Note: Descriptions are shown in the official language in which they were submitted.
- iO~4~4 J.487
, .
This invention relates to absorbent materials, more
especially absorbent materials suitable for use in absorbent
disposable products such as, for example, sanitary towels or
napkins, tampons and diapers. The invention also relates to
processes for producing such materials and to absorbent articles
containing such materials.
A number of absorbent materials have been suggested for use
in absorbent disposable products, among the first being cellulose
in fibre form. Cellulose fibre absorbs by a capillary action
and as a result suffers from the serious disadvantage that the
absorption is reversible, that is when subjected to pressure the
cellulose fibres expel the absorbed liquid.
There has more recently been suggested in US Patent
No.3,070,095 the use of certain gums ln articles to improve
their absorbency characteristics. These materials are, however,
prone to dissolve in an excess of fluid to give a gummy solution.
As a result of this tendency to dissolve, gums have not found
extensive use as a primary absorbent in disposable absorbent
articles.
To overcome the disadvantage of the absorbent materials
described in US Patent No.3,070,095, there have been suggested
the use of certain absorbent polymers such as the synthetic
polymers of US Patent Specifications Nos.3,669,103 and 3,670,731
and the modified cellulosic fibre described in US Patent
No.3,589,364. These polymers also have the desirable property
of irreversible absorption so that absorbed fluid cannot be
squeezed out under the pressures normally associated with the
use of absorbent disposables.
.
. ;~
- 2 - /
` 10~49~4 J.~87
We have now discovered that a highly absorbent material,
particularly suitable for use in absorbent disposable products
such as sanitary towels, tampons and diapers, which is
substantially water-insoluble9 is capable of absorbing
irreversibly and which is substantially dry and non-sticky to
the touch in the swollen state, can be obtained from st~rch.
According to the invention there is provided a highly
absorbent material which is substantially dry and non-sticky to
the touch in the swollen state being a substantially water-
insoluble cross-linked gelatinised starch, in which the degree
of substitution of the cross-linking groups is 0.001 to 0.04,
which i9 substituted by ionic groups which are attached to the
starch by ether linkages and which groups are associated with
mono- or di-valent counterions, and which has a urine retention
value of at least 8 g/g.
Gelatinised starch is starch the granules of which have
been disrupted. Gelatinised starch which has not been cross-
linked i9 soluble in cold water.
The urine retention value for an absorbent material is
determined in the way already well kno~n for water retention
values but using a synthetic urine instead of water. Thus in
determining the urine retention value the sample to be tested
(0.20 g) is weighed out into a pre-weighed sintered glass Gooch
crucible. Synthetic urine (5 ml) is added to the sample
ensuring that the sample is completely wetted and it is left to
soak for 10 minutes before being placed in a centrifuge tube and
spun for 10 mlnutes at 850 rpm in a~centrifuge having a head
~ ~ ~ 3 ~ /---
.
49~
radius of 9 cm. The crucible with contents is then reweighed.-
The urine retention value is expressed as the weight of urine
retained per gram of dry absorbent. The formula of synthetic
urine, derived from the information given in the Handbook of
Clinical Laboratory Data, 2nd Edition, 1968, pages 17-20, is a
solution in 5 litres of water of the following:
grams
C C12 2 3.680
K2SO4 0.175
KCl 44.740
KOH 2.190
NH4C1 6.020
Citric acid 2.630
Water retention values referred to herein were obtained by the
same procedure except that distilled water (10 ml) was used in-
stead of the synthetic urine. Experiments have shown that the
same urine retention values are obtained using natural urine in
place of the synthetic urine. The absorbent materials of this
invention have urine retention values of at least 8 g/g and are
desirably in the range 8-20 g/g.
The absorbent starch derivatives of this invention are
substantially water-insoluble containing at least 90%, prefer-
ably at least 95~, of insoluble carbohydrate. The most prefer-
red materials of the invention are those having a water insolu-
bility of 99~ or higher.
., . , -
1~4~14 J.487
A feature of the absorbent materials of the present
invention is that although the degree of substitution of the
cross-linking groups is relatively low (being much smal~er, for
example, than that of the cross-linked starch products described
in Examples 1 to 6 of Canadian Patent No.960,652 or the starch
product of Example 2 of British Patent No.936,039) they are
substantially insoluble in water. The more highly cross-linked
starch products described in these patents are substantially
less absorbent than the materials of the present invention.
The cross-linking of the starch molecules may be effected
by ether bridges of the formula -0-R-0- where R is an aliphatic
group, which may be substituted by one or more hydroxy groups,
containing 1 to 10 carbon atoms. Preferably R is CH2CE(OE)CE2-,
which is the case when the starch is cross-linked using
epichlorhydrin as cross-linking agent.
The ionic groups preferably have the formula Z-R1- where
R1 is an alkylene group having 1 to 5 carbon atoms and Z is an
anion$c group selected from carboxyl, sulphonic or phosphonic
groups or a cationic group of the formula
/ R
- N - R
\ R4
where R is hydrogen or lower alkyl, and R3 and R4 are lower
alkyl or are alkylene groups linked together to form a five or
six-membered heterocyclic ring. Particularly suitable
materials are those wherein R1 is an alkylene group containing
1 or 2 carbon atoms and Z is -C00 and preferred materials are
- 5 - /
~491~ J.487
carboxymethylated cross-linked gelatinised starches. The
degree of substitution of the ionic groups will generally be at
least 0.1 and is desirably at least 0.2 to obtain the preferred
higher urine retention values.
When Z is an anionic group the counterion preferably is an
alkali metal, alkaline earth metal, ammonium or substituted
ammonium ion. The substituted ammonium derivatives may be
those in which one or more hydrogen atoms are replaced by C1 4
alkyl or C2 4 hydroxyalkyl groups or in which the nitrogen atom
forms part of a heterocyclic ring. An example of such a
substituted ammonium ion is tetramethylammonium. Preferred
counterions when Z i9 an anionic group are the sodium, ~otassium
and ammonium ions. When Z is a cationic group, the counterion
may be, for example, chloride, bromide or sulphate.
Particularly preferred absorbent materials of this invention
are the sodium and ammonium salts of carboxymethylated
epichlorhydrin cross-linked gelatinised starch having a urine
retention value of at least 10 g/g and being insoluble in water
to the extent of at least 99/~ by weight.
The invention is also concerned with a process for making
the above-described absorbent materials, which process comprises:
1. gelatinising starch;
. .
2. during the gelatinisation or thereafter treating
the starch with a cross-linking bifunctional compound
to produce a cross-linked gelatinised starch which is
substantially insoluble in water and in which the
- 6 - /
10~9~4 J.g8~
degree of substitution of the cross-linking groups is
from 0.001 to 0.04; and
3. during the gelatinisation or thereafter reacting
the starch with a monofunctional etherifying agent to
substitute the starch by ionic groups which are
attached to the starch by ether linkages and which
groups are associated with mono- or di-valent
counterions, the degree of substitution of the ionic
groups being such that the urine retention value of the
substituted cross-linked gelatinised starch is at least
6 g/g,
In a preferred way of conducting this process, steps (1)
and (2) are carried out by:
(a) forming an aqueous alkaline slurry of starch
granules containing the cross-linking bifunctional
compound; and
(b) rapidly heating the slurry by applying the slurry to
a surface heated to 100-180C to cause gelatinisation of
the starch, reaction therewith of thé cross-linking
bifunctional compound and simultaneous drying, to produce
cross-linked gelatinised starch in dry form.
In an alternative process steps (1) and (2) are carried out by:
(c) form-ing an aqueous slurry of starch granules;
- 7 - /
J 48~
1~4914
(d) applyin~ the slurry to a surface heated to 100-180C
to cause gelatinisation of the starch and simultaneous
drying; and
(e) subsequently reacting the gelatinised starch with the
cross-linking bifunctional compound in the presence of
water and alkali to produce cross-linked gelatinised starch.
In this procedure, the alkali may be included in the slurry.
The gelatinisation is very conveniently e.fected by feeding the
aqueous starch slurry onto the surface of a heated drum upon
which it can be pressed out into a thin film. The gelatinisation
of starch by applying an aqueous slurry thereof to the surface
of a heated drum is in itself a very well known process which
has been called the cold-swelling starch process (see for
example British Patent No.787,153).
The reaction of the starch with the monofunctional
etherifying agent may be carried out before, during, or after
treatment of the starch with the bifunctional cross-linking
compound.
To effect the cross-linking of the starch a bifunctional
cross-linking agent is used and this may be a compound of thé
formula Q-~5-Y where R5 is an alkylene group, which may be
substituted by one or more hydroxy groups, containing 1 to 10
carbon atoms, and Q and Y each represent a halogen atom or an
epoxy group. Suitable cross-linking agents are epichlorhydrin,
dichlorohydrin, dibromohydrin, 1,2-3,~-diepoxybutane, 1,2-7,8-
diepoxyoctane, bis-epoxypropylether, 1,4-butane-diol-bis-
- 8 - /
`
J.~87
~0~49~
epoxypropylether. The amount of cross-linking agent employed
is that required to give a degree of substitution of the cross-
linking groups within the range 0.001 to 0.04, corresponding to
one cross-linking group for each 1,000 anhydroglucose units to
one cross-linking group for each 25 anhydroglucose units.
Preferably an amount of cross-linking agent is employed to give
a degree of substitution of the cross-linking groups of from
0.003 to 0~02. The function of the cross-linking agent is to
insolubilise the gelatinised starch. Cross-linking
significantly beyond that required to insolubilise the gelatinised
starch is not employed since increasing amounts of the cross-
linking agent gives products having, for a given degree of ionic
substitution, lower water and urine retention values.
A preferred method of effecting the cross-linking employs
epichlorhydrin and is effected with the gelatinisation of the
starch on the surface of a heated drum. In this process the
amount of epichlorhydrin (or other volatile cross-linking agent)
employed should take account of the loss by vapourisation from
the heated surface of part of the cross-linking agent.
For effecting the cross-linking some alkaline substance is
required to be present in the reaction mixture, save that when
formaldehyde is employed acid conditions are required, as is
well known. Sodium hydroxide is quite suitable but other
alkalis may of course be used. Since the degree of cross-linking
effected is small the amount of alkali required to promote the
cross-linking reaction is also small. This has the advantage
that in forming the aqueous slurry of starch granules to be
g _ / -
108~914 J.487
applied to the heated surface the concentration of the alkali in
the slurry can be insufficient to effect any substantial
gelatinisation of the starch before the slurry is heated enabling
the slurry to be pumped easily through pipes from a ho~ding
vessel to the heated surface where gelatinisation, and, if
desired, cross-linking and/or substitution by ionic groups, is
effected.
This aqueous slurry desirably contains about 1 to 2 parts by
weight of water per part of starch although higher amounts of
water could be used.
Where cross-linking is effected after gelatinisation and
in the presence of aqueous alkali, the amount of water required
to be present can be as low as 0.1 to 0.5 parts per part of
starch. A surprising feature of the invention is that although
cross-linking of the starch (during or after gelatinisation) can
be effected in the presence of the above minor amounts of water,
the final cross-linked substantially water-insoluble ionically
substituted product nevertheless has high water and urine
retention values.
By means of the monofunctional etherifying agent ionic
substituent groups are introduced linked to the starch by an
ether group. These ionic groups may have the formula Z-R1-
where Z and R1 have the above meanings. The monofunctional
etherifying agent may have the formula Z1-R1-X where R1 is an
alkylene group of from 1 to 5 carbon atoms, zl is an anionic or
cationic group Z as defined above, or a group capable of being
converted into such an ionic group, and X is halogen or an epo~y
-- 1 0
J.487
101~4914
group. However, activated olefinic compounds carrying an ionic
group or a group capable of being converted into an ionic group
could be used. The group R1 is preferably an alkylene group
containing 1 or 2 carbon atoms and zl is a carboxylic acid group
or a salt thereof. Examples of suitable monofunctional
etherifying agents are monochloracetic acid, bromopropionic acid,
chloroethylene sulphonic acid, chlor~hydroxypropane sulphonic
acid, epoxypropane sulphonic acid or 2-chlor-N,N-diethyl-
ethylamine hydrochloride. Preferred etherifying agents are
monochloracetic acid and the sodium salt thereof. When Z is a
basic group, this may be quaternised, if desired, prior to
etherification of the starch, for example etherification may be
conducted with the quaternary ammonium salt formed between
epichlorhydrin and triethylamine. Examples of etherifying
agents containing an activated olefinic group and a group capable
of being converted into an ionic group, eg with alkali, are
acrylamide, acrylonitrile and ethyl acrylate. The etherification
i8 carried out in the presence of alkali. Sodium hydroxide is
the preferred alkali. The introduction of the ionic groups
increases the urine retention value of the starch derivative.
The substitution by ionic groups is effected to such degree as to
give a salt having a urine retention value of at least 6 g/g.
It will be appreciated from the above that the actual
urine retention value of the product obtained after step (3) is
dependent both on the cross-linking and on the ionic-
substitution stages. These steps are preferably effected in
such manner as to produce an ionically substituted cross-linked
-- 11 -- / . . .
J.487
9~
gelatinised starch having a urine retention value of at least
8 g/g, more preferably 10-20 g/g. Generally speaking, the
substitution by ionic groups should be carried out to result
in a degree of substitution of at least 0.1, preferably at
least 0.2.
When the substitution stage results in a salt of a
carboxylic starch derivative, the process preferably also
comprises the additional steps of:
4. treating said starch derivative with an acid to
convert the carboxyl groups into their acid form;
5. washing said acid form of the starch derivative
with water to remove any soluble salts; and
6. neutralising the acid form of the starch derivative
with an alkali to reconvert the starch derivative into
an ionic form as an alkali metal, alkaline earth metal,
ammonium or substituted ammonium salt.
Conversion of the carboxy group to its acid form and subsequent
neutralisation has the advantage that the washing and
subsequent drying are facilitated on account of the low water
retention of the acid form. Preferably in step (6) the acid
form of the starch derivative is neutralised with excess
ammonia solution whereafter by heating excess ammonia is removed
and the ammonium salt dried.
The starch derivatives of this invention may be obtained
from, for example, potato starch, maize starch, wheat starch or
tapioca starch.
- 12 - /---
J.487
4914
The invention also relates to liquid absorbent articles
containing the absorbent material of the invention, including
that prepared by the process of the invention. The liquid
absorbent article may comprise a fibrous carrier or support for
the absorbent material, such as a woven or unwoven material such
as cotton cloth, rayon, wool, surgical gauze or paper as well as
cellulosic fluff, on or within which the absorbent material is
supported. The absorbent material may be spread on the carrier
or it may be mixed with loose fibres to make a composite fluff
or wadding which can be enclosed between cover sheets of paper --
or cloth. The article may also be in the form of a laminate.
In a particular form, the carrier comprises two sheets between
which the absorbent material is sandwiched.
The absorbent materials of this invention are also useful
lS in other fields, for example as a drying agent; for absorbing
perspiration; as a litter material for pets; as a water
reservoir agent, eg in horticultural use; and as a carrier for
various materials, eg perfume~.
- 13 - /
J.487
9~
The preparation of absorbent materials in accordance with
the invention will now be described with reference to the
following Examples 1 to 19 given by way of illustration only.
In these examples the bed volumes of the products obtained
at various stages of the processes described are referred to.
The bed volume of an absorbent material is determined by allow-
ing 1 gram of the material to stand in excess water in a
graduated vessel and reading off the swollen volume.
Urine and water retention values were obtained as described
above and are expressed to the nearest quarter of a unit.
The solubility data for the starch derivatives given in
the examples were obtained as follows. The absorbent (1 g) was
slurried in distilled water (100 ml) at room temperature with
stirring for 15 minutes. The slurry was allowed to stand over-
night before filtering. The dissolved carbohydrate in thefiltrate was measured by the known colorimetric method employing
the use of the phenol/sulphuric acid test for soluble carbohydrate.
In these determinations to 1 ml of the sample of the test
solution were added 1 ml of phenol solution (5% w/v) followed
by 5 ml of concentrated sulphuric acid and the liquids ~ixed by
shaking. After leaving to cool for about an hour the
concentration of the soluble carbohydrate was determined using
a Unicam SP 800 ultra-violet spectrophotometer from the
absorbence at the peak at 4~3 nm by reference to a glucose
standard.
- 14 -
J.487
Example 1
Potato starch (1,000 g) was slurried in water (950 ml)
containing epichlorhydrin (8.4 ml; 1.0% epichlorhydrin by
weight of starch). Sodium hydroxide (5 g) in water (50 ml)
was added with stirring and the mixture was applied to a heated
roller via a feeder roller to form a layer on the surface of the
roller of about O.S mm thickness. The roller itself was
heated using steam at 3.77 bars (140C3. The cross-
linked starch derivative was removed from the roller as a flake
material to yield 914 g of product. The soluble content of the
product was found to be 25.0 mg/g and the product was found to
have a bed volume of 13.5 ml/g. Since about half of the
epichlorhydrin was lost by evaporation from the heated ~oller
the degree of substitution of the cross-linking groups was
lS about 0.01.
Sodium hydroxide (34 g) in water (66 ml) followed by mono-
chloracetic acid (39 g) in water (11 ml) was slowly added with
stirring to the cross-linked potato starch (100 g) as prepared
above. The mixture was aged overnight in a polythene bag.
The theoretical degree of substitution was 0.67.
The moist carboxymethyl derivative was repeatedly dispersed
in water and filtered until the filtrate was neutral. The
highly water swollen washed cake was dried in a forced air oven
(7VC) and milled through a 2 mm screen. The milled product
(102.7 g) had a water retention value of 24.75 gJg, a urine
retention value of 13.V0 g/g, a solubility of 0.6~ and a bed
volume of S0 m]/g.
- lS -
9 1 ~ J.487
Example 2
Example 1 was repeated exactly as far as ageing the carboxy-
methylated mixture in a polythene bag. The theoretical degree
of substitution was again 0.67.
The moist carboxymethyl derivative was dispersed in 10 times
its weight of lN hydrochloric acid and soaked for 15 mi~utes and
then filtered. The gel cake was repeatedly dispersed in water
and filtered until the filtrate was substantially free of
chloride ions. Ammonium hydroxide, specific gravity 0.910,
1~ (70 ml) was mixed with the water swollen washed cake before
drying in a forced air oven (70C) and milling (2 mm screen).
The milled product had a water retention value of 20.00 g/g, a
urine retention value of 10.25 g/g, a solubility of 0.3% and a
bed volume of 51 ml/g.
Example 3
Malze starch (500 g) was slurried in water (475 ml)
containing epichlorhydrin (4.2 ml; 1% epichlorhydrin by weight
of starch). Sodium hydroxide (~.5 g) in water (25 ml) was
added with stirring and the mixture was applied to a heated
roller as in Example 1. The cross-linked starch derivative was
found to have a bed volume of 8.5 ml/g.
The cross-linked maize starch was carboxymethylated as in
Example 1 and the product washed and isolated as the a~onium
salt as in Example 2 by treatment first with hydrochloric acid
and then ammonium hydroxide. The milled product had a water
retention value of 16.25 g/g, a urine retention value of 8.75 g/g,
a solubility of 1.5% and a bed volume of 44 ml/g.
- 16 -
J.487
1~49~
Example 4
Potato starch (100 g) was slurried in water (80 ml)
containing 1,2-7,8-diepoxyoctane (0.8 ml). Sodium hydroxide
(0.5 g) in water (20 ml) was added with stirring and the slurry
applied to a heated roller as in Example 1. The soluble content
of the product was 11.6 mg/g and the bed volume 15.5 ml/g.
The cross-linked potato starch derivative (60 g) milled
through a 2 mm screen was carboxymethylated as in Example 1 and
the product, after ageing, was washed and isolated as the
ammonium salt as in Example 2. The milled product had a water
retention value of 17.25 g/g, a urine retention value of 10.00
g/g, a solubility of 0.5~ and a bed volume of 33 ml/g.
Example 5
. 1% Cross-linked potato starch (100 g) as prepared in Example
1 was carboxymethylated as in that example, aged overnight in a
polythene bag and treated with lN HCl and washed by being
repeatedly dispersed in water as in Example 2. To the water
swollen washed cake (964 g) was added with stirring a solution
of sodium carbonate (16.2 g) in water (100 ml) before drying in
a forced air oven (70C). The milled product (102.1 g) had a
water retention value of 19.25 g/g, a urine retention value of
11.50 g~g, a solubility of 0.8% and a bed volume of 42 ml/g.
Example 6
To a cake (878.5 g) of acid washed carboxymethylated cross-
linked starch, obtained as in the preceding Example, was added
with stirring a solution of magnesium carbonate (16.8 g) in water
(100 ml) before drying in a forced air oven ~70C). ~he milled
- 17 - /
- J.487
1~4~4
product (113.5 g) had a water retention value of 9.25 g/g, a
urine retention value of 8.75 g/g, a solubility of 0.6% and a
bed volume of 23 mllg-
Example 7
S The sodium salt of carboxymethylated cross-linked starch
prepared as in Example 1 (20 g) was soaked in lM magnesium
chloride solution (1,000 ml) with occasional stirring for 24
hours then repeatedly washed and filtered until the filtrate was
substantially free of chloride ions and dried in a forced air
oven (70C). The milled product (16.8 g) had a water retention
value of 12.50 g/g, a urine retention value of 10.50 g/g and a
bed volume of 29 ml/g.
Example 8
Alkali potato starch was prepared exactly as the cross-
linked starch in Example 1 except that no epichlorhydrin was
added to the slurry before roller drying. Water (20 ml) was
sprayed onto the alkali starch (100 g) which was then transferred
to a sea]able jar where epichlorhydrin (0.17 ml; 0.20% by
weight of starch) was added and the jar tightly sealed and placed
in an oven at 50C for 1 hour. The cross-linked starch product
(bed volume 13 ml/g, soluble carbohydrate content 7.0 mg/g,
degree of substitution of cross-linking groups of about 0.004)
was immediately carboxymethylated as in Example 1, aged overnight,
treated with acid and washed as in Example 2 until the filtrate
was substantially free of chloride ions and the water s~ollen
cake (1,339 g) ammoniated (70 ml of ammonium hydroxide solution
sg 0.910) and dried in a forced air oven (70C).
- i8 - /,
J.487
14
The milled product (108.6 g) had a water retention value of
12.25 g/g, a urine retention value of 9.00 g/g, a solubility of
0.6~, and a bed volume of 28 ml/g.
Examples 9 to 11
Alkali potato starch was prepared exactly as the cross-
linked starch in Example 1 except that no epichlorhydrin was
added to the slurry before roller drying. Water (20 ml) was
sprayed onto alkali starch (100 g) which was then transferred to
a jar where epichlorhydrin was added as indicated in Table 1
below and the jar tightly sealed and shaken for 0.5 hour then
left at room temperature for 22.5 hours. The cross-linked
starch products were then immediately carboxymethylated as in
Example 1, aged overnight, treated with hydrochloric acid and
washed as in Example 2 until the f~ltrates were substantially
chloride free and the water swollen cakes ammoniated (70 ml of
ammonium hydroxide solut,ion sg 0.910) and dried in a forced air
oven (70C).
The milled products were tested for water retentior value,
urine retention value, solubility and bed volume. ,The data
are given in Table 1.
-- 19 -- /
J 4~37
1~84~
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C~ O U~ O
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~ ~ ~ ~ ~ ~ C~
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-- 20 -- / -
~ 9~4 J.487
Examples 12 to 16
lr/O Cross-linked potato starch (100 g) was carboxymethylated
as in Example 1 to a degree of substitution as shown
in Table 2. The aged moist carboxymethyl derivative was then
repeatedly dispersed in distilled water (& l) and filtered until
the filtrate was neutral. The highly water swollen cakes were
dried in a forced air oven (70C). Urine retention values are
given in Table 2.
Table 2
Sodium Monochlor- Degree of Urine
Example Hydroxide acetic acid Substitution Retention
12 19.8 23.3 ~.25 1~.50
13 29.6 35.0 0.42 12.25
14 39.5 46.6 0.56 13.75
49.4 58.3 ~.66 13.25
16 74.1 87.4 0.71 14.50
Example 17
Sodium hydroxide (12.5 g) in water (30 ml) followed by
acrylamide (8.8 g) in water (30 ml) was slowly added with
stirring to 1% cross-linked potato starch (20 g); the
theoretical degree of substitution was 1Ø 'rhe mixture was
aged overnight in a polythene bag then repeatedly dispersed in
water (2 l) and filtered until the filtrate was neutral. The
highly water swollen cake (704 g) was dried in a forced air oven
(70C) The carboxyethylated starch product (23 g) had a water
retention value of 21.25 g/g, a urine retention value of 11.75
g¦g, a solubility of 1.3~ and a bed volume of 46 ml/g.
- 21 - /
108~4 J.487
Example 18
Triethylamine (85.5 ml), epichlorhydrin (48.4 ml) and
water (200 ml) were stirred together for 16 hours to form the
quaternary ammonium salt. Potato starch (25 g), epichlorhydrin
(0.25 ml) and the quaternary adduct (35 ml) were mixed together
for 1 minute and then the suspension dried to a flake on a
roller drum drier (heated to 140C) upon which gelatinisation,
cross-linking and substitution of the starch all took place.
The dried flake was milled through a 1 mm screen. The product
had a urine retention value of 11.25 g/g. The starch was
substituted by quaternised groups of the formula
-C~2cH(OH)cE2 N (C2H5)3 Cl -
Example 19
0.5/0 Cross-linked potato starch was prepared exactly as in
Example 1 but using half the stated amount of epichlorhydrin.
6 kg of this product were dispersed in aqueous isopropanol (42 l
of 91% isopropanol) and heated to 40-50C in a 100 1 jacketed
reaction vessel. Sodium hydroxide solution (5 kg of 35%) was
added and the mixture stirred for 30 minutes. Monochloracetic
acid (3 kg of 75%) was added (corresponding to a theoretical
degree of substitution 0.67) and the temperature raised to 83C
and stirring continued for 4 hours. After settling, t~e
organic solvent was partly decanted and the pE of the mixture
adjusted to pE 1 using 2N hydrochloric acid. Acetone was then
added and the mass filtered on a suction filter and repeatedly
washed with 65/c aqueous acetone until the filtrate was free of
chloride ions. The damp cake was stirred with an excess of 25
_ 22 -
~ 914 J.48~
ammonium hydroxide solution and then dried overnight in a vacuum
drier at 55C and 30 mm ~g. The milled product had a water
retention value of 25.00 g/g, a urine retention value of 12.75
g/g, a solubility of 2.8% and a bed volume of 6~-80 ml/g.
All the materials produced in carrying out the above
Examples were substantially dry and non-sticky to the touch in
the swollen state9 they absorbed water and urine irreversibly,
and in spite of being substantially insoluble in water had high
urine retention values which is a desired characteristic of
absorbent materials for use with disposable products such as
sanitary towels and tampons.
~ he production of liquid absorbent articles comprising the
absorbent material of the invention will now be described with
reference to the accompanying diagrammatic drawings in which
lS Figure 1 shows an apparatus for applying the absorbent ~aterial
to a carrier layer; Figure 2 shows a san~tary towel; and
Figures 3 and 4 show a tampon.
Referring to Figure 1, a hopper 1 contains particulate
absorbent material prepared as described in any of Examples 1
to 19. A vibratory feeder 2 is arranged to feed this material
into the nip of a pair of rollers 3, 4 of which the upper roller
3 is of steel and the lower roller 4 of rubber so as to
accommodate variations in the size or evenness of the particle
layer.
Also feeding into the nip of the rollers 3, 4 are two
layers of tissue carrier material 5, 6 supplied from supply rolls
7, 8 via intermediate feed rollers 9. In each case a water
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~4914
spray device 10 is provided which wets the tissue carrier webs
5 and 6 before they reach the nips of rollers 3 and 4.
The wetted carrier layers 5, 6 then receive the particulate
absorbent material at the nip of the two rollers 3 and 4 and
thereafter feed forward as a composite sandwich ply through a
heating chamber 11 which removes moisture from the tissue carriers
and absorbent material, round a cooling roller 12 and thence to a
storage reel 13.
The heating chamber 11 is an enclosure consisting essentially
of an open feedthrough system of rollers 14, radiant heaters 15,
and forced extraction exhaust duct 16.
The sanitary towel shown in Figure 2 consists of a non-woven
longitudinal layer rayon ~abric outer wrapper ~, which may be
water soluble. This wrapper is transversely sealed at its ends
B.
Immediately below the wrapper is a stain reducing layer C.
This is desirably a silicone-treated perforated non-woven layer.
Below the stain-reducing layer is a penetration layer D
consisting of 16 layers of multi-ply crepe of 26 grammes per
square metre weight. Then below the penetration layer are
three layers of absorbent coated sandwich material E made as
described above with reference to Figure 1.
Around the three layers E is a lower absorbent sbeet F,
which also consists of a tissue carrier layer carrying a
continuous deposit of the absorbent material.
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Then finally below the absorbent sheet is an imper--ious
polyethylene layer G, and on the outside a gripstrip keeper
which is a conventional silicone-treated adhesive tape for
keeping the towel in position in use.
Figures 3 and 4 show a tampon formed from a rolled sheet 20
of the absorbent coated sandwich material made as described
above with reference to Figure 1 interspersed with a layer 21 of
a long staple fibrous material of cotton, rayon or a cotton/
rayon mix. A withdrawal cord 22 is provided.
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