Note: Descriptions are shown in the official language in which they were submitted.
.~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,
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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
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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
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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
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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
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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
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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
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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
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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.
2~9~9~
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
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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
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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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209991 ~
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,
19
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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
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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.
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