Note: Descriptions are shown in the official language in which they were submitted.
:`
-1--
This invention relates to polymeric films based on
acrylic acid and an acrylate.
A variety of hydrophilic polymers which are useful
in the manufacture of water absorbent films and fibers have
been reported in the prior art. U.S. Patent 3,915,921 dis~
closes copolymers of unsaturated carboxylic acid monomers with
alkyl acrylate esters wherein the alkyl group contains 10 to
30 carbon atoms. However, because of the high Tg of these
polymeric materials, it is difficult to extrude them in fiber
or film form. Furthermore, films pressed from the powders
require high temperatures, the films are brittle and fragile,
and have a reduced initial rate of water absorption.
U.S. Patènt 4,062,817 discloses polymers of un-
saturated copolymerizable carboxylic acids, at least one
alkyl acrylate or methacrylate wherein the alkyl group has 10
to 30 carbon atoms and another alkyl acrylate or methacrylate
wherein the alkyl group has 1 to 8 carbons. This composition
alleviated many of the deficiencies of the earlier compositions.
Further improvements in the hydrophilic properties were obtained
by compositions disclosed in U.S. Patent 4,066,583. This Patent
discloses a composition comprising (1) a copolymer of the type
disclosed in the '817 patent, except that after copolymerization
30 to ~0 percent of the carboxylic groups were neutralized with
an alkali metal or ammonia and (2) an aliphatic glycol, a
plasticizer which is important in facilitating extrusion of
the polymer.
Most recently, U.S. Patent 4,167,464 discloses
highly water absorbent polymers obtained by photopolymerizing
an alkaline metal salt of acrylic acid, a long chain alkyl
acrylate or methacrylate and a short chain alkyl acrylate
or methacrylate in the presence of a photoinitiator.
~z~s~
\
--2--
In accordance with the invention there is provided
a water insoluble, flexible~ highly water absorbent polyMeric
film having up to 25 mil thickness and containing water, said
film being prepared by photopolymerizing a monomer mixture
consisting of: (a) 65 to 95 weight percent of acrylic acid,
60 to 100 percent of the carboxylic groups having been
neutralized with an alkali metal hydroxide or ammonia base
prior to polymerization, (b) 5 to 35 weight percent of a co-
monomer selected from the group consisting of 2-hydroxyethyl
methacrylate and dialkylaminoalkyl acrylate or methacrylate
wherein each alkyl of the dialkyl groups has 1 to 8 carbons
and the other alkyl group has 2 to 6 carbons, (c) 0.01 to 5
weight percent, based on the total weight of the monomers, of a
photoinitiator, (d) 0 to 5 weight percent3 based on the
weight of the monomers, of a cross-linking agent which contains
two or more ethylenic unsaturations, and (e) a sufficient
amount of water to render the resulting film flexible.
The aqueous monomer mixture can be spread to the
desired thickness and then polymerized by exposure to
a UV light or radiation sources. If photopolymerized, a
photoinitiator must be employed.
The film of the invention has outstanding absorption
and retention properties of water and ionic solutions such as
urine or blood.
~,i'"'`l
-- 3 --
Suitably about 70 to 100, preferably 80 to 100
percent of the carboxylic groups of the acrylic acid have
been neutralized prior to polymerization.
Examples of dialkylaminoalkyl acry~ates and
methacrylates are dimethylaminoethyl acrylate, which is
preferred, dimethylaminobutyl acrylate, dimethylaminohexyl
acrylate, diethylamiroethyl acrylate, diethylaminobutyl
acrylate, dipropylaminohexyl acrylate, dipropylaminopropyl
acrylate, dibutylaminoethyl acrylate, dibutylaminobutyl acrylate,
.. ..
. .~, .
'''`` ~L2~JLP~
dibutylaminohexyl acrylate, di-n-hexylaminoethyl acry-
late, di-n-octylaminoethyl acrylate, di-n~oc~ylamino-
butyl acrylate, dimethylaminoethyl methacrylate, di-
methylaminobutyl methacrylate, dimethylaminohexyl meth-
acrylate, diethylaminoethyl methacrylate, die~hylamino-
butyl methacrylate, di-n-octylaminohexyl me~hacrylate
and the like.
In addition to the above discussed monomers
from which the copolymers of this invention are prepared,
minor amounts,that is less than 5 weight percent,of
additional monomers may also be used. Whether these
additional monomers are employed will depend on the end
use and the physical properties required, that is, the
speed and degree of absorption and the tear strength
needed for the film or fabric. Such additional monomers
are discussed below.
One type of such additional monomers are ~
olefinically unsaturated nitriles,preferably the mono-
olefinically unsaturated nitriles,having from 3 to 10
carbon atoms such as acrylonitrile, methacrylonitrile,
ethacrylonitrile, and the like. Most preferred nitriles
are acrylonitriles and methacrylonitrile.
~ nother useful class of additional monomers
which may be incorporated in the interpolymers of this
invention is monoethylenically unsaturated amides which
have at least one hydrogen on the amide nitrcgen and the
olefinic unsaturation is alpha,beta to the carbonyl group.
The preferred amides have the structure
CH2=C--C-NH-R4
R3
wherein R3 is a member o the group conslsting of hydro-
gen and an alkyl group having from l to 4 carbon atoms
and R4 is a member of the group consisting of hydrogen
and an alkyl group having from 1 to 6 carbon atoms.
z~
Representative amides include acrylamide, methacryla-
mide, N-methy~ acrylamide, N~t-hutyl acrylamide, N-
cyclohexyl acrylamide, N-ethyl acrylamide and others.
Of the amides most preferred are acrylamide and meth-
5 acrylamide.
Other acrylic amides include N-alkylol am~des
of alpha,beta-olefinically unsaturated carboxylic acids
including those having from 4 to 10 carbon atoms such
as N-methylol acrylamide, N-ethanol acrylamide, N-pro-
10 panol acrylamide, and the like. The preferred monomersof the N-alkylol amide type are the N-alkylol amides of
alpha,beta-monoolefinically unsaturated monocarboxylic
acids and the most preferred is N-methylol acrylamide.
Also useful are N-alkoxymethyl acrylamides
15 which have the structure
~ I
CH =~- -N-C~2-O-R6
whexein R5 is selected from the group consisting of
hydrogen and methyl, and R6 is an alkyl group having
from 1 to a carbon atoms. It is thus intPnded that
20 where references axe made herein regarding the essential
N-substituted alkoxymethyl amides, the term "acrylamide"
includes 'Imethacrylamide'~ within its meaning. The
preferred alkoxymethyl acrylamides are those wherein R~
is an alkyl group containing from 2 to 5 carbon atoms,
25 and especially useful is N-butoxymethyl acrylamide.
The above discussed monomers can be copoly-
merized by subjecting the monomer mixture to UV light.
If a film is desired the monomer can be spread on a
surface to the desired thickness, e.g. 1 mil to 25 mil,
30 and then subjected to UV light for a short time, e.g.one
second to several minutes. The actual length of ir-
radiation will depend on a number of factors, such as
~l2~$5~
the thickness o~ the monome~ film, the distance from
and the intensity of the source of irradiation, the
specific monomers employed and the ratio o~ such mono-
mers to each other, the presence or absence ofadditional
comonomers and the nature and the amount of the photo-
initiator employed. The type o~ photoinitiator employed
will depend at least in part on the type of UV irradia-
tion employed (particularly its wave length) since
various photoinitiators may be decomposed by W light
of different wavelengths. If it is desired that the
material be in the form of fibers, the monomer mixture
can be thickened and then spun in~o fibers whichl upon
exposure to W light, are polymeriæed.
In order to effect quic~ and efficient poly-
merization under UV li~ht, 0.01 to 5 weight percent of
a photoinitiator, preferably 0.1 to 5 percent and more
preferably 0.3 to 1.0 weight percent, must be incorpor-
ated into the monomer mixture. ~ny compound which
dissociates into free radicals when exposed to UV
radiation can be employed. There are many known photo-
initiator~ or photosensitizers such as acetophenone,
propiophenone, benzophenone, xanthone, fluorenone,
benzaldehyde, fluorene, anthraquinone, triphenylamine,
carbazole, 3- or 4-methylacetophenone r 3- or 4-penty-
lacetophenone, 3- or 4-methoxyacetophenone, 3- or 4-
bromoacetophenone, 3- or 4-allylacetophenone, p-di-
acetylbenzene, 3- or 4-methoxybenzophenone, 3- or 4-
methylbenzophenone, 3- or 4-chlorobenzophenone, 4,4-
dimethoxybenzophenone, 4-chloro-4' benzylbenzophenone,
3-chloroxanthone, 3,9-dichloroxanthone, 3-chloro~8-
nonyl-xanthone, 3 methoxyxanthone, 3-iodo~7-methoxy
xanthone, 2,2-dimethox~acetophenone, 2,2-dimethoxy-2-
phenylacetophenone, 2,2-diethoxyacetophenone, 2,2-
dibutoxyacetophenone, 2,2-dihexoxyacetophenone, 2,2-
di(2-ethylhexoxy) acetophenone, 2,2-diphenoxyacetophen-
-
5~
-- 7 --
one, benzoin, methyl benzoin ether, ethyl bezoin ether,
isopropyl benzoin ether, bu.tyl benzsin ether, isobutyl
benzoin ether, benzoin acetate, benzoin phenyl carbamate,
~ diethoxyacetophenone, ~,a-diethoxy-a-phenyl-aceto~
phenone, ~u-dimethoxy-a-phenylacetophenone~ 4,4 -
dicarboethoxybenzoin ethyl ether, ~-chloroacetophenone,
~-bromoacetophenone, benzoin phenyl ether, a-methylben~
zoin ethyl ether, benzoin acrylate, ~-methylolbenzoin
methyl ether, ~ trichIoroacetophenone, o-bromoaceto-
phenone, 4-(benzoylphenylmethoxycarbonylimino)-2-
(acrylyloxyethoxycarbonylimino)-l-methylbenzene, cumene
. hydroperoxide t benzoyl peroxide, dicumyl peroxide, tert-
butyl perbenzoate, ~,~-azobisisobutyronitrile, phenyl
disulfide, chloromethylbenzanthrone, chloromethylanthra-
quinine, chloromethylnaphthalene, bromomethylbenzan-
throne, bromomethylanthraquinone, bromomekhylnaphthalene,
and the like, and mixtures thereof.
In addition to the photoinitiator it may be
advantageous to employ also from 0.3 to 5.0 percent of an
activator. Illustrative examples of such activators are
mercaptoacetic acid, mercaptoethanol, or organic amines
such as methylamine, decylamine, diisopropylamine, tri-
butylamine, tri-2-chloroethylamine, ethanolamine, ~ri-
ethanolamine, methyldiethanolamine, 2-aminoethylethanol-
~5 amine, allylamine, cyclohexylamine, cyclopentadienyl-
amine, diphenylamine, ditolylamine, trixylylamine, tri-
benzylamine, N-cyclohexylethyleneimine, piperidine, 2-
methylpiperidine, N-ethylpiperidine, 1,2,3,4-tetrahydro-
pyridine, 2- or 3- or 4-picoline, morpholine,N-methylmo~
pholine, piperazine, N-methylpiperazine, 2,2-dimethyl-
1,3-bis-[3~(N-morpholinyl)propionyloxy]-propane, 1,5-
bis [3-(N-morpholinyl)propionyloxy]di-ethyl ether, and
the like.
The monomer mixtures are prepared as aqueous
dispersions which eliminates the need for organic sol-
vents. Thisavoids the pollutionproblems caused by the
~z~ s;~
removal of organic solvents or the cost associated with
the removal of the pollutants. In order to obtain a
stable homogeneous dispersion of the monomers, it is
preferred that the aqueous dispersions contain 0.01 to
5 5%, and preerably 0.1 to 1%, of a surface active agent
such as an anionic, amphoteric, or nonionic dispersing
agent or a mixture of dispersants. Useful anionic dis-
persing agents include alkali metal or ammonium salts of
the sulfates of alcohols having from 8 to 18 carbon atoms
such as sodium lauryl sulfate; ethanolamine lauryl sul-
fate, ethylamine lauryl sulfate~ alkali metal and am-
moni~um salts of sulfonated petroleum and paraffin oils;
sodium salts of aromatic sulfonic acids such as dodecane-
l-sulfonic acid and octadecane-l-sulfonic acid; aralkyl
sulfonates such as sodium isopropyl benzene sulfonate,
sodium dodecyl benzene sulfonate and sodium isobutyl
naphthalene sulfonate; alkali metal and ammonium salts
of sulfonated dicarboxylic acid esters such as sodium
dioctyl sulfosuccinate, disodium-n-octadecyl sulfosuc-
20 cinate; alkali metal or ammonium salts of free acid ofcomplex organic mo~o-and diphosphate esters, sulfosuc-
cinic acid derivatives (AEROSO~ dispersants), organic
phosphate esters (GAFACXdispersants~ and the like.
Nonionic dispersants such as octyl-or nonylphenyl poly-
ethoxyethanol as well as the PLURONIC*and the TRITO~dispersants may also be used. Also useful are ampho-
teric dispersants such as dicarboxylic coconut deriva-
tives (MIRANOL~. Further examples of useful dispersants
are those disclosed beginning on page 102 in J. Van
Alphen's "Rubber Chemicals",Elsevier Publishing Co.,1956.
The monomer mixture can also ba polymerized withr
out first neutralizing the carboxylic groups. The poly-
merization can be carried out in an inert diluent having
some solubilizïng action on one or more of the monomeric
ingredients but substantially none on the resultant poly-
~r mer. Polymerization in mass may be employed but is not
* trade mark
_ 9 _
preferred because of the difficlllty in working up thesolid polymeric masses obtained. Polymerization in an
aqueous medium containing a water-soluble free radical
catalyst peroxyyen is useful. Polymexization in an
organic liquid which i5 a solvent for the monomers but
a non-solvent for the polymer, or in a mixture of such
solvents, in the presence of a solvent-soluble catalyst
is more preferred because khe product is usually obtained
as a very fine friable and often fluffy precipitate
which~ after solvent removal, seldom requires grinding or
other treatment before use, The polymerizations pre-
ferably are conducted in the presence o~ a haloethane or
halomethane containing at least four halogen atomsO
Representative materials include for example, a fluoro-
ethane, fluoromethane, chlorofluoromethane, bromofluoro-
ethane~ or preferably a chlorofluoroethane or chloro-
fluoromethane containing at least four halogen atoms.
Polymers obtained from free radical polymer-
izations generally do not attain their maximum proper-
ties until converted to a partial alkali, ammonium oramine salt. The neutralizing agent is preferably a
monovalent alkali such as sodium, potassium, lithium
or ammonium hydroxide or the carbonates and bicarbonates
thereof, or mixtures of the same, and also amine bases
~5 having not more than one primary or secondary amino
group. Such amines include, for example, triethanol-
amine, ethanolamine, isopropanolamine, triethylamine,
trimethylamine, and the like.
The procedures to be employed in free radical
pol~merizations of such monomers, neutralization of the
resulting polymers and their work up is disclosed in
greater detail in U.S. Patent 4,062,817.
~ lthough cross-linking agents are not
rPquired to obtain useful, highly absorbent composi-
i
-- 10 --
tions o this invention, it may be desirable toincorporate a cross-linking agent since films prepared
from compositions containing a cross-linking agent
tend to have greater gel strength and an improved
ability for the copolymers to swell under a confining
pressure. Cross-linking agents may be used in the
concentration of about 0.01 to about 50% by weight
based on the total weight o the monomers, and
preferably about 0.1 to about 5%.
Useful cross-linking monomers are polyalkenyl
polyethers having more than one alkenyl ether grouping
per molecule or monomers which contain two to six
ethylenically unsaturatedgroups such as allyl, acrylate,
or vinyl groups. The most useul possess alkenyl
groups in which an olefinic double bond is attached to
a terminal methylene group, CH2=C ~ . Other cross-
linking monomers include, for example diallyl esters
or ethers, allyl or methallyl acrylates and acrylamides,
diacrylates and dimethacrylates, divinyl compounds and
the like. Illustrative examples o polyfunctional
cross linking agents are polyethyleneglycol diacrylate
and dimethacrylate, ethylene glycol dimethacrylate,
tetraethyleneglycol diacrylate, 1,3-butyleneglycol di-
methacrylate, diethyleneglycol divinyl ether, trimethy-
lolpropane diallyl ether~ divinyl benzene, trimethy-
lolpropane triacrylate, trimethylolpropane trimethacry-
late, triallyl cyanurate, pentaerythritol triacrylate,
diallyl itaconate, methylene bis(acrylamide), allyl
pentaerithritol, allyl sucrose, 1,6-hexanediol diacry-
late, tetramethylene glycol diacrylate and dimethacry-
late, ethylene glycol diacrylate and dimethacrylate,
triethylene glycol dimethacrylate, triallyl cyanurate,
triallyl isocyanurate, diallyl itaconates and the like.
As discussed above, the interpolymers of5 this invention can be photopolymerized. Additionally,
~.2~ 5~ -
these interpolymers can be obtained by radiation poly-
merization by subjecting said monomers to electron beam
radiation of sufficient intensity to cause said monomers
to polymerize substantially completely. The amount and
the intensity of radiation required will depend on the
thickness of the film, the specific monomers employed,
and the speed and the degree of polymerization desired.
Generally, for the applications for which the resulting
polymers are especially useful films, sheets or fibers
in the range from 0.5 to 5 mils are most desirable.
Therefore, relati~ely low intensity electron beam
sources, generally less than 200 K~, would be sufficient
to effect polymerization. Generally for the type of
monomer systems employed in this invention from 1 to 15
M rads of radiation is required. However, it should
be pointed out that the amount and intensity of radi-
ation must be optimized for each system taking all
variables into consideration, i.e., the monomers
employed, the thickness of the film, the desired speed
of polymerization, the desired degree of polymerization
and the rate of radiation.
When employing photopolymerization or radia-
tion polymerization methods, the polymers of this inven-
tion can be polymerized in a film or a fiber form. The
resulting film or fiber is an elastic, flexible
material that has an appreciable degree of strength.
If a fine, flaky form is desired, the film can be con-
verted to such a form by drying and then pulverizing or
grindiny it in standard equipment.
As water absorbent materials these polymers
find many uses in film, fiber, abric and similar forms.
They are of particular utility in the disposable non-
wo~en industry where there is need for polymers which
will absorb and retain watar and ionic physioLogical
fluids. An important feature of these polymers is their
5Z~
- 12 -
enhanced thickening property even in the presence of a
salt. Specific applications include disposable diapers,
medical-surgical supplies and personal care products.
Such applications require a polymer which must imbibe
the liquid to be absor~ed rapidly and be a polymer that
will not dissolve. Further, the fluid must be immobil-
ized or congealed in some way to be retained. The
materials may also be used as suitable additives to
greatly increase the absorptive power of conventional
absorbents such as cotton, wood pulp and other cellu-
losic absor~ents used in applications such as wiping
cloths, surgical sponges, catamenial devices, and the
like. In a specific application, for example, a dis-
posable diaper, there i5 an inner layer of a soft
absorbent nonwoven material that absorbs and passes
urine to an inner layer of fluffy fibrous absorbent
material, wherein during the construction of this non-
woven fiber agglomerates or fibers of the polymers of
this invention may be included and an additional imper-
vious plastic layer, as polyethylene. A film of thecopolymers of this invention may be used between the
outer plastic layer and the inner fluffy absorbent
layer. Use of the polymers of this invention can result
in reduction in the bulk size of many disposable non-
~5 wovens.
The instant copolymers can also be used asflocculants in water treatment, in metallurgical pro-
cesses, in ore beneficiation and flotation, in agricul-
tural applications such as in soil treatment or seed
coating or in any applications where the inherent
properties of the polymer are desirable, such as its
thickening property in an aqueous medium.
To prepare the cured copolymers of this inven-
tion, the monomers, a dispersant and a photoinitiator,
lf used, are mixed in a vessel. Then either a film or
~2'.P~S~
~ibers are produced from the monomer mixture which,
upon exposure to UV light or radiation, are rapidly
polymerized. The various steps in the procedure are
described in greater detail below.
Monomer Mixture Preparation: The monomer
mixture can ~e prepared by following one of two simple
procedures. One method is to dissolve a previously
prepared and dried alkali metal or ammonium salt of
acrylic acid in water to which is then added a disper-
sant. To the aqueous solution is then added the acxy-
late or the methacrylate es~er which already contains
a photoinitiator if one is employed. Another method is
to prepare the acrylic acid salt in situ by adding
acrylic acid to the proper amount of cold aqueous base
~e.g. KOH, NaOH or NH40H~ with cooling. To the aqueous
solution is then added a mixture of the acrylate or the
methacrylate ester to which, if required, a photo-
initiator was previously added; the dispersant is added
last.
Film Preparation: The aqueous monomer dis-
persion is spread to a desired thickness (e.g. by the
use of Boston-Bradley adjustable blade, by spraying or
other known means~ on a suitable substrate (e.g. Mylar,
polyethylene, paper, etc.). The liquid film is then
exposed to a UV or radiation source which polymerizes
the monomer mixture into a soft, pliable form. Ir
desired, this film can be dried in an oven at about
50 C for l to 15 min. After drying the film may still
retain some flexibility or become bri-ttle and flaky,
depending on the length of drying.
Fiber Preparation: The aqueous monomer dis-
persion is thickened to the desired degree with a non-
reactive thickening agent such as a cellulose derivative
as, for example, hydroxypropyl cellulose, high molecu-
lar weight polyvinyl pyrrolidone and the like; natural
~2~S~
- i4 -
gums such as guar gum, locust bean gum, gum trayacanth;
agar, naturally occuring hydrocolloids such as alginates
and the like. Fibers are then spun froma spinneret in
a regular manner and immediately exposed to a W or
radiation source.
To further illustrate the present invention
the following examples are presented. The copolymers
and the films were prepared according to the procedures
described above. The copolymers of Examples 1 to 9,
10 presented in Table I, have been photopolymerized using
QC 1202 Processor manufactured ~y Radiation Polymer Co.
(with belt speed of 0 to 1000 ft/min 304.8 m/min) having
2 medium pressure quartz mercury vapor lamps at 200
watts/lineal inch (watts/lineal 2.54 cm.). The distance
from the lamps to the film was 15 cm. and the exposure
time was 20 sec. at belt speed of 20 ft/min. (6 m/min.).
Comonomers employed in the Examples and
identified in Table I by capital letters A to C, are
identified below:
A - 2-~ydroxyethyl methacrylate
B - Dimethylaminoethyl acrylate
C - Mixture of 17.0 g. DMAEA + 1.9 g.
trimethylolpropane triacrylate
~5~ 'r'i
;1
,:..
5~
, .
- 15 -
~o
9a~J O O cr~ ~\J N
'O ~ C) . . . I
tY~ I LO OJ ~) 0 ~1 ~1
~7 1 ~ Ll~ 0 ~1
;~
C
~ O
O ~
~>
~o O
~D ~O O O ~ ~ I a~
I j ~ Ln 0 ~ (D
H H ~ o
~ o o
o a~
Q
o o o ~ ~o I "
. ~ r~ i ~ ~ ~ o o :~
u~ 0 ~ ~: X
~ ~ o
a>
E
O
u~ ~
~ to
a> ~1
X O ^ --~ o Lr
O ~1 ~ ~ 5~ ~ ~ ~D
X s~ -- O ~ ~:
~ :~ N r~ o L~ ~ * u~
z ~ ~ ~ S~ O a
E3 J ~s:: o v~ ¢ a
,I E ~ 1 0 0
E ~,1 0Q~ , o o c~ v cc H
X ~ E~ Zt~ ~ O ~;~
X~1~ r~ ~ H ~ _ _ *
~2~$.~
- 16 -
Copol~mers having substantially the same
properties are obtained when in some of the above
compositions potassium hydroxide was employed in place
of sodium or ammonium hydroxide, 2,2~diethyoxyaceto-
5 phenone in place of IRGACURE~651 and an oligomericsurfactant POLYWET~KX-3 (from Uniroyal) or TRITON N-lll
(monophenoxy polyethoxy ethanol) in place of AEROSOL
Al02.
A number of testsare available to determine
10 the absorbency of a material. Following are descrip-
tions of the two test procedures which were employed in
evaluating absorbency of the interpolymers of this
invention.
Static Test (ST) - A weighed film sample is immersed in
15 a test liquid for 10 minutes. It is then removed from
the liquid, the excess liquid drained for a few seconds
and then shaken lightly several times. The swelled
sample is weighed again to determine the weight of liquid
absorbed by the polymer.
20 Demand Wettability Test (DWT) - A test diaper is con-
structed rom a-4 inch diameter pad (10.16 cm.) using
materials from a commercial diaper. A film prepared
from a polymer to be tested for absorbency is placed
in the center of the test diaper between two layers of
25 fluff (wood pulp?. A diaper without the polymer film
is used as a blank. The demand-wettability apparatus
is a burette filled with the test fluid and rirmly
stoppered at the top, with an air bleed on the side r and
a delivery orificeon the bottom connected by a flexible
30 tube to the sample holder. The sample holder has an
opening in the center which is connected to the flexible
tube that leads to the delivery orifice of the burette.
The sample holder is level with the air ble~d opening
in the burette. With this closed-system arrangement
35 the fluid in the flexible tube that comes up to the
* trade mark
` ~z~s~
- 17 ,-
opening in the sample holder is at zero pressure. Thus
when the test diaper is placed on the sample holder over
the opening it will absorb the fluid on its own through
wicking action. The sample's own absorbent powder will
5 determine the rate and amount of fluid that will be
withdrawn from the ~urette. The amount of fluid with-
drawn at any given time can be easily read from the
burette calibration. An additional feature is that
absorbency can be measured against a range of pressures
that can be obtained by placing various weights on top
of the test diaper. Such pressures are intended to
simulate the pressures applied on a diaper in actual use.
This test is described in greater detail by
Lichstein, "Demand Wettability, a New Method for
15 Measuring Absorbency Characteristics of Fabrics",
Symposium Papers-INDA Technical Symposium, 1974, pp.
129-142.
Compression Test (CT) - This test is a follow up test to
the Demand-Wettability Test (DWT). After the sample has
20 absorbed the liquid against a lower pressure in a DWTest,
it is removed from the DWT apparatus and placed atop a
porous filter funnel. The sample is then subjected to
1.5 psi (0.105 kg/cm ) of pressure for 1 minute and the
amount of liquid that is squeezed from the sample is
25 measured. Said pressure corresponds to the maximum
pressure that is exertea on portions of a diaper when a
toddler is picked up or held. This is 10 to 15 times
the pressure that the diaper normally would experience.
The sample is then weighed to determine the amount of
fluid in grams retained per one gram of polymer.
In Table II below is presented data comparing
the absorbency properties of the copolymer of this
invention with two other polymers. The polymer number
in the Table corresponds to the example describing the
35 preparation of that specific polymer.
9,
TABLE II
ST DWT CT
Polymer ( g/g )( ml /g )( g/g )
26 ---- ----
2 -- 27 22
3 __ 37 31
. j~
