 |
Description  |
|
|
BACKGROUND OF THE INVENTION
(1) Field of the Invention
This invention relates to a foamed product made by combining biodegradable
cellulose fibers material and a superabsorbent polymer. More specifically,
this invention relates to a foamed product made from cellulose fibers and
a superabsorbent polymer, which is especially useful as a cushioning
material, and to methods of making the foamed products.
(2) Description of the Prior Art
The prior art is replicate with products useful as cushioning or packaging
material. These products are generally known as dunnage material. When
shipping articles, especially fragile articles, it is desirable to make
sure that the articles are safely packaged using dunnage material in one
form or another. Dunnage materials include such things as bubble paper,
styrofoam pellets, commonly known as "peanuts", ordinary tissue paper,
embossed paper, foamed in place plastic materials and the like. While all
of these dunnage materials provide a certain effectiveness as packaging
materials, they are not universally suitable for every packing need.
Additionally, because disposal of waste paper in an increasing problem in
our society, it is desirable to find beneficial uses for waste paper and
certain other biodegradable fibrous materials. Reusable and biodegradable
dunnage material provides a valuable use. Of course, there have been
attempts to convert newsprint and other waste paper into useful products.
Among the difficulties encountered in attempts to convert waste newsprint
into useful products is newsprint's short length fibers and low potential
strength.
There have also been disclosed numerous ways to form sheets of absorbent
material from wood fibers and superabsorbent polymers. In such products,
the wood fibers and the superabsorbent polymer are fixed in place
mechanically and embossed to mechanically set in place the superabsorbent
polymer. The thus formed product is used to absorb water or other liquid
material. Such products have for years been converted into products to
increase the absorbency such as diapers, sanitary napkins, absorbent
cloths and pads, and the like. For example, one such product is disclosed
in EPO Patent Application 255,654, wherein there is described an approach
to making sheets of fibrous material in which cellulose fibers and
superabsorbent polymers in the form of fibrils are formed into dry sheets.
The fibers and superabsorbent polymer are suspended in an air stream of a
mixture of fibers and polymer and dry formed onto one face of a moving
permeable forming surface and hot calendaring or embossing to bind the
materials.
Other approaches for combining cellulose fibers and superabsorbent polymers
have been proposed. Some of these approaches use binders to attach the
superabsorbent polymer and fibers together to make products useful for
absorbing liquids. One such approach is set forth in PCT application WO
90/1181 which discloses coating fibers with at least about 7% by weight of
one or more one or more liquid binders and applying a superabsorbent
polymer to the fiber while the liquid binder on the fiber is still at
least partially wet to uniformly adhere to the fibers.
The various products formed from combining cellulose fibers and
superabsorbent polymers have been found useful as absorbent wipes or
converted into other products but they have not been designed to meet the
specific needs of the packaging industry.
SUMMARY OF THE INVENTION
In accordance with the present invention a biodegradable foam product is
formed from cellulose fibers and a superabsorbent polymer. The product is
made by mixing cellulose fibers or similar biodegradable material with a
superabsorbent polymer and shaping it into a desire form. This product is
allowed to expand by letting the superabsorbent polymers soak up water.
Upon drying, the superabsorbent polymer gives off water and shrinks to its
original size leaving voids between the fibers which maintains the
expanded dimensions. The superabsorbent polymer also acts as a binder for
the cellulose fibers. In another embodiment of this invention, the
superabsorbent polymer and water are mixed and the polymer allowed to
absorb the water prior to mixing with the fibers. Alternatively, the foam
product may be made by forming a slurry of fiber and water, blending the
superabsorbent polymer with the slurry and drying.
In accordance with a preferred method of this invention, cellulose fibers
and up to about 25% by weight of said fibers of superabsorbent polymer,
are blended in the absence of water to produce a blended mixture. Sheets
are formed from the mixture by dry-laying wherein the blended mixture of
cellulose fibers and superabsorbent polymer suspended in an air stream are
laid onto the face of a moving porous web and calendared to the desired
thickness or formed into some other desired shape. The sheets are wetted
with sufficient water to allow the superabsorbent polymer to fully expand
and then dried to drive off the water.
In another aspect of this invention, additional binding properties may be
achieved by incorporating small amounts of latex adhesive in the water
during the wetting process.
Thus, it is an object of this invention to provide a cushioning material
which may be made from waste paper or other biodegradable fibrous material
into a size and shape which is useful for packaging.
Another object of the present invention is to provide a biodegradable
foamed product in which cellulose fibers and a superabsorbent polymer are
formed together.
A further object of this invention is to provide a method of making a
biodegradable foam product by blending fibers and superabsorbent polymer,
forming a sheet or other shape of the fiber/polymer mixture, wetting the
sheet to allow the superabsorbent polymer to swell and drying.
BRIEF DESCRIPTION OF THE DRAWINGS
Other objects, features and advantages of the invention will be readily
understood from the following detailed description and drawing in which:
FIG. 1 is a flow sheet showing the various steps in the manufacture of the
foam product of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The foam products of the invention comprise making a product from fibers of
biodegradable material and a superabsorbent polymer formed to any size and
shape appropriate to its intended use. The foamed products are made from
biodegradable fibrous material such as natural cellulose fibers,
preferably from wood pulp. While any paper fibers may be used, the
economically preferred end use of the products dictates the desirability
for using waste or recycled paper, especially waste newsprint. It is not
necessary to deink or bleach the paper. Preferred is waste newsprint which
is commonly obtained in baled form and must be fiberized, for example, in
a hammer mill, to be useful. Fiberizing the waste newsprint forms, for the
most part, individual relatively short fibers generally about 25 mm. to
150 mm. long. The fiberized material may contain small amounts of fiber
bundles but these fiber bundles are seldom detrimental to the final
product.
Furthermore, it is not necessary that the foamed products of this invention
be limited to recycle paper as any natural cellulose fibers may be used.
Virgin wood pulp fibers from well-known pulping processes may also be
used. Other natural cellulose fibers include a variety of materials such
as bagrasse, hemp, jute, rice and corn stalks, cotton linters and the
like. Also, other ground up, fiberized biodegradable material may be used,
such as natural fibers, e.g., cotton linters.
The fiberized cellulose material is blended with a hydrophilic polymer,
especially the so-called "superabsorbent" polymers. Superabsorbent
polymers are synthetic cross-linked polymetric materials that are capable
of absorbing many times their own weight of water or other liquids.
Because superabsorbent polymers are significantly cross-linked, they are
difficult to put into solution. Therefore, superabsorbent polymers are
most commonly used as powders or granules.
The superabsorbent polymers suitable for application in the present
invention are conventional superabsorbent polymers as that term is
commonly applied in the art. Superabsorbent polymers are generally from
one of three classes, namely starch graft copolymers, cross-linked
carboxymethyl cellulose derivatives and modified hydrophilic
polyacrylates. Examples of such materials are polymers of water soluble
acrylic or vinyl monomers that are cross-linked with a polyfunctional
reactant. Also included are starch modified polyacrylic acids and
hydrolyzed polyacrylonitrile and their alkali metal salts. The acrylic
polymers are preferred and are commercially available in particulate form
mainly as polyacrylic acid.
A number of acrylic based superabsorbent polymers are commercially
available and these are suitable for use in the present invention. A
preferred commercially available superabsorbent polymer is Sanwet.RTM., a
starch modified superabsorbent polymer available from Hoechst Celanese
Corporation, Charlotte, N.C. Sanwet.RTM. is a starch grafted polyacrylate
sodium salt that has the capacity to absorb as much as 800 times its own
weight in liquid. Other commercially available superabsorbent polymers
include, for example, DRYTECH.RTM. 520 superabsorbent polymer available
from Dow Chemical Co., Midland, Mich. (Drytech.RTM. is a superabsorbent
derived from polypropenoic acid.); AQUA KEEP manufactured by Seitetsu
Kagaku Co., Ltd.; ARASORB manufactured by Arakawa Chemical USA) Inc.;
ARIDALL 1125 manufactured by Chemdall Corporation; and FAVOR manufactured
by Stockhausen, Inc.
Among the superabsorbent polymers of the carboxymethyl cellulose derivative
type are carboxymethyl cellulose or an alkaline metal salt thereof such as
sodium carboxymethyl cellulose, hydroxy-ethyl cellulose,
hydroxy-propylomethyl cellulose, methyl cellulose, regenerated cellulose
derived from solutions of cellulose xanthate, carrageenan and collagen.
The blending may be accomplished using equipment well known in the art. It
is important to make sure that the superabsorbent polymer are thoroughly
distributed throughout the fibers to obtain a consistent product. Enough
superabsorbent polymer is added to effectively form a foamed product when
dried. The amount of superabsorbent polymer added is at least enough to
effectively form the foamed product but it is not necessary to add more
than 25% by weight. The upper limit of about 25% is a practical limit in
that as the amount of superabsorbent polymer included in the foam product
is increased about 25% the strength and density of the foam product
decreases to the point where it is ineffective as a cushioning material.
It is preferred that from about 5% to about 20% by weight of
superabsorbent polymer be blended with the fibers. The higher the
superabsorbent polymer loading, the less dense will be the resulting foam
product.
It has been found that articles of a desired shape and size, e.g., a sheet,
can be formed before adding water. The biodegradable foam product of the
present invention can be dry-laid wherein the blended mixture of fibers
and superabsorbent polymer is suspended in an air stream onto the face of
a moving web and calendared to the desired thickness. Alternatively, water
may be added directly to the superabsorbent polymer and the polymer
allowed to swell before the fiber is blended with the swollen
superabsorbent polymer. A rather thick gel is formed which may be extruded
or cast into flat sheets of varying thickness for wrapping articles for
cushioning protection or hollow tubes to be used as loose fill to cushion
articles. The foamed products made by whichever process desired may be
formed into specifically shaped members for supporting articles in place
within a shipping container. Among such examples are corner posts and the
like. Depending upon the article to be supported by, for instance, a
corner post, the characteristics of the foam may be tailored to the
specific need by adding to the product, where desirable, a latex adhesive.
In an alternative embodiment of this invention, the foam product may be
made by forming a slurry of fiber and water blending the superabsorbent
polymer with the slurry and drying.
In a preferred embodiment, once the desired size and shape has been formed,
water is added to the fiber/superabsorbent polymer blend in an amount
sufficient to allow the superabsorbent polymer to swell to its desired
extent. The superabsorbent polymer swells rapidly, in most circumstances
in about a minute. The amount of swelling will determine the density of
the final product. If a denser foamed product is desired either a small
amount of superabsorbent polymer may be added or less water, which causes
less swelling of the polymer and therefore less expansion of the foam.
The swollen article is fed to a drying oven where the heat drives off the
water leaving voids between the cellulose fibers. The presence of the
superabsorbent polymer also keeps the fibers bound together in one
structure. The dried product will have an open cell foam structure and a
density from about 1.0 to about 3.0 lbs/ft.sup.3, preferably from about
1.5 to about 2.0 lbs/ft.sup.3. The product is biodegradable and
disintegrates easily in water.
In an alternative embodiment small amounts of a water soluble adhesive,
such as a latex adhesive may be added to the water to form a stiffer
product. It has been found that a latex binder of butadiene, acrylic or
vinylacetate is particularly suitable. The latex may be added in amounts
up to about 10% by weight, with about 5% by weight being preferred. As
more than about 10% by weight latex is added, the foamed product begins to
lose flexibility and therefore becomes undesirable as a cushioning
material. Depending upon the amount of latex added to the water, the
foamed article can be made from very soft and flexible to very hard and
stiff.
While not of primary concern of cushioning material, the foamed product has
a high liquid absorbing capacity. Despite having a high liquid absorbing
capacity, the foam products of this invention are unsuitable for such uses
because when used to absorb liquid, the foam products of the invention
disintegrate into a gel-like mass. The high liquid absorption capacity of
the final product can be minimized, if desired, by treating the product
with sodium bicarbonate or similar salts to deactivate the superabsorbent
polymer, in an amount of about 1% by weight.
In yet another embodiment, the foam product may be made with skins on one
or both sides of the foam. In such embodiment, a sheet of thin dry-formed
paper, Kraft paper or tissue paper is disposed under the air-laid intimate
blend of fibers and superabsorbent polymer prior to adding water to form a
composite sheet. The fiber/superabsorbent layer may also be covered by a
second layer of thin dry-formed paper, Kraft paper, tissue paper, or the
like.
Referring now to the drawings, there is shown in FIG. 1 a flow sheet of a
preferred method for making the foam product of this invention. Cellulose
material 10, preferably bales of waste paper, is fiberized in a suitable
vessel such as a hydropulper, but preferably a hammermill 11, to separate
the fibers. For most uses of the products of this invention, it is not
necessary that the paper, if waste paper is used, be deinked. The paper
fibers are conveyed via blower 12 to blender 13 where the fibers are
intimately mixed with a superabsorbent polymer from feed 14.
From blender 13 the mixed fibers are moved to a formation zone which may be
in line with the blender or may be separate equipment. The final product
may be formed or shaped by extrusion from the blender into any desired
form, such as sheets, tubes and the like. As shown in FIG. 1, the material
20 is air laid onto a moving permeable forming surface and formed into a
sheet 21. The air-laid sheet is passed through calendar rolls 15 to
compress the sheet to the desired thickness.
The sheet is passed on open-mesh conveyor 17, driven by rollers, through
water feed station 16 While passing through water feed station 16, the
sheet is sprayed with sufficient water to allow the superabsorbent polymer
to swell to the desired extent. Excess water is collected and recovered
from excess water box 23. The swollen sheet is then fed into drying oven
18 where the sheet is supported on open-mesh conveyor belt 19, driven by
rollers, while the water is evaporated from the swollen
fiber/superabsorbent sheet and the polymer shrinks to its original size,
leaving voids in between the paper fibers. This process keeps the fibers
bound together in one structure to form the foam product. The sheet of
paper foam is passed through winder station 22 where it may be wound into
a roll.
The following examples are provided to further illustrate various
embodiments of the present invention. The examples are presented solely
for purposes of illustration and are not to be construed as limiting the
invention in any manner.
EXAMPLE 1
Compressed pulp board was fiberized in a hammer mill. The fiberized fluff
was blended with 20% by weight of dry superabsorbent polymer fibrils,
Stockhausen-Favor 900, a cross-linked polyacrylic salt using a desk top
blender. The blended mixture was spread evenly on a 13 lb.wet strength
tissue (approximately 6".times.12") to form a mat. Another piece of wet
strength tissue was placed on the top to cover the mat. These tissues need
to be used only if an outer skin is desired on the final product.
Water was sprayed on the mat and the mat was allowed to expand as the
superabsorbent polymer soaked up the water. The mat soaked up about 35-40
times the weight of the fluff mat in about 1 minute. Once the desired
expansion was obtained, the swollen mat was dried in a conventional oven
at 125.degree. C. for 10 minutes. As the water evaporated, the
superabsorbent polymer fibrils shrank to their original size, leaving
voids between the fluff matrix. The resulting product was a flexible foam
having a density of 1.5 lbs/ft.sup.3. The product disintegrated when
placed in water. The product was soft and provided excellent cushioning
properties.
EXAMPLE 2
Compressed pulp board was fiberized in a hammer mill. Superabsorbent
polymer particles (Favor 900 from Stockhausen) were mixed with water and
allowed to swell. The swollen superabsorbent polymer [15% by weight] was
blended with the fiberized fluff in a desk top blender to form a
paste-like mixture. The resulting paste-like mixture was molded into a
tube like configuration and dried. The resulting product was a foam
article having a density of 1.8 lbs/ft.sup.3 and was suitable as a
cushioning material. It disintegrated when placed in water.
EXAMPLE 3
A foamed sheet was made according to the procedure used in Example 1 except
that a 1% solution of latex (Elmer's white glue) was added to the
fluff/SAP mixture instead of water. The resulting product had a density of
2.0 lbs/ft.sup.3 and was somewhat stiffer than the product of Example 1.
While the invention has been described and illustrated herein by references
to various specific materials, procedures and examples, it is understood
that the invention is not restricted to the particular materials,
combinations of materials, and procedures selected for that purpose.
Numerous variations of such details can be employed, as will be
appreciated by those skilled in the art.
* * * * *
|
|
 |
|
 |
Description |
|
