CA2099919A1 - Absorbent structure, and method of making same - Google Patents

Abstract

Abstract of the Disclosure There is disclosed a dry laid, substantially biodegradable and/or disintegradable liquid absorbent structure having randomly incorporated therein solid particulate superabsorbent material.
A coating of latex or polyvinyl alcohol is applied on at least one surface of said web in sufficient quantity to impart integrity to said structure without substantially impairing the effectiveness of said superabsorbent material to absorb liquid.
A liquid-barrier member selected from the group consisting of a film of paraffin wax, and a webbing of wax paper, is formed on one surface of the structure. In a preferred embodiment, a cellulase enzyme is incorporated into the structure.

Description

.~BSORBENT ST~UCTURE, AND ~ETHOD oP XAXING gAXæ

Field of t~e Invontion This invention relates to liquid absorbent structures. In its more specific aspect, this invention r01ates to dry laid webs for use as liquid absorbent structures which exhibit improved biodegradation. Another aspect of the invention includes the method for making such structures.

Background o~ the Invention and Prio~ Art Disposable products have been extremely use~ul to the consumer, but there is public concern regarding waste management and the degradation of these materiale. For example, a number of dispo6able products comprise in whole or in part plastic, which is clas~ified as nondegradable, and it therefore would be desirable to substant~ally reduce the percent plastic in a product or to ~ake a product of degradable material~. Disposable products such as commercially available diapers or feminine napkins, which are liquid absorbent, comprise a cellulosic batt typically ~dmixed with plastic fibers and opposed surface members or cover sheets of plastic film or webbing. It would be desirable, therefore, to provide such disposable products comprised of materials which are biodegradable and/or disintegradable.

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Dry forming systems, and in particular air laying systems, in which the fiber orientation is randomly distributed in the plan~e of the web or fabric, are used now commercially in the manufacture of a ~ariety of liquid absorbent products, including disposable products. Generally, in the air forming process the fibers, which may be cellulosic, synthetic, or a combination of both, are suspended.in a gas stream (e. g., air~ and then conveyed to a forming screen where the fibers are formed-or condensed into a web. However, the resulting web lacks integrity, and therefore one of several techniques is used to bond the fibers and thereby stabilize the structure. The fabric products produced are soft, flexible and porous, and are suitable for a number of commercial products, particularly dlsposable products. ~he f~ber content, at least to a large extent, used in many of these products are hydrophilic or can ~e rendered hydrophilic, and therefore are especially useful as liquid absorbent products, such as disposable diapers, incontinent pads, wipes, and feminine napkins.
In the conventional manufacture of air laid products, the loose web condensed on the forming screen is typically stabilized by mechanical, thermal, or chemical means. Mechanical or thermal means have been used extensively, and usually require fiber entanglement or fiber bonding. Chemical bonding utilizes a solvent or adhesive, and United States Patent 3,575,749 to Kroyer discloses bonding the fibrous layer with a latex binder, which ~ay be applied to one or both sides of the web.
In order to increase the absorptive capacity of the web, 2 ~
water insoluble hydrogels or superabsorbent materials, typically in particle for~, have been incorporated into the fibrous web These hydrogels have an absorptive capacity for water and body fluids far exceeding that of the hydrophilic fiber, e. g. wood pulp fiber used in the web, and in fact are capable of absorbing twenty times or more their own weight of water and retain this fluid under pressure. Hydroqels, which are available commercially, have been used as soil conditioners, sod farm, and seedling, and are considered environmentally friendly.
The cellulosic materials used in these disposable products are biodegradable if placed in right condition. However, products such as diapers and feminine napkins include a substantial percent of plastic constituents, which are normally classified as nondegradable. This invention has, therefore, as its purpose to provide a liquid absorbent structure that exhibits improve~ biodegradation.

Sua~ry o~ tho Inv~ntion In its broadest aspect, the invention provides for a method of making a dry laid, liquid absorbent structure which comprises first dry laying a continuous web of cellulosic fi~ers having incorporated therein a water insoluble hydrogel or superabsorbent. Latex or polyvinyl alcohol is applied as a liquid to at least one surface of the resulting web, and is rendered active as by curing with heat. The latex or polyvinyl alcohol is applied in sufficient quantity to impart integrity to the structure without substantially impairing the effective absorbent capacity of the hydrogel to absorb liquid by 2~9991 controlling the depth of penetration of the latex or polyvin alcohol into the web and the degree of coverage of the hydrogel particles by the latex or polyvinyl alcohol. There is applied to one surface of the web a liquid barrier member selected from the group consisting of paraffin wax, and wax paper. The resulting structure is essentially biodegradable ùnder the right conditions, e.g. moisture, microbial population, temperature, nutrients, and aeration. In a preferred embodi~ent, a cellulase enzyme is incorporated into the structure or product, which attacks and weakens the cellulosic structure. Thus, when the product is disposed following use by the consumer, the cellulosic fibers degrade, thereby disintegrating the structure and its component parts.
A conventional air forming sy~tem includes two or more distributors, and fibers are conveyed from each distributor to the forming screen, whereby plies of ~ibers are condensed on the screen as a web. The hydrogel or superabsorbent material may be incorporated into the fibrous plies or web at any convenient or desired point in the system, such as between plies or within the plies. Water insoluble hydrogels or superabsorbent materials, which are commercially available polymeric materials and are considered environmentally friendly, are applied to the fibrous layer or batt as a solid and in particulate for~, including, for example, powders, particles, flake, fibers, globules, and the like. Typically, the hydrogel is distributed or deposited onto a layer or ply of fiber about midway during the formation of the ~Q~
web. Where desired, the absorbent structure may include a porous reinforcing web either as an outside layer, or as an interjacent layer with the hydrogel applied to one side only of the re inf orcing web.
When such fibers are dry laid, there i6 some mechanical entanglement but not sufficient to provide good integrity to the structure. Latex or polyvinyl alcohol, as an emulsion or solution, typically in an aqueous medium, is applied to one or both surfaces of the web to provide a coating which partially impregnates the web, and upon curing stabilizes the structure.
The latex or polyvinyl alcohol may be applied to the web by any suitable means such as spraying, brushing, flooding, rolling, and the like. The amount of latex or polyvinyl alcohol applied and the degree of penetration are controlled so as to avoid impairing the effective absorbency of the hydrogel and the effectiveness of the enzyme, thereby achieving a product of relatively high basis weight.
Because the fibrous structure of the present invention exhibits high liquid absorbency and retention, including body fluids, i6 soft, and ha6 low bulk, the structure is especially useful in disposable products such as diapers and feminine pads.
Further, because the structure exhibits improved biodegradation, the structure is en~ironmentally friendly.

Brl~ De$crlption of the Dra~ngs Figure 1 is a schematic flow diagra~ of a process for making a liquid absorbent structure in accordance with the present invention.

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Figure 2 ls a cross-sectional view on an enlarged scale of an absorbent ~tructure made in accordance with the present invention.
Figures 3A and 3~ are schematic flow diagrams of a process of the invention similar to that of Figure 1 but embodying a modification.
Figures 4A and 4~ are cross-sectional views of alternative embodiments of structures made in accordance with the modified processes of Fiqures 3A and 3B.
Figure 5 is a perspective view partially broken away illustrating another embodiment of the absorbent structure of this invention and particularly useful a~ a diaper.
Figure 6 i6 a perspective view of a sanitary napkin embodying the structure of this invention, and partially broken away to illustrate the structure.
Figure 7 is a graph showing the effectiveness of two enzymes on degradation of samples of air laid structures made in accordance with the present lnvention.

~ota~l~d Descr1ptian of t~e Invention The absorbent structures of the present invention may be made using conventional equipment designed for dry laying systems, and although the invention is described hereinbelow with particular reference to airlaid structures, it should be understood that other dry laid systems, e. g. carding, are also applicable. Referring to the drawings wherein like reference numerals refer to similar parts throughout, and as described in the aforesaid application Serial No. 07/5~1,452 which is incorporated herein by reference, there is shown in Figure 1 a preferred embodiment for the manufacture of the liquid absorbent structure of the invention. In accordance with this embodiment, the air forming system, indicated generally by the numeral 10, includes a distributor unit 12 disposed transversely above a continuous for~ing screen 14 mounted on rollers 16 and driven by a suitable motor (not shown), and vacuum means or suction ~ox 18 is positioned beneath the screen. In a conventional air forming system, upstream of the distributor unit is a defibrator or feeder (not shown), such as a hammermill or Rando-Feeder, where bales, laps or the like are defiberized, and further the fibers may be cleaned and/or blended if necessary or desired depending largely on the type of fibers used, the blend of fiber~ used, and the end product sought. The fibers are carried by an air stream via conduit 20 to the distributors. The porous forming screen 14 is essentially coextenslv~ with the distrlbutors, and the suction box 18 beneath the screen draws the air stream downwardly and conveys the fi~ers to the surface of the screen thereby forming plies or a loose web 22. At this stage in the process, the web exhibits little integrity, and the vacuum means retains the loose, fibrous web on the screen. It should be understood that the system may bo modified to control the composition and thickness of the end product. For example, the distributor unit typically comprises a plurality of individual distributors, and although Figure 1 shows schematically four distributors at 12A, 12B, 12C and 12D, this number of distributors and particular 2 ~
arrangement can ~e altered or varied depending on such factors as machine speed, capacity, type of f ibers, and end product desired.
Web 22 formed on screen 14 has incorporated therein a water-insoluble superabsorbent material. In a preferred embodiment as sho~n in Flgure 1, a dosing unit or feed hopper 24, containing superabsorbent particles 26, is positioned in the middle of the distributor unit, i. e. between distributors 12~ and 12C. In this manner, superabsorbent particles are deposited between plies of fluff laid by each distributor. That is, the superabsorbent particles are discharged from hopper 24 onto the moving layer of fluff laid down by distributors 12A and 12B, and the plies of fluff laid down by distributors 12C and 12D are laid over the superabsorbent particles. It should be understood, however, that the plies are relatively porous, and therefore the particles tend to migrate somewhat into adjacent plies. Where desired, the superabsorbent particles may be blended with the fibers in one or more distributors, such as in distributor 12B or 12C, thereby for~ing a web with superabsorbent particles intermixed with one or more fibrous plies of the web. Also, at this stage of the process a cellulase enzyme, described below in detail, may be incorporated into the web as by admixing the cellulase with the superabsorbent, or by adding the cellulase separately. If the cellulase enzyme is nor~ally liquid, the enzyme can be first encapsulated, as with carboxymethyl cellulose, starch, or sugar, and then incorporated into the web as by admixing the enzyme with 2~9~9 the superabsorbent. Where desired, a liquid enzyme may be applied to the web by spraying after the heating step, as described below.
At this stagb of the process, the web 22 condensed on forming wire 14 has very little integrity and requires stabilization. The web is advanced by the continuous screen, and where desired, the web first may be passed between compression rollers 28, which may be heated, to densify the web, but this step is optional. This densification step enhances the penetration of the latex or polyvinyl alcohol into the web, and the degree or percent of densification can vary depending on such factors as the amount of hydrogel, basis weight o~ the web, the desired degree of penetration of the latex or polyvinyl alcohol into the web, and the end product sought. From there, the web is transported to a sultable dispensing means 30, such as a spray nozzle, doctor blade, rollor applicator, or the like, where latex or polyvinyl alcohol is applied to the surface of the loose web.
A vacuum applied by suction box 31 positioned beneath the dispensing means and screen helps to draw the latex or polyvinyl alcohol into the web. The di~pensing means or applicator is essentially coextensive with the width of the web, and preferably a sub6tantially uniform coating is applied to the web surface.
However, the latex or polyvinyl alcohol may be applied as a nonunifor~, random or pattern coating, and because the latex or poly~inyl alcohol i~ water-based, it will diffuse throughout the web and function as a binder when cured. The latex or polyvinyl alcohol when cured imparts integrity to the web, and therefore some penetration of this component is required. The 2 ~
extent or degree of penetration of the latex or polyvinyl alcohol into the web is controlled by controlling the amount applied and by controlling the vacuu~ applied to the web in that the vacuum helps to draw the latex or polyvinyl alcohol into the web. The latex or polyvinyl alcohol is usually applied as an aqueous solution, and is thermosetting. In order to activate the latex or polyvinyl alcohol, it contains a suitable curing agent or cross-linking agent, and after the web is coated, the latex or polyvinyl alcohol is cured to effect cross-linking. Most typically, curing is accomplished by passing the coated web through a hot air oven or through air drier 32, and the temperature typically ranges from about 200 to 500 F but this depends upon the specific type of latex or polyvinyl alcohol resin used, upon the curing ~gent or cross-linking agent, upon the amount of polyvinyl alcohol, the thickness of the web, the degree of vacuum, and the machine speed. It is desirable to coat both surfaces of the web with either latex or polyvinyl alcohol, and this is readily accomplished by reverse rolling the web so that the top surface at the dispensing means 30 becomes the bottom surface. Thus, web 22 is transferred to a second screen 34 and then advanced to a second dispensing means 36, including suction box 37, where latex or polyvinyl alcohol is now applied to the opposite side. This second coating is li~ewise cured by passing the web through a second oven 38 within about the same temperature range.
The resulting web structure 40 exiting from the last oven now exhibits sufficient integrity and a liquid barrier film can be applied to one side of the web. As shown, a liquid-barrier member of a film of paraffin wax having a melting point of at least about 120 F, or a webbing of wax paper from an unwind role (not shown), is applied at source 41 to one surface of the web 40, and may be pressed into contact by a bonding roll (not shown). The resulting laminate may be cut, rolled, and pac)caged, or may be taken up on roller 42 and used as stock for a finished product such as of the type described below in detail.
In a modified embodiment, a porous reinforcing web such as creped paper or 3D formed paper (characterized by relatively large number of fiber-filled nubs) is incorporated into the fibrous web structure either as a surface web or as an intermediate web disposed interjacent the surfaces of the fibrous web. There are shown in Figures 3A and 3B the alternative steps in applying the reinforcing web depending on its desired position in the finished structure. The air forming system shown generally at 10 is similar to that shown in Figure 1. If it is desired to form the reinforcing web at one outer surface of the fibrous structure as shown in Figure 4A, the reinforcing web 52A
is fed from a source roll 53 across idler roll 54 and onto the continuous screen 14. Fibers from distributor 12A are conveyed onto the web 52A to form a first ply, and the fibers become somewhat ~echanically entangled with this web. Additional fibers, ~ydrogel particles, and optionally cellulase enzyme, are conveyed to the screen zone bearing reinforcing web and fibers to build the desired loose web. The fibrous web is then transported to dispensing means 30 where the latex or poly~inyl alcohol is 2 ~
applied and then cured on passing through hot air o~en 32.
Paraffin wax (or wax paper) is applied at 41, and cooled to room temperature, and the structure is then wound on roller 58.
As a further modification to this embodiment employing a reinforcing web, the reinforcing web may be embedded within of the fibrous web, as shown in Figure 3B. Reinforcing web 52B is fed from source roll 57 positioned intermediate the distributors, such as between distributors 12B and 12C as shown, and into converging relation with formed plies condensed on the screen from the distributors positioned upstream of roll 57.
Superabsorbent material from hopper 24 is deposited onto the surface of web 46B, and additional plies of fibers are for~ed over the superabsorbent particles. Where desired, the superabsorbent material may have admixed therewith a cellulase enzyme. An application or coating of latex or polyvinyl alcohol .
is then formed on one or both surfaces of the fibrous web, and the coating composition is cured. Paraffin wax (or wax paper) is applied to one surface of the web. ~he finished structure is wound on roller 58, as dsscribed above. This embodiment with the reinforcing web interjacent the surfaces has the desirable feature in that this reinforcing web prevents the hydrogel particles from migrating to the underside of the fibrous web thereby maintaining the particles in the desired location toward or in the vicinity of the center of the web.
Fibrous structures made in accordance with the foregoing process are illustrated in Figures 2, 4A and 4B. The structure of Figure 2, indicated generally by the numeral 44, comprises 2 ~
randomly distributed fibers 46, such as wood pulp fibers, and superabsorbent particles 48, and cellulase enzyme particles if used, are randomly distributed in the web. It will be observed that the particles of hydrogel are more concentrated in the middle zone of the web, but some particles migrate to other sections of the web. Both surfaces of the web bear a coating 50 of latex or polyvinyl alcohol, which has penetrated or impregnated the web to soms degree and has partially coated some of the fi~ers and hydrogel particles, and one surface of the web is coated with a paraffin wax or wax paper. As explained above, the penetration is controlled so as not to substantially impair the absorbent capacity of the hydrogel. Notwithstanding this coating, the web is soft yet strong and absorbent, exhibiting a relativ~ly high tensile strength and breaking length. It is desirable for fibrous structures of thls type to have relatively low bulk, because a more dense web, when compar0d to similar structures containing no latex or polyvinyl alcohol and of about equal absorptive capacity but of higher bulk, can be thinner yet highly absorbent and consequently less bulky. A reduction in bulk, which means a reduction in volume the web is occupying, without sacrificing significantly other desired properties is important from the standpoint of manufacturing, storage and packaging. Hence, for products of my invention the basis weight ranges from about 25 to 500 grams per square meter, and more preferably from about 75 to 350. There can be manufacturing constraints in producing a web having a basis weight lower than about 25 grams per square meter in that such a web lacks desired 2 ~
strength. When the basis weight exceeds the upper limit, the product may be too stiff and therefore not useful for most applications.
There is shown in Figures 4A and 4B the absorbent fibrous structure made in accordance with this embodiment utilizinq a reinforcing web. Referring to Figure 4A, fibrous structure 59 comprises fibers 60, and hydrogel particles 61 interspersed in the web but more concentrated in the middle zone. Where desired, a cellulase enzyme may be incorporated into the web. Reinforcing web 62 is formed on one surface of the web structure, and the opposite surface bears a cured polyvinyl alcohol coating 64. In the alternative embodiment shown in Figure 4~, the reinforcing web 62 is interjacent the 6urfaces of the fibrous web.
Figures 5 and 6 depict useful products embodying the fibrous structure of thi6 invention. There is shown in Figure S a diaper compri~ing a moisture-permeable facing me~ber 66 for the body-side of the pad, such as rayon, and a moisture-impervious backing member 68, such a6 a paraffin wax or wax paper. The diaper is the typical hour-glass configuration with cut-out leg sections 70 and crotch section 72. Tabs 74 are provided in order to secure the diaper around the waist of the wearer. In the middle portion or crotch 6ection, there is provided the fibrous absorbent structure or core of the type shown in Figure 2, comprising cellulosic fi~ers 76 and superabsorbent particles 78. If desired, a cellulase enzyme may be lncorpor~ted into the structure and particularly into the absor~ent core. A coating 80 of latex or polyvinyl alcohol is provided on both surfaces, and 2Q3~
the latex or polyvinyl alcohol partially penetrates the web and coats a portion only of the fibers and hydrogel particles. The diaper is sealed along the marginal edges by conventional means.
~he body fluid permeates fabric 66, and because of the wicking action of the fibers, the fluid is transported to all areas of the batt and absorbed by the hydrogel and fibers. The body facing fabric, being liquid-permeable, is perceived by the wearer as dry even when the inner batt or web is saturated. Because the liquid absorbent structure is relatively dense and exhibits high absorbency, the diaper made utilizing this structure is exceptionally thin, and the absorbency rate compares very favorably with a more bulky pad bearing no applied latex or polyvinyl alcohol. It should be understood that the term "diaper" as used herein and in the appended claim~ includes adult incontinent diapers.
There i8 shown in Figure 6 a feminine napkin with a broken away portion to be illustrate the construction of the pad. The napkin comprises a moisture-permeable facing member 82, such as rayon, a moisture-imper~eable backing member 84, such as a paraffin wax film or wax paper, and the napkin is sealed along the marginal edges in a conventional manner. The absorbent core comprises fibers 86, hydrogel particles 88, and a latex or polyvinyl alcohol coating 90. Optionally, cellulase enzyme particles may be incorporated into the napkin and particularly into the absorbent core. The absorbent structure for this feminine pad is ~oft, dense, and highly absorbent.

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It will be observed that the structures or products of this invention, ~nd as shown more specifically in Fiqures 4A, 4B, 5 and 6, are made of materials which are environmentally friendly.
Thus the structures are formed from cellulosic fluff, rayon, paraffin wax or wax paper, and latex or polyvinyl alcohol. In addition, the structure may lnclude a cellulase enzyme to facilitate biodegradatlon and/or disintegration.
A wide variety of superabsorbent materials or hydrogels are well known and readily available from a number of sources.
Superabsorbent polymers useful in the absorbent structures of this invention are substantially water insoluble but water sweliable and comprise, for example, s~ponified starch-polyacrylonitrile graft copolymers, starch-polyacrylic acid graft copoly~ers, cross-linked/grafted cellulose, saponified vinyl acetate-acrylic acid copolymers, starch grafted polyvinyl acetate, acrylic acid polymers, cross-linked polyethylene oxide, isobutylene maleic anhydride copolymers, and the like. The hydrogels used in the fibrous web structures may be the same or a mixture of absorbent polymers, and are incorporated into the web as a discontinuous solid material. The amount of hydrogel can vary widely depending on the end use of the product, and the weight percent can b~ determined, taking into account the end use, through experiment by one having skill in the art. For example, if the absorbent structure is used in a wipe, a useful range for the hydrogel has been found to be from as low as 1 percent up to about 10 percent by weight. If used in a diaper or feminine pad, the weight percent hydrogel usually ranges from 2~9~9 about 10 to 65 w~lght percent of the struct~re~ and preferably from about 15 to 55 weight percent. If for the end u~e application sought, the percent hydrogel is too low, the product will not be sufficiently absorbent ~ecause the latex or polyvinyl alcohol does obscure to some extent the absorbent properties of b~th the hydrogel and fibers. On the other hand, there appears to be no benefit in using an excessive amount or more than a predetermined maximum, but it should be understood that the amount can vary depending on such factors as type of fiber, the absorbent capacity of the hydrogel for the particular fluid to be absorbed, the amount of latex or polyvinyl alcohol, and basis weight of the structure. The absorbent particulates may be in the for~ of fibers, flakes, particles, granules, powder, and the like. Particularly useful hydrogels comprise particles having a size of from about 40 to 700 microns. Particulate within this size range are relatively easy to handle and further ensure a rapid and even distribution o~ sùch particles in the web. Also, particulate too small have a greater tendency to migrate or sift fro~ the structure and be lost or generate excessive dust.
The latex or polyvinyl alcohol is applied as an aqueous solution or emulsion, which typically contains about 45 to 65 percent solids, and these material6 are commercially available from several manufacturers. The latex and polyvinyl alcohol useful in this invention are those grades which are environmentally friendly. Latex available are classified by chemical family, and those particularly useful include vinyl acetate and acrylic ester copolymers, ethylene vinyl acetate , 2 ~
copoly~ers, styrene butadiene carboxylate copolymers, and polyacrylonitriles, and sold, for example, under the trade names of Airbond, Airflex and Vinac of Air Products, Inc,, and Hycar and Geon of Goodrich Chemical Co. Polyvinyl alcohol is readily available from many sources, and includes, for example, Airvol product line of Air Products, Inc.. A~ discussed in the article entitled "Some Charactéristics of Pseudomonas 0-3 which Utilizes Polyvinyl Alcohol~ by Suzuki, et al, published in Agr. Biol.
Chem, 37(4), 747-756, 1973, known bacterium from soil produce an inducible enzyme which degrades polyvinyl alcohol. Also, the polyvinyl alcohol and the latex compositions are thermosettin~, and in order to effect cross-linking, the composition contains a small amount of a suitable cross-linking agent which are well known chemical Agents for this purpose and commercially available. The amount of latex or polyvinyl alcohol used in the structure cannot be 50 high as to substantially impair or obscure the effective absorbent propsrtie6 o~ the hydrogel and hydrophilic fibers, or as to impart a stiffness to the structure as to render it impractical. I have found that the latex or polyvinyl alcohol may range from about 5 to 30 weight percent of the structure, and preferably from about 10 to 20 weight percent.
The liquid impervious member, which is applied to one surfac~ of the absorbent structure is selected from the group consisting of paraffin wax, preferably having a melting point of at least about 120 F, and wax paper. More specifically, the paraffin wax has a melting point of from about 120 to 170- F, and - ~

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should exhibi~ good barrier properties to moisture and be highly pliable. Suitable paraffln wax compositions include, for example, those sold by National Wax Company such as wax product 60431. Wax papers, which comprise a cellulosic web i~pregnated with a suitable paraffin wax such as those described, are liquid impervious. For purposes of this invention, the wax papers should contain sufficient wax to pro~ide an adequate barrier to the body fluid, and the amount of wax ranges from about 3 to 10 weight percent wax based on the total weight of the paper.
In a preferred embodiment of the invention, a cellulase enzyme is incorporated into the structure to facilitate biode~radation and/or disintegration. The amount of enzyme is relatively small, and may range from a~out 0.1 to 1 percent by weight based on the total weight of the product. Where desired, the cellulase may be coated to provide for a slow release of the enzyme into the structure. Suitable coating materials, which are soluble in the body fluid for which the product is intended, e.
g. urine for a diaper product, include carboxymethyl cellulose, starch and sugar. Suitable enzymes include "Celluzyme", which is the secreted product of Humicola insolens fungi, and "Celluclast", whic~ is the secreted product of Trichoderma rusei fungi, and both made and distributed by Novo Norisk Bioindustrles, Inc., Danbury, CT. Although a cellulase, per se, may be used, a cellulase-producing bacteria or fungi may be used, such as brown rot fungi, which selectively attack cellulose. As a consequence, the cellulosic structure is weakened thereby exposing the structure, including the latex or polyvinyl alcohol, .

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to biodegrada~ion and/or disintegration. Further, the structure may be subject to anaerobic digestion, as in a septic tank, thereby obviating the need for open air and sunlight digestion, In order to demonstrate the utility of the invention, samples were made substantially in accordance with the procedure shown in Figure 1, and then tested for biodegradation and/or disintegration. Accordingly, layers of fibers were airlaid and hydrogel particles deposited between layers to form the loose web. The webs were densified, both sides of each web impregnated with latex, and the webs then dried in a forced hot air oven.
The absorbent webs were prepared using 100~ Southern pine bleached Kraft pulp from Weyerhaeuser Company at a basis weight of about 100 g/m', and IH-1500 superabsorbent powder manufactured by Celanese Chemical Co. was added at a weight of about 80 g/m~.
The webs were coated on both sides with A-109 (R) latex from Air Products and Chemicals, Inc., and the resulting webs comprised about 17% by weight latex.
Three solutions of Celluclast and Celluz,vme enzymes werç
pre~lred at concentrations of 0.1%, 0.5~, and 1.0~ weight/volume.
Samples measuring 3 x 6 cm were cut (machine direction) from the web, and the samples placed in bottles containing solutions of the cellulase enzymes. A control was also used containing water only. The samples were kept in a controlled roo~ at a temperature of 100 F. The samples were tested for tensile strength on an Instron tensile tester at weekly intervals. Five replicates were done for each solution at each concentration.
Since the samples were soaking in liquid, each sample was placed , ' 2~9~
on a blotter for five seconds to soak up the excess liquid, and then placed in the Instron. After one week, the samples treated with Celluclast were degraded in such a manner that they could not ~ tested for strength loss at any concentration, which is shown in the graph in Figure 7. The 0.1% solution samples tore while putting them in the Instron or picking the~ out of the bottle, the 0.5% solution sa~ple6 fell apart while picking them up; and the samples in the 1.0% solution were in pieces. A
strength reduction was shown for those samples treated with Celluzyme, as shown in the graph, the first two to three weeks showing the most substantial change, after which the degradation leveled off and there was essentially no change in the air laid strength. The control showed essentially little variation in strength. It should be understood,.however, that because the control comprises biodegradable coDponents, degradation of the control will occur depending on such factors as hu~idity, soil composition, 80il pH, and air, and therefore a product of this co~position is suitable for a compost pile. As can be seen from the graph, the Celluclast had the most dramatic sffect on strength reduction (which is an indication of degradation); and for Celluzy~e, the effect on strength was greater with the higher concentrations. Hence, the products of this invention are advantageou~ because of improved biodegradation and/or disintegration.

Claims (18)

1. A method for making a liquid absorbent structure, which comprises: (a) forming a dry laid cellulosic web having incorporated therein particulate superabsorbent material, (b) applying to at least one surface of said web a liquid latex or polyvinyl alcohol in sufficient quantity to impart integrity to said structure without substantially impairing the effectiveness of said superabsorbent material to absorb liquid by controlling the depth of penetration of said latex or polyvinyl alcohol into said structure and by controlling the degree of coverage of said superabsorbent material by said latex or polyvinyl alcohol, and (c) applying to one surface of said web a liquid-barrier member selected from the group consisting of a film of paraffin wax, and a webbing of wax paper.

2. A method according to Claim 1 wherein said liquid-barrier member is a film of paraffin wax having a melting point of at least about 120° F.

3. A method according to Claim 1 wherein said liquid-barrier member is wax paper containing from about 3 to 10 weight percent paraffin wax.

4. A method according to Claim 1 wherein said structure includes a cellulase enzyme.

5. A method according to Claim 4 wherein said cellulase enzyme is provided with a water soluble coating.

6 A method according to Claim 5 wherein said coating is selected from the group consisting of carboxymethylcellulose, starch, and sugar.

7. A method according to Claim 2 wherein said structure includes a cellulase enzyme.

8. A method according to Claim 7 wherein said cellulase enzyme is provided with a water soluble coating.

9. A method according to Claim 8 wherein said coating is selected from the group consisting of carboxymethylcellulose, starch, and sugar.

10. A method according to Claim 3 wherein said structure includes a cellulase enzyme.

11. A method according to Claim 10 wherein said cellulase enzyme is provided with a water soluble coating.

12. A method according to Claim 11 wherein said coating is selected from the group consisting of carboxymethylcellulose, starch, and sugar.

13. A dry laid, liquid absorbent structure, which comprises: a dry laid cellulosic web having randomly incorporated therein solid particulate superabsorbent material, a coating of latex or polyvinyl alcohol on at least one surface of said web in sufficient quantity to impart integrity to said structure without substantially impairing the effectiveness of said superabsorbent material to absorb liquid, and on one surface of said web a liquid-barrier member selected from the group consisting of a film of paraffin wax, and a webbing of wax paper.

14. A structure according to Claim 13 wherein said liquid-barrier member is a film of paraffin wax having a melting point of at least about 120° F.

15. A structure according to Claim 13 wherein said liquid-barrier member is wax paper containing from about 3 to 10 weight percent paraffin wax.

16. A method according to Claim 13 wherein said structure includes a cellulase enzyme.

17. A structure according to Claim 16 wherein said cellulase enzyme is provided with a water soluble coating.

18. A structure according to Claim 17 wherein said coating is selected from the group consisting of carboxymethylcellulose, starch, and sugar.