Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
The subject of the present invention is a cellular
cellulosic material -or sponge- with improved retention of water (and,
more generally, of aqueous liquids). It also relates to a process
for the preparation of such a material.
S The applicant has deYeloped a new product of the sponge
type which, in addition to the fact that it possesses an improved
capacity for water retention, remains moist and supple for a longer
time than a sponge of t~e prior art. To the touch and in appearance
it is also improved.
In fact, in the dry state, a sponge is rough and retracts,
whereas when it is moist it has a soft and pleasant feelO This change
of state is seen particularly in thin sponges which become warped
when dry.
In order to solve this problem -maintain a sponge humid
and supple, particularly when it is being stored or on sale- it has
been suggested, according to the prior art, that magnesium chloride
and glycols be incorporated within the said sponge. This solution
does not prove to be completely satisfactory. The said magnesium
chloride and the said glycols are leached out as soon as the sponges
are used and then no longer play their role in water retention and
as plasticizers of the cellulose.
The applicant now suggests the introduction of particles
of a superabsorbent polymer in the buLk of the said cellu1ar
cellulosic material~ The specifications for the said particles will
be provided below.
Particles of a superabsorbent polymer are already used
advantageously in disposable products such as diapers.
Their introduction, according to the invention, into the
area of sponges -within the cellulose network- is not an obvious step.
In fact, the simple incorporation of particles of a
superabsorbent polymer during the manufacturing process for sponges
or cellular cellulosic materials -cal~ed the viscose process without
protection of the said particles invariably leads to degradation of
the latter by hydrolysis and/or compression and, consequently 9 to
a considerable loss of thei} water-retaining capacity.
The addition of the said particles after manufacture of the said
cellular cellulosic material does not enable them to be inserted
into the interior of the said material and be retained there
mechanically. Furthermore, the presence of the said particles at the
surface of the said material or sponge in the swollen state after
absorption of water confers on it a slimy, sticky feel hardly
appropriaee to its use, particularly in the area of household cleaning.
Absorbent articles obtained by the viscose process and
containing particles of a superabsorbent polymer have been described
in the patent application EP-A-0 293 ~08. The said particles are not
trapped in the cellulose network at the interior of these articles.
The said articles are usually laminated materials; thus5 the particles
of superabsorbent polymer are found betweell two layers of compressed
cellulosic material.
The applicant now suggests a method for the incorporation
of particles of superabsorbent pol~mer into the structure of cellular
cellulosic materials without degradation and in a stable manner in
order to obtain the expected results set out above.
Such materials, including the said particles in their
cellulosic structure, constitute a subject of the invention; the
process for their preparation constitutes another.
Thus, the subject of the present invention is a cellular
cellulosic material with improved water retention, characterized in
that it contains particles of a superabsorbent polymer trapped in
the cellulose network.
Characteristically, the particles of superabsorbent polymer
are found in the sponges of the invention, trapped in the cellulose
network. They are localized in the interstices of the said cellulose.
It has been possible to produce such a currently novel
structure by means of the process described below; the viscose process
~known to the person skilled in the art- in which, according to the
invention, the temporarily protected particles of superabsorbent
polymer are introduced into the viscose before the acidic regeneration
of ehe cellulose.
The particles of su~erabsorbent polymer assume the function
of retainers of water or any other liquid. They are particles of
superabsorbent polymers (usually known under ~he abbreviation S.A.P.:
Super Absorbent Polymer~.
These polymers may be of natural or synthetic origin and,
for the purposes of the invention, are advantageously insoluble in
water.
For reasons of convenience r we will sometimes use the
abbreviation S.A.P. in the continuation of the presen~ description.
These polymers - S.A.P.- when placed in contact with water
form a physical or chemical gel, also called hydrogel, capable of
absorbing considerable amounts of water in its macromolecular network.
Superabsorbent polymers (S.A.P.) of natural origin are for
example polymers, the macromolecular network of which is of the
polysaccharide type such as agar--agar, gelose, alginate, carboxy-
methylcellulose, such as is described in particular in the patent
US-A-3 58~ 364, hydroxyethylce]lulose, methylcelllllose, gelled
cellulose triacetate as is described in particular in the patents
US-A-l 693 8~0 and US-A-3 ~346 404, polyacrylonitrile-grafted starch
as is described in particular in the patents US-A-3 93~ 099 and US-
A-3 661 815 and acrylic acid-grafted starch such as is described in
the patent FR-A-2 305 452.
Superabsorbent polymerc (S.A.P.) of synthetic origin are
polymers, for example, the macromolecular network of which is ~ormed
by acrylic polymers; hydroxyethyl methacrylate poLymers, cross-linked
polyvinyl alcohol; polyacrylamide; partially hydrolysed poly~inyl
acetate; hydroxyethyl acrylate; mono-acrylate of diethylene-glycol;
monomethacrylate of diethylene-glycol; 2-hydroxypropyl acrylate; 2-
hydroxypropyl methacrylate; 3-hydroxypropyl acrylate; 3-hydroxypropyl
methacrylate; monomethacrylate of dipropylene-glycol; vinylpyrrolidone;
acrylamide; methacrylamide; N-propylacrylamide; N-isopropyl-
methacrylamide; N-methylacrylamide; N-2-hydroxyethylmethacrylamide;
hydrogels of polyurethane, composed of lightly cross-linked polymers
of prepolymers terminated by an isocyanate which are the products
of reaction of a poly(alkylenoxy)polyol with an organic diisocyanate
lightly cross-]inked with water or an organic polyamine~ as described
in the patent US-A-3 939 105; copolymers of acrylate monomers with
ethylenic unsaturation and hydroxyalkyl methacrylates and acrylates
and methacrylates of alkoxyalkylene-glycols, as described in the patent
US-A-4 038 264 as well as other superabsorbent polymers (S.A.P.) known
to the person skilled in the art.
The superabsorbent polymers ~S.A.P.~ of synthetic origin
and insoluble in water are preferred because they are thermally more
stable and les~s susceptible to degradation by the action of
microorganisms.
The superabsorbent polymers (S.A.P.), lnsoluble in water,
are obtained by the cross-linking of macromolecules and are available
in the form of flakes, powders, films, fibres and spheres or "beads"
For the purposes of the invention, particles of spherical
form, possessing a diameter included between about 50 and 400 ~m,
will preferably be used.
For reasons of homogeneity of the water retention effect,
it is desirable that the said particles are uniformly distributed
and particles of S.A.P. possessing a diameter included between 50
and 200 ~m will advantageously be used.
In particular, products called "beads", produced by
polymeri~ation in reverse suspension, will be used.
At present, such products are marketed in EUROPE by the
HOECHST (ref. PL ~2'i5) 7 BASF ~Luquasorb HC 9797) and NORSOLOR (X 5
TS) companies.
In order l:o obtain the desired result, the cellular
cellulosic materials according to the invention usually contain about
1 to 5% by weight of particles of S.A.P. with respect to the weight
of dry cellulose. That they may contain a larger amount, up to 10%
or more, is in no way excluded. It will obviously be advisable to
check thAt the amounts incorporated do not or not excessively impair
the properties of the flnished product: feel, appearance, mechanical
behaviour,
According to a variant of the invention, the cellular
cellulosic material is line~ on at least one of its faces with another
material. It may be any type of material compatible with the cellular
cellulosic material and the introduction of which presents any interest
in the field of application of the said celLular cellulosic material.
As an illustration in no way limiting, mention should be made of the
introduction of an expanded latex foam, cross-linked in particular
like the one constituting the ~opping face of the product described
in the patent application EP ~8 401 930.8 of the applicant, published
under the number 0 335 050.
It has been observed tha~ the introduction of such a
synthetic latex foam also improves the water retaining power of the
cellular cellulosic material to which the foam is attached. The
kinetics of the evaporation of water are found to be diminished without
impairment of any of the properties of the sponge-type product
possessing at least one mopping face made of synthetic latex.
Advantageously, such a composite material also contains
particles of a superabsorbent polymer between the said cellular
cellulosic material and the said other material.
Thus, at the interior of this composite material, particles
of a superabsorbent polymer are encountered at the interface cellular
cellulosic material/other material and in the bulk of the said
cellular cellulosic material.
As specified above, the cellular cellulosic materials of
the invention owe their attractive properties to ~he fact that they
contain non-degraded particles of S.A.P.within their cellulose network.
The method of incorporation of the said particles within
the said materials thus constitutes a key element of the present
invention. This incorporation takes place during the prepara~ion of
the said material by the viscose process, known to the person skilled
in the art.
This process for the production of cellular cellulosic
materials is summarized below.
Wood pulp is used as starting material. It is dissolved
by means of ~he viscose process through the intermediary of the
xanthate derivative with addition of an expanding agent and fibres.
The pulp obtained may ~e coated, ior example, on either side of a
grid. This coating step is followed by a step of acidic regeneration
of the cel~ulose. The pulp may also be introduced into a mould, then
regenerated in a basic medium. The cellulose thus regenerated is then
rinsed~ subjected to a bleaching treatment, Ctlt up and packaged. This
process may optionally include one or more steps to modify the finished
product, and in particular the lining of at least one of the faces
of the said product with another material.
The cellular cellulosic material of the invention is
produced in the framework of the viscose process with the addition
of the following steps:
- incorporation of temporarily protected particles of a
superabsorbent polymer into the cellulose xanthate (viscose) before
regeneration,
- optionally, dusting of temporarily protected particles
of a superabsorbent polymer on a~ least one face of the said cellular
cellulosic material obtained with acidic or basic regeneration of
the cellulose, before the lining of the said face with another
material,
- and deprotection of the said particles of superabsorbent
polymer in the last stage of manufacture of the materialO
According to a first variant, the said particles of S.~.P.
are introduced into the cellulose xanthate (viscose) preferably after
the addition of the expanding aKent and ~he fibres.
In this lat:ter case, they are incorporated either into the
mixer generating the mixture of the said expanding agent 7 fibres and
the xanthate derivate, or during the coating of the mixture obtained
-xanthate derivative (viscose) + fibres + expanding agent- and
preferably between two layers of the said mixture.
The said particles of superabsorbent polymer are thus
introduced into the process, temporarily protected. Their pro~ection
must be such that, on the one hand, they withstand the steps of the
viscose process that they may be re~uired to undergo and/or the
additional steps of modificaticn of the product obtained by the said
viscose process wlthout being damaged and, on the other, they can
be deprotected without impairment of the said particles, their
properties and the material in which they are present.
They can be ensured such protection by encapsulation in
a monolayer or bilayer membrane, consisting essentially of one (or
two) mixture(s) of at least one film-forming polymer and at least
one hydrophobic crystalline material.
Such a membrane is the subject of a French patent application
filed in the name of the Applicant on 12 September ~989 under the
No. 89 11 924.
The combination of these two types of materials -film-forming
polymer(s), hydrophobic crystalline material(s)- enables a ~ight
membrane to be produced under the harsh conditions of the viscooe
process; a membrane which nonetheless permits the release of the
encapsulated S.A.P. The degradation or removal of the said membrane
for the release of the S.A.P. may be accomplished in particular by
mechanical means (compression, grinding, ultrasonics), by thermal
means (heating, freezing), by actinic radiation (U.V., I.R., beams
of electrons, microwaves) and by chemical means (change of pH,
dissolution, chemical attack). Usually, the said S.A.P. is released
by fusion of the hydrophobic crystalline material(s), involved in
the composition of its membrane.
Advantageously, the said membrane materials are organo--
soluble compounds. Their solubility in organic solvents enables
particularly efficient techniques to be employed for coating the
particles of the superabsorbent polymer (S.A.P.); techniques which
will be specified below.
However, the invention does not exclude the employment of
compoun~s slightly or not at all organosoluble in conjunction with
the use of other techniques of coa~ing or surface film formation.
The film-forming polymer entering into the composition of
the membrane according to the invention may be selected from the
polymers of natural origin, the polymers of synthetic origin or their
mixtures.
It may be advantageously selected from the cellulose
derivatives -such as the ethylcelluloses, the acetophthalates or
acetobutyrates of cellulose- or their mixtures.
Similarly, it may advan1_ageously be selected from the
(co)polymers of styrene, vinylidene cllloride-based (co)polymers
or their mixtures~
As indicated above, it may even consist of a mixture of
at least one polymer of natural origin and at least one polymer of
synthetic origin.
The hydrophobic crystalline material entering into the
composition of the membrane is advantageously selected from the fatty
acids, the derivatives of fatty acids (amides or bistearamides of
fatty acids...), the microcrystalline waxes and their mixtures. In
particular, behenic acid, stearic acid, stearamide, bistearamide or
erucamide may be used. Advantageously a "pure" crystalline material~
possessing a sharp melting point, is selected. Then, in order to
release the encapsulated particle of superabsorbent polymer (S.A.P.)
it is always possible to raise the temperature of the medium -celiular
cellulosic material- in which it is found to at least and possibly
above the said sharp melting point.
The two principle constituents of the membrane are
advantageously used in the following proportions by weight: about
10 to 90% of film-forming polymer for about 90 to 10% of hydrophobic
crystalline material.
A mixture, particularly preferred when a polymer of natural
origin is used, contains about 30% of the said film-forming polymer
and 70% of the hydrophobic crystalline material.
In addition to its two principle constituents, the membrane
may contain additives and in particular products intended to improve
its wettability and/or its hydrophobicity and/or its adhesion to the
particle of superabsorbent polymer (S.A.P.). For example, mineral
lamellar fillers such as mica may be added in order to improve the
hydrophobicity and the watertight of the membra~e.
According to one of the preferred variants of the invention,
encapsulated particles of S.A.P. may be included ln a monolayer
membrane consisting essentially of a mixture of about 30% by weigh~
of polystyrene and about 70~ by weight of stearamide.
According to another preferred variant of the invention,
encapsulated particles of S.A.P. are included in a bilayer membrane,
r~ r l --~ r~
the first layer of which consists essentially of a mixture of about
30~ by weight of polystyrene and about 70% by weight of stearamide
and the second layer of which, the layer in contact wi~h the particle
of S.A.P., consists essentially o~ a mixture of about 30% by weight
of ethylcellulose and about 70% by weight of behenic acid.
It is obvious that the nature of the constituents entering
into the composition of the membrane and the proportions in which
they occur play an important role in the efficacy and duration of
the protection of the encapsulated S.A.P. Other factors also need
to be taken into account, in particular the thickness of the said
membrane as well as the process used for its constitution.
The person skilled in the art is in the position to determine
each of the said parameters for the optimi~ation of the said
protection.
As far as the thickness of the membrane is concerned, it
is obvious that by increasing it,the protection of the encapsulated
product (S.A.P.) is improved.
In general, an effective protection -during the preparation
of the cellular cellulosic materials of the invention- of the
encapsulated S.A.P. is obtained with a membrane thickness included
between 10 and 50 ~m.
The thickness of the monolayer or bilayer membrane, the
nature of the constituents of which has been specified above, is
advantageously included between 25 and 40 ~m.
All known suitable encapsulation techniques may be employed
for the encapsulation of the particles of S.A.P.
Advantageously, the said S.A.P. may be encapsulated by
spraying of the materials required to constitute the successive
membranes, the said materials being dissolved in a suitable solvent.
This process can be implemented in particular with organosoluble
materials, dissolved in an organic solvent which does not cause the
superabsorbent polymer (S.A.P.) to be encapsulated to swell. Usual
solvents such as alcohols t chlorinated solvents, alkanes..~ or their
mixtures may be used.
This process is advantageously implemented in order to bring
about encapsulation by means of surface film formation, in particular
in a fluidi~ed bed. Techniques such as those used in the ~urster, Top
Spray or tangential spraying processes can be used. These processes
enable successive films to be formed around the particle of super-
absorbent polymer by repeated exposure of the latter close to the
nozzle of the spray.
Other coating techniques, known to the person skilled in
the art, enable the particles of S.A.P. for the purposes of the
invention to be produced. Special mention should be made of the
techniques by fusion.
The tight of the coated particles obtained may
be further improved, in some cases, by a thermal or annealing treatment
(at a temperature lower than the melting point of the hydrophobic
crystalline material).
Such a thermal treatment can be performed after the coating
with a single layer or af~er coating with a first layer and/or after
coating with a second layer.
The particles thus encapsulated preserve their water
retention capacity intact. It has been possible to observe that even
if the transfer of the particle between the different reaction mPdia
rendered the shell brittle, the protection remained efficacious.
The problem of ~he deprotection of the said particles arises
when the manufacturing process of the material is complete.
Advantageously, the said deprotection is performed during
a final step in the manufacture of the said material.
This deprotection, in par~icular when it consists of removing
the monolayer or bilayer membrane described above, may be performed
by mechanical means, by thermal means or by actinic radiation and
chemical means.
The deprotection by fusion (thermal means) is preferred.
For this purpose, the product obtained may be treated thermally either
in a hot air tunnel or by hot water vapour or by microwaves or high
frequency... In order to obtain the desired result -removal of che
membrane described above- the product is usually treated at at least
100C for several seconds.
It should be noted that advantageously the said deprotection
can be produced simultaneously with the cross-linking of a material
applied to at least one face of the cel lular cellulosic material. It
has been seen that such ~aterials may CO1lSiSt of an e~panded latex foam.
The cel]ular cellulosic material of the invention can thus
be obtained by the viscose process with the introduction of the
temporarily protected particles of S.A.P~
This protection can be provided by the monolayer or bilayer
membrane described above.
Other types of protection can be developed and are not
excluded from the framework of the present inventionO
The applicant specifies below two preferred variants of
the method for the preparation of the cellular cellulosic materials
according to the invention.
According to the first variant, sponges are prepared in
bulk in which particles of S.A.P. are preEerably uniformly
distributed.
The viscose process is used. The encapsulated particles
of S.A.P. are incorporated into the cellulose xanthate (viscose).
The product obtained undergoes an acidic regeneration. After rinsing
and bleaching, the cellular cellulosic material obtained is subjected
to a thermal treatmen~.
The aim of the said thermal treatment i5 to release the
said particles of S.A.P. distributed in the bulk of the said material.
It is performed at at least 100C for several seconds.
According to the second Yariant, a mopping cellular
cellulosic material is prepared such as that described in the
application EP O 335 050 of the Applicant :
On one face of a cellular cellulosic material obtained
by the viscose process as modified abo~e (by incorporation of
encapsulated particles of S.A.P. in the cellulose xanthate)
encapsulated particles of S.A.P. are dusted. The said face is then
coated with a non-crosslinked latex foam. The entire preparation is
then subjected to a thermal treatment, the parameters of which are
fixed in order ensure both ~he cross linking of the said foam and
12
the release of the encapsulated particles of S.A~P. The de~erminatlon
of these parameters lies wlthin the competence of a person skilled
i~ the art.
In the ~ccompanying drawings-:
FIGURE 1 is a graphical presentation of water
retention and absorption r~sults obtained acc~rdirlg to
Example 2 helow;
FIGURE 2 is a photomicrograph of a section
through a product according to the invention.
The examples helow illustrate the invention and confirm
its v~lu~.
Example 1 (prior art)
This example is given for reference~
Manufacture of a standard sponge without addi~ion of S.A.P.
a) Wood pulp
1 NaOH
b) Alkali-cellulose
CS2
c) Cellulose xanthat:e (viscose)
l Addition of fibres and expanding agent
d) Pulp
1 Coating on both sides of a grid
1 Acid baths
e~ Regenerated cellulose
Rinsing - bleaching
Incorporation of MgCl2
~ , Cutting up - packaging
f) F inished product (290 g/m2 of dry cellulose)
. Dimensions 20 x 20 cm
30 ' . Thickness 6 mm
. Weight of cellulose 10 g
. Weight of magnesium
chloride MgCl2 3 g
. Weight of water (8) 15 8
13
Example 2
Manufac~u~e of a sponge according to the invention containing
5% of S.A.P. in its bulk.
a) Wood pulp
S 1 NaQH
b) Alkali-cellulose
CS
~ 2
c) Cellulose xanthate (~iscose)
1 Fibres ~ expa~ding agent
d) Pulp
Coating of the pulp and dusting of encapsulated S.A.P~ as
a sandwich be~ween two layers of viscose
Acid bath
e) Regenerated cellulose
Rinsing - bleaching
Thermal treatment (100C for 10 seconds)
~ Cutting up packaging
f) F nished product
. ~imensions20 x 20 cm
. Thickness 6 mm
. Weight of cellulose 10 g
. Weight of S~A.P. 0.5 g
. Weight of wa~er20 g
Characteristics of the particles of S.A.P. incorporated:
- Diameter of the S.A.P. 280 - 400 ~m
- Bilayer coating:
internal layer: behenic acid - ethylcellulose ~70/30)
external layer: stearamide - polyst~rene (70/30
- Ccating thickness 30 ~m
Samples from examples 1 and 2 were tested.
The table 1 below and the accompanying figure 1 lllustrate
the impact of the modifications contributed according to the in~ention
on the characteris~ics of absorption and retention of water of ~he
products as well as on the kinetic~ of eYaporatioll of water.
2 ~
14
Table 1
Absorption and retention of tap water by samples 1 and 2
S _ _ .................. ___ _ l
1) Water absorption (g) 2) Water retention (g)
_ ____
Sample ex 1100 - 120 10 - 15
Sample ex 2175 - 200 ¦ 80 - 90
(1) Total tap water absorption measured according to the Edana standard
10.1.-72
(2) Retention of tap water after centrifugation (3000 rev/mn 12
seconds). The centrifugation corresponds to a mean manual
expression of absorbed water by the product.
The cur~es for water evaporation (figure 1) were drawn up
under controlled atmospheric conditions: 20C - 50% R.H. They give
the kinetics of evaporation of water from the samples after one rinsing
with tap water followed by a centrifugation under the conditions taken
from (2) above.
Table 1 and figure 1 demonstrate the desired impro~ement
in water retention.
In figure 2 - micrograph through a section of a sponge fabric
of the invention, micrograph obtained by means of scanning electron
microscopy (enlargement x 35)- it can be clearly seen that the
particles of the superabsorbent polymer are in the interior of the
interstices of the cellulose (in the network).
