Note: Descriptions are shown in the official language in which they were submitted.
This invention relates to materials having a high
degree of absorbency for water and aqueous salt solutions.
More specifically, it relates to the preparation of such
materials based on cellulose in a Eibrous form having a
S coating of a superabsorbent material on its surface.
In recent years, considerable ef~ort has been expended
pended toward finding or developing materials having great-
er powers of absorbency for water and aqueous salt solu-
tions than the conventional materials hitherto employed
for use in absorbent products. Typical of the absorbent
products to which reference is made are such things as
diapers, bandages, hospital and nursery bed pads and canta-
menial devices. To date, products of these types have been
based primarily on cotton, rayon, wood pulp or materials
of this nature.
A number of materials have been found which exhibit
substantially better absorbency and retention properties
than do those conventionally used in these applications.
Generally, these have been polymeric materials which are
normally water-soluble but which are treated as, e.g., by
cross-linking, to render them substantially water-insoluble
but capable of absorbing 1 arge amounts of water or aqueous
salt solutions. Many of these absorbent materials are
cross-linked, water-swellable but water-insoluble, poly-
saccharide derivatives. Exemplary of these are cross-
linked sodium carboxymethyl cellulose, cross-linked partial
free aci~ carboxymethyl cellulose ~carboxymethyl cellulose
will hereafter be referred to as CMC), cross-linked syn-
thetic polymers such as cross-linked acrylamide--sodium~ 30 acrylate copolymers and cellulosics, and starches, grafted
with vinyl materials such as acrylic acid salts, acryloni-
-2-
trile, and acrylamide. Materials of this type will be
referred to hereinafter as "superabsorbent materialsl'.
While materials of the type described are highly
absorbent, they have not been totally successful when used
as such in absorbent products. In many cases, their
absorbency is so great that they form gels which retard or
prevent further absorption of liquid. ~ost lack sufficient
wlcking action to perform satisfactorily as absorbents.
Moreover, these materials are frequently provided in fine
particle form, making it difficult to form stable blends
of them with long ~iber cellulosic furnishes.
In accordance with this invention a cellulosic fiber
having a rapid rate of absorption and a high absorption
capacity for water or aqueous salt solutions comprises a
long-fiber cellulose in the form of separate and discre-te
fibers having on their surfaces a coating of water-insol-
uble, water-absorbent polymer in an amount equal to 15 to
90% by weight based on the total weight of the coated
fiber.
Also according to the invention a method of preparing
cellulosic fibers having a rapid rate of absorption and a
high absorption capacity for water or aqueous salt solu-
tions comprises the steps of preparing an aqueous suspen-
sion of separate and discrete long-fiber cellulose fibers
containing a water-insoluble, water absorbent polymer,
stirring this suspension until water-insoluble, water-
absorbent polymer forms an aqueous gel. adding to this
suspension an inert water-miscible diluent in which the
polymer is neither soluble nor swellable to precipitate
the polymer onto the surface of the long-fiber cellulose,
and thereafter dehydrate in the coated fibers by contacting
them with a water-miscible diluent in which the polymer is
neither soluble nor swellable, removing the diluent and re-
covering separate and discrete long-fiber cellulose fibers.
The discrete coated cellulose fibers thus produced exhibit
extremely good absorbency properties as to both rate of
absorption and to volume of fluid that can be absorbed.
- In the attached drawings, Figs. 1 and 2 are graphical
. . . . ~ . ;;;, ~ ,. ,
, ~ , ;, , . :, . : :
: ,: : , , ::,: . ., , ~ ' ' ' ' ` : ; :
f.~
presentations of data showin~ the absorption properties of
some hereinafter exemplifled embodiments of the invention,
and comparison of products of this invention with physical
blends of superabsorben~s and long fiber substrates having
the same content of superabsorbent.
Applicable superabsorbent materials include any water-
insoluble, water-swellable polymers, including synthetic
polymers such as cross-linked acrylamide--sodium acrylate
copolymers. ~he superabsorbent materials of choice in this
invention are based on polysaccharides, either natural or
synthetic. Materials of this class include, e.~., cross-
linked, normally water~soluble cellulose derivatives which
are cross~linked to water-insoluble, water-swellable com-
pounds, such as cross-linked sodium CMC, and cross-linked
hydroxyethyl cellulose, cross-linked partial free acid CMC,
and cellulose, starch, and guar gum yrafted with acrylamide
and acrylic acid salts in combination with divinyl com-
pounds/ e.g., methylene-bis-acrylamide. The most preferred
materials are the CMC derivatives, either cross-linked
sodium CMC or partial free acid CMC. Both of these mate-
rials are known to the art to be highly absorbent.
Sodium CMC can be cross-linked with any of a number
of reagents which are difunctional with respect to cellu-
lose. Cross-linking methods applicable to sodium CMC are
discussed in, e.g., U.S. patents 3,168,421 and 3,589,364.
Reagents which are difunctional with respect to cellulose
include formaldehyde, epichlorohydrin and diepoxide re-
agents. Epichlorohydrin is a particularly useful cross-
linker. Cross-linking can be accomplished by either the
wet or dry method taught in the reference patents. Either
technique produces a water-insoluble but bibulous, highly
absorbent product which can be employed in the practice of
this invention.
Partial free acid CMC is also a known material. It
is substantially insoluble in water bu~ will absorb and
retain large quantities of water. It is prepared from the
conventional sodium salt of CMC by acidifying, as by the
method described in U.S. patent 3,379,720. Upon drying,
, ,. : .
. ' ' ' ' , ' ~ ` '
, : -,'~ '~,,'. ; ,
the CMC is believed to cross-link via an internal esterifi-
cation reaction, leading to the highly absorbent state de-
sired in the instant invention and described in U.S. patent
3,678,031. The latter reference teaches a method of pre-
paring this product directly without first forming the com-
pletely neutralized sodium salt. The product resulting
from this process is likewise highly absorbent and suitable
fQr use in the instant invention. When reference is made
hereinafter to partial free acid CMC, it can be taken to
indicate the dried, cross-linked watee-insolub1e material.
~ n carrying out ~he process of ~his invention, the
superabsorbent material and long fiber substrate are added
to a quanti~y of water or aqueous organic medium in excess
of that which the superabsorbent material can absorb. Hy-
dration of the superabsorbent occurs to the point where theindividual particles swell, forming an aqueous gel slurry.
Upon agitation, these superabsorbent particles are dis-
persed throughout the aqueous suspension of long fiber sub-
strate (e.g., chemical cotton, wood pulp, staple cotton,
rayon, plant fibersj.
The long fiber cellulose can be chemical cotton, wood
pulp, staple cotton, rayon or plan9c fibers, for example.
Usually, such fibers are about 2 tv 50 mm. in length. The
fibers are discrete, i.e., in fibrous state rather than
being incorporated into a fabric or other wet structure.
The superabsorbent can be added before, after or dur-
ing the addition of a long fiber cellulose furnish. In
either case, agitation is continued for a time sufficient
to form a homogeneous mixture of discrete cellulose fi~ers
in the gel and to allow the gel to impregnate the fibers.
~he agitation should be sufficiently strenuous to disperse
the particles of gelled superabsorbent while not damaging
the long fiber cellulose furnish.
The superabsorbent material is recovered from the gel
state and precipitated onto the long flber cellulose fur~
nish by contacting the gel slurry while continuing agita-
tion with a water-miscible, organic liquid which neither
dissolves nor swells either the cellulose furnish or the
~ ~ 9 ~
: - .... - : : ~., ,: .: :: , :, : . -
.:, .:: :: . : : . : . : ..
superabsorbent. Precipitation of the superabsorbent is
followed by removal of excess liquid ~via centrifuging,
vacuum and/or pressure filtration or pressing and decant-
ing). Dehydration with the same water-miscible organic
nonsolvent, or by another which meets the same limitations,
then follows. Dehydra~ion can be carried out by contacting
the product from the precipitation stage with successive
lots of water-miscible nonsolvent. q~he product is then
dried to remove the water-miscible organic nonsolvent.
Preferred water-miscible nonsolvents are the water-miscible
ketones and lower alcohols.
The specified method of water removal is critical.
In practice, drying can be accomplished by simply evaporat-
ing the water. Drying by this technique is difficult and
very time-consuming, due to the affinity of the superabsor-
ben~ material for water. A much more serious problem, how-
ever, if drying is accomplished by simple evaporation, is
that the gel particles tend to coalesce as the water evapo-
rates, forming a matrix in which the cellulose Eibers are
fused together rather than being separate and discrete.
This matrix is stiff and horny and unsatisfactory as an ab-
sorbent material in many applications as it lacks absorbent
capacity and rapid rate of absorption.
By contrast, when dehydration is carried out by the
method specified herein, water is removed from the super-
absorbent without the coalescence and matrix formation
described above. Discrete fibers are recovered which are
fluffy and soft to the touch. These exhibit excellent
water absorbency both as to quantity and rate of absorp-
tion. They also exhibit excellent wicking action suchthat absorbed water can be transmitted throughout a body
of the fibers rapidly and relatively uniformly.
The superabsorbent material is added to the long
fiber cellulose furnish to add-on levels of about 15 to
90~ and preferably from about 40 to 90% based on the weight
of the coated long fiber cellulose. However, substantial
improvements in absorption properties over the fibrous
substrate occur even at superabsorbent add-on levels of 15
:. :,... .... :. -: . : :: :
--6--
~o 30% based on the weight of the coated long fiber. On
the other hand, above ahout 90% add-on, the total absor-
bency and the rate of absorption begin to decline.
In observing the tstal absorbency and the rate of
absorption of the coated long fiber cellulose, it has been
noted that the superabsoxbent material increases the absor-
bency of the long fiber cellulose synergistically at add-on
levels above about 50%. That is to sayr the coated long
fiber cellulose will absorb as well or better than will the
superabsorbent material alone.
The coated long fiber cellulose of this invention can
be used as an absorbent medium alone or in combination with
uncoated long fiber cellulose in a ratio such that the
total concentration of superabsorbent is between about 15
and ~0% to form highly absorbent products for use in, e.g.,
medical, health care and catamenial products~ When used
in combination with uncoated long fiber cei]ulose~ the
wicking action of the coated fiber affords good total
absorbency to a product prepared therewith. In fact, in
most cases, the absorbency of a blend of coated and
uncoated fibers is greater than that of a physical blend
of superabsorbent and uncoated cellulose having an equiva-
lent total content of superabsorbent material. Such a
characteristic is of considerable economic importance as
it enables one to prepare superior absorbent products with
lower concentrations of the more expensive superabsorbent
materialO
In evaluating the absorbent performance of the prod-
ucts according to this invention, two tests axe used prin-
cipal]~. These are referred to as the l'CAP test" whichmeasures absorbent capacity and initial rate of absorption,
and the "Syringe test" which measures absorption rate and
wicking ability.
The apparatus employed for the CAP test consists of a
Buchner ~ritted glass funnel, with a rubber tube attached
to its neck; the tube is attached at the other end to a 50
ml. burette The burette is filled with the test solution~
and the level of liquid is allowed to rise until it just
. ,:: .: :: ,:: . , , - -,.,.; . . . . .-
makes contact with the bottom of the frit in the funnelO
The level oE liquid in the burette can be anywhere from a
to 60 cm. below the bottom of this frit. The test sample
is placed on top of the frit and a weight exerting a pres-
sure of from Ool to 0.4 psi is applied to the sample. Thetest is then begun, and the loss of fluid in the burette
i5 monitored as a function of time to give the rate of
absorption. When equilibrium is reached, the capacity is
calculated by dividing the total fluid absorbed at equilib-
rium, or at the end of 45 minutes, by the weight of thepolymer sample. The conditions used with the CAP test for
this work we~e:
(1) Pressure exerted on ~he sample was 0.11 psi;
(2) All of the tests were done with the liquid in
the burette 2 cm. below the fritted glass
initially. This level was allowed to
continually change as absorption occurred;
(3) Pore size of the frit was about 4-5.5 microns.
In carrying out the Syringe test, a 10 cc~ calibrated
syringe is filled with 1.0 gram of test sample and com-
pressed with the syringe plunger to give a uniform column
of material. The volume to ~hich the material was com
pressed varied with the bulk of the sample. For most
fibrous samples, the compressed volume was 5 ml., but a few
very bulky samples could be compressed only to about 8 cm.
Granular materials occupied a volume between 1 and 3 cm.
The syringe, without the plunger of a needle, is
immersed to the 1 cc. mark in a beaker of dyed blue test
solution. The rate of uptake of the test solution is ob- `
served, and either the time required for a 5-ml. rise or
the volume attained at 30 minutes is recorded.
The invention is illustrated in the examples set forth
below. In these examples absorbent properties are demon~
strated with a 1~ NaCl solution to simulate human body
fluids. Other salt solutions or plain water could also be
used depending upon the application contemplated for the
product.
,' ' " , : ~ . . ' ' . ~ ' ', ': ~ :
-8~
~e~ .
lA
In a Waring Blendo ~jar containing 400 ml. of water
was dispersed l g. of Grade 85 Chemical Cotton (Hercules
Incorporated, Wilmington, De]aware). To this was added g
g. of partial free acid CMC (made from Grade 85 Chemical
Cotton) and stirring was continued for 5 minutes. The
slurry was then allowed to stand at room temperature for
lO minutes. ~fter another minute of stirring at low speed,
the aqueous slurry was transferred to a 2-liter beaker. To
this was added, with agitation, 600 ml. of acetone. The
Blendor jar was rinsed with 200 ml. of additional acetone
which was also~added to the 2-liter beaker. After 10 min-
!' utes oE low speed stirring in the: beaker, excess liquid
was removed by alternately pressing and decanting superna-
tant fluid. The sample was then steeped three times in
600 ml. aliquots of acetone for about 5 minutes each time.
Excess acetone was then removed via pressing and decanting
and the sample was dried in vacuum at 60C~ for 1.5
hours.
-
Example lA was repeated using 8.0 g. of partial free
acid CMC and 2O0 g. chemical cotton.
lC
The procedu~e of ~xample~lA wa~ repeated except that
3 g. of chemical cottQn was used and 7 9. of partial free
acid CMC.
-
Example lC was repeated except that the water slurry
was added to 800 ml. of acetone contained in the ~-liter
beakerO
_
Example lA was repeated with 4 g. of chemical cotton
and 6 g. of cross-linked partial free acid CMC.
lF
The procedure of Example lA was répeated with 5 g.
chemical cotton and 5 g. of partial free acid CMC.
~
.. .. .. : ~ . , . , . , ' .
:: . :;,: .. .. , .- .
lG
Example lA was repeated using 6 9. of chemical cotton
and 4 9~ of partial free acid CMC.
lH
Example lA was repeated using 7 g. of chemical cotton
and 3 g. of partial free acid CMCo
lI
Example lA was repeated using 8.5 gO of chemical
~ cotton and 1.5 9. o~ partial free acid CMC.
Each of the above materials was tested for 1% NaCl
solution absorbency using the tests described previously.
; Simu].taneous control tests were run employing uncoated
chem.ical cotton and fibrous partial free acid CMCo Perti-
nent data concerning these materials are recorded in Table
I.
.
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The C~P test data in TabIe I show that the equilib-
rium absorption capacity of the coated chemical cotton
reaches a maximum at about 90~ add-on of par~ial free acid
CMC. Also, coated samples containing between about 60 and
90~ partial free acid CMC have absorption capacities equal
to or greater than the partial free acid itself. The
coated products containing 40 to 90~ partial free acid CMC
have faster initial rates of absorption than the partial
free acid CMC by itself.
Lower Syringe Test values for the coated samples
indicate better wicking ability and faster rate of absorp-
tion than the partial free acid CMC alone.
Example 2
2A
In 400 ml. of water in a Waring Blendor ~6 g. of
fluffed wood pulp was slurried along with 4 9. of partial
free acid CMC made from shredded chemical cotton sheets.
After about 5 minutes agitation, the slurry was poured
into 800 ml. of acetone and agitated at high speed with an
air-driven agitator. Excess liquid wa~ removed, as de-
scribed in Example 1, and the slurry was steeped three
times in 600 ml. of acetone for about 5~10 minutes each
time. After removal of excess acetone as described in
Example 1, a sample was dried in vacuum at 60C. for
about 1.5 hours.
-
Example 2A was repeated using 5 9. of fluffed wood
pulp and 5 g. of partial free acid CMC.
2C
Example 2A was repeated using 4 g. of fluffed wood
pulp and ~ g. of partial free acid CMC.
2D
Example 2A was repeated using 3 g. of fluffed wood
pulp and 7 g. of partial free acid CMC~
3S 2E
Example 2A was repeated using 2 g~ of fluffed wood
pulp and 8 g. of partial free acid CMC.
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-12
2~
~ xamp]e 2A was repeated using 1 g. of fluffed wood
pulp and 9 g. of partial free acid CMC.
These samples were tested for their absorbent charac-
teristics using the CAP test and simultaneously runningcontro~ specimens of uncoated fluffed wood pulp and the
: partial free acid CMC used for coating. The results are
: recorded in Table II.
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-14- ~ 2
I'he CAP test data in Table II show that the equilib-
rium absorption capacity of the coated wood pulp reaches a
maximum at about 90% add-on of the partial free acid CMC.
Coated samples containing between about 60 and 90% partial
free acid CMC have absorption capacities equal to or
greater than the partial free acid CMC itself. The coated
samples containing 40 to 90% partial free acid CMC have
initial rates of absorption equal to or faster than the
partial free acid CMC itself.
These results are in agreement with the CAP test data
for the Example 1 series where a different cross-linked
CMC and fibrous substrate were used.
Examele 3
lS To a wide-mouthed 32 oz. plastic bottle was added 400
ml. of water and 3.0 g. of staple cotton ~extra long fiber
furnish). Then 7 g. partial free ~cid CMC made from Grade
85 Chemical Cotton was added. The bottle was sealed,
placed on rollers and rolled for one hour. The contents
were then transferred to a 2-liter beaker and the eotton
fibers which had become matted and entangled were pulled
apart by hand to give a more uniform slurry in the beaker,
following which 600 ml. of acetone was poured into the
beaker. The bottle was rlnsed with another 200 ml. of
acetone which was also added to the beaker. The slurry
was stirred by hand with a spatula for about 5 minutes,
then allowed to stand at room temperature for 15 minutes.
Excess liquid was removed by pressing, following which the
sample was dehydrated by steeping with three 600-ml. por-
tions of acetone for 10 minutes each steep. After removalof excess acetone, the sample was dried in vacuum at
60C. for 1.5 hours. The resultant sample was tested
for its absorbency characteristics using the CAP test and
1~ sodium chloride solution. A control was run simultan-
eously using just the uncoated cotton. The control fromExample 1 series served as a control for the partial free
acid CMC in this case~
, ~ , . . .
:,- ,: -:. . : ~ ,, , ; ; .
-15
3B
Example 3A was repeated using staple rayon instead of
staple cotton as the long fiber furnish. A control was
run simultaneously using just the uncoated rayon.
Pertinent data are recorded in Table III.
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32
-17-
The CAP tes~ data show that coated fiber Example 3A
containing 70~ partial free acid CMC as coating has about
the same absorption capacity, but a faster initial rate of
absorption than the partial free acid CMC itself. Example
3A also exhibited better wi.cking action than the partial
`; ~ree acid CMC itself, having a lower Syring test value of
5 ml. in 34 seconds compared to 5 ml. in 14 minutes for the
modified CMC.
The CAP test data show that the rayon staple control
` 10 has a ]ower absorption capacity than the stapie cotton.
-~ This difference is reflected in the lower absorption capa-
city of Example 3B as compared to Example 3A. The wi~king
action of Example 3B is comparable to that of Example 3A,
however, and thus is superior to the partial free acid CMC
itself.
:, ~
4A
,, ~
; ~ This example compares a~ueous acetone solutions with
water as the slurry medium. To a Waring Blendor~jar con-
taining 200 g. o~ water was added 4 g. of Grade 85 Chemical
Cotton and 6 g. of partial free acid CMC prepared from
fine-cut chemical cotton. The slurry was s~irred at slow
speed for about 5 minutes, let~stand for 10 minutes,
stirred for one minute, and then transferred to a l-liter
~` 25 beaker. Four hundred ml. of acetone was added to precipi-
tate the CMC on the chemical cotton. The slurry was
stirred for 10 minutes with an air stirrer. Excess liquid
was then removed by suction filtration on a coarse sintered
glass filter to about 50% solids content and the wet pad of
sample was steeped three times with 60 ml. of acetone each
steep. The three steeps were carried out on the glass fil-
ter also, allowing each 60 ml. lot of acetone to drain
through the wet pad of sample for 5 minutes and on the
glass filter also, then suction iltering for about 5 min-
; 35 ut~s. After excess acetone was removed from the sample
folJowing the third steep, the sample was dried in vacuum
;~ - at 60C. for 1.5 hours.
..
.. ! ..: .. . .'.: ' :-;.. :! ' `: ,, , '
-: . , -: ~: .``., . ~, ` '` :`:'' ,. '
-18-
4B
Example 4A was repeated except that the slurry medium
was 200 g. of 20~ acetone in water and 266 ml. of acetone
was used in the precipitation step.
S ~C
Example 4A was repeated using 200 g. of 30% aqueous
acetone solution as the slurry medium and 202 ml. of
acetone in the precipitation stepO
4D
; lO Example 4A was repeated using 200 9. of 40% aqueous
acetone solution as the slurry~medium and 137 mlO of
acetone in the precipitation step.
4E
Example 4A was repeated using 200 ~. of 50% aqueous
acetone solution as the slurry medium and 72 ml. of
acetone in the precipitation step.
Syringe test data are given in Table IVa. CAP test
data are recorded in ~able IVb.
TABLE IVa
Example
No. Slurry Medium _Syringe Test Value*
4A Water 4.2 ml. in 30 minutes
4B 20% aqueous acetone 5 ml. in 16 minutes
4C 30% aqueous acetone 5 ml. in 6.5 minutes
4D 40% aqueous acetone 5 ml. in 7 minutes
4E 50% aqueous acetone 5 ml. in 1.25 minutes
*Rate of climb o~ 1% NaCl solution in Syringe
TABLE IVb
Example Absorption/Time Interval*
~o. 1 3 S lO 15 20 25
_
4A 2.0 4.9 6.9 8.6 8.8 8.8 8.8
4B 2.3 5.4 7.2 8.3 8.4 8.4 804 -'
4C 2.3 5.0 7.7 8.4 8~6 8.6 8.6
4D 2.5 5~7 7.4 8.0 8.1 8.1 8~1
4E 1.8 4.4 6.3 7.6 7.7 7.8 7.8
*Absorption of 1% NaCl solution (ml./g. of sample)
at various tlmes in minutes
~; The Syringe test data in Table IVa indicate that
coated products prepared with aqueous acetone as the
s]urry medium have better wicking action than those pre-
'~
.
, , ,,,. , ~ - , , , . : ~ -
.. . . ...
19
pared in water. However r at 40 and 50% aqueous acetone
levels, t~e coated samp]es have slightly less absorption
capacity than the coated sample prepared with water as the
slurry medium, as shown in Table IVb.
s Exam~le 5
5~
To 400 ml. of water in a Waring Blendor*jar was added
5 g. of fluffed wood pulp and 5 g. of partial free acid CMC
made from shredded chemical cotton sheets. After 5 minutes
stirring, the slurry was let stand for 10 minutes, stirred
one minute and then the slurry was poured into 1700 ml. of
methanol and stirred vigorously with an air-driven agita-
tor. After draining off excess liquid, the slurry was
steeped three times in methanol using 600 ml. of methanol
for each steep. Steeps were of about 5 to 10 minutes dura-
tion. The sample was dried in vacuum at 60C. for 1.5
hours.
Example 5A was repeated using 800 ml. of isopropanol
as precipitant and steeping with 600 ml. of isopropanol 3
times.
These specimens were tested using the CAP test and
Syringe test. Pertinent data are recorded in Table V.
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While both precipitants yielded good products, the
isopropano] was preferred over methanol since it required
only 800 ml. to accomplish the objective. Acetone is pre-
ferred over both methanol and isopropanol, however, as
less acetone is required than methanol, and acetone impar~s
better absorption properties to the coated fiber than does
isopropanol.
To a Waring Blendor~jar containing 400 ml. of water
was added 6 g. of fluffed wood pulp and 4 g. of a densi-
fied powdery CMC prepared from fine cut cellulose and
cross-linked with epichlorohydrin according to the proce-
dures taught in Dean et al, U.S. patent 3r589t364O The
slurry was stirred for 5 minutes at low speed in the
Blendor, and then let stand for 10 minutes at room temper-
ature. After stirring for one minute, the slurry was
poured into 800 ml. of acetone contained in a 2-liter
beaker. The mixture was stirred with an air driven
stirrer. After about 10 minutes stirring, excess liquid
was removed via alternately pressing and decanting, and
the sample was dehydrated by steeping in acetone three
times (600 ml. of acetone per steep of about 10 minutes
duration). Excess acetone was removed by alternately
presising and decanting, and ~he same was dried in vacuo at
~,~ 25 60C. The absorbent characteristics of this material
were tested according to the CAP test and Syringe test.
The results are recorded in Table VI.
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The CAP test and Syringe test data in Table VI show
that Example 6, with 40% cross-linked CMC as coa~ing, has
a higher absorption capacity and better wicking action
than the cxoss-linked CMC itself.
Example 7
l 7A
~, ~
Eight grams of Grade 85 Chemical Cotton was slurried
in 400 ml. of water contained in a Waring Blendor~jar.
Two grams of fine-particle, water-insoluble but water-
~! .
swellabJe cross-linked grafted cellulose (acrylamide:sodium
acrylate grafts cross-linked with methylene-bis-acrylamide)
was added. The mixture was stirred at low speed in the
Blendor for 5 minutes and then le~ stand 10 minutes. After
another minute of stirring, the slurry was transferred to
a 2-liter beaker and 800 ml. of acetone was added with
stirring via a Lightning Air Stirrer. Stirring was contin-
ued for 10 minutes, after which the slurry was left un~
stirred for 10 minutes. Excess liquid was then removed by
a]ternately decanting and pressing. The sample was steeped
in acetone three times, using 600 ~1. of acetone per steep
of at least 10 minutes duration. After removal of excess
acetone by decanting and pressing, the sample was dried in
vacuo at 60C. for 1.5 hours.
7B
~s 25 The procedure for Example 7A was repeated, replacing
.~ the cross-linked grafted cellulose witX`2 g. of similarly
cross-linked grafted starch powder and replacing the Grade
85 Chemical Cotton with 8 g. of fluffed wood pulp.
7C
The procedure for Example 7A was repeated, replacing
the cross-linked grafted cellulose with 2 9. of similarly
cross-linked grafted guar gum in fine particle form.
7D
The procedure for Example 7~ was repeated, replacing
the cross-linked grafted cellulose with 3 g. o~ water-
insoluble, but water-swellable, fine particle acrylamide--
sodium acrylate copolmer cross-linked with methylene-bis-
acrylamide and using 7 g. of ~rade 85 Chemical Cotton.
G ~
24~ 2
The initial slurry was made up in 500 ml. of water in this
case. The slurry became too thick to stir adequately in
the Blendor, so the mixture was stirred with a spatula by
hand ~or the required time~ -
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-26-
As shown by the CAP test and Syringe test data in
Tab]e VII, coated fiber samples prepared according to the
procedures in Examples 7A, 7B, 7C and 7D were superior to
their corresponding fine particle superabsorbent in absorp-
tion capacity, initial rate of absorption and wickingaction.
Example 8
~r
To a Waring Blendor jar containing 400 ml. of acetone
was added 6 g. of Grade 85 Chemical Cotton and 4 g. of par-
tial free acid CMC to form a blend containing 40% partialfree acid CMC in which the chemical cotton fibers were not
coated. Stirring was continued at low speed for 2 minutes,
following which excess acetone was removed and the sample
was dried in vacuum at 60C.
The absorbency of this material was determined via
the CAP test. Results of this test, as compared with Exam-
ple lG, show that coated fiber containing 40% partial free
acid CMC add-on is considerably more effective as an absor-
bent medium in both initial rate and absorption capacity
than is the blend of partial free acid CMC and chemical
cotton of the same CMC content. The data are presented
graphically in Fig. 1.
Exam~le 9
9A
In a Waring Blendor~jar containing 400 ml. of acetone
was blended 8 g. of a material similar -to that of Example
lF containing 50% partial free acid CMC and 2 g. of Grade
; 85 Chemical COttO}I, resulting in a sample having a total
partial free acid CMC content of 40 weight per cent.
Excess acetone was removed and the sample dried in vacuum
` at 60C.
; 9B
Example 9A was repeated using 6 g. of a material
similar to that of Example lF and 4 g. of Grade 85
Chemical Cotton, resulting in a sample having a total
`~ partial free acid CMC content of 30 weight per cent.
~ ~ 9C
-
Example 8 was repeated using 7g. of Grade 85 Chemical
, ~ .: : .
,: , : ;, , ;
~ 4~
Cotton and 3 g. of partial free acid CMC to form a blend
containing 30 weight per cent of partial free acid CMC and
containing no coated fibers.
Absorption characteristics of these materials were de-
S termined using the CAP test~ The comparison of these data,along with data of Example 8, is presented graphically in
Fig. 2. The data in this graph show the improved absor-
bency (faster initial rate and higher absorption capacity)
exhibited by a blend of the coated iber and chemical cot-
ton as compared to a blend of partial free acid CMC withuncoated chemical cotton in which the total CMC content is
the same.
Example 10
lOA
An aq~eous slurry was prepared as described in Example
7D. After the required stirringr the slurry was trans-
ferred to an aluminum panj and the water removed by drying
in vacuo at 60C. It required a total of 10 hours to
dry to constant weight. The sample formed a dense, brittle
20 mat on drying, in contrast to the soft, fluffy material
prepared by the Example 7D procedure where acetone was
used to remove the water prior to drying from the acetone~
wet state.
The CAP test data in Table V~II show that drying from
25 the acetone-wet s~ate as in Example 7D is much superior to ~;
drying from the water-wet state as in this example, leading
to a faster initial rate of absorption and a higher absorp-
tion capacity. y
lOB
An aqueous slurry was prepared as described for Exam-
ple lF. After the required stirring, the slurry was placed
in an aluminum pan, and the water removed by drying at
100C. in an air-draft oven. It required 7 hours to dry
; to constant weight. This sample, though not as dense and
brittle as lOA, was brittle and hard. In contrast, the
material of Example lD, dried from the acetone~wet state,
was soft and fluffy.
Again, the CAP test data in Table VIII show that
;
- - , : ~ -:: : ~ . '' . ... :: . - .:.
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-~8~
superior absorption properties result by drying from the
acetone-wet state rather than drying from the water-wet
state.
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