CATIONIC POLYMER

POLYMERE CATIONIQUE

English Abstract

The invention relates to a cationic polysaccharide, preferably in fibrous
form, having superabsorbent characteristics, the polysaccharides being
substituted by quaternary ammonium groups and having a ds of at least 0.5,
preferably 0.5 to 2.5, and the polysaccharides being cross-linked to a
sufficient extent that it remains insoluble in water. The polysaccharide is
preferably cellulose. An increased number of functional groups in the product
improves superabsorbent properties, whereas the use of a cross-linking agent
makes it possible to control the gel strength of the product and makes it
easier to tailor the characteristics of the product to those which are
required.

French Abstract

L'invention porte sur un polysaccharide cationique, de préférence sous forme fibreuse, présentant des caractéristiques superabsorbantes, les polysaccharides étant substitués par des groupes ammonium quaternaires et présentant un ds (degré de substitution) d'au moins 0,5 et de préférence compris entre 0,5 et 2,5, et les polysaccharides étant suffisament réticulés pour rester insolubles dans l'eau. Le polysaccharide est de préférence de la cellulose. Le nombre accru des groupes fonctionnels du produit en améliore les proprités superabsorbantes, tandis que le recours à un agent de réticulation permet d'ajuster la résistance à l'état de gel du produit et d'en adapter plus facilement les caractéristiques à celles demandées.

Claims

21
THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A cationic polysaccharide having superabsorbent
characteristics, the polysaccharide being substituted by
quaternary ammonium groups and having a ds of at least
0.5, and the polysaccharide being cross-linked to a
sufficient extent that it remains insoluble in water.
2. A cationic polysaccharide according to claim 1
wherein the polysaccharide is cellulose.
3. A cationic polysaccharide according to claim 1 or 2
in fibrous form.
4. A cationic polysaccharide according to any one of
claims 1 to 3 wherein the quaternary ammonium groups are
derived from a quaternary ammonium compound of one of the
general formulae (I) and (II):
<IMGS>
wherein n is an integer from 1 to 16;
X is halogen;
Z- is an inorganic or organic anion;

22
R, R1, R2 and R3, which may be the same or different are
each hydrogen or an organic radical; or additionally R2 may
represent a group of formula (III) or (IV):
<IMGS>
in which p is an integer from 2 to 10;
and n, R, R1, R2, R3, X and Z are as defined above.
5. A cationic polysaccharide according to claim 4
wherein each of R, R1, R2 and R3 is hydrogen or an alkyl,
hydroxyalkyl, alkenyl or aryl group containing up to 10
carbon atoms.
6. A cationic polysaccharide according to claim 5
wherein each of R, R1, R2 and R3 is hydrogen.
7. A cationic polysaccharide according to claim 5 or 6
wherein the quaternary ammonium compound is selected from:

23
glycidyltrimethylammonium chloride;
2, 3-epoxypropyl-N,N,N-trimethylammonium chloride;
3-chloro-2-hydroxypropyl-N,N,N-trimethylammonium
chloride;
3-chloro-2-hydroxypropyl-N,N,N-
dimethylethanolammonium chloride; and
1,3-bis-(3-chloro-2-hydroxypropyl-N,N-
dimethylammonium)-N-propane dichloride.
8. A cationic polysaccharide according to any one of
claims 1 to 7 having a ds of from 0.5 to 2.5.
9. A process for the production of a cationic
polysaccharide having superabsorption characteristics
which comprises:
(i) reacting a polysaccharide with an excess of a
quaternary ammonium compound containing at least one
group capable of reacting with polysaccharide
hydroxyl groups to provide a polysaccharide with a ds
of at least 0.5; and simultaneously or subsequently
(ii) reacting the derivatised polysaccharide with a
cross-linking agent to provide a degree of cross-linking
sufficient that the product remains insoluble in
water.
10. A process according to claim 9 wherein the
polysaccharide is cellulose.
11. A process according to claim 9 or 10 wherein the
polysaccharide is a fibrous polysaccharide

24
12. A process according to any one of claims 9 to 11
wherein the quaternary ammonium compound is a compound of
one of the general formulae (I) and (II):
<IMGS>
wherein n is an integer from 1 to 16;
X is halogen;
Z- is an inorganic or organic anion;
R, R1, R2 and R3, which may be the same or different are
each hydrogen or an organic radical; or additionally R2 may
represent a group of formula (III) or (IV):
<IMGS>

25
in which p is an integer from 2 to 10; and
n, R, R1, R2, R3, X and Z are as defined above.
13. A process according to claim 12 wherein each of R, R1,
R2 and R3 is hydrogen or an alkyl, hydroxyalkyl, alkenyl or
aryl group containing up to 10 carbon atoms.
14. A process according to claim 13 wherein each of R, R1,
R2 and R3 is hydrogen.
15. A process according to claim 13 or 14 wherein the
quaternary ammonium compound is selected from:
glycidyltrimethylammonium chloride;
2,3-epoxypropyl-N,N,N-trimethylammonium chloride;
3-chloro-2-hydroxypropyl-N,N,N-trimethylammonium
chloride;
3-chloro-2-hydroxypropyl-N,N,N-dimethylethanolammonium
chloride; and
1,3-bis-(3-chloro-2-hydroxypropyl-N,N-dimethylammonium)-N-propane
dichloride.
16. A process as claimed in any one of claims 9 to 14
wherein the cross-linking agent is a diepoxy compound or a
haloepoxy compound.
17. A process as claimed in claim 16 wherein the
cross-linking agent is 1,3-bis(glycidyl dimethylammonium)
propane dichloride or epichlorohydrin.
18. A process as claimed in any one of claims 9 to 17
wherein step (ii) is carried out subsequently to step (i).
19. A process as claimed in any one of claims 9 to 17
wherein the quaternary ammonium compound is used in a

26
molar ratio based on saccharide units in the
polysaccharide of 5:1 to 40:1.
20. A process as claimed in claim 19 wherein the
quaternary ammonium compound is used in the molar ratio
based on saccharide units in the polysaccharide of 20:1 to
40:1.
21. A process as claimed in any one of claims 9 to 17
wherein the reaction is carried out in two or more steps
and a molar ratio of 10:1 to 20:1 is applied in each step.
22. A process as claimed in any one of claims 9 to 21
wherein derivatisation and cross-linking reactions are
carried out in the presence of base.
23. A process as claimed in claim 22 wherein the base is
an alkaline earth metal hydroxide or alkoxide.
24. A process as claimed in claim 23 wherein the base is
sodium hydroxide.
25. Use of a cationic polysaccharide as claimed in any
one of claims 1 to 8 as an absorbent.
26. Use according to claim 25 as an absorbent in hygienic
or sanitary articles.

Description

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CATIONIC POLYMER
The present invention relates to a cationic polymer more
particularly a water absorbent polymer of the type commonly
referred to as a "superabsorbent".
The substances currently termed "superabsorbents" are
typically slightly cross-linked hydrophillic polymers. The
polymers may differ in their chemical nature but they share
the property of being capable of absorbing and retaining even
under moderate pressure amounts of aqueous fluids equivalent
to many times their own weight. For example superabsorbents
can typically absorb up to 100 times their own weight or even
more of distilled water.
Superabsorbents have been suggested for use in many
different industrial applications where advantage can be
taken of their water absorbing and/or retaining properties
and examples include agriculture, the building industry, the
production of alkaline batteries and filters. However the
primary field of application for superabsorbents is in the
production of hygienic and/or sanitary products such as
disposable sanitary napkins and disposable diapers either for
children or for incontinent adults. In such hygienic and/or
sanitary products, superabsorbents are used, generally in
combination with cellulose fibres, e.g. cellulose fluff, to
absorb body fluids such as menses or urine . However, the
absorbent capacity of superabsorbents for body fluids is
dramatically lower than for deionised water. It is generally
believed that this effect results from the electrolyte
content of body fluids and the effect is often referred to as
' "salt poisoning".
The water absorption and water retention characteristics
of superabsorbents are due to the presence in the polymer
structure of ionisable functional groups. These groups may

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2
be carboxyl groups, a high proportion of which are in the
salt form when the polymer is dry but which undergo
dissociation and solvation upon contact with water. In the
dissociated state, the polymer chain will have a series of
functional groups attached to it which groups have the same
electric charge and thus repel one another. This leads to
expansion of the polymer structure which, in turn, permits
further absorption of water molecules although this expansion
is subject to the constraints provided by the cross-links in
the polymer structure which must be sufficient to prevent
dissolution of the polymer. It is assumed that the presence
of a significant concentration of electrolytes in the water
interferes with dissociation of the functional groups and
leads to the "salt poisoning" effect. Although most
commercial superabsorbents are anionic, it is equally
possible to make cationic superabsorbents with the functional
groups being, for example, quaternary ammonium groups. Such
materials also need to be in salt form to act as
superabsorbents and their performance is also affected by the
salt-poisoning effect.
A cationic superabsorbent based on a polysaccharide such
as cellulose will have polysaccharide hydroxyl groups reacted
with a reagent (a derivatising reagent) which converts these
hydroxyl groups into a cationic group, e.g. a quaternary
ammonium group. For use as a superabsorbent, particularly in
hygienic and/or sanitary products, it is advantageous that
the product should be based on fibrous cellulose since this
can be combined and processed more easily with cellulose
fluff which also has a fibrous character.
WO 92/19652 relates to a fibrous cationic polysaccharide
which can be obtained by reacting fibrous polysaccharides
such as cellulose with an excess of quaternary ammonium
compounds containing at least one group capable of reacting
with the polysaccharide hydroxyl groups. Whilst the product
of WO 92/19652 shows useful properties as a superabsorbent

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3
there is a limit to the absorption properties which can be
achieved.
As explained above, the absorption of water by a
superabsorbent involves the functional groups attached to the
polymer chain and, in principle, the absorption capacity
depends on the ratio of functional groups to the remainder of
the polymer, i.e. the more functional groups that are
introduced the greater the repulsion between the polymer
chains and the greater the potential for water absorption.
On the other hand, whilst cellulose in its natural state is
insoluble in water, derivatisation of cellulose, in
particular introduction of hydrophillic groups, tends to
increase solubility in water. Accordingly attempts to
increase water absorption of the product of WO 92/19652 by
increasing the ds would be likely to lead to a water soluble
polymer rather than a superabsorbent which, by definition,
must remain insoluble in water.
In addition, the fibrous form o~ the ma~P:a: -~a::s
that
it is difficult for the derivatising aye::: _- ~~_-. .~-~ess
to
polysaccharide hydroxyl groups w;~::o;:-. ~P~:. ~ . _.
_ the
structural backbone of the materia: . ..... _ . ~_ ~::w,:c::
WO
92/19652 gives a nominal figure of 0.5 to ;.: :~: ~'.he degree
of substitution ("ds") with the derivatising agent it is
not
generally possible to obtain a ds higher than about 0.7
without activation of the polysaccharide wh ich damages
the
structural integrity of the polysaccharide fibres thereby
leading to solubilisation of the cellulose. Activation can
take the form, for example, of application of pressure
to
burst the fibres open and expose more pot ential reaction
sites, or use of a chemical activation agent such as zinc
chloride. Example 6 of WO 92/19652 achieves a ds of 1.10
but
only by using activation with zinc chloride and the product
would have been largely soluble.
Processes are known for the cross-linking of cellulose

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4
using cross-linking agents such as formaldehyde,
epichlorohydrin, diepoxides, dicarboxylic acids, dialdehydes
and diisocyanates to obtain highly water insoluble products.
However the presence of a cross-linking agent would increase
the molecular weight of the material and thus, in principle,
decrease superabsorbent properties. Processes are also known
for the derivatisation of cellulose in crystalline or powder
form but these are generally of lower molecular weight than
fibrous cellulose with the hydroxyl groups more accessible so
that different approaches are applicable to derivatisation of
crystalline and powder form cellulose than to fibrous
cellulose.
An object of an aspect of the present invention is to provide a
superabsorbent polymer based on a polysaccharide, preferably
a fibrous polysaccharide, more preferably fibrous cellulose
which has improved superabsorbent properties. It has now
surprisingly been found that such a product can be produced
by combining derivatisation of the polysaccharide with a
appropriate degree of cross-linking to maintain water
insolubility. The improvement in superabsorbent properties
brought about by an increased number of functional groups
(higher ds> more than outweighs any effect that the cross-
linking agent has on super-absorbent properties and the
product has improved superabsorbent properties, for example
as compared to products of the type disclosed in WO 92/19652.
Thus use of a cross-linking agent makes: it possible to
control the gel strength of the product and makes it easier
to tailor the characteristics of the product to those which
are required
SUMMARY OF THE INVENTION
According to one aspect the present invention provides
a cationic polysaccharide,
having superabsorbent characteristics, the
polysaccharide being substituted by quaternary ammonium
groups and having a ds of at least 0 . 5 ,
and the polysaccharide being cross-linked to a

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sufficient extent that it remains insoluble in water. The
cationic polysaccharide is preferably a fibrous cationic polysaccharide
having a ds of 0.5 to ~.5.
In accordance with a further aspect, a process for
production of a cationic polysaccharide having superabsorption
characteristics comprises:
(i) reacting a polysaccharide with an excess of a quaternary
ammonium compound containing at least one group capable of
reacting with polysaccharide hydroxyl groups to provide a
polysaccharide with a ds of at least 0.5; and
simultaneously or subsequently
(ii) reacting the derivatised polysaccharide with a cross-
linking agent to provide a degree of cross-linking
sufficient that the product remains insoluble in water.
DETAILED DESCRIPTION OF THE INVENTION
The polysaccnariae according to the present =nvention is
preferably based on cellulose, more preferably yibrous
cellulose, although the invention can also be applied to
other polysaccharides such as starch and natural products
based on saccharide units. The present invention car. be
applied to fibrous cellulose derived by any chemical and/or
mechanical treatment, for example cellulose fibres obtained
from wood pulp purified by the sulphate process or the
bisulphite process, cellulose fibres obtained from wood pulp
by thermomechanical or~mechanical treatment, beet cellulose,
regenerated cellulose or cotton !inters. Preferably the
cellulose fibres are obtained from wood pulp purified by the
sulphate process or as cellulose "fluff" derived from
mechanical treatment or wood pulp and are of the type
generally used for the preparation of absorbent pads in
disposable products, for example sanitary napkins and towels
and diapers. The invention may also be applied to cellulose
powders.

CA 02205026 1999-09-20
5a
The polysaccharide according to the invention ca:. De
prepared by a process which involves derivatisinc a
polysaccharide, preferably a fibrous polysaccharide, with
quaternary ammonium groups and cross-linking with a suitable
cross-linking agent. The derivatising and cross-linking can
generally be carried out under similar conditions so that it
is possible to carry out both reactions in a single~stage.
However, the reactions may become competitive so that it is
preferred to carry out the derivatising reaction as a first
stage, followed by cross-linking as a separate second stage.
This two stage approach allows greater control of the
reaction in terms of ds, degree of cross-linking, freedom
from undesired secondary products, etc.
According to another aspect, the present invention
provides a process for the production of a cationic

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6
polysaccharide, preferably a fibrous cationic polysaccharide,
having superabsorption characteristics which comprises:
( i ) reacting a polysaccharide with an excess of a quaternary
ammonium compound containing at least one group capable of
reacting with polysaccharide hydroxyl groups to provide a
polysaccharide with a ds of at least 0.5; and simultaneously
or subsequently
(ii) reacting the derivatised polysaccharide with a cross-
linking agent to provide a degree of cross-linking sufficient
that the product remains insoluble in water.
Preferably the polysaccharide is in fibrous form.
Preferably step (ii) is carried out subsequently to step
(i) with or without intermediate isolation of the product of
step (i). Use of the cross-linking agent in the process
according to the invention improves the yield of the process
by reducing the amount of soluble product which is obtained.
When the derivitisation reaction starts the polysaccharide
substrate is insoluble but after derivatisation all or part
of the substrate (depending on degree of substitution) may
become soluble. Cross-linking may cross-link soluble polymer
chains together or with insoluble polymer chains thereby
preventing loss of material by solubilisation.
The reaction with the quaternary ammonium compound is
generally carried out in the presence of base and preferably
in aqueous medium. However, other protic or aprotic solvents
for example alcohols, preferably lower alkanols such as
ethanol, propanol or isopropanol, or amides such as DMF, can
- also be used either alone or in admixture with water.
. Suitable bases include alkali and alkaline earth metal
hydroxides and alkoxides, for example the hydroxide,
methoxide, ethoxide, propoxide, isopropoxide, n-butoxide or
t-butoxide of an alkali metal such as potassium or preferably

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7
sodium.. The most preferred base is generally sodium
hydroxide.
Suitable quaternary ammonium compounds can be
represented by one of the following general formulae (I)
and ( I I )
R1 +
CH2 - CH - (CHR)n N - R2 Z- (I)
X OH R3
R1 +
CH2 CH - (CHR)n N R2 Z- (II)
R3
wherein n is an integer from 1 to 16;
X is halogen, in particular fluorine, chlorine, bromine or
iodine, preferably chlorine;
Z- is an anion which may be inorganic, for example halide
(fluoride, chloride, bromide or iodide, preferably chloride) ,
nitrate, nitrite; phosphate or hydroxide, or organic, for
example carboxylate such as acetate or propionate;
R, R1, R2 and R3, which may be the same or different, are
each an organic radical, preferably containing up to l0
carbon atoms, or preferably hydrogen; or additionally R2 may
represent a group of formula (III) or (IV):
R1 +
(CH2)P N - (CHR)n CH ---CH2 Z- (III)
R3 OH X

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8
Rl +
(CH2)p N (CHR)n CH - CH2 Z- (IV)
13
R O
in which p is an integer from 2 to 10: and
n, R, R1, R3, X and Z are as defined above.
The preferred meaning for each of R, R1, R2 and R3 is
hydrogen. When one of these groups is an organic radical
this should not contain any substituent having an
unacceptable adverse effect on the derivatisation reaction or
the subsequent cross-linking reaction or on the properties of
the material produced, for example superabsorbent properties.
Suitable organic groups include alkyl, hydroxyalkyl, alkenyl
and aryl. Large organic groups increase the molecular weight
of the product so that smaller groups are preferred. The
most preferred organic group is methyl or hydroxymethyl.
Many compounds having the above formulae are known or
can be prepared by conventional procedures. Some such
compounds are commercially available. Examples of suitable
quaternary ammonium compounds include:
glycidyltrimethylammonium chloride;
2,3-epoxypropyl-N,N,N-trimethylammonium chloride
(commercially available from Degussa A.G. as a 70% aqueous
solution under the name QUAB 151 or as the pure compound in
solid form from Fluka under product code 50045);
3-chloro-2-hydroxypropyl-N,N,N-trimethylammonium
chloride (commercially available from Degussa A.G. as a 65%
aqueous solution under the name of QUAB 188);

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9
3-chloro-2-hydroxypropyl-N,N,N-dimethylethanolammonium
chloride (commercially available from Degussa A.G. as a 650
aqueous solution under the name of QUAB 218);
1,3-bis-(3-chloro-2-hydroxypropyl-N,N-dimethylammonium)
N-propane dichloride (commercially available from Degussa
A.G. as a 65% aqueous solution under the name of QUAB 388);
A particularly preferred quaternary ammonium compound is
glycidyltrimethylammonium chloride.
The derivatisation reaction with the quaternary ammonium
compound can be carried out in a single step or as two or
more steps with or without intermediate separation and
purification of the product. In the or each step, the
reaction is carried out by contacting the polysaccharide with
the base, preferably in aqueous medium.
Typically, the quaternary ammonium compound is used in
excess, for example in a molar ratio based on saccharide
units in the polysaccharide of 5:1 to 40:1, more particularly
20:1 to 40:1. Where the derivatisation reaction is carried
out in two or more steps a molar ratio of 10:1 to 20:1
preferably applies in each step. The base, preferably sodium
hydroxide, is used in the or each step in a molar ratio of
1:3 to 3:1 based on hydroxyl groups in the monosaccharide
units and in a molar ratio of 5:100 to 300:100, preferably
100:100 to 300:100, based on the quaternary ammonium compound
where this is a compound of formula (I) or 10:100 to 50:100
where this is a compound of formula (II). The reaction
temperature for the or each step may be from 15 to 120oC,
preferably 70 to 100oC, and the reaction time overall may be
for example 1 to 20 hours . Where the derivatisation reaction
is carried our in two or more stages, the reaction time for
each stage will generally be 0.25 to 5 hours, preferably 0.25
to 2 hours.
The derivatised product may be isolated and purified by

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removing excess alkali by washing to neutrality, for example
with dilute, e.g. 4%, aqueous sodium chloride. The product
may then be converted to salt form by treatment with a strong
excess of acid, e.g. 4% aqueous hydrochloric acid, and washed
5 to neutral. The product is then dehydrated, for example with
acetone and recovered by filtration and/or centrifugation.
Derivatised polysaccharides prepared as described above
in which one or more of R1, R2 and R3 is hydrogen can
l0 subsequently be converted into the corresponding compounds in
which one or more of R1, R2 and R3 is a hydrocarbon group by
an N-alkylation reaction, for example with a compound of
formula RSHal where R5 is an optionally substituted
hydrocarbon group, for example alkyl, hydroxyalkyl or alkenyl
and Hal is halogen, more particularly fluorine, chlorine,
bromine or iodine, to effect quaternisation of some of all of
the ammonium groups.
As indicated above, the polysaccharide is cross-linked
either in the same reaction as the derivatisation reaction or
preferably subsequently thereto.
Suitable cross-linking agents for polysaccharides such
as cellulose include:
formaldehyde;
methylolated nitrogen compounds such as dimethylolurea
dimethylolethyleneurea and dimethylolimidazolidone;
diacarboxylic acids such a malefic acid;
dialdehydes such as glyoxal;
diepoxides such a 1,2:3,4-diepoxybutane and 1,2:5,6-
diepoxyhexane;
diisocyanates;
divinyl compounds such as divinylsulphone;
dihalogen compounds such as dichloroacetone,
dichloroacetic acid, 1,3-dichloropropan-2-ol,dichloroethane,
2,3-dibromo-1-propanol, 2,3-dichloro-1-propanol and 2,2
dichloroethyl ether;

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halohydrins such as epichlorohydrine;
bis(epoxypropyl)ether;
vinylcyclohexenedioxide;
ethylene glycol-bis(epoxypropyl)ether;
1,3-bis(f3-hydroxy-r-chloropropoxy)-2-propanol;
1,3-bis(i3-hydroxy-r-chloropropoxy)ethane;
methylenebis(acrylamide);
N,N'-dimethylol(methylenebis(acrylamide));
triacrylolhexahydrotriazine;
acrylamidomethylene chloroacetamide;
2,4,6-trichloropyrimidine;
2,4,5,6-tetrachloropyrimidine
cyanuric chloride;
triallylcyanurate
phosphorusoxychloride;
bis(acrylamido)acetic acid
For further information concerning suitable cross-
linking agents, reference can be made to US-A-3658613, US-A-
3589364, US-A-4066828 and US-A-4068068.
Preferred cross-linking agents include di-epoxy
compounds and haloepoxy compounds such as 1,3-bis
(glycidyldimethylammonium)propanedichloride and
epichlorohydrin.
Where the cross-linking and derivatisation reactions are
carried out together, the conditions are as described above
for the derivatisation reaction. Where the cross-linking
reaction is carried out as a subsequent step following the
derivatisation reaction, the reaction conditions are also
generally as described above for the derivatisation reaction.
The amount of cross-linking agent which is necessary will
depend on the nature of the agent, the starting material and
the conditions of the cross-linking reaction. In all cases
the reaction should be such as to provide a degree of cross-
linking which imparts the desired water insolubility to the

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12
polymer but does not interfere with the water absorption
properties of the polymer (superabsorbent properties)
imparted by the quaternary ammonium group.
Preferably the cross-linking reaction is carried out at
a temperature of 15 to 110oC, more preferably 35 to 85°C for
a time of 1 to 20 hours, preferably 2 to 10 hours.
The degree of substitution and the degree of cross-
linking can both be controlled by appropriate variation in
the amounts of starting materials and the reaction
conditions, in particular the concentration of the
derivatising and/or cross-linking reagent, reaction time,
amount of base, .reaction temperature, and the nature of the
substrate. Where the process according to the invention is
applied to a polysaccharide other than cellulose, then
appropriate modifications will need to be made to the
reaction conditions and, for example, it is known that starch
is generally more reactive than cellulose.
The process as described above :earls t~ the
polysaccharide derivative in base form as a :es::~; ~'_ :,..~.e use
of base (e.g. sodium hydroxide) as :.a~a:ys; _.. the
derivatisation -and cross-linking reactions. n general the
polysaccharide is required in salt form and this can be
prepared by treatment with strong acid (e . g . HC1 ) followed by
washing with water to neutral pH. If necessary, the
polysaccharide in salt form can be converted to base form by
treatment with strong base (e. g. NaOH) followed by washing
with water.
According to one embodiment of the invention, cellulose,
for example in the form of cellulose Kraft pulp, is
derivatised with glycidyltrimethylammonium chloride, for
example to a ds of about 0.65, and then cross-linked with
1,3-bis(glycidyldimethylammonium)propane dichloride in the
presence of sodium hydroxide. The reaction scheme can be
represented as follows:

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-13-
1 Derivatisation
nv
_ 0 0 Cellulose
l0
HO OH ---
O -~ C1~ + NaOH
C 1~
I
p HO OH
2 5 -~~.~- 4 0
0
HO OH OH
Cationic Cellulose

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-14-
2 Cross-Linkincr C1~ C1~
I~ O
+ NaOH
O
C 1~ C 1~
p '~ ~ p OH
I i
pH OH
OH
O O
OH I~ OH
OH
OH OH
C1'
O
The cationic cross-linked cellulose according to the
present invention can be prepared without a limitation on ds
imposed by increasing water solubility. The material can be
used as an absorbent for water or saline in either salt of
basic form.
In use in absorbing saline, for example in the form of
salt containing liquids such as urine or menses, there are
considerable advantages in using the polysaccharide according
to the invention in basic form. In this case, at the same
time as absorbing the liquid, the polymer also has a
desalting effect on the liquid by virtue of the fact that on
being placed in salt solution the quaternary ammonium groups
in basic form act as a strong anion exchanger and convert
spontaneously to salt form.

CA 02205026 2000-03-16
The absorbent according to the present -invention is
particularly suitable for use in applications where it is
desired to absorb salt containing aqueous liquids.
Examples of such liquids include in particular menses and
5 urine and particularly when in fibrous form the absorbent
material can be used as the filling in catamenials and
diapers, generally in admixture with a fibrous absorbent
such a cellulose fluff. The absorbent according to the
present invention, in base form can also be used in
10 conjunction with an anionic superabsorbent in free acid
form or a cation exchanger in acid form.
According to a further aspect the present invention
provides the use of a cationic polysaccharide, preferably
15 a fibrous cationic polysaccharide, as defined above as an
absorbent, more particularly as an absorbent in hygienic
and/or sanitary articles.
The invention is illustrated by the following
examples:

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Example 1
g of cellulose Kraft pulp were mixed with 6.7 g of
NaOH -and 28 ml distilled water. The mixture was cooled for
5 30 minutes in an ice-salt bath and 46.74 g of glycidyl
trimethyl ammonium chloride in 20 ml of distilled water were
added. The temperature was maintained at 80 to 85oC for 30
minutes with continuous stirring. After this time the same
quantity of glycidyl trimethyl ammonium chloride in water was
10 added and again the mixture was maintained at 80 to 85~C for
30 minutes with continuous stirring. The procedure was
repeated a further three times (a total of 5 additions of
glycidyl trimethyl ammonium chloride).
The sample was then washed with NaCl (4% in water: 2
litres) and filtered under vacuum using a Buchner filter
(water pump vacuum). The sample was transferred to a 5 litre
vessel and treated with 2.5 litres of 4% hydrochloric acid
followed by filtration as previously described. The sample
was then washed with water to neutral pH, filtered as
previously described and then dried by adding a large amount
of acetone. The ds of the product at this stage (defined as
the number of quaternary ammonium groups per cellulose
anhydroglucose units and measured as described in WO
92/19652) was 0.65.
a) 1 g of the derivatised product was mixed with 5 ml of
19% aqueous sodium hydroxide. C.88 g of a 65% aqueous
solution of 1,3-bis(glycidyl dimethyl ammonium)propane
dichloride was added under stirring at room temperature and
maintained under these conditions for 16 hours. The sample
was the washed with water to neutral pH and lyophilised.
The sample had an absorbency (tea-bag test as described
below) of 54 (after draining) and 29 (after centrifugation at
60 g) .

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b) The experiment of (a) above was repeated but using an
amount of cross-linking agent reduced by half.
The sample had an absorbency ( tea-bag test ) of 21 ( of ter
draining) and 18 (after centrifugation at 60 g).
The tea-bag test was performed by weighing about 0.3 g
of the product into a tea-bag envelope which was itself then
weighed and immersed in 150 ml of liquid (1% NaCl Solution or
distilled water) in a 250 ml beaker for 1 hour. The envelope
was then removed from the liquid and allowed to drain for 10
minutes, weighed, and then centrifuged at 60 g for 10 minutes
and weighed again. Absorbency is calculated as follows:
A = (Wwet - wdry) /G
where:
A - absorbency (after draining or centrifugation);
Wwet - weight of envelope containing sample after
draining or centrifugation (grams);
Wdry - weight of envelope containing sample before
immersion (grams);
G - weight of sample used for the test (grams).
Use of distilled water in the above test gives a measure of
maximum swelling power whereas saline gives a reduced figure
which is more predictive of the behaviour of the material in
practice.
Example 2
(a) 10 g cellulose powder (Farmitalia Carlo Erba SpA, Rome,
Italy) were mixed with 6.5 g NaOH dissolved in 28 ml
distilled water. The mixture was cooled for 30 minutes in an
ice-salt bath and 46.74 g of glycidyl trimethyl ammonium
chloride in 20 ml of distilled water were added. The

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-18-
temperature was maintained at 80°C for 30 minutes with
continuous stirring. The same quantity of glycidyltrimethyl
ammonium chloride in water was then added and again the
mixture was maintained at 80°C for 30 minutes. The procedure
was then repeated twice more (a total of 4 additions of
glycidyltrimethyl ammonium chloride). The product was
purified by the method described in Example 1 and the product
had a ds of 0.53.
(b) 0.5 g of the purified product was mixed with 2.5 ml of
19% NaOH and 0.44 ml of 650 1,3-bis(3-chloro-2-
hydroxylpropyl)dimethylammonium propane dichloride in water
with continuous stirring for 5 hours. The temperature was
maintained at 25°C and after addition of 10 ml of distilled
water the temperature was maintained for 16 hours. The gel
obtained was purified as described in Example 1 and
lyophilized.
The product had an absorbency (tea-bag test in
accordance with Example 1) of 50 (after draining) and 39
(after centrifugation).
Exam le 3
(a) The procedure of Example 2(a) was repeated to produce a
different sample of essentially the same product but with a
ds of 0.50.
(b) The procedure was as in Example 2(b) except the
temperature was maintained at 20°C.
The product had an absorbency (tea-bag test in
accordance with Example 1) of 34 (after draining) and 29
(after centrifugation) .
In summary the results obtained were as follows:

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Product ds of ratio of Absorbency
inter- inter-
mediate mediate
after after
to cross-
draining
centri-
linker
fugation
Example 0.65 2.5:1 54 29
1 (a)
Example 0.65 5:1 21 18
1 (b)
Example 0.53 2.5:1 50 39
2 (b)
Example 0.5 2.5:1 34 29
3 (b)
ds of the intermediates is measured as described in WO
92/19652. The ds of the final product was not measured but
would not be expected to differ significantly from the
intermediate.

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Comparative Example
The product of Example 2 of WO 92/19652 had a ds 0.64,
and an absorbency (tea-bag test in accordance with Example 1)
of 42.9 (after draining) and 23.2 (after centrifugation) .
0.25 g of the same product in a tea-bag type envelope is
placed in 1 litre of 0.1 N NaOH (aqueous solution) for 10
hours with mechanical stirring and is then washed with water
to neutrality and dried with acetone to produce the product
in unsalified form which had an absorbency of 42.9 (after
draining) and 23.2 (after centrifugation).
The products of Examples 1(a) and 1(b) show improved gel
strength and are obtained in improved yield relative to
WO 92/19652. The products of Examples 2(b) and 3(b) were
obtained from intermediates which were soluble.