereas, in an aqueous solution, the hydrophilic groups are oriented towards the water phase while the hydrophobic groups are oriented away from the water phase, which means that a reorienta¬ tion of the polyelectrolyte has to occur for the hydrophobic groups to be able to interact with a hydrophobic polymer surface.

Detailed Description of the Invention

As used herein, the term "hydrophobic fibrous material" means any fibrous material which is hydrophobic, i.e., not wettable with water. In general, the fibrous material may be a woven or nonwoven web or fabric. When a nonwoven web is employed, it may be made by any process known to those having ordinary skill in the art. Such processes include, for example, meltblowing, coforming, spunbonding, hydroentan- gling, carding, air-laying, wet spinning, dry spinning, solution spinning, and wet-forming. A nonwoven web desirably will be formed by such well- known processes as meltblowing, coforming, spunbonding, and the like. By way of illustration only, such processes are exemplified by the following references:

(a) meltblowing references include, by way of example, U.S. Patent Nos. 3,016,599 to R. W. Perry, Jr., 3,704,198 to

J. S. Prentice, 3,755,527 to J. P. Keller et al. , 3,849,241 to R. R. Butin et al., 3,978,185 to R. R. Butin et al., and 4,663,220 to T. J. Wisneski et al. See, also, V. A. Wente, "Superfine Thermoplastic Fibers", Industrial and Engineering Chemistry. Vol. 48, No. 8, pp. 1342-1346 (1956); V. A. Wente et al., "Manufacture of Superfine Organic Fibers", Navy Research Laboratory, Washington, D.C, NRL Report 4364 (111437), dated May 25, 1954, United States Department of Commerce, Office of Technical Services; and Robert R. Butin and Dwight T. Lohkamp, "Melt Blowing - A One-Step Web Process for New Nonwoven Products", Journal af the Technical Associa¬ tion of the Pulp and Paper Industry. Vol. 56, No.4, pp. 74- 77 (1973);

(b) coforming references (i.e., references disclosing a meltblowing process in which fibers or particles are com¬ mingled with the meltblown fibers as they are formed) include U.S. Patent Nos. 4,100,324 to R. A. Anderson et al. and 4,118,531 to E. R. Hauser; and

(c) spunbonding references include, among others, U.S. Patent Nos. 3,341,394 to Kinney, 3,655,862 to Dorschner et al., 3,692,618 to Dorschner et al., 3,705,068 to Dobo et al., 3,802,817 to MatSUki et al., 3,853,651 to Porte, 4,064,605 to Akiyama et al., 4,091,140 to Harmon, 4,100,319 to Schwartz, 4,340,563 to Appel and Morman, 4,405,297 to Appel and Mor an, 4,434,204 to Hartman et al., 4,627,811 to Greiser and Wagner, and 4,644,045 to Fowells. The hydrophobic fibrous material typically will be made of a synthetic hydrophobic polymer. Such polymers in general give contact angles with water of at least about 60° and typically have surface free energies of less than about 45 dynes/cm. Examples of such polymers include, by way of illustration only, aromatic polyesters, polyolefins, poly¬ tetrafluoroethylene, poly(methyl methacrylate) , poly(vinyli¬ dene fluoride) , polyamides, and polystyrenes.

Aromatic polyesters include, by way of example only, poly(ethylene terephthalate) , poly(tetramethylene terephthal¬ ate) , poly(cyclohexane-l,4-dimethylene terephthalate), and thermotropic liquid crystalline such as the copolymers of hydroxybenzozic acid and hydroxynaphthoic acid.

Examples of polyolefins include, again by way of illustration only, polyethylene, polypropylene, poly(l- butene) , poly(2-butene) , poly(l-pentene) , poly(2-pentene) , poly(3-methy1-1-pentene) , poly(4-methy1-1-pentene) , and the like. In addition, such term is meant to include blends of two or more polyolefins and random and block copolymers prepared from two or more different unsaturated monomers. Because of their commercial importance, the most preferred polyolefins are polyethylene and polypropylene.

Polyamides include, by way of example only, poly(6- aminocaproic acid) (nylon 6) , poly(hexamethylene sebacamide) (nylon 6,10), and poly(octamethylene suberamide) (nylon 8,8). The term "amphiphilic polyelectrolyte" is used herein to mean any material having both a plurality of polar, water- soluble groups and a plurality of nonpolar, water-insoluble groups. For example, the amphiphilic polyelectrolyte may a surfactant/polyelectrolyte complex. The surfactant may be either cationic or anionic. When the surfactant is cationic, the polyelectrolyte will be anionic. Similarly, when the surfactant is anionic, the polyelectrolyte will be cationic.

The polyelectrolyte portion of a surfactant/polyelectro- lyte complex may be natural or synthetic. Natural polyelec- trolytes include, by way of illustration only, polysac¬ charides, such as chitosan, glycol chitosan, cellulose, sodium carboxymethylcellulose, and sodiumcarboxymethylhydroxyethy1- cellulose; dextran sulfates; hyaluronic acid; heparin, chondroitin sulfate, and poly(galacturonic acid).

Synthetic polyelectrolytes include, also by way of illustration only, poly(acrylic acid) , poly(methacrylic acid) , poly(ethylenesulfonic acid), poly(vinylsulfonic acid), poly(styrenesulfonic acid) , poly(vinylphenylsulfuric acid) phenol ester, maleic acid/alkene copolymer, maleic acid/vinyl alkyl ether copolymer, poly(glutamic acid) , polylysine, poly(vinyl amine) , polyethyleneimine, poly(viny1-4-alkylpyri- dinium salt), poly(methylene)-N,N-dimethylpiperidinium salt, poly(vinylbenzyltrimethylammonium salt), poly(dimethyldiallyl- ammonium chloride), poly(N,N,N' ,N'-tetramethy1-N-β-xylylene- propylenediammoniumchloride) , poly(N-ethyl-4-vinylpyridinium bromide) , poly(vinyl-butylpyridinium bromide) , poly(vinyl- N-methylpyridinium bromide), and poly(methacryloxyethyltri- ethylammonium bromide) . In general, a synthetic polyelectro¬ lyte may have a weight-average molecular weight of from about 5,000 to about 1,000,000 Daltons. For example, the poly- electrolyte may have a weight-average molecular weight of from about 20,000 to about 100,000 Daltons.

Surfactants which may be used in a surfactant/polyelec- trolyte complex are well known to those having ordinary skill in the art. Such surfactants include anionic and cationic surfactants, examples of which include, by way of illustration only, quaternary amine salts, such as dodecyltrimethylammonium chloride, didodecyldimethylammonium bromide, hexadecyltri¬ methylammonium chloride, cetyldimethylethylammonium bromide, tallowtrimethylammonium chloride, methyl bis(2-hydroxyethyl)- cocoammonium chloride, methyldodecylbenzyltrimethylammonium chloride, lauryldimethylbenzylammonium chloride, octyl- phenoxyethoxyethyldimethylbenzyl ammonium chloride, 2- hydroxyethylbenzylstearylimidazolinium chloride, diethylhep- tadecy1imidazoliniumethylsulfate, laurylpyridiniumchloride, and lauryl isoquinolinium bromide; fatty acid salts, such as lithium stearate, sodium myristate, sodium stearate, sodium naphthenate, potassium caprate, potassium undecylenate, ammonium laurate, morphoiine oleate, and triethanolamine linoleate; sulfates, such as sodium n-octyl sulfate, sodium 2-ethylhexyl sulfate, sodium cetyl sulfate, triethanolamine lauryl sulfate, poly(oxyethylene) octylphenol sodium salt, sulfated lauryl ether of tetraethyleneglycol sodium salt, and sulfated butyloleate sodium salt; sulfonates, such as sodium toluene sulfonate, sodium tridecylbenzene sulfonate, ammonium zylenesulfonate, triethanolammoniumdodecylbenzenesulfonate, ammonium petroleum sulfonate, ethylenediamine petroleum sulfonate, disodium dibutylphenylphenol disulfonate, sodium amyl sulfooleate, sodium lauryl sulfoacetate, and sodium diamyl sulfosuccinate. See, for example, W. Linfield, Editor, "Anionic Surfactants," Marcel Dekker, New York, 1973; and E. Jungermann, Editor, "Cationic Surfactants," Marcel Dekker, New York, 1969.

Other surfactants include, by way of illustration only, amines and amine derivatives, such as Q-tetradecylamine, cocoamine, hydrogenated tallow amine, soya amine, dimethyl octadecylamine, poly(oxyethylene) stearyl amine, poly(oxy- ethylene) coco amine, octadecylamine acetate, sodium car- boxymethylnonylhydroxyethyl imidazolinium hydroxide, disodium- N-lauryl-β-imino dipropionate, cetyl betaine, myristamido- propyl betaine, and N-lauryl sarcosine.

As another example, the amphiphilic polyelectrolyte may be a polymeric surfactant, such as hydrophobically modified poly(acrylic acid) (partial esterification with long chain aliphatic alcohols) , poly(methyl vinyl ether/ aleic an¬ hydride) , polystyrene-block-poly(2-vinylpyridine) , hydroxy¬ ethyl cellulose reacted with a lauryl dimethylammonium substituted epoxide (Polyquarternium-24® and Quatrisoft®, Amerchol Corporation, Edison, NewJersey) , partially alkylated poly(vinyl pyridine), poly(oxyethylene)-alkyl glycol copoly¬ mers, and poly(vinyl pyrrolidone)/polyalkene copolymers. See, e.g., J. Piirma, "Polymeric Surfactants," Marcel Dekker, New York, 1992.

As a further example, the amphiphilic polyelectrolyte may be a protein. As yet another example, the amphiphilic polyelectrolyte may be an associative thickener. See, for example, J. E. Glass, Editor, "Polymers In Aqueous Media. Performance Through Association," Advances in Chemistry Series 223, American Chemical Society, Washington, D.C, 1989. In its most broad embodiment, the method of the present invention involves coating the hydrophobic fibrous material with a foam composed of an amphiphilic polyelectrolyte and water under conditions sufficient to substantially uniformly coat the hydrophilic substrate with the amphiphilic polyelec- trolyte.

Without wishing to be bound by theory, it is believed that the use of foams maximizes exposure of the hydrophobic regions of the amphiphilic polyelectrolyte to the hydrophobic fibrous material surfaces, thereby promoting the homogeneity and durability of the amphiphilic polyelectrolyte coatings on the fibrous material. The generation of foams is believed to maximize these hydrophobic interactions by increasing the surface area of the air/solution interface, in which the amphiphilic polyelectrolytes orient their hydrophobic groups away from the aqueous solution and toward air and, consequent¬ ly, toward the surfaces of the hydrophobic fibrous material. As stated earlier, the foam is generated from a solution of the amphiphilic polyelectrolyte in water. The solution may contain other materials, such as acids or bases which may be needed to ionize weak polyelectrolytes or surfactants based on amines or carboxylic acids; small particles with absorbent properties, such as zeolites and activated carbon; dyes; metal salts having bioactivity; and minor amounts of water-miscible organic solvents. Desirably, the foam employed to coat the hydrophobic fibrous material will be relatively unstable. As used herein, the term "relatively unstable" means only that the foam collapses on the fibrous material, either spontaneously or as a result of a subsequent action. For example, the foam may be destabilized by the presence of the fibrous material. Alternatively or additionally, the foam may be destabilized by shear forces. Shear forces may be generated, for example, by nipping the fibrous material after applying the foam. Shear forces also may be generated by applying the foam to the fibrous material and then vacuum extracting the foam through the material, resulting in an even distribution throughout the material. If desired, the fibrous material may be nipped after the vacuum extracting step to remove excess fluid and also aid in collapsing the foam.

The present invention is further deεcribed by the examples which follow. Such examples, however, are not to be construed as limiting in any way either the spirit or the scope of the present invention. In the examples, the hydrophobic fibrous materials employed were 0.5 ounce per square yard or osy (about 17 grams per square meter or gsm) polypropylene meltblown nonwoven webs and 0.8 osy (about 27 gsm) polypropylene spunbonded nonwoven webs. Both materials were prepared in accordance with known procedures. In addition, all percents are percents by weight, unless indicated otherwise.

Example 1

Quatrisoft® LM200 is a hydrophobically-modified, cationic cellulosic polymer. Chemically, it is Polyquarternium-24 hydroxyethyl cellulose reacted with a lauryl dimethylammonium substituted epoxide (Amerchol Corporation, Edison, New Jersey) . It was used as a model material to investigate foam coating methods. Quatrisoft® LM200 combines the properties of a surfactant/polymer mixture and displays some of their properties. When dissolved in water, it self-associates by hydrophobic interactions, producing structures exhibiting high viscosity. This type of structure also has the ability to solubilize water-insoluble materials, including dyes, and produces very stable foams.

For the initial investigations, a solution of 1.5 percent Quatrisoft® LM200 was prepared for initial investigations of foam generation. A mixture of 1.5 g Quatrisoft® and 100 ml of deionized water was tumbled for one hour in a Glas-Col Laboratory Rotator (Catalog No. RD 4512, Glas-Col, Terre Haute, Illinois) on the #5 setting. Ten ml of the resulting solution was placed in a 25-50 micrometer glass frit while air was passed through it to generate a foam (liquid blow-through method) . A second method which gave a more stable foam employed a hand mixer to whip 50 ml of the 1.5 percent solution for one minute.

Foams also were prepared from .5 percent and 1.0 percent Quatrisoft® solutions using the two methods described above to determine the best concentration and method for preparation of the most stable foam. The hand mixer produced the best foam and was used to prepare the foams for the remaining experiments.

Quatrisoft® produced a very stable foam when agitated with a hand mixer at the "whip" setting. The liquid blow- through method generated bubbles that were much more airy and polyhedral in shape than with the hand mixer. All three solutions produced stable foams using the hand mixer. No preferential concentration of solids in the Quatrisoft® foam was observed. That is, the 1.5 percent Quatrisoft® solution resulted in a foam which also had a solids content of 1.5 percent.

The viscosities of the Quatrisoft® solutions were determined using a Brookfield Model DVII+ viscometer with a spindle number of cp-41 and a spindle speed of 100 rpm (Brookfield Engineering Laboratory, Inc., Stoughton, Mas¬ sachusetts). The viscosities for the 0.5 percent, 1.0 percent, and 1.5 percent solutions were 3.8 x IO³ Pa s, 13.0 x 10^'3 Pa s, and 36.1 x 10^'3 Pa s, respectively. The surface tensions were 58.2 x 10^'5 N, 57.3 x 10^'5 N, and 56.4 x 10^'5 N, respectively) . Surface tension was determined by means of the DuNouy Ring method with a Fisher Scientific Model 20 Surface Tensiometer (Fisher Scientific Corporation, Pittsburgh, Pennsylvania) . Seven inch-diameter pieces of the meltblown web were coated with foams prepared from the three Quatrisoft® solutions. Each piece of nonwoven web was coated by means of a doctor blade set at a height of 100 mil (about 2.5 mm) . The samples then were dried in an oven at about 77°C The uniformity of each coating was characterized using iodine staining and an optical microscope. Iodine staining was carried out by placing the treated samples in an enclosed glass chamber with solid iodine for 30 minutes. Iodine vapor resulted in the staining of poly¬ electrolytes (primarily quartemized species) on the surfaces of the fibers of the nonwoven webs. The development of a rust color verified modification of the fibers surfaces by the polyelectrolyte and allowed visual assessment of the homogene¬ ity of the coating.

Visual assessment was accomplished by means of an Olympus BH-2 microscope equipped with an MTV-3 video adaptor, Hitachi video camera, Panasonic Ag-EP60 color video printer and Sony CVM-1271 monitor. A Bausch & Lomb stereo microscope was used to observe foam collapse.

After careful analysis, the 1.5 percent solution resulted in the most promising foam coating; i.e., it provided the best coverage. The lower concentrations did not coat the material as uniformly and consistently as shown through iodine staining and optical microscopy. However, none of the coatings were uniformly present on all of the fibers.

Example 2

Accordingly, the procedure of Example 1 was repeated, followed by nipping after application of the foam. Specifi¬ cally, a foam was prepared from a solution of 1.5 percent Quatrisoft® by means of the hand mixer on the "whip" setting. The 100 mil foam thickness was applied as described above to a seven inch-diameter piece of meltblown web using a Pacific® Scientific doctor blade. The foam-coated sample was nipped in an Atlas Laboratory Wringer having a 30-lb (13.6-kg) nip setting (Atlas Electric Devices Company, Chicago, Illinois) and then placed in an oven at 77°C for 45 minutes. The foam coatings then were characterized by means of iodine staining. Again, coatings were nonuniform and substantially absent from the underside of the fibers.

Since the use of a doctor blade and nip did not provide complete coating of the meltblown fibers, vacuum extraction of foam through the web was investigated. Samples of meltblown web were coated with foam produced from a 1.5 percent solution of Quatrisoft® as described above. Each foam-coated sample then was placed in either an eight-inch diameter Buchner funnel or a medium porosity glass frit mounted in a filtering flask having a side-arm connected to a vacuum source. Vacuum was applied until the foam was aspirated through the entire sample.

Nipping was used in conjunction with the vacuum extrac¬ tion to eliminate excess foam on the fibers and to yield a more even coating distribution. The coated and nipped samples were dried in an oven at 77^βC for 45 minutes. Coverage was again assessed via iodine staining.

The glass frit eliminated much of the excess foam observed with the Buchner funnel above the holes of the funnel and provided more uniform coverage. The samples were observed to have uniform coverage on both sides of the web as well as the interior of the web.

Example 3

The spunbonded web was used in further experiments because the fibers were much larger than those on the meltblown web and could be viewed through the optical microscope to more easily observe the foam coatings on individual fibers.

The use of a heat gun was investigated to determine if the foam would collapse more quickly on fibers under direct heating. The differences in coatings imparted by varying drying techniques were monitored through iodine staining and microscopy. The following foam coating techniques were employed (in each case, the foam was prepared from a solution of 1.5 percent Quatrisoft® by means of the hand mixer on the "whip" setting) : Sample A

Doctor blade at 100 mil (about 2.5 mm), vacuum extrac- tion, nipped at 30 lb (13.6 kg), oven-dried at 77°C for 45 minutes.

Sample B

Doctor blade at 100 mil (about 2.5 mm), vacuum extrac¬ tion, nipped at 30 lb (about 13.6 kg), dried with a heat gun at 260°C for 3 minutes. Sample C

Doctor blade at 100 mil (about 2.5 mm), vacuum extrac¬ tion, oven-dried at 77°C for 45 minutes. Sample D Doctor blade at 100 mil (about 2.5 mm), vacuum extrac¬ tion, dried with a heat gun at 260°C for 3 minutes.

Differences in drying methods did not make a significant difference in the uniformity of the coatings. The immediate drying from the heat gun did not have any benefit on the result coating over oven drying, but drying in the oven required 30 minutes while the heat gun took 3 minutes. The oven was selected as the drying technique of choice because it was less labor intensive.

In order to investigate the effect of heat on foam collapse, samples of foam prepared with the hand mixer from a 1.5 percent Quatrisoft® solution were placed in petri dishes and exposed to direct heat from a heat gun at 260°C Upon drying, the collapsing of the foam was observed by means of a Bausch & Lomb stereo microscope at 30x magnification. A similar experiment was performed to observe the foam collaps¬ ing onto the spunbonded web after different drying times. Four different samples of foam-treated spunbonded web having various drying times were observed under the optical micro¬ scope at 40x and lOOx magnification to determine if the foam differed as a result of the drying. Sample E

Doctor blade at 100 mil (about 2.5 mm), vacuum extrac¬ tion, nipped at 30 lb (about 13.6 kg), iodine stained for 5 minutes. Sample F

Doctor blade at 100 mil (about 2.5 mm), vacuum extrac¬ tion, nipped at 30 lb (about 13.6 kg), dried in a convection oven at 72°C for 5 minutes, iodine stained for 5 minutes.

Sample G Doctor blade at 100 mil (about 2.5 mm), vacuum extrac¬ tion, nipped at 30 lb (about 13.6 kg), dried in a convection oven at 72°C for 10 minutes, iodine stained for 5 minutes.

Sample H

Doctor blade at 100 mil (about 2.5 mm), vacuum extrac- tion, nipped at 30 lb (about 13.6 kg), dried in a convection oven at 72°C for 15 minutes, iodine stained for 5 minutes.

The Quatrisoft® foams were very stable, apparently as a result of the high solution viscosity. The foams did not spontaneously collapse on drying in the petri dishes or on the spunbonded web. In each case the dried foam retained its original bubble shape. In such cases, a physical collapsing of the foam through, for example, nipping is necessary.

Example 4

The procedure of Example 3 was repeated in order to evaluate the effect of foam thickness on coating quality. Foam thicknesses of 100 mil (about 2.5 mm) and 50 mil (about 1.2 mm) were coated on separate spunbonded nonwoven web samples by means of a doctor blade, followed by vacuum extraction, nipping at 30 lb (about 13.6 kg), and drying in a convection oven at 72°C The uniformity of each coating was assessed by means of iodine staining.

Similar experiments were performed to evaluate the effect of using a constant add-on weight using two different concentrations of the Quatrisoft® solution from which the foam was prepared. A 100-mil (about 2.5-mm) thick foam prepared from a 1.5 percent solution and a 150-mil (about 3.8-mm) thick foam prepared from a 0.5 percent solution each gave a 2 percent by weight add-on on a dry weight basis. As before, the foams were applied by doctor blade, followed by vacuum extraction, nipping at 30 lb (about 13.6 kg), and drying at 72°C in a convection oven. Iodine staining was used to evaluate the samples.

Changing the initial foam thickness using the doctor blade resulted in differences in foam coatings when used with a constant concentration of solution - a greater foam thickness provided better coverage. For a given percent solids solution, a 100-mil (about 2.5-mm) foam thickness proved to be sufficient. The higher concentration of Quatrisoft® provided a better coating, even at a lower thickness. A decrease in foam thickness with the same percent Quatrisoft gave a less evenly coated web.

Example 5

The procedure of Example 3 was repeated to permit a comparison of foam coating with solution coating. A first sample of the spunbonded nonwoven web was coated with a solution containing 0.5 percent Quatrisoft® by vacuum extraction. The sample then was nipped as described earlier and dried at 72°C for 45 minutes in a convection oven. After nipping, the sample had a wet add-on of 100 percent.

A second sample of the spunbonded web was coated with foam prepared from a 1.5 percent solution of Quatrisoft® as already described (doctor blade at 100 mil or about 2.5 mm, vacuum extraction, nipping at 30 lb (about 13.6 kg), and drying in a convection oven at 72°C) .

The durability of the solution and foam coatings was assessed by iodine staining and wettability to sessile drops. The wettability of the treated samples was measured by placing drops of water on a surface of each sample. If the drops of water were absorbed into the material, the treated sample was considered wettable. The durability of the surface treatments or coatings was assessed by soaking the treated sample in 100 ml of water for 30 minutes and then allowing it to dry in the convection oven at 72°C for 30 minutes. Iodine staining and wettability by drops of water were used to evaluate the coating's durability to this water soak.

Based on the iodine staining results as observed through an optical microscope, the solution-coated first sample did not show as complete coverage of the fibers as did the second, foam-coated sample. There were patches of areas on the solution-treated sample that did not have any coating present.

Durability studies also showed the efficacy of using foam coating over solution coating. After rinsing the samples in water, Quatrisoft® remained on the surfaces of the fibers. There was a decrease in the amount of Quatrisoft®, but foam- coated samples retained greater levels of coating after a water rinse than solution-coated samples. Wettability studies also showed the efficacy of using foam coatings. Following rinsing, the foam-treated sample continued to be wettable. Water wettability was decreased significantly for the solu¬ tion-treated sample.

Example 6

Polyelectrolyte/surfactant complexes were also investi¬ gated. The complexes were prepared from a polyacrylic acid having a weight-average molecular weight of 50,000 daltons (obtained as a 25 percent by weight aqueous pH 7 solution from Polysciences, Warrington, Pennsylvania) and didodecyl- dimethylammoniumbromide (AldrichChemical Company, Milwaukee, Wisconsin, and J.T. Baker, Phillipsburg, New Jersey) . Solutions having molar ratios of polyacrylic acid (polyelec¬ trolyte or P) to didodecyldimethylammonium bromide (surfactant or S) of 100:1, 50:1, 20:1, 10:1, and 5:1 were prepared as summarized below. Solution A

P:S of 100:1, consisting of 6.4 ml 1 percent surfactant solution and 100 ml of 1 percent polyelectrolyte solution. The viscosity of the solution was 2.7 x 10^'5 N and its surface tension was 38.4 x 10^'3 Pa s.

Solutjpn. B

P:S of 50:1, consisting of 12.85 ml of 1 percent surfactant solution and 100 ml 1 percent polyelectrolyte solution. The viscosity and surface tension of the solution were 3.2 x 10^'5 N and 31.7 x IO^"3 Pa ε.

Solution C

P:S of 20:1, consisting of 0.33 g of surfactant sonicated in 22 ml of water and 100 ml of 1 percent polyelectrolyte solution. Solution viscosity and surface tension were not determined. soiutipn P

P:S of 10:1, consisting of 0.66 g of surfactant sonicated in 22 ml of water and 100 ml of 1 percent polyelectrolyte solution. The viscosity of the solution was 2.5 x io^'5 N. The surface tension of the solution was 30.4 x 10^'3 Pa s. Solution E

P:S of 5:1, consisting of 1.32 g of surfactant sonicated with in 33 ml water and 100 ml of polyelectrolyte solution. The viscosity of the solution was 2.2 x 10^'5 N and its surface tension was 31.8 x 10^'3 Pa s.

Because the polyelectrolyte/surfactant complex solutions had low viscosities, the hand mixer did not produce suffic¬ iently stable foams to permit the subsequent application of foam to a substrate. Accordingly, the liquid blow-through method described in Example 1 was employed to generate the foams.

Foams were generated from Solutions A and D and placed on a polypropylene film. The coated films were observed under the stereo microscope while drying with the heat gun at 260^βC The foams collapsed on the film, apparently because of the low viscoεity of the solutions from which the foams were gener¬ ated. Foams were prepared from all five solutions. The foams were applied as described in Example 1 to 2.25-inch (about 5.7-cm) diameter samples of the spunbonded nonwoven web, followed by vacuum extraction, nipping at 30 lbs (about 13.6 kg), and drying in a convection oven at 72°C for 30 minutes. The foam coatings were compared to solution coatings with characterization by iodine staining and microscopy. The less viscous polyelectrolyte/surfactant solutions were found to provide a less stable foam that readily collapsed on a substrate, including both film and fibers. The collapsing of the foams resulted in better coverage on the PP fibers.

Durability was assessed for coatings of foams prepared from a 1 percent surfactant solution (Control) , Solution A, and Solution D by iodine staining and testing wettability by drops of water as already described.

The Control solution had a low viscosity but produced a relatively stable foam using the liquid blow-through method. However, the foam prepared from the Control did not provide the necessary functionality for coating durability that a polyelectrolyte/εurfactant complex provided. Solution D generated the best foam. Solution A did not contain suffi¬ cient surfactant to produce a sufficiently stable foam; Solution E was not used because it formed a precipitate.

The polyelectrolyte/surfactant complex demonstrated an enriched concentration of solids in the foam; e.g., with Solution D, 2.6 percent solids in the foam compared to 1.4 percent solids in the solution.

The polyelectrolyte/surfactant complex solutions generally produce a sufficiently stable foam to coat the spunbonded nonwoven web samples. Iodine staining indicated that foam coatings using Solution D provided uniform coverage of web fibers, while Solution A foam did not substantially coat the fibers. Iodine staining, however, does not confirm the presence of the polyelectrolyte on the surfaces of the fibers. The presence of the polyelectrolyte was confirmed by attenuated total reflectance Fourier-transform infrared spectroscopy. A strong absorbance at 1545 cm^' and a lesser one at 1400 cm^'1 were indicative of a carboxylic acid salt anion (COO ) . Note that the polyacrylic acid is converted to the salt form due to its interactions with the cationic surfactant. The attenuated total reflectance Fourier-trans- form infrared spectroscopy was carried out by placing the sample to be analyzed on the top surface of a ZnSe crystal with a face angle of 45°. The estimated depth of penetration was approximately 2 micrometers (Nicolet Model 740 Fourier Transform Infrared Spectrophotometer with a SpectraTech Horizontal ATR Accessory) .

Coatings made from Solution D produced the best in¬ dividual fiber coverage with an increase in uniformity. Durability tests showed that the such coatings remained on the fibers after water rinsing. Solution D, applied as a solution and not as a foam, did not show much decrease in coating after rinsing with water, but the solution gave an uneven coating.

The reduction in surface tension of water after exposure to a treated sample was measured by first determining the surface tension of 75 ml of water in a 100 ml beaker. The surface tension of the water then was measured after a treated sample was soaked for 30 minutes. The surface tension reduction studies indicated that water wettability occurs without water surface tension reduction for materials treated with a Solution D foam coating. Materials treated with the Control (surfactant alone) foam and solution both wet upon soaking in water. The levels of these coatings were not reduced considerably by soaking, but water wettability occurred by means of surface tension reduction. This demonstrateε the efficacy of using a polyelectrolyte/sur- factant complex for providing a modified polymer surface for wettability without surface tension reduction in contrast to traditional surfactant treatments.

While the specification has been described in detail with respect to specific embodiments thereof, it will be appreci- ated that those skilled in the art, upon attaining an understanding of the foregoing, may readily conceive of alterations to, variations of, and equivalents to these embodiments. For example, more than one amphiphilic polyelec¬ trolyte may be present in the solution from which a foam is produced. As another example, more than one surfactant and/or more than one polyelectrolyte may be employed when the amphiphilic polyelectrolyte is a surfactant/polyelectrolyte complex. Other variations and equivalents will be readily apparent to those having ordinary skill in the art. Accord¬ ingly, the scope of the present invention should be assessed as that of the appended claims and any equivalents thereto.

Claims

WHAT IS CLAIMED IS:

1. A method of coating a hydrophobic fibrous material with an amphiphilic polyelectrolyte which compriseε: coating the hydrophobic fibrous material with a foam comprising an amphiphilic polyelectrolyte and water under conditions sufficient to substantially uniformly coat the hydrophilic fibrous material with the amphiphilic polyelectro¬ lyte.

2. The method of claim 1, in which the hydrophobic fibrous material is a polyolefin.

3. The method of claim 2, in which the polyolefin is polyethylene or polypropylene.

4. The method of claim 1, in which the hydrophobic fibrous material is a nonwoven web.

5. The method of claim 4, in which the nonwoven web is a meltblown nonwoven web.

6. The method of claim 4, in which the nonwoven web is a spunbonded nonwoven web.

7. A method of coating a hydrophobic fibrous material with an amphiphilic polyelectrolyte which comprises: preparing an aqueous solution of an amphiphilic polyelec¬ trolyte; generating a foam from the aqueous solution; and coating the hydrophobic fibrous material with the foam under conditions sufficient to substantially uniformly coat the hydrophilic fibrous material with the amphiphilic polyelectrolyte.

8. The method of claim 7, in which the hydrophobic fibrous material is a polyolefin.

9. The method of claim 8, in which the polyolefin is polyethylene or polypropylene.

10. The method of claim 7, in which the hydrophobic fibrous material is a nonwoven web.

11. The method of claim 10, in which the nonwoven web is a meltblown nonwoven web.

12. The method of claim 10, in which the nonwoven web is a spunbonded nonwoven web.

13. The method of claim 7, in which the amphiphilic polyelectrolyte is a polymer.

14. The method of claim 7, in which the amphiphilic polyelectrolyte is a surfactant/polyelectrolyte complex.

15. The method of claim 7, in which the amphiphilic polyelectrolyte is a polymeric surfactant.

16. A method of coating a hydrophobic nonwoven web with an amphiphilic polyelectrolyte which comprises: preparing an aqueous solution of an amphiphilic polyelec¬ trolyte; generating a foam from the aqueous solution; coating the hydrophobic fibrous material with the foam; vacuum extracting the coated nonwoven web; nipping the vacuum-extracted coated nonwoven web; and drying the nipped nonwoven web.

17. The method of claim 16, in which the nonwoven web is a meltblown nonwoven web.

18. The method of claim 16, in which the nonwoven web is a spunbonded nonwoven web.

19. The method of claim 16, in which the amphiphilic polyelectrolyte is a polymer.

20. The method of claim 16, in which the amphiphilic polyelectrolyte is a surfactant/polyelectrolyte complex.

21. The method of claim 16, in which the amphiphilic polyelectrolyte is a polymeric surfactant.