SELF-BONDED CELLULOSIC NONWOVEN WEB AND METHOD FOR MAKING

BACKGROUND

Nonwoven webs are used in a wide variety of applications. Such webs are often made by collecting a mass of fibers and bonding at least some of the fibers to each other to form a web. Often, such fibers are melt-bonded to each other, and/or a binder is added that can bind the fibers together.

SUMMARY

In broad summary, herein is disclosed a self-bonded nonwoven web, comprising at least some cellulosic fibers that are self-bonded to each other at points of intersection of the cellulosic fibers with each other; and, an ionic liquid. Methods of making such a web are also disclosed. These and other aspects will be apparent from the detailed description below. In no event, however, should this broad summary be construed to limit the claimable subject matter, whether such subject matter is presented in claims in the application as initially filed or in claims that are amended or otherwise presented in prosecution.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a portion of an exemplary self-bonded nonwoven web as disclosed herein.

FIG. 2 is a magnified view of a portion of the web of FIG. 1.

FIG. 3 is a optical micrograph (320×) of a portion of an exemplary self-bonded nonwoven web.

FIG. 4 is a optical micrograph (240×) of a portion of an exemplary fiber mat from which a nonwoven web of the general type shown in FIG. 3 can be produced.

Like reference numbers in the various figures indicate like elements. Some elements may be present in identical or equivalent multiples; in such cases only one or more representative elements may be designated by a reference number but it will be understood that such reference numbers apply to all such elements. FIGS. 1 and 2 are not to scale and are used for the purpose of illustrating different embodiments of the invention. In particular the dimensions of the various components are depicted in illustrative terms only, and no relationship between the dimensions of the various components should be inferred. Although terms such as “top”, bottom”, “upper”, lower”, “under”, “over”, “front”, “back”, “outward”, “inward”, “up” and “down”, and “first” and “second” may be used in this disclosure, it should be understood that those terms are used in their relative sense only unless otherwise noted. As used herein as a modifier to a property or attribute, the term “generally”, unless otherwise specifically defined, means that the property or attribute would be readily recognizable by a person of ordinary skill but without requiring absolute precision or a perfect match (e.g., within +/−20% for quantifiable properties). The term “substantially”, unless otherwise specifically defined, means to a high degree of approximation (e.g., within +/−10% for quantifiable properties) but again without requiring absolute precision or a perfect match. Terms such as same, equal, uniform, constant, strictly, and the like, are understood to be within the usual tolerances or measuring error applicable to the particular circumstance rather than requiring absolute precision or a perfect match. Those of ordinary skill will appreciate that as used herein, terms such as “substantially no”, “substantially free of”, and the like, do not preclude the presence of some extremely low, e.g. 0.1% or less, amount of material, as may occur e.g. when using large scale production equipment subject to customary cleaning procedures.

DETAILED DESCRIPTION
Glossary

The term cellulosic broadly encompasses polysaccharides including e.g. native cellulose, regenerated cellulose (viscose), and the like. It also encompasses naturally-occurring cellulose derivatives such as e.g. hemi-cellulose, chitin, chitosan, and the like. It also encompasses cellulose that has been partially derivatized, e.g. that has been partially esterified, hydrolyzed, nitrated, etc., or in which some hydroxyl groups have been converted to ether groups, as long as sufficient hydroxyl groups are retained that the partially derivatized cellulose is able to be activated by an ionic liquid as disclosed herein.

The term self-bonded as applied to two cellulosic fibers means that, at an intersection of the two fibers, the fibers are bonded to each other by cellulosic bonding material (e.g., in the form of a “globule” as described later herein) that extends between the fibers. In at least some embodiments, at least a portion of the cellulosic bonding material is derived from at least one of the bonded fibers.

The terms “intersect”, “intersection”, and the like, as applied to two fibers denotes a location at which the two fibers are in direct contact with each other or are in close adjacency with other (e.g. are within a few microns of each other at their point of closest approach).

The term “web” denotes a mass of nonwoven fibers that are bonded to each other sufficiently that the mass of fibers has sufficient mechanical integrity to be handled as a self-supporting layer; e.g., that can be handled with conventional roll-to-roll web-handling equipment. The term “mat” denotes a mass of fibers that are not bonded to each other sufficiently to form a self-supporting web (e.g. a mass of air-laid fibers that are not yet bonded to each other).

The term ionic liquid denotes a material that, when provided in neat form (in the absence of diluent or solvent) at or below 100 degrees C., takes the form of a liquid comprising cations and anions. Such an ionic liquid can be thought of as being a salt in liquid form. The term ionic liquid does not encompass materials (such as e.g. NaCl) that are solid when provided in neat form at or below 100 degrees C., are solid.

Shown in FIG. 1 in side perspective view is a portion of an exemplary self-bonded nonwoven web 100 as disclosed herein; a portion of web 100 is shown in magnified view in FIG. 2. Web 100 comprises at least first, cellulosic fibers 110 arranged (optionally in combination with second, non-cellulosic fibers 120) to provide a fibrous nonwoven web with interior 106 and with first major surface 102 and second, oppositely-facing major surface 104. At least some of the first, cellulosic fibers 110 are self-bonded to each other by self-bonds 111 at points of intersection of the first, cellulosic fibers 110 with each other.

Activation and Self-Bonding

Such self-bonding may be achieved by contacting a mass of cellulosic fibers with an ionic liquid that at least partially dissolves the cellulosic material of some, but not all, of the cellulosic fibers. This process, which will be referred to by the shorthand of “activation” for convenience of description herein, can be accelerated e.g. by raising the cellulosic fibers and/or the ionic liquid to an elevated temperature. At locations at which two such activated cellulosic fibers intersect each other, at least partially dissolved cellulosic material from one fiber may at least slightly intermingle with similar at least partially dissolved material of the other fiber. Fibers that have been activated in this manner can then be processed (e.g., by cooling) so that the at least partially solubilized cellulosic material is solidified with the result that a self-bond between the two fibers is formed at one or more points of intersection between the two fibers. Such a cellulosic self-bond does not require added binder or adhesive to be used and is thus analogous to a melt-bond between two thermoplastic fibers, except it is achieved by a solvation/solidification mechanism rather than by a melting/solidification mechanism.

It will be appreciated that in some circumstances the activation process may require only the partial solvation of e.g. just enough cellulosic material on the surface of fibers to achieve the desired intermingling such that subsequent solidification results in the formation of a self-bond. However, in some circumstances at least some cellulosic fibers (e.g., relatively small-diameter fibers) may be substantially, or essentially completely, dissolved, while at least some portions of at least some other cellulosic fibers (e.g., core portions of relatively large-diameter fibers) remain undissolved. In such cases, the herein-described self-bonding specifically includes the bonding of two such at least partially undissolved fibers to each other, even if such bonding is performed at least partially by the solidification of cellulosic material derived from one or more dissolved fibers rather than solely by the solidification of cellulosic material derived from the at least partially undissolved fibers themselves. (The ordinary artisan will appreciate that in many instances, a combination of both mechanisms may be present). However, in either case, the herein-described activation/self-bonding process is distinguished from processes in which a cellulosic material is essentially completely dissolved and then regenerated to provide newly-formed fibers. In contrast to such processes, the processes described herein can provide bonding between cellulosic fibers while leaving at least some portions (e.g., radially-inwardmost portions) of at least some of the cellulosic fibers generally or substantially in their original form.

It is emphasized that it is not necessary to use populations of small and large diameter cellulosic fibers to achieve the affects described herein. For example, a certain population of cellulosic fibers might have a particular composition, surface treatment, and so on, that renders this population more or less able to be activated by an ionic liquid, than a second population of cellulosic fibers. And, of course, a population of fibers (e.g., that is relatively homogenous) may be exposed to an ionic liquid under conditions (e.g., time, temperature, and so on) that limit the activation to only some portions of some fibers.

As noted above, at least some of first, cellulosic fibers 110 are self-bonded to each other by self-bonds 111. In some embodiments, such self-bonds 111 may occur at points of (direct) contact of fibers 110 with each other (e.g., points 113 as shown in exemplary embodiment in FIG. 2). However, in at least some embodiments, such self-bonds may be provided at least partially by cellulosic bonding material that is in the form of “globules” 112 as also shown in exemplary embodiment in FIG. 2. Such globules may e.g. bridge between adjacent portions of two or more cellulosic fibers to form self-bonds. The term “globule” is used to broadly encompass a parcel of cellulosic bonding material of any shape or aspect ratio, noting that such globules do not necessarily have to be spherical or even approximately spherical in shape. Numerous globules 112 are depicted in exemplary manner in FIGS. 1 and 2 (actual globules 112 are visible in the microphotograph of FIG. 3). Although some globules may be located on individual fibers and thus may not necessarily contact other fibers, in some embodiments at least some globules 112 may be present at points of intersection of fibers with each other (as depicted in exemplary manner in FIG. 2) and thus may provide self-bonds 111.

Globules 112 may not necessarily be comprised of essentially 100 wt. % cellulosic material. Rather, in many embodiments, at least some ionic liquid (and, in some cases, possibly a small amount of residual water) may remain on or within (e.g., entrapped within) the solidified cellulosic material of globules 112. This may advantageously provide finished web 100 with one or more properties or characteristics that are attributable to the ionic liquid, as discussed later herein. In fact, it appears that at least some of the ionic liquid may be entrapped in the web in a form in which it is not removable even by contacting (e.g. soaking) the web with a liquid that would be expected to remove any ionic liquid that was e.g. freely accessible on the surface of the web fibers, as demonstrated in the Examples herein. Thus, the discussions herein that the globules (or, in a more general sense, the material that provides self-bonds 111 between cellulosic fibers 110) are comprised of cellulosic material, does not preclude the presence of at least some amount of ionic liquid in the self-bonding material. Likewise, in some circumstances at least some portion of the “solidified” self-bonding cellulosic material may be partially swollen by ionic liquid rather than being e.g. completely “solid” (e.g. crystalline).

Nonwoven web 100 comprises at least first, cellulosic fibers 110. Such fibers may be e.g. native cellulose, a naturally-occurring cellulose derivative, regenerated cellulose (e.g. rayon, viscose, lyocell, and so on), or a partially derivatized cellulose, as noted above. In specific embodiments, such cellulosic fibers may be chosen from e.g. fibers derived from cotton, wool, jute, agave, sisal, coconut, soybean, hemp, flax, kenaf, bamboo, abaca, henequen, sunn, ramie, sisal, chitin, chitosan, and any combination or blend of such fibers. In particular embodiments, such cellulosic fibers may be a blend of cellulose, chitin and/or chitosan, such as the materials available under the trade designation CRABYON. As mentioned, cellulosic fibers 110 may include cellulose that has been derivatized, e.g. partially hydrolyzed, esterified (e.g., to form acetyl, propionate, and/or butyrate groups), nitrated, and so on. Such derivatization may be chemical, enzymatic, etc.

First, cellulosic fibers 110 may comprise any suitable diameter. In various embodiments, fibers 110 may comprise a diameter of at least about 1, 2, 4, or 8 μm. In further embodiments, fibers 110 may comprise a diameter of at most about 200, 100, 60, 40, or 20 μm. Any desired mixture of fiber diameters may be used. For example, a first population of cellulosic fibers may be used that comprises a relatively small average diameter and a second population of cellulosic fibers may be used that comprises a relatively large average diameter.

In some embodiments, the fiber material of web 100 may be comprised of essentially 100 wt. % cellulosic fibers, based on the total weight of the fiber material of the web, disregarding the presence of any non-fiber material (e.g. ionic liquid, a particulate additive, and so on) in the web. In other embodiments, at least some second, non-cellulosic fibers 120 may be present. In such embodiments, web 100 should comprise a high enough weight fraction of cellulosic fibers to enable the herein-described self-bonding to be satisfactorily performed (it will be appreciated, of course, that the degree of self-bonding that is needed may vary widely depending on the application). In various embodiments, cellulosic fibers may make up at least about 20, 40, 60, or 80 wt. % of the fiber material of web 100 (exclusive of non-fiber components). In particular embodiments web 100 (e.g., self-bonding sites 111, in particular globules 112) is substantially free of any non-cellulosic non-fibrous polymer material (e.g., a binder (e.g. in the form of a latex or emulsion), an adhesive or the like). In specific embodiments, self-bonding sites 111 are substantially free of any bonding material that is not derived from cellulosic fibers of the mass of fibers that is contacted with the ionic liquid. In other embodiments, at least one non-cellulosic non-fibrous binder may be present in web 100.

Second, non-cellulosic fibers 120, if present, may be of any suitable composition, may take any suitable physical (e.g., geometric) form, and may have been made by any desired process. Thus, second fibers 120 may be chosen from e.g. monocomponent fibers, multicomponent fibers, crimped fibers, meltblown fibers, meltspun fibers, and any combination of any such fibers. In various embodiments, such fibers may be essentially continuous (e.g., meltspun fibers), or may be cut to a predetermined length (e.g., staple fibers). A non-limiting list of general polymer types that might be suitable for second fibers 120 includes e.g. polyolefins, polyamides, polyesters, and so on. Such compositions may be generally or substantially nonpolar (e.g., polyolefins and the like), or may be generally or substantially polar (e.g. polyethylene oxide and the like), or may lie somewhere in between such extremes. Any or all such second fibers may be surface-treated (whether e.g. by chemical grafting, by deposition of a surface coating, and so on) if desired for a particular application. A non-limiting list of materials potentially suitable for use as second fibers 120 includes polymers and/or copolymers selected from poly(propylene), poly(ethylene), poly(butane), poly(ethylene) terephthalate, poly(butylene) terephthalate, poly(ethylene) napthalate, poly(amide), poly(urethane), poly(lactic acid), poly(vinyl)alcohol, poly(phenylene) sulfide, poly(sulfone), liquid crystalline polymer, poly(ethylene)-co-poly(vinyl)acetate, poly(acrylonitrile), cyclic poly(olefin), poly(oxymethylene), poly(olefinic) thermoplastic elastomers, recycled fibers containing any of the preceding thermoplastic (co)polymers, and any combination thereof. If desired, second fibers 120 can include biodegradable fibers such as fibers comprising a substantial amount of aliphatic polyester (co)polymer derived from poly(lactic acid), poly (glycolic acid), poly (lactic-co-glycolic acid) blends, and/or a combination thereof.

In some embodiments, any or all of second fibers 120 may comprise at least one component with a melting point sufficiently low that at least some second fibers 120 may be melt-bonded to other second fibers 120 (e.g., in a preliminary pre-bonding step, as discussed in further detail later herein). In particular embodiments, at least one component of at least some second fibers 120 may exhibit a melting point that is below the decomposition temperature of cellulosic fibers 110, to facilitate such a pre-bonding step. In some embodiments such a melting point of at least some second fibers 120 may be chosen to be above an activation temperature that is used to form the cellulosic self-bonds (so that the only significant effect of the activation is to form cellulosic-cellulosic self-bonds). In other embodiments, such a melting point of at least some second fibers 120 may be chosen to be in the same range (or below) the activation temperature, so that the activation process may result in at least some fiber-fiber melt-bonding of second fibers 120 in addition to resulting in the formation of cellulosic-cellulosic self-bonds.

At least some portion of an ionic liquid that is used to activate cellulosic fibers 110 for self-bonding may remain in the finished self-bonded web. (The terms “an” ionic liquid and “the” ionic liquid encompass not only single ionic liquids, but also any desired mixture of any number of ionic liquids.) In some embodiments, an ionic liquid may provide at least about 1% by weight of the total material of web 100 (including fibers, the ionic liquid, any particulate additives, and so on). In various embodiments, an ionic liquid may provide at least about 2, 5, 10, 15, 20, or 30% by weight of the total material of web 100. In further embodiments, an ionic liquid may provide at most about 70, 60, 50, 40, 30, 20, 10, 5, or 2% by weight of the total material of web 100. As discussed previously, in at least some embodiments at least some of the ionic liquid may remain in web 100 at least partially by way of being present in globules 112 that are distributed throughout at least a portion of web 100.

Any ionic liquid that is capable of activating cellulosic fibers as described herein may be used. In various embodiments, suitable ionic liquids may be chosen from imidazolium ionic liquids, pyridinium ionic liquids, ammonium ionic liquids, and mixtures and combinations thereof. Any such ionic liquid may comprise any suitable (anionic) counterion. In various embodiments, the ionic liquid can include at least one anionic counterion that is selected from the group consisting of halogen anions, fluorine containing anions, alkyl sulfate anions, alkyl phosphate anions, acetate anions, dicyanamide (N(CN)₂) anions, or thiocyanate (SCN) anions.

A non-limiting list of suitable imidazolium ionic liquids includes e.g. 1-methyl-3-methylimidazolium, 1-ethyl-3-methylimidazolium, 1-propyl-3-methylimidazolium, 1-butyl-3-methylimidazolium, 1-pentyl-3-methylimidazolium, 1-hexyl-3-methylimidazolium (sometimes referred to by the nomenclature [C₁MIM]-[C₆MIM]), with any suitable (anionic) counterion. Suitable counterions for MIM-based ionic liquids may include e.g. chloride, bromide, methanesulfonate, methylsulfate, ethylsulfate, hydrogensulfate, thiocyanate, acetate, formate, dihydrogen phosphate, dimethyl phosphate, diethyl phosphate, and benzoate. Suitable pyridinium ionic liquids may include e.g. 1-butyl-3-methylpyridinium, e.g. with a counterion chosen from chloride, bromide, thiocyanate, and acetate. Suitable ammonium ionic liquids may include e.g. tetrabutylammonium, e.g. with a formate counterion. Potentially suitable ionic liquids are described in further detail in U.S. Pat. No. 6,824,599 to Swatloski, which is incorporated by reference herein in its entirety for this purpose. In particular embodiments, the ionic liquid may be chosen from 1-butyl-3-methylimidazolium chloride, 1-allyl-3-methylimidazolium chloride, and 1-ethyl-3-methylimidazolium acetate, and any combination thereof.

As discussed in the Examples herein, in at least some embodiments the contacting of an ionic liquid with a mass of fibers can promote self-bonding that advantageously enhances the mechanical properties (e.g. tensile strength) of the mass of fibers. In some embodiments, the presence of an ionic liquid (e.g., in a form in which it is generally or substantially non-removable from the self-bonded web) in self-bonded web 100 may advantageously provide one or more non-mechanical enhanced characteristics to nonwoven web 100. Such characteristics (depending e.g. on the particular ionic liquid used) may include e.g. enhanced fire retardant properties, enhanced antistatic properties, enhanced antimicrobial properties (e.g., antibacterial and/or antifungal properties), enhanced lubricating or friction-reduction properties, or a combination of one or more of these properties.

In some embodiments, the ionic liquid (with or without diluent) may contain any suitable additive(s), provided for any purpose. Such additives might be chosen from e.g. stabilizers, surfactants, wetting aids, anti-foams, dispersants, processing aids, leveling agents, mineral fillers, and so on. In some embodiments, at least one such additive may remain in the finished self-bonded web and may impart one or more desired functional properties to the finished web. Such functional additives might be chosen from e.g. dyes, pigments, opacifiers, antimicrobial agents, anti-oxidants, UV-stabilizers, thermochromic agents, detergents, and so on. Any desired combination of any such additives may be used. However, in some embodiments the ionic liquid (or ionic liquid/diluent mixture) is substantially free of any additives.

In some embodiments, nonwoven web 100 may optionally include a plurality of particulates 130 as shown in FIG. 2. Optional particulates 130 can be selected e.g. from the group consisting of abrasive particulates, detergent particulates, anti-bacterial particulates, adsorbent particulates, absorbent particulates, and any combination thereof.

The methods disclosed herein may be applied to any mass of collected nonwoven fibers to which it is desired to impart one or more advantageous properties as disclosed herein. In some embodiments, the ionic liquid may be contacted with an unbonded mass of collected fibers (e.g., a fiber mat in which the fibers have not been pre-bonded to each other to any significant extent). In such embodiments, it may be convenient to position an ionic liquid impingement apparatus in-line with the fiber-collecting apparatus. In other embodiments, the ionic liquid may be contacted with a pre-bond web, with the term pre-bond web denoting a mass of collected fibers that has been subjected to at least light bonding (of e.g. second, non-cellulosic fibers 120 to each other) so as to transform the mass of fibers from an unbonded mat into a web that has at least sufficient mechanical integrity to be handled in roll-to-roll processing equipment. In such embodiments, it may not be necessary to provide an ionic liquid impingement apparatus in-line with the fiber-collecting apparatus or the fiber-pre-bonding apparatus, although this can be done if desired.

A nonwoven fiber mat may be obtained by any suitable fiber-collecting process. Potentially suitable processes include e.g. air-laying, wet-laying, carding, garnetting, melt-spinning, melt-blowing, electro-spinning, solvent-spinning, and so on. In some embodiments, a nonwoven web may be made by air-laying of fibers, e.g. staple fibers (as performed e.g. by the use of so-called Rando Webber apparatus, commercially available from Rando Machine Corporation, Macedon, N.Y.). In some embodiments, a type of air-laying may be used that is termed gravity-laying, as described e.g. in U.S. Patent Application Publication 2011/0247839 to Lalouch, which is incorporated by reference herein for this purpose.

As mentioned above, in some embodiments a mass of collected fibers may be processed to (e.g., lightly) bond at least some second, non-cellulosic fibers 120 to each other to transform the fiber mat into a pre-bond web. In some embodiments, such bonding may be performed by fiber-fiber melt bonding (e.g. of second fibers 120) and/or by use of a binder or by any combination thereof. In particular embodiments, the mass of collected fibers may include at least some second fibers 120 (e.g., bicomponent fibers and/or fibers often referred to by the nomenclature of “melty” fibers) that contain at least one component with a melting point in a range such that these fibers, when exposed to an appropriate temperature, can provide melt-bonding between at least some of second fibers 120. (Some bonding of these fibers to first, cellulosic fibers 110 may also occur, of course.) In some embodiments, other bonding methods may be performed either instead of, or as an adjunct to, the above methods. Such other bonding methods might include e.g. needle-tacking, stitch-bonding, hydroentangling, cross-lapping, and so on. By the use of any such pre-bonding method or methods, a pre-bond web can be provided that can be inputted to the ionic liquid-contacting process to achieve the desired self-bonding. However, this is not necessarily required, and the self-bonding can be performed on a mass of unbonded fibers if desired. In particular embodiments, a self-bonded web 100 may be substantially free of any added non-fibrous binder (i.e., free of any binder added in the form of a liquid, latex, powder, or the like), noting that this requirement does not exclude the presence of e.g. bicomponent fibers in web 100.

As disclosed herein, an ionic liquid (with or without diluent) is contacted with a mass of fibers. The term contact broadly encompasses any situation in which a moving ionic liquid is contacted with (e.g., impinged onto the surface of) a mass of fibers, in which a moving mass of fibers is contacted with (e.g., is submerged in) ionic liquid, and any combinations thereof. In some embodiments, it may be convenient to impinge an ionic liquid onto a major surface of a mass of collected fibers (e.g., an unbonded fiber mat or a pre-bond web) by any suitable method, e.g. spraying, knife coating, roll coating, slot coating, gravure coating, screen printing, and the like. The impingement may be carried out such that the ionic liquid penetrates e.g. essentially completely throughout the thickness of the mass of fibers; or, it may be performed so that the ionic liquid is preferentially located proximate one major surface of the mass of fibers.

Thus, in some embodiments, self-bonds (e.g., globules 112) may be provided throughout web 100 (e.g., throughout interior 106 from first major surface 102 to second major surface 104), e.g. in an at least generally uniform distribution. In other embodiments, self-bonds may be preferentially provided e.g. only in a portion of web 100 that is proximate one major surface of web 100.

In various embodiments, the ionic liquid may be provided as a mixture (e.g., a solution) with a diluent (solvent). Water may be a convenient diluent. In such embodiments, the ionic liquid may be provided at sufficiently high concentration to achieve the desired activation (in combination with other process parameters as discussed herein). In various embodiments, the ionic liquid may be present in an ionic liquid-diluent mixture at least at about 5, 10, 20, 30, or 40 wt. % (at the time that the mixture is contacted with the fibers). In further embodiments, the ionic liquid may be present in the ionic liquid-diluent mixture at most at about 80, 70, 60, or 50 wt. %. In various embodiments, any desired portion of such a diluent may be removed from the self-bonded web (e.g. by exposure to elevated temperature), as desired.

A mass of fibers containing ionic liquid impregnated at least partially thereinto, may be carried (e.g., on a moving belt) into an oven so that the fibers and/or the ionic liquid can be exposed to a first, elevated temperature to activate the cellulosic fibers as described herein. The term “oven” is used broadly to encompass any suitable heating device (e.g., a through-air bonder, which term is familiar to those of ordinary skill in the nonwovens arts) that may be used. To aid in such heating (or as an alternative to using an oven), any other means such as e.g. infrared heating, microwave heating, passing the mass of fibers over or between heated rolls, and so on, may be used. Any suitable exposure temperature and line speed may be used, as long as they combine to allow the ionic liquid and/or the cellulosic fibers to be exposed to a first, elevated temperature, for a sufficient time, to activate at least some of the cellulosic fibers as disclosed herein. In various embodiments, such a first temperature may be at least about 100, 120, or 140 degrees C. In further embodiments, this first temperature may be at most about 180, 160, or 150 degrees C. If desired, the ionic liquid and/or the mass of fibers may be preheated (e.g., before the mass of fibers and an ionic liquid contacted therewith are collectively exposed to an elevated temperature) in order to enhance the activation process.

After a suitable exposure to the first, elevated temperature, the mass of activated fibers can be exposed to a second temperature that is lower than the first temperature and that is sufficiently low to cause at least some of the at least partially dissolved cellulosic material to solidify to form cellulosic self-bonds 111 at points of intersection of first, cellulosic fibers 110 with each other. In various embodiments, this second temperature may be less than about 100, 80, 60, 40, or 30 degrees C. It may be convenient that the second temperature be generally in the range of room temperature (e.g., about 20-30 degrees C.). Such a second temperature may be attained e.g. by simply removing the web from the oven, or the cooling process may be accelerated e.g. by actively impinging moving air onto the web. If desired, refrigeration may be used so that the second temperature may be e.g. less than about 20, 15, or 10 degrees C.

It will be appreciated that if a diluent (such as water) is used that has a boiling point that is significantly lower than the boiling point of the ionic liquid, and particularly if the first temperature to which the ionic liquid-diluent mixture is exposed is near, or somewhat greater than, the boiling point of the diluent, a large fraction (e.g., 80, 90, 95, 98 wt. % or more) of the diluent may be removed during the exposure to the first, elevated temperature. (In fact, it will be appreciated that preferential evaporation of such a diluent may result in a momentarily higher concentration of ionic liquid in the ionic liquid/diluent mixture and thus may aid in the activation of the cellulosic fibers by the ionic liquid.) As such, in many embodiments it may not be necessary to expose the nonwoven web (after cooling from the first temperature to the second temperature) to a drying process for purposes of further removing residual diluent. However, such a secondary drying process can be performed if desired.

As disclosed herein, cooling of the cellulosic fibers and the ionic liquid (from the first, elevated temperature) is all that is necessary to complete the self-bonding process. That is, the disclosed process does not require, and does not encompass, the use of a regenerating liquid (e.g. a liquid that is a sufficiently strong non-solvent for cellulosic materials that it causes any at least partially dissolved cellulosic material to e.g. precipitate from solution) that is brought into contact with the ionic-liquid-impregnated mass of fibers in order to form the self-bonds. Moreover, in at least some embodiments the disclosed process does not include a washing step in which a significant portion (e.g., substantially all) of the ionic liquid is preferentially removed from the mass of fibers. (However, the disclosed process does allow the use of any process, e.g. a mechanical squeezing process, that can non-preferentially remove both ionic liquid and any diluent from the mass of fibers.) In some embodiments, a finished self-bonded web can be subjected to at least one secondary (post-treatment) process of any desired type. Such a process might include e.g. printing on a surface of the finished web, rinsing the web, impregnating the web e.g. with a detergent composition, and so on. However, such a post-treatment will not change the character of the web in a manner inconsistent with the disclosures herein.

The various process parameters and fiber compositions may be chosen and controlled so as to achieve, in combination, the advantageous effects documented herein. For example, the concentration of ionic liquid in a diluent mixture, the amount of ionic liquid-diluent mixture used per area of fiber mat, the temperature to which the fibers and liquids are exposed, the time of exposure to the elevated temperature, and the amount of cellulosic fibers in the web, may all be chosen in combination so ensure that the effects disclosed herein are achieved. As noted, the contacting of ionic liquid with a mass of fibers, and the resulting penetration of ionic liquid into the interior of the mass of fibers, may be controlled as desired. In specific embodiments, the ionic liquid may be e.g. impregnated into the mass of fibers from one major surface only, thus resulting in a selective enhancement of properties (whether mechanical or other) only in a particular layer of the web. Such approaches may advantageously provide nonwoven articles with differential performance on different major surfaces of the article.

In some embodiments, the self-bonding process may increase the tensile strength (e.g. the downweb tensile strength) of a mass of fibers, e.g. of a pre-bond web, by at least about 10, 20, 40, or 80%. In further embodiments, the self-bonding process may increase the tensile strength by a factor of at least about 2, 3, 4, or 5. Specific exemplary effects are documented in the Examples herein. In specific embodiments, the self-bonding process may transform a mass of unbonded fibers (e.g. a fiber mat) into a bonded nonwoven web that has sufficient mechanical integrity to e.g. be handled in conventional roll-to-roll processing. Regardless of the degree to which such mechanical enhancements may result, in some embodiments the self-bonding process (specifically, the presence of the ionic liquid in the web as the result of the self-bonding process) may provide other, non-mechanical enhancements, e.g. an increase in fire retardant properties, anti-static properties, and so on, as discussed earlier herein.

A self-bonded web 100, produced e.g. as described above, can undergo any subsequent processing as desired. In various embodiments, it might be rolled up into a continuous roll good, or might be cut to form discrete articles that can be stacked, stored, etc. Various post-processing operations (e.g., converting, packaging, and so on) can be performed as desired. Self-bonded web 100 can be used in any desired application. In various embodiments, web 100 may be used in applications involving cleaning, scouring, absorbing of liquids, distribution (e.g., wicking) of liquids, abrading of surfaces, and so on. Other applications are also possible.

LIST OF EXEMPLARY EMBODIMENTS

Embodiment 1 is a self-bonded nonwoven web, comprising at least first, cellulosic fibers, wherein at least some cellulosic fibers of the web are self-bonded to each other at points of intersection of the first, cellulosic fibers with each other; and, from about 1% by weight to about 50% by weight of an ionic liquid. Embodiment 2 is the nonwoven web of embodiment 1 wherein the first, cellulosic fibers include fibers chosen from the group consisting of cellulose fibers, regenerated cellulose fibers, and partially derivatized cellulose fibers, and any combination thereof. Embodiment 3 is the nonwoven web of any of embodiments 1-2 wherein the first, cellulosic fibers include natural fibers chosen from the group consisting of fibers derived from cotton, wool, jute, agave, sisal, coconut, soybean, hemp, flax, kenaf, bamboo, abaca, henequen, sunn, ramie, sisal, chitin, chitosan, and any combination of such fibers.

Embodiment 4 is the nonwoven web of any of embodiments 1-3 wherein the nonwoven web comprises from about 2% by weight to about 40% by weight of an ionic liquid. Embodiment 5 is the nonwoven web of any of embodiments 1-4 wherein the nonwoven web comprises from about 4% by weight to about 30% by weight of an ionic liquid. Embodiment 6 is the nonwoven web of any of embodiments 1-5 wherein at least some of the self-bonds between the first, cellulosic fibers are provided by globules of cellulosic bonding material that are distributed throughout at least a portion of the nonwoven web, and wherein at least some of the globules bridge gaps between adjacent portions of first, cellulosic fibers at points of intersection of the first, cellulosic fibers.

Embodiment 7 is the nonwoven web of any of embodiments 1-6 wherein the ionic liquid is an imidazolium ionic liquid. Embodiment 8 is the nonwoven web of embodiment 7 wherein the ionic liquid comprises a counterion selected from the group consisting of chloride, methanesulfonate, acetate, methylsulfate, ethylsulfate, and thiocyanate, and any combination thereof. Embodiment 9 is the nonwoven web of embodiment 7 wherein the ionic liquid is chosen from the group consisting of 1-butyl-3-methylimidazolium chloride, 1-allyl-3-methylimidazolium chloride, and 1-ethyl-3-methylimidazolium acetate, and any combination thereof. Embodiment 10 is the nonwoven web of any of embodiments 1-9 wherein the ionic liquid provides at least one enhanced characteristic to the nonwoven web, the enhanced characteristic selected from the group consisting of a fire retardant characteristic, an antistatic characteristic, an antibacterial characteristic, an antimicrobial characteristic, an antifungal characteristic, a friction-reducing characteristic, and any combination thereof.

Embodiment 11 is the nonwoven web of any of embodiments 1-10 wherein the web further comprises at least second, non-cellulosic fibers, and wherein the web comprises at least about 40 wt. % first, cellulosic fibers, based on the total weight of the fiber material of the web. Embodiment 12 is the nonwoven web of embodiment 11 wherein the at least second, non-cellulosic fibers include at least some fibers that are melt-bonded to each other at points of contact of the second-non-cellulosic fibers with each other. Embodiment 13 is the nonwoven web of any of embodiments 11-12, wherein the at least second, non-cellulosic fibers include fibers selected from the group consisting of monocomponent fibers, multicomponent fibers, staple fibers, crimped fibers, meltblown fibers, and meltspun fibers, and any combination thereof.

Embodiment 14 is the nonwoven web of any of embodiments 1-13, wherein the nonwoven web includes a population of particulates, further wherein the particulates are selected from the group consisting of abrasive particulates, detergent particulates, anti-bacterial particulates, adsorbent particulates, absorbent particulates, and any combination thereof. Embodiment 15 is the nonwoven web of any of embodiments 1-14 wherein at least about 20 wt. % of the ionic liquid is in the form of an entrapped ionic liquid that remains in the nonwoven web after the web has been contacted with quiescent 21° C. water for two hours.

Embodiment 16 is a method for making a self-bonded nonwoven web comprising at least at least first, cellulosic fibers, the method comprising: contacting at least some of the first, cellulosic fibers with an ionic liquid; exposing the ionic liquid and the first, cellulosic fibers to a first temperature, which first temperature is sufficiently high to cause at least some of the cellulosic material of at least some of the fibers to be at least partially dissolved by the ionic liquid; exposing the ionic liquid and the first, cellulosic fibers to a second temperature that is lower than the first temperature, which second temperature is sufficiently low to cause at least some of the at least partially dissolved cellulosic material to solidify so as to form a cellulosic self-bond at points of intersection of first, cellulosic fibers with each other. Embodiment 17 is the method of embodiment 16 wherein the method does not include contacting the ionic liquid and/or the first, cellulosic fibers with a regenerating liquid. Embodiment 18 is the method of any of embodiments 16-17 wherein the method does not include a washing step that would selectively remove ionic liquid from the self-bonded web, and wherein the self-bonded web comprises from about 1% by weight to about 50% by weight of ionic liquid.

Embodiment 19 is the method of any of embodiments 16-18 wherein the ionic liquid is provided as a mixture with a diluent and wherein the ionic liquid is present in the diluent at from about 10 wt. % to about 70 wt. %. Embodiment 20 is the method of embodiment 19 wherein the ionic liquid is present in the diluent at from about 20 wt. % to about 50 wt. %. Embodiment 21 is the method of any of embodiments 19-20 wherein the diluent is water. Embodiment 22 is the method of any of embodiments 16-21 wherein the first temperature is least about 100 degrees C. Embodiment 23 is the method of any of embodiments 16-21 wherein the first temperature is at least about 120 degrees C. Embodiment 24 is the method of any of embodiments 16-23 wherein the second temperature is less than about 80 degrees C. Embodiment 25 is the method of any of embodiments 16-23 wherein the second temperature is less than about 40 degrees C.

Embodiment 26 is the method of any of embodiments 16-25 wherein the at least first, cellulosic fibers are provided as a mat that is a layer of collected, unbonded fibers and wherein the contacting at least some of the first, cellulosic fibers with an ionic liquid is performed by contacting the ionic liquid with at least a first major surface of the mat. Embodiment 27 is the method of any of embodiments 16-25 wherein the at least first, cellulosic fibers are provided in the form of a pre-bond web that further comprises at least second, non-cellulosic fibers and wherein at least some of the second, non-cellulosic fibers are melt-bonded to each other at points of contact of the second-non-cellulosic fibers with each other, and wherein the contacting at least some of the first, cellulosic fibers with an ionic liquid is performed by contacting the ionic liquid with at least a first major surface of the pre-bond web. Embodiment 28 is the method of embodiment 27 wherein the web comprises at least about 40 wt. % cellulosic fibers, based on the total weight of the fiber material of the web.

Embodiment 29 is a method of treating a target surface, the method comprising contacting a major surface of the nonwoven web of any of embodiments 1-15 with the target surface and moving the nonwoven web and/or the target surface relative to each other.

Examples
Test Methods

Testing of sample webs and/or mats was carried out according to the methods described below. In some testing procedures, a Comparative Example was evaluated for comparison as noted later. Each such Comparative Example consisted of the corresponding mat or web that had not been exposed to an ionic liquid.

Basis Weight

The basis weight of mat or web samples was measured by weighing a sample of known area with a Mettler Toledo XS4002S electronic balance or the equivalent.

Tensile Strength and Percent Elongation

Tensile strength and percent (%) elongation measurements were carried out on mat or web samples (cut to strips of nominal size 15×2.5 cm, typically oriented along the downweb axis (machine direction) of the web) using an Instron 5965 machine with a maximum load of 100N. For each sample, at least three samples were measured and the average obtained. Tensile strength and percent elongation are recorded at break and are reported in Kg/cm².

Surface Resistivity

Electrical surface resistance was measured with a Keithley Model 6517 A electrometer with 100 femtoAmp resolution and an applied voltage of 500 Volts. The Keithley Model 8009 Resistivity test fixture was used with compressible conductive rubber electrodes and 1 lb electrode force over approximately 2.5 inches of electrode and sample. The corresponding detection threshold for surface resistivity was approximately 10¹⁷ohms. Each sample was measured once, and an electrification time of 60 seconds was employed. A high resistance sample PTFE, a low resistance sample (bulk loaded carbon in kapton), and a moderate resistance sample (paper) were used as reference standards. Results are reported in ohms.

Materials

Unless otherwise noted, all parts, percentages, ratios, etc. in the Examples and the rest of the specification are by weight. Solvents and other reagents used may be obtained from Sigma-Aldrich Chemical Company (Milwaukee, Wis.) unless otherwise noted. In addition, Table 1 provides abbreviations and a source for various materials used in the Examples.

TABLE 1

Material
Supplier

1-ethyl-3-methylimidazolium acetate
Iolitec GmbH

Viscose Fibers (40 mm, 1.7 dTex)
Lenzing AG

Polyester Fibers (20 denier)
Palmetto Synthetics LLC

Nylon Fibers (60 mm, 20 dTex)
EMS-GRILTECH

Melty Fibers (20 denier)
Huvis

CRABYON Fibers (1.5 denier, 38 mm length)
Tec Service

Production of Self-Bonded Nonwoven Webs

Mat/(Web) Formation

Airlaid mats were prepared comprising a blend of 80 wt. % viscose fibers and 20 wt. % melty fibers. Viscose and melty fibers at the targeted ratio were weighed and passed through a fiber opener (available from Laroche). The combined fibers were then processed and collected as fiber mats using a conventional air-laying apparatus (available from the Rando Machine Company, Macedon, N.Y., under the trade designation “RANDO WEBBER”), targeting a nominal area weight (basis weight) in the range of 80 grams per square meter (gsm). The collected fiber mats were then passed through a heating apparatus (a through-air bonder) in which hot air (set at approximately 130° C.) was drawn through the thickness of the collected fiber mat to lightly melt-bond some of the fibers to each other. The result was lightly-bonded pre-bond webs that were sufficiently self-supporting to be handled as webs and stored until subjected to further processing as described below.

Other airlaid mats were prepared comprising a blend of 45 wt. % viscose fibers, 45 wt. % nylon fibers and 10 wt. % melty fibers. The fibers were air-laid and through-air bonded to form pre-bond webs in generally similar manner as described above, with a targeted nominal area weight in the range of 75 gsm.

Carded mats were prepared comprising CRABYON fibers (at essentially 100 wt. %, no other fibers being present). The CRABYON fibers were passed through a fiber opener and then processed using a conventional carding machine (available from Cosmatex), targeting a nominal area weight in the range of 35 gsm. The fibers were not bonded to form pre-bond webs.

Contacting with Ionic Liquid

The 1-ethyl-3-methylimidazolium acetate ionic liquid was added at 10-50 wt. % to tap water, as listed in detail later herein. The mixture was stirred until the ionic liquid was fully dissolved in the water.

Roll Coating and Bonding

Pre-bond webs (viscose/melty and viscose/nylon/melty) were impregnated with an ionic liquid/water mixture using a conventional roll coating apparatus available from Cavitec. The roll coater had an upper backing roll and a lower gravure coating roll. The webs were impregnated from the lower surface (the surface against the gravure roll) under conditions such that the liquid mixture generally penetrated through the entire thickness of the pre-bond web. The pre-bond webs were then through-air bonded with heated air (set at various temperatures as outlined in the Tables below). The line speed for the through-air bonding was typically 1 meter/minute; the through-air bonder was approximately 4 meters in length. The thus-produced self-bonded webs are denoted as Working Example series VM (viscose/melty) and series VNM (viscose/nylon/melty) in the Tables below.

Spray Coating and Bonding

Fiber mats (made of carded CRABYON fibers) were impregnated with an ionic liquid/water mixture using a spray coating apparatus available from 3M Company under the trade designation Paint Preparation System. The fiber mats were then through-air bonded with heated air (set at 100° C.) to produce self-bonded webs in similar manner as described above. The thus-produced self-bonded webs are denoted as Working Example series C (CRABYON) in the discussions below.

Evaluation of Self-Bonded Webs

Mechanical Properties

Mechanical properties of various self-bonded webs (and Comparative Examples) were evaluated according to the procedures described above. The results are recorded in Table 2.

TABLE 2

Ionic liquid

Oven temp
conc. in H2O
Tensile

Sample
(° C.)
(%)
Strength
Elongation (%)

CE-VMN*
—
—
0.00
0.16

VMN-1a
100
10
0.03
28.3

VMN-1b
100
10
0.01
26.7

VMN-1c
100
10
0.02
32.2

VMN-2a
100
20
0.04
33.9

VMN-2b
100
20
0.03
31.8

VMN-2c
100
20
0.04
25.3

VMN-3a
120
50
0.08
23.5

VMN-3b
120
50
0.12
29.7

VMN-3c
120
50
0.13
29.1

CE-VM*
—
—
0.02
35.7

VM-1a
120
50
0.26
21.4

VM-1b
120
50
0.43
19.7

*Comparative Example, viscose/melty/nylon

**Comparative Example, viscose/melty

Surface Resistivity

Surface resistivity of various samples was evaluated according to the procedures described above. Samples (approximately 10×10 cm) of the general type described above as VM-1 were soaked in approximately 100 mL of water and heated to 60° C. for 15 minutes. The samples were then removed from the water (or, in some cases, the water was poured off), excess water was allowed to drip momentarily, then the samples were allowed to air-dry at room temperature overnight. The surface resistivity of two such ionic liquid-exposed, water-soaked samples was measured and is reported (as the bottom two items) in Table 3. The surface resistivity of a Comparative Example (CE-VM) that had not been exposed to ionic liquid; and, the surface resistivity of an ionic liquid-exposed sample that had not been subsequently water-soaked, are also reported in Table 3. It can be seen that although the surface resistivity of the ionic liquid-exposed, water-soaked samples was higher than that of the ionic liquid-exposed sample that had not been water soaked, the surface conductivity did not increase back to the level found in the sample (CE-VM) that had never been exposed to an ionic liquid, indicating that at least some of the ionic liquid in the web was not easily removed by a water soak.

TABLE 3

Sample
Surface resistivity

CE-VM
7.1E+11

VM-1 without water soak
5.8E+07

VM-1 after water soak
7.0E+10

VM-1 after water soak
1.3E+11

Microscopic Evaluation

A self-bonded web of Working Example series C (comprised of self-bonded CRABYON fibers) was examined via microscopy. In FIG. 3 is shown an optical micrograph (320×) of a representative portion of such a sample. Numerous self-bonded sites (e.g. in the form globules as described herein) are visible in the optical micrograph. For reference, in FIG. 4 is shown an optical micrograph (320×) of a CRABYON mat in which the fibers were not self-bonded (i.e., in which the CRABYON fibers had not been exposed to an ionic liquid).

The foregoing Examples have been provided for clarity of understanding only, and no unnecessary limitations are to be understood therefrom. The tests and test results described in the Examples are intended to be illustrative rather than predictive, and variations in the testing procedure can be expected to yield different results. All quantitative values in the Examples are understood to be approximate in view of the commonly known tolerances involved in the procedures used.

It will be apparent to those skilled in the art that the specific exemplary elements, structures, features, details, configurations, etc., that are disclosed herein can be modified and/or combined in numerous embodiments. All such variations and combinations are contemplated by the inventor as being within the bounds of the conceived invention, not merely those representative designs that were chosen to serve as exemplary illustrations. Thus, the scope of the present invention should not be limited to the specific illustrative structures described herein, but rather extends at least to the structures described by the language of the claims, and the equivalents of those structures. Any of the elements that are positively recited in this specification as alternatives may be explicitly included in the claims or excluded from the claims, in any combination as desired. Any of the elements or combinations of elements that are recited in this specification in open-ended language (e.g., comprise and derivatives thereof), are considered to additionally be recited in closed-ended language (e.g., consist and derivatives thereof) and in partially closed-ended language (e.g., consist essentially and derivatives thereof). Although various theories and possible mechanisms may have been discussed herein, in no event should such discussions serve to limit the claimable subject matter. To the extent that there is any conflict or discrepancy between this specification as written and the disclosure in any document incorporated by reference herein, this specification as written will control.

SELF-BONDED CELLULOSIC NONWOVEN WEB AND METHOD FOR MAKING

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