Note: Descriptions are shown in the official language in which they were submitted.
~Z~33
The present invention relates to new a~sorbent polymers,
their manufacturing process and theix use.
Ilydrophilic cross-linked polymers, which are insoluble
in water, based on acrylic acid and an alkali metal acrylate
are widely used today in articles of hygiene due to their
astonishing absorption power for physiological fluids: urine,
blood, etc... The market, which is buoyant for this type of
product, is a buyer of products which either perform better,
or are more economical or more ecologically sound.
Now the Rpplicant has discovered, with astonishment, new
highly absorbent polymers with absorbent properties which are
superior to the products currently commercially available or
described, whilst on the one hand being less expensive and on
the other hand having less impact on the environment.
The highly absorbent polymers according to the present
invention are cross-linked, in the form of micropearls,
hydrophilic, insoluble in water, based on acrylic acid
partially salified by an alkali metal and silica.
By "micropearls", is meant approximately spherical
pearls with a diameter of between 0.05 and 1 mm.
sy "insoluble in water", is meant that the polymers
contain, at ambient temperature, less than 5% by weight of
products which are soluble in ~ater.
Within the scope of the present invention, the term
"silica" designates amorphous colloidal silica, in a particle
state ~ith particles of an average diameter between 7 and 150
nm, which are non--agglomerated between themselves by siloxane
bonds : Si-O-Si.
Currently, it is not known exactly how the colloidal
silica is fixed in the polymers of the present invention;
however it is known that the discrete particles of silica are
uniformly spread in the polymer micropearls.
Among the polymers defined above, there can be more
particularly mentioned acrylic acid - alkali metal acrylate -
silica polymers containing, by weight, 2 to 25% of silica and98 to 75% of acrylic acid of which 60 to 80% is salified by
an alkali metal. Advantageously, the alkali metal is sodium
or potassium and preerentially, the alkali metal is
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potassium.
More particularly a subject of the invention is polymers
as defined above containing, by weight, from 5 to 20% of
silica and from 95 to 80% of acrylic acid of which 65 to 75%
is salified by an alkali metal.
According to the invention, the polymers defined above
can be prepared by a polymerization process as a water-in-oil
suspension carried out in an inert atmosphere, characterized
in that an aqueous phase obtained extemporaneously,
preferably as the introduction proceeds, starting with, on
the one hand, an aqueous solution, preferably de-oxygenated,
containing one or more hydrosoluble polymerization initiators
which are free radical generators and, on the other hand, an
aqueous phase containing the silica and chosen monomers at a
concentration of 50 + 15% by weight is introduced slowly,
under agitation, into the oil phase which is de-oxygenated,
preferably completely, maintained at boiling point and
containing a colloid protector. Then, when the polymerization
is finished, the solvents are eliminated by azeotropic
distillation until a suspension with a dry content of about
+ 10% by weight is obtained and finally the desired
polymer is isolated, notably by filtration.
The oil phase is constituted by one or more hydrocarbons
which are non-miscible with water, inert with regard to the
polymerization initiators and capable of forming an
azeotropic mixture with water such as cyclohexane or
petroleum fractions with a boiling point comprised between 50
and 180C.
The colloid protector, preferably used at the rate of
0.4 to 2% by weight relative to the weight of monomers, is
chosen from those currently used in this type of
polymerization in suspension (cf. Kirk-Othmer, Encyclopaedia
of Chemical Technology, 3rd edition, vol. 1, page 400).
Advantageously a cellulose ether will be chosen and,
preferably, a cellulose ethylether with an ethoxyl content of
48 to 49.5% (cf. Encyclopaedia of Polymer Science and
Engineering, 2nd edition, vol. 3, page 254). The colloid
protector is dissolved or dispersed beforehand in the oil
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phase. The polymerization reaction is carried out at the
boiling point of the reaction mixture, usually at ambient
pressure. It can also be carried out at a lower or higher
pressure than ambient pressure.
The polymerization reaction is initiated by one or more
hydrosoluble free radical generators, advantageously with a
half-life at 70C of greater than 2 hours. Such initiating
agents are notably certain mineral peroxides such as sodium
peroxodisulphate or certain azo-compounds such as 4,4'-
dicyano-4,4'-azopentanedioic acid. They are advantageously
used at a concentration of 200 to 3,000 ppm relative to the
weight of monomers and advantageously at a concentration of
500 to 1,500 ppm. The initiating agent or agents used are
dissolved in water, then this solution is carefully de-
oxygenated.
The potassium acrylate is obtained advantageously in
aqueous solution, by direct salification of an aqueous
solution of acrylic acid with potash. This salification is
advantageously carried out at a temperature of between 20C
and 35C. The monomers used are dissolved in water at a
concentration of about 50 + 15% by weight.
The silica is used in the form of concentrated aqueous
suspensions of non-agglomerated particles of amorphous silica
which is commercially available notably, by the Applicant,
under the brand name "KLEBOSOL".
The aqueous solution of the initiator and the aqueous
phase containing the monomers and the silica are mixed
extemporaneously, in an inert atmosphere, as their
introduction into the agitated oil phase proceeds, completely
de-oxygenated and maintained at boiling point by external
heating, if necessary. They therefore remain in contact for
only a few seconds before their use and they are introduced
slowly into the boiling reaction mixture. The duration of the
introduction can vary according to the operating parameters,
but generally it is between one and two hours. At the end of
the introduction, it is advantageous to maintain the reaction
medium at boiling point and under agitation in order to
complete the polymerization. After the polymerization is
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finished, the reaction solvents are eliminated by azeotropic
distillation until a suspension is obtained which has a dry
content of 85 + 10% and the expected product is isolated.
With a view to this isolation, the suspension is filtered and
the polymers according to the invention thus recovered are
dried at 60C until the dry content is greater than 90%. Thus
the polymers according to the invention are obtained in the
form of micropearls which are devoid of fines.
In the course of the polymerization reaction, the
polymers formed spontaneously cross-link with each other to
create cross-linked polymers which are insoluble in water,
with a very strong hydrophilic character and a very low
proportion of residual monomers, which is always less than
0.01% by weight.
15The cross-linking is accordingly more promoted as the
degree of neutralization of the acrylic acid is lower and as
the polymerization temperature is higher. The copolymers of
the present invention are therefore cross-linked thermally
- and, due to this fact, become insoluble in water and acquire
` 20 hydrophilic properties.
These properties are easily determined by a set of
simple tests.
Therefore, the water absorption capacity of the polymer,
designated TG, is determined at 20C, by agitating 0.4 g of
polymer in 500 g of water for 30 minutes, then by weighing
the drained polymer gel obtained. The weight found is
rounded to 1 g of dry polymer. The copolymers of the present
invention show, in this test, an absorption capacity in the
order of 300 to 700 g per gram of dry polymer. By "dry
polymer", a polymer with 100% active material is referred to.
The absorption capacity of the polymer for salty
physiological solutions, designated TGS, is determined at
20C, by agitating 2 g of polymer in 500 g of a salty
physiological solution for 30 minutes, then by weighing the
drained polymer gel obtained. The weight found is rounded, as
previously, to 1 g of dry polymer. The copolymers of the
present invention show, in this test, an absorption capacity
in the order of 40 to 70 g per gram of dry polymer.
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-- 6
The proportion of extractables, designated TE, is
determined according to the following method:
- 1 g of test polymer is placed in 200 g of salty
physiological solution;
S - this suspension is agitated for one hour at 20C then
left at rest for 15 hours at 20C;
- the polymer gel obtained is drained and the filtrate
is collected;
- the carboxylic and carboxylate functions present are
determined for 100 cm3 of filtrate;
- the result of this determination is expressed in grams
of polymer dissolved per 100 g of dry polymer.
In this test, the polymers of the present invention show
a p~oportion of extractables of 1-5%.
The absorption capacity by capillary action under a load
of 15 g per cm2, designated TGC, is determined at 20C
according to the following procedure: 40 g of Fontainbleu
sand with a granulometry of 0.100 to 0.300 mm, 2 g of test
copolymer and lastly 40 g of Fontainbleu sand are spread
successively and uniformly on a 90 mm diameter filtering
plate, with a porosity of 1, in a cylindrical funnel. Then a
total load of 954 g is placed on top of the upper layer of
sand with a 90 mm diameter glass disc as intermediary, then
the funnel is plunged into a tank containing a salty
physiological solution, at constant level, in such a way that
the water level completely covers the upper face of the
sintered glass and the quantity of salty physiological
solution absorbed by capillary action by the copolymer over
minutes is measured. The result is expressed in grams of
salty physiological solution per gram of dry polymer.
The polymers of the present invention therefore have
very useful absorbent properties which justify their use as
an absorption agent and also a subject of the invention is,
as absorption agents , the polymers as defined previously,
notably for the manufacture of articles of hygiene,
particularly babies' nappies.
The following examples illustrate the invention without
however limiting it.
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Bxamp~les
Example 1
- 3.5 g of cellulose ethylether, designated EEC,
containing 48 to 49.5% of ethoxylated groups and having, at
25C, a viscosity of 200 mPa.s, in solution at 5% in a
mixture of toluene-ethanol 80-20 by weight,
is dispersed, in an inert atmosphere,
- in 634 g of cyclohexane designated CY.
In this dispersion, which is carefully de-oxygenated,
agitated and maintained at boiling point, the following
solution, which is mixed extemporaneously during the
introduction, is introduced over 90 minutes in an inert
atmosphere:
- on the one hand, a de-oxygenated solution of:
0.467 g of sodium peroxodisulphate, designated PDS,
dissolved in 10 g of water,
- on the other hand, 624 g of a solution prepared
extemporaneously by dissolving the following at a temperature
lower than 30C:
- 230 g (3.19moles)of acrylic acid, designated AA, in:
- 314 g of an aqueous solution of potash containing
128.9 g (2.3 moles) of potassium hydroxide and 185 g of
water, then adding 80 g of a silica sol containing 50% silica
in the form of particles with an average diameter, designated
Dm, of 50 nm, having a pH of 9 and stabilized with sodium
hydroxide at 0.3% by weight (KLEBOSOL, PL 1346 Na).
The solution obtained is then subjected to azeotropic
distillation until 240 g of water is eliminated and, finally,
it is cooled down to ambient temperature and filtered. The
precipitate is then dried to 96% dryness under reduced
pressure at 60C in a ventilated oven.
In this way 372 g of an acrylic acid - potassium
acrylate - silica polymer is obtained, which is insoluble in
water and is in the form of pearls of a few tenths of a
millimetre in diameter. This polymer has a proportion of
residual monomers which is less than 0.005% by weight, a
water absorption capacity of about 430 g per gram, an
absorption capacity for a salty physiological solution of
8 2042183
about 53 g per gram and an absorption capacity under load of
23.5 g per gram.
The proportion of extractables, TE, is 2.8%.
Examples 2 - 10 and comparative example 11
Examples 2 - 10 and comparative Example 11 are carried
out by following the operating procedure described in Example
1. Tables I and II mention the quantities of raw materials
used, expressed in grams as well as the characteristics of
the polymers obtained. The very absorbent polymer obtained in
comparative Example 11 does not contain silica and is known.
Comparative Example 12
11.7 g of silica with an average particle diameter of 10
micrometers is mixed carefully with 88.3 g of the very
absorbent polymer prepared in Example 11. The mixture
obtained has a TGS of 8.3 and a TGC of 13.5, these values
being clearly lower than those shown by the original polymer.
It is therefore noted that silica which is simply mixed with
a very absorbent known polymer, instead of increasing the
absorption characteristics of the polymer, reduces them
drastically.
Examination of table II allows it to be stated that the
presence of combined silica in the polymers of the present
invention improves their absorption capacity under load, TGC,
by almost 30 + 5%. Now, for their use in articles of hygiene,
this property is important, indeed essential. Furthermore,
this benefit is obtained with less organic materials, which
constitute the most important part of the cost price of the
polymer and the main expense in their destruction after use.
The polymers of the present invention therefore have superior
characteristics to those of the prior art.
9 2042~83
TABLE I
No. Oi 1 p] lase A lueous pha ~e Silica sol
Df EEC CY Weight PDS AA KOH WATER Weight %SiO2 Dm Total
Ex. (g) (g) (g) weight
_ _ ._
1 3.5 634 637.5 0.467 230 129.2 195.3 80 50 50 nm 634.5
2 3.5 634 637.5 0.467 230 129.2 195.3 80 30 25 nm 634.5
3 3.5 634 637.5 0.467 230 129.2 195.3 80 30 13 nm 634.5
4 3.5 634 637.5 0.467 230 129.2 235.3 40 30 25 nm 634.5
3.5 634 637.5 0.467 230 129.2 195.3 80 15 7 nm 634.5
6 3.5 607 610.5 0.318 230 107.7 189.6 80 50 50 nm 607.3
7 3.5 619 622.5 0.318 ~30 116.7 192.6 80 50 50 nm 619.3
8 3.5 634 637.5 0.318 230 129.2 195.3 80 50 50 nm 634.5
9 3.5 634 637.5 0.318 230 129.2 115.3 16050 50 nm 634.5
10 3.5 634 637.5 0.467 230 129.2 115.3 80 30 9 nm 634.5
11 3.5 634 637.5 0.467 230 129 2 275.3 0 _ 634.5
1 o 2042183
TABLE II
No. TN~ - %Sio2 TG TGS TGC TE TMR~*
1 72% 357 11.2430 53 23.5 2.8 c50 ppm
2 72% 341 7.04414 52 19.5
3 72% 341 7.04426 52.5 21
4 72% 329 3.6571 51.5 17.3 4.8 <50 ppm
72% 329 3.6357 50 21.5 4.0 ~50 ppm
6 60% 343 11.7677 61 22.5
7 65% 349 11.4608 58 22
8 72% 357 11.2617 60 22
9 72% 397 20.1480 48 19.5
72% 341 7.04333 48 24
11 72% 317 0 447 57 17
12 60% 100 11.7 8.3 13.5
_ .
* TN : neutralization percentage
** PP : weight of dry polymers expressed in grams
*** TMR : proportion of residual monomers expressed in ppm
:
