U.S. patent application number 10/878459 was filed with the patent office on 2004-11-25 for acidic superabsorbent polysaccharides.
Invention is credited to Bemporad, Luca, Besemer, Arie Cornelis, Kalentuin, Pia, Schraven, Bas, Thiewes, Harm Jan, Thornton, Jeffrey Wilson, Van Brussel-Verreast, Dorine Lisa, Verwiiligen, Anne-Mieke Yvonne Wilhelmina.
Application Number | 20040236016 10/878459 |
Document ID | / |
Family ID | 27239452 |
Filed Date | 2004-11-25 |
United States Patent
Application |
20040236016 |
Kind Code |
A1 |
Thornton, Jeffrey Wilson ;
et al. |
November 25, 2004 |
Acidic superabsorbent polysaccharides
Abstract
A process is disclosed for producing an acidic superabsorbent
polysaccharide derivative, comprising the steps of. (a)
crosslinking at least one polysaceharide containing acidic groups,
such as carboxymethyl cellulose and/or 6-carboxy stanch, with a
crosslinking agent to produce a gel; (b) if necessary, adjusting
the pH of the polysaccharide to a value between 3.5 and 5.5; (c)
comminuting the acidified polysaccharide gel; and (d) drying the
comminuted polysaccharide at elevated temperature. The
superabsorbent polysaccharide obtainable by this process has a pH
below 5 and provides odour control when contacted with malodorous
fluids.
Inventors: |
Thornton, Jeffrey Wilson;
(Huizen, NL) ; Schraven, Bas; (Nijmegen, NL)
; Thiewes, Harm Jan; (Woudenberg, NL) ; Van
Brussel-Verreast, Dorine Lisa; (Bodegraven, NL) ;
Bemporad, Luca; (Gothenburg, SE) ; Verwiiligen,
Anne-Mieke Yvonne Wilhelmina; (Zeist, NL) ; Besemer,
Arie Cornelis; (Amerongen, NL) ; Kalentuin, Pia;
(Torslanda, SE) |
Correspondence
Address: |
BURNS DOANE SWECKER & MATHIS L L P
POST OFFICE BOX 1404
ALEXANDRIA
VA
22313-1404
US
|
Family ID: |
27239452 |
Appl. No.: |
10/878459 |
Filed: |
June 28, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10878459 |
Jun 28, 2004 |
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09868139 |
Sep 19, 2001 |
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6765042 |
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09868139 |
Sep 19, 2001 |
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PCT/NL99/00776 |
Dec 16, 1999 |
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Current U.S.
Class: |
525/54.3 ;
525/54.31 |
Current CPC
Class: |
A61L 15/28 20130101;
A61L 15/60 20130101; C08B 15/005 20130101; Y10S 526/903 20130101;
A61L 15/28 20130101; C08L 1/26 20130101; A61L 15/28 20130101; C08L
3/04 20130101 |
Class at
Publication: |
525/054.3 ;
525/054.31 |
International
Class: |
C08F 002/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 16, 1998 |
EP |
98204273.1 |
Apr 23, 1999 |
EP |
99201286.4 |
Jun 15, 1999 |
EP |
99201915.8 |
Claims
1-15. (Cancelled)
16. A superabsorbent polysaccharide derivative obtained by the
process of: (a) crosslinking at least one polysaccharide containing
acidic groups with a crosslinking agent to produce a gel; (b)
ensuring that the pH of the polysaccharide is between 3.5 and 5.5;
(c) comminuting the acidified polysaccharide gel; and (d) drying
the comminuted polysaccharide at elevated temperature; the
superabsorbent polysaccharide derivative, when wetted, having a pH
below 5.
17. A superabsorbent polysaccharide derivative according claim 16,
also comprising an acid selected from organic di- and
polycarboxylic acids, hydroxycarboxylic acids and benzoic
acids.
18. An absorbent article comprising a superabsorbent polysaccharide
derivative according to claim 16.
19. A superabsorbent polysaccharide derivative, the polysaccharide
derivative containing acidic groups and being crosslinked,
comminuted and dried, and, when wetted, having a pH below 5.
20. A superabsorbent polysaccharide derivative according to claim
19, also comprising an acid selected from organic di- and
polycarboxylic acids, hydroxycarboxylic acids and benzoic
acids.
21. A superabsorbent polysaccharide derivative according to claim
19, in which the polysaccharide containing acidic groups comprises
carboxymethyl-cellulose.
22. A superabsorbent polysaccharide derivative according to claim
19, in which the polysaccharide containing acidic groups is a
carboxymethyl polysaccharide further containing carboxyl groups
resulting from oxidation of saccharidic hydroxymethyl or
hydroxymethylene groups, or phosphonic or sulphonic acid
groups.
23. A superabsorbent polysaccharide derivative according to claim
19, in which the polysaccharide containing acidic groups comprises
a 6-carboxy polysaccharide.
24. A superabsorbent polysaccharide derivative according to claim
23, in which the polysaccharide containing acidic groups comprises
a 6-carboxy polysaccharide mixed with a carboxyalkylated
polysaccharide.
25. A superabsorbent polysaccharide derivative according to claim
19, in which the polysaccharide containing acidic groups contains
0.3-3.0 carboxyl groups per monosaccharide unit.
26. An absorbent hygiene article comprising a superabsorbent
polysaccharide, the polysaccharide containing acidic groups and
being crosslinked, comminuted and dried, and, when wetted, having a
pH below 5.
27. An absorbent hygiene article according to claim 26, in which
the polysaccharide containing acidic groups contains 0.3-3.0
carboxyl groups per monosaccharide unit.
28. An absorbent hygiene article according to claim 26, in which
the polysaccharide containing acidic groups comprises 6-carboxy
starch.
29. A method of absorbing liquids, comprising contacting the liquid
with a superabsorbent polysaccharide derivative, the polysaccharide
derivative containing acidic groups and being crosslinked,
comminuted and dried, and, when wetted, having a pH below 5.
Description
[0001] The present invention relates to a superabsorbent material
which has enhanced odour control and prevents bacterial growth,
based on polysaccharides, and to a method of producing such
material.
[0002] Superabsorbent materials of various types are known in the
art. Examples are crosslinked polyacrylates and polysaccharides
grafted with polyacrylates. A problem related to the use of
superabsorbent materials is the odour caused by urine components
which cause superabsorbent materials to become objectionable long
before their maximum absorbing capacity has been used. Furthermore,
the known absorbent materials are normally based on non-renewable
and/or non-biodegradable raw materials. Consequently, there is a
need for superabsorbent materials, which have odour control and
reduced bacterial growth when contacted with body fluids, and which
are biodegradable.
[0003] WO 98/27117 discloses a superabsorbent polysaccharide
derivative obtained by oxidation and crosslinking of a
polysaccharide such as starch, in which at least 0.1 carbinol group
per monosaccharide unit of the polysaccharide derivative has been
oxidised to a carboxyl group, the total number of carboxyl groups
per monosaccharide unit being 0.2-3.0, and the derivative results
from reaction with at least 0.001 equivalent of crosslinking agent
per monosaccharide unit. The derivatives are not devised for odour
control. U.S. Pat. No. 5,247,072 describes superabsorbent
carboxyalkyl polysaccharides, especially carboxymethyl cellulose,
without odour control, obtained by crosslinking as a result of heat
treatment. EP-A-202127 discloses superabsorbent articles for
reducing diaper rash, which contain acid in distinct zones to
control the skin pH between 3.0 and 5.5.
[0004] It has been found that a superabsorbent polymer with
improved odour control can be produced by a process comprising the
steps of:
[0005] (a) crosslinking at least one polysaccharide containing
acidic groups with a crosslinking agent to produce a gel;
[0006] (b) ensuring that pH of the polysaccharide is between 3.5
and 5.5 and, if necessary, adjusting the pH to between 3.5 and 5.5,
especially to between 3.9 and 4.9;
[0007] (c) comminuting the acidified polysaccharide gel; and
[0008] (d) drying the comminuted polysaccharide at elevated
temperature.
[0009] The term "polysaccharide containing acidic groups" is
understood to comprise polysaccharides having a pK of less than 5,
down to about 1.5. Such polysaccharides may contain carboxylic
groups, sulphonic groups (--(O)--SO.sub.2--OH), phosphonic groups
(--(O)--PO(OH).sub.2), ammonium groups (--NR.sub.2H.sup.+, wherein
R is alkyl or hydrogen) and combinations thereof The carboxylic
groups may be present as a result of carboxyalkylation, in
particular carboxymethylation, or as a result of reaction with an
anhydride such as maleic or succulic anhydride or as a result of
oxidation, e.g. of a hydroxymethyl group (--CH.sub.2OH, usually at
C6 of a monosaccharide unit), or of a bis(hydroxymethylene) group
(--CHOH--CHOH--, usually at C2-C3 of a monosaccharide unit).
[0010] The phosphonic groups may be present as phosphate groups,
resulting e.g. from reaction with phosphorylating agents (see e.g.
WO 97/28298), or as phosphonic or phosphinic acid groups, resulting
e.g. from reaction with halomethyl phosphonic acids. The sulphonic
acids may be present e.g as sulphate groups or as a result of
sulphite addition to polysaccharide aldehydes (see e.g. WO
99/29354) or to maleic anhydride adducts (products with
--O--CO--CH--CH(COOH)--SO.sub.3H groups). The ammonium groups are
also acidic groups, and can result from protonation of amine
groups, such as in chitosan-type polysaccharides or in
aminoalkylated polysaccharides.
[0011] The polysaccharides may be .alpha.-glucans like starch,
amylose and amylopectin, .beta.-glucans like cellulose and chitin
and scleroglucan, galactomannans like guar gum (guaran) and locust
bean gum, glucomannans including e.g. xanthan gum, fructans,
(arabino)xylans, galactans including alginates and pectin and other
mixed polysaccharides. Starch and cellulose are particularly
preferred. Starch may be derived from any suitable source, such as
corn, wheat, potato, rice and the like; it may also be a residual,
crude or lower-grade starch product containing minor amounts of
other biopolymers such as cellulose, pectin or protein. Cellulose
may also contain minor amounts of other materials such as
hemicellulose.
[0012] The polysaccharides may comprise non-ionic, non-carboxylated
derivatives such as hydroxyalkyl polysaccharides, but the presence
of such non-ionic derivatives does not have a particular advantage.
The chain length of the polysaccharides is important although there
is no critical minimum for the molecular weight. In general,
polysaccharides having a molecular weight of more than 1,000 are
preferred. A molecular weight above about 25,000 may have a
positive effect on the properties of the oxidised product.
[0013] The acidic polysaccharide can be a carboxymethyl
polysaccharide without further substitution, such as carboxyrnethyl
cellulose, preferably having a degree of substitution of 0.3-3.0,
more preferably 0.5-1.5. For such carboxymethylated
polysaccharides, the process advantageously comprises the further
step of contacting the crosslinked polysaccharide with an organic
solvent which is at least partly miscible with water, between step
(b) and step (c). The organic solvent is preferably a
water-rmiscible alcohol such as methanol, ethanol, methoxyethanol
or isopropanol, a water-miscible ether such as dioxane,
tetrahydrofiran or dimethoxyethane, or a water-miscible ketone,
such as acetone. Most preferred are methanol and ethanol. The
amount of solvent can be e.g. 2-30 times the amount of the gelled
poly-saccharide. The water-miscible solvent is evaporated before or
during step (d).
[0014] The carboxymethylated polysaccharide can also be a
carboxyrnethyl polysaccharide containing further carboxyl groups
produced by oxidation of saccharide carbinol groups. Such carboxyl
groups may be 2- and/or 3-carboxyl groups obtained by oxidation of
anhydroglycose rings of the polysaccharide using hypochliorite or
periodate/chlorite, but preferably they are 6-carboxyl groups
obtained by oxidation of the 6-hydroxymethyl group, e.g. with a
nitroxyl compound (TEMPO) as a catalyst In such
carboxy-carboxymethyl poly-saccharide, such as
6-carboxycarboxymethyl starch or 6-carboxy-carboxymethyl-cellulose,
the degree of substitution for carboxymethyl is preferably 0.2-0.8,
especially 0.3-0.6, and the degree of subtitution for (6-carboxyl
groups is preferably 0.1-0.5, more preferably 0.15-0.4.
[0015] Suitable oxidation methods are described in WO 98/27117 and
references cited therein. TEMPO oxidation may be performed with
hypochlorite with or without bromide as a catalyst, or with
peracid/bromide or another oxidant. Unsubstituted TEMPO or
4-hydroxy or 4-acetamido-TEMPO or mixtures thereof may be used.
When oxidations resulting in salt production are used, the salts
may advantageously be removed after the oxidation reaction.
[0016] Similarly, the acidic polysaccharide may contain both other
acidic groups obtained by substitution, and carboxyl groups
obtained by oxidation. Such other acidic groups obtained by
oxidation include e.g. phosphonic groups obtained by
phosphorylation of the polysaccharide, sulphonyl groups and
carboxyalkylcarbonyl groups obtained by reaction with a
dicarboxylic anhydride. Substitution and oxidation may be performed
in either order, e.g. first phosphorylation and then oxidation, or
first oxidation and then phosphorylation. Combinations of different
acidic substituents e.g. carboxylalkyl groups and phosphonic groups
are also suitable.
[0017] In such oxidised and subsituted (carboxyalkyl or other)
polysaccharides the addition of an organic water-miscible solvent
can be dispensed with, as a gel with the required structure already
results from direct cross-linking.
[0018] The polysaccharide containing acidic groups can also be a
carboxylated poly-saccharide wherein the carboxyl groups have been
introduced by oxidation of saccharide carbinol groups in a manner
as described above, without carboxyalkylation. Such oxidised
polysaccharides include dicarboxy polysaccharides (obtained by
C2-C3 oxidation) and, especially 6-carboxy polysaccharides, e.g.
obtained by TEMPO oxidation, especially 6-carboxy starch. These
polysaccharides do not require the use of a water-miscible solvent
after crosslinking.
[0019] The polysaccharide containing acidic groups may also be a
mixture of acidic poly-saccharides as described above. A
particularly useful mixture is a mixture of carboxymethyl cellulose
and 6-carboxy starch, e.g. in a ratio of between 1:1 and 1:20.
Other mixtures are also quite useful, e.g. carboxymethyl cellulose
and carboxymethyl starch, or carboxymethyl starch and cellulose
phosphate having a degree of substitution of about 0.3 to about
0.5.
[0020] The polysaccharide containing acidic groups is reacted with
a crosslinking agent to produce a gel. A gel is defined herein as a
polymeric network based on polysaccharides, which swells in water
and does not dissolve in water. Crosslinking agents are reagents
containing two or more functions capable of reacting with a
hydroxyl group, resulting in intra- and inter-molecular bonds
between different mono-saccharide units. Suitable cross-linking
agents may act on the hydroxyl groups of different polysaccharide
chains and include divinyl sulphone, epichlorohydrin,
diepoxybutane, diglycidyl ethers, diisocyanates, cyanuric chloride,
trimetaphosphates, phosphoryl chloride, and mixed anhydrides, and
also inorganic crosslinkers such as aluminium and zirconium ions,
but are not restricted to these examples. Mixtures of crosslinkers
may also be used.
[0021] Especially preferred crosslinkers, in particular for
crosslinking at elevated temperature and/or concentration, are
crosslinkers that are active under neutral or acidic conditions,
such as bis-epoxy crosslinkers, for example diepoxybutane,
1,5-diepoxyhexane, 1,7-diepoxyoctane, bis-glycidyl ether, glycol
bis-glycidyl ether, butanediol bis-glycidyl ether and the like, as
well as mixtures of different crosslinkers. Crosslinking can also
be performed using carboxyl or aldehyde groups formed by oxidation
or carboxyl groups introduced by carboxyalkylation, e.g. using
polyols, polyamines or other polyfunctional reagents.
Esterification and other crosslinking methods described herein can
also be effected intramolecularly at the surface between the
carboxyl group of one polysaccharide chain and a hydroxyl group of
another chain as known in the art. This interhain crosslinking can
be catalysed by an acid or a multivalent ion such as magnesium or
calcium, or by heating. Divinyl sulphone is another preferred
crosslinker. Crosslinking of starch and other poly-saccharides is
well-known in the art. A description of crosslinking agents and
reaction conditions can be found e.g. in "Starch Derivatives:
Production and Uses" by M. W. Rutenberg and D. Solarek, Acad. Press
Inc., 1984, pages 324-332.
[0022] According to a preferred embodiment of the invention,
crosslinking is performed under conditions of increased
temperatures and high concentrations. The temperatures are
typically at least 100.degree. C., more preferably between 120 and
180.degree. C. The concentration of the polysaccharide to be
crosslinked is at least 20% by weight, more particularly between 25
and 65% by weight with respect to the total aqueous crosslinking
mixture. The crosslinking mixture may further contain a plasticiser
such as a polyol. Suitable polyol plasticisers include glycerol,
ethylene glycol, propylene glycol, polyethylene glycol,
polypropylene glycol, glycol and glycerol monoesters, sorbitol,
mannitol, monosaccharides, citric acid monoesters and the like. The
amount of plasticiser may vary from 1 to 25% weight of the
crosslinking mixture. The crosslinking can be conveniently
performed in a kneading apparatus or an extruder under conditions
of reactive processing. The various components of the crosslinking
mixture can be mixed before entering the extruder, or one or more
of them, e.g. the crosslinking agent, may be added at a later stage
in the extruder.
[0023] After crosslinking, the crosslinked polysaccharide is
treated with an acid so as to reduce the pH to 3.5 to 5.5. However,
if the crosslinking is performed under acidic conditions, such as
with bis-epoxy crosslinkers, the acidification takes place before
cross-linking, and an adjustment of a pH to between 3.5 and 5.5 may
or may not be needed after the crosslinking step. Suitable
acidifying reagents include inorganic and organic acids such as
hydrochloric, phosphoric, acetic acid etc. If crosslinking is
performed under normal conditions (ambient temperature or up to
about 100.degree. C., atmospheric pressure, lower concentration) or
before acidification, it is preferred that the polysaccharide is
acidified to pH 4.9 or lower. After acidification, the
cross-linked, gel-like material is comminuted to smaller particles,
e.g. in the range of 0.5-5 mm.
[0024] Instead of or in addition to the treatment with the
water-miscible organic solvent described above, an additional
post-crosslinking step (surface crosslinking) may be applied to
strengthen the gel. This post-crosslinking may be performed after
the comminuting step c or even after the drying step d, resulting
in different swelling degrees of the gel particles obtained. The
crosslinking agent to be used in this post-crosslinking step can be
the same as those referred to above for the first crosslinking
step. In this procedure, the gel particles are slightly swollen,
and treated and mixed with a crosslinking agent, and subsequently
the particles are dried at a temperature which depends on the
liquid used to swell the gel particles and on the crosslinking
agent. The post-crosslinking may be performed in the presence of
compounds providing further crosslinks at the outside of the gel
particle. Such compounds may include bifunctional or
multifunctional capable of reacting with hydroxyl and (if still
present) carboxyl functions, for example diamines, polyamines,
polyamide-amine-epichlorohydrin (PAE resin), bis-epoxy compounds,
chitosan-like compounds, metal salts (zirconium, aluminium),
dialdehydes, or polyaldehyde-polycarboxy starch derivatives.
[0025] The comminuted material is dried, preferably in a fluidised
bed drier. Drying can be performed at ambient temperatures, but
preferably increased temperatures are used, in particular above
50.degree. C., more in particular above 70.degree. C. Drying times
from 15 minutes up to 8 hours or more can be applied. Preferably an
additional heat treatment is performed after the initial (fluidised
bed) drying; this additional drying step can be performed at
80-150.degree. C. e.g. for 2 minutes to 2 hours, and results in a
further enhanced gel strength of the product.
[0026] The invention also pertains to a bacteriologically stable
superabsorbent poly-saccharide derivative having odour control of
absorbed liquid, as well as to a superabsorbent article in which
this derivative is incorporated. The derivative and the article
preferably have a pH below 5 (down to 3.5) when contacted with
neutral or near-neutral water; if necessary, an acidifying agent
can be incorporated in a sufficient amount to maintain the required
low pH. Suitable acidifying agents include organic di- or
poly-carboxylic acids such as citric, maleic, fulmaric, oxalic,
malonic, succinic, tataric and similar acids, hydroxyacids such as
gluconic, ascorbic, glycolic, glyceric, lactic, malic, salicylic
acid and the like, as well as benzoic acid and phosphoric and other
inorganic acids. These acids may be used in combination with their
partially neutralised salts (e.g. monosodium citrate or
monopotassium phosphate) to provide buffering capacity. Also,
neutral materials such as acid anhydrides and lactones, e.g. maleid
anhydride, succinic anhydride, .delta.-gluconolactone, can be
incorporated for lowering the pH.
[0027] The superabsorbent polysaccharides combine high absorption
capacity with control of bacterial growth and control of odour, as
well as with biodegradability. The absorption capacity can be
expressed as free swelling capacity (FSC) and the centrifugal
retention capacity (CRC), and with the absorption under load (AUL),
using synthetic urine (SU) as test liquid. The composition of the
synthetic urine is as follows: 300 mM urea, 60 mM KCl, 130 mM.
NaCl, 2.0 mM CaSO.sub.4.2H.sub.2O, 3.5 mM MgSO.sub.4, and 1 mg/l
Triton X-100 in deionised water.
[0028] The superabsorbent polysaccharide derivatives of the
invention can be used for absorbing liquids, especially of body
fluids which contain various salts and non-ionic substances. The
product is particularly suitable for the production of absorbent
hygiene articles, such as diapers, sanitary napkins and the like.
Such articles can be produced entirely on the basis of the
polysaccharides according to the invention, but they can also
contain conventional absorbent materials, such as cellulose pulp in
addition to the absorbents according to the invention. The
absorbent article is preferably part of a layered product, in which
the superabsorbent polymer constitutes at least one layer. The
absorbent layer can be located between a liquid-pervious top layer
and a liquid-impervious bottom layer. In particular the product may
have four layers. The first one can be a thin, non-woven layer of
polyester fibres or other fibres. The second layer can be a wadding
which is used for acquiring and spreading the absorbed fluid such
as urine. The third layer can consist of fluff pulp wherein the SAP
is spread as fine particles, especially 50-800 .mu.m. The last
layer can be a back sheet of a water-resistant material such as
polyethylene, which prevents leakage from the layered absorption
product.
EXAMPLE 1
Absorbent 6-carboxy-carboxymethyl Potato Starch
[0029] Carboxymethyl starch (degree of substitution 0.5) derived
from potato starch was converted to 6-carboxy carboxymethyl starch
by TEMPO-catalysed oxidation (degree of oxidation 0.25). A 20%
aqueous solution of the product was cross-linked with different
amounts of divinyl sulphone (0.5, 0.6, 0.7 mol % DVS). After 15
hours, an insoluble network was formed. The gel was brought into
distilled water and allowed to swell. The pH of the material was
lowered to pH 4.1 by controlled addition of 1M HCl. After
equilibration, the gel was filtrated and dried in a fluidised bed
drier at 70.degree. C. The following absorption characteristics
(FSC, CRC, AUL at 2.0 kPa) measured in synthetic urine (SU) were
obtained:
1 Cross-linking degree AUL (g/g) (mol % DVS) FSC (g/g) CRC (g/g) 2
kPa pH gel 0.5 31 19 12 4.1 0.6 30 18 14 4.1 0.7 27.5 17 18.5
4.1
EXAMPLE 2
Absorbent 6-carboxy-carboxymethyl High Amylose Corn Starch
[0030] Carboxymethyl starch (degree of substitution 0.53) derived
from high amylose corn starch was converted to 6-carboxy
carboxymethyl starch by TEMPO-catalysed oxidation (degree of
oxidation 0.09). A 20% aqueous solution of the product was
cross-linked with different amounts of divinyl sulphone (1.0, 1.5,
2.0, 2.5 mol % DVS). After 16 hours, an insoluble network was
formed. The gel was brought into distilled water and allowed to
swell. The pH of the material was lowered to about pH 4.1 by
controlled addition of 1M HCl. After equilibration, the gel was
filtrated and dried in a fluidised bed drier at 80.degree. C. The
above table summarises the absorption characteristics (FSC, CRC,
AUL) measured in synthetic urine (SU) as obtained.
2 Cross-linking degree AUL (g/g) (mol % DVS) FSC (g/g) CRC (g/g) 2
kPa pH gel 1.0 29.5 20 17 4.0 1.5 34.5 20.5 13 4.1 2.0 33.0 18 16
4.3 2.5 28.5 16 17 4.0
EXAMPLE 3
Absorbent carboxymethyl cellulose Treated with Methanol
[0031]
3 XL reaction.sup.2 FBD FSC CRC AUL DXL.sup.1 cond. (.degree. C./h)
(.degree. C./min) (g/g) (g/g) (g/g) 10 20.degree./20 h.sup.3
100.degree./10 m 29 11 17 10 20.degree./20 h 100.degree./10 m 34 16
22 10 80.degree./3 h 100.degree./10 m 38 18 20 20 50.degree./8 h
100.degree./10 m 19.5 6.5 14 10 50.degree./8 h 100.degree./10 m
28.5 12 19.5 5 50.degree./8 h 100.degree./10 m 31.5 15 20.5 5
50.degree./15 h 100.degree./15 m 34.5 18 23 5 50.degree./15 h
80.degree./15 m 40 19.5 21 5 50.degree./15 h 60.degree./15 m 34
15.5 20 5 50.degree./15 h 40.degree./30 m 33 15 18.5 .sup.1degree
of crosslinking used, (mol % BDDE) .sup.2crosslinking reaction
.sup.3pH controlled by acetic acid instead of HCl.
[0032] A 2 wt. % aqueous solution of CMC (Cekol 50,000 from Metsa
Specialty Chemicals, degree of substitution 0.8) was prepared and
the pH was adjusted to 4.0 by slow addition of HCl under stirring
(alternatively, glacial acetic acid can be used according to WO
86/00912, example 2b). The required amount of a 10 or 20 vol. %
aqueous solution of 1,4-butanediol diglycidyl ether (BDDE) was
added and the reaction mixture was thoroughly mixed. The gel
obtained was cut into pieces and suspended overnight in a fivefold
excess of methanol. The methanol was filtered out and the gel was
milled in a blender, and the particles were dried in a fluidised
bed drier (FBD). The dried product was ground in a mortar. The
absorption characteristics for synthetic urine (SU) are summarised
in the table above, with details on crosslinking and drying.
EXAMPLE 4
Absorbent carboxymetlzyl cellulose Treated with Methanol
[0033] A 2 wt. % solution of CMC (Cekol 50,000 from Metsa Specialty
Chemicals, degree of substitution 0.8) in 0.05 M aqueous NaOH was
reacted with 14 mol % of DVS for 18 hours at room temperature. The
gel obtained was chopped in pieces of roughly 3-4 cm and the pieces
were brought in a fivefold excess of methanol. The gel was then
acidified using 1M HCl to a pH varying from 4.4 to 4.0. After about
24 h the swollen gel was milled in a blender to obtain smaller
particles, and then put back in the methanol for another 24 h to
achieve homogeneous acidification of the gel material. Thereafter
ground particles were dried in a fluidised bed drier at 100.degree.
C. for 30 min, and then further heat-treated at 120.degree. C. in
an oven for about 30 min. The absorption characteristics for SU are
summarised in the following table.
4 before After thermal treatment thermal treatment amount of acid
FSC CRC AUL FSC CRC AUL added (ml) pH gel (g/g) (g/g) (g/g) (g/g)
(g/g) (g/g) 28 4.4 83 64 10 40 26 17 30 4.2 57 42 12 29 17 16.5 33
4.0 55 41 13 28 15 16 35 4.0 39 26 13 21 11 15
EXAMPLE 5
Absorbent carboxymethyl cellulose Treated with Ethanol
[0034] Ten grams of CMC (Cekol 50,000) were dissolved in 500 ml
NaOH (0.05 mol/l). At room temperature 0.62 ml DVS (14 mol %) was
added under stirring. After 18 hours the crosslinked gel (450 g)
was chopped into pieces and 28 ml of 1 mol/l HCl was added and
thoroughly mixed to decrease the pH of the gel to 4.4. After 1 h
1400 ml of ethanol was added. After one week, the precipitated gel
was ground with a blender and dried in an FBD for 30 minutes at
100.degree. C. The dry particles were milled and sieved to obtain a
final particle size of 100-800 .mu.m. The following absorption
characteristics (FSC, CRC, AUL) measured in synthetic urine were
obtained: FSC: 132 g/g; CRC: 111 g/g; AUL: 11 g/g; pH gel 4.4.
EXAMPLE 5a
Absorbent carboxymetlyl cellulose Treated with Ethanol
[0035] In addition to the sample of example 5, a heat treatment was
applied for 30 minutes at 120.degree. C. in an oven to improve the
gel strength (AUL). The following absorption characteristics
measured in synthetic urine were obtained: FSC: 52 g/g; CRC: 37
g/g; AUL: 17 g/g; pH gel 4.5.
EXAMPLE 6
Absorbent carboxymethyl cellulose Treated with Ethanol
[0036] Ten grams of CMC (Cekol 50,000, DS 0.8) were dissolved in
500 ml water and 8.5 ml 1 mol/l HCl (pH 4.4). Then 1.27 ml of 20%
(v/v) BDDE in water (3 mol %) was added with stirring. After 8
hours at 50.degree. C., the crosslinked gel was suspended in a
threefold volume of ethanol with stirring. After one week, the
precipitated gel was ground into small pieces with a blender and
dried in a FBD for 15 minutes at 100.degree. C. The dry particles
were milled and sieved to obtain a final particle size of 100-800
.mu.m. The following absorption characteristics measured in
synthetic urine were obtained: FSX: 21 g/g; CRC: 13 g/g; AUL: 18
g/g; pH gel 4.3.
EXAMPLE 7
Absorbent 6-carboxy Starch/CMC Crosslinked under Alkaline
Conditions
[0037] Five g of TEMPO-oxidised starch (TOS, degree of oxidation
0.70) and 0.4 g of CMC (Cekol 50,000 from Metsa Specialty
Chemicals, degree of substitution 0.8) were dissolved in 20 ml of
0.05 M aqueous NaOH (pH 12) under mechanical stirring for 4 h. The
mixture was crosslinked with 0.8 mol % of DVS (23 .mu.l) at
5.degree. C. for 18 hours. Three g of the gel obtained was chopped
in pieces and the pieces were brought in 600 ml of demi water and
acidified with 1.8 ml of 1M HCl with mild stirring (stepwise
addition of acid). The next day, the swollen gel was filtered over
a 80 .mu.m sieve, and brought in another 600 ml of demi water for
half an hour. Subsequently the gel was dried in a fluidised bed
drier at 80.degree. C. for 1 hour. The material was characterised
in synthetic urine with the following results: 93% TOS/7% CMC: FSX:
30 g/g, CRC: 17 g/g. AUL: 16.5 g/g, pH gel 4.6.
EXAMPLE 8
Absorbent 6-carboxy Starch/CMC Crosslinked under Acidic
Conditions
[0038] Five g of TEMPO-oxidised starch (TOS, degree of oxidation
0.70) and 0.4 g of CMC (Cekol 50,000 from Metsa Specialty
Chemicals, degree of substitution 0.8) were dissolved in 20 ml of
demi water under mechanical stirring for 1 h. The pH was adjusted
to 4.5 using 25% HCl. The mixture was crosslinked with 1.4 mol % of
BDDE (1,4-butanediol diglycidyl ether) (78 .mu.l) at 50.degree. C.
for 18 hours. The gel was chopped and the pieces were dried in a
fluidised bed drier for 30 minutes at 100.degree. C. The dried gel
was ground and washed with excess demi water on a 80 .mu.m sieve to
remove any salts present. Then the gel was dried in the fluidised
bed drier at 80.degree. C. for 1 hour. The material was
characterised in synthetic urine with the following results: 93%
TOS/7% CMC: FSC: 26 g/g, CRC: 15.5 g/g, AUL: 19 g/g, pH gel
4.9.
EXAMPLE 9
Absorbent 6-carboxy Starch Crosslinked under Acidic Conditions
[0039] Five g of TEMPO-oxidised starch (TOS, degree of oxidation
0.70) was dissolved in 20 ml of demi water under mechanical
stirring for 1 h. The pH was adjusted to 4.5 using 25% HCl. The
mixture was crosslinked with 2.0 mol % of BDDE (113 .mu.l) at
50.degree. C. for 18 hours. The gel was chopped and the pieces were
dried in a fluidised bed drier for 30 minutes at 100.degree. C. The
dried gel was ground and washed with excess demi water on a 80
.mu.m sieve to remove any salts present Then the gel was dried in
the fluidised bed drier at 80.degree. C. for 1 hour. The material
was characterised in synthetic urine with the following results:
100% TOS: FSC: 27 g/g, CRC: 16 g/g, AUL: 19 g/g, pH gel 4.8.
EXAMPLE 10
Crosslinking of 6-carboxy Starch by Extrusion
[0040] In an extruder, 50 grams of 6-carboxy starch (0.25 mol) is
mixed with 50 ml of a 0.3 M HCI solution containing 30 .mu.l
butanediol diglycidyl ether (0.15 mmol). The paste is then extruded
at 150.degree. C. with an average residence time of 1 minute in the
extruder. At the extrusion die the crosslinked polysaccharide is
chopped into small pieces. The small pieces of gel are then dried
in a fluidised bed drier for 30 minutes at 100.degree. C. The dried
particles are ground and sieved to obtain a final particle size of
100-800 .mu.m. The absorption properties are comparable to those of
the superabsorbent polysaccharide crosslinked in a conventional
way.
EXAMPLE 11
Absorbent 6-carboxy Starch/CMC Crosslinked under Acidic
Conditions.
[0041] Three batches of 4 g of desalted TEMPO-oxidised starch (TOS,
degree of oxidation 0.70) were dissolved in demi water to obtain 20
wt %, 40 wt % and 50 wt % TOS solutions, respectively. The pH of
the solutions was about 4.6. To the solutions 0.124 g of CMC (Cekol
50,000, degree of substitution 0.8) was added, followed by
thoroughmixing. The mixtures were crosslinked at 50.degree. C. for
18 hours, with 1.4, 0.7, and 0.5 mol % of BDDE, respectively. Gels
obtained were sized and, subsequently, dried in a fluidised bed
drier for 1 hour at 100.degree. C. The dried gels were ground and
re-swollen in an excess of demi water. By addition of 2 M HCl, pH
of the gel was adjusted to pH of 4.7-4.8 in demi water.
Subsequently, the re-swollen gels were washed with excess demi
water on a 80 .mu.m sieve to remove salts present. Then the gels
were dried in the fluidised bed drier at 100.degree. C. for 1 hour.
The materials were characterised in synthetic urine with the
following results for the 40% TOS material: DXL (=degree of
crosslinking in mol % BDDE): 0.7; FSC: 26.5 g/g; CRC: 15.5 g/g; AUL
14 g/g; pH gel:4.2. Comparable results were obtained when using 20%
or 50% TOS solutions, instead of 40%.
EXAMPLE 12
Absorbent 6-carboxy Starch Crosslinked under Acidic Conditions.
[0042] Three batches of 4 g of desalted TEMPO-oxidised starch (TOS,
degree of oxidation 0.70) were dissolved in demi water to obtain 20
wt %, 40 wt % and 50 wt % TOS solutions, respectively. The pH of
the solutions was about 4.6. The solutions were cross-linked at
50.degree. C. for 18 hours, with 2.0, 0.75, and. 0.6 mol % of BDDE,
respectively. Gels obtained were sized and, subsequently, dried in
a fluidised bed drier for 1 hour at 100.degree. C. The dried gels
were ground and re-swollen in an excess of demi water. By addition
of 2 M HCl, pH of the gel was adjusted to pH of 4.7-4.8 in demi
water. Subsequently, the re-swollen gels were washed with excess
demi water on a 80 .mu.m sieve to remove salts present Then the
gels were dried in the fluidised bed drier at 100.degree. C. for 1
hour. The materials were characterised in synthetic urine with the
following results for the 40% TOS material: DXL 0.75; FSC: 28 g/g;
CRC: 15 g/g; AUL 14 g/g; pH gel: 4.1. Comparable results were
obtained when using 20% or 50% TOS solutions instead of 40%.
EXAMPLE 13
Absorbent 6-carboxy Starch/CMC Crosslinked under Acidic
Conditions
[0043] Three batches of 4 g of desalted TEMPO-oxidised starch (TOS,
degree of oxidation 0.70) were dissolved in demi water to obtain
40wt% TOS-solutions. The pH of solutions was about 4.6. To each
solution 0.124 g of CMC (Cekol 50,000, degree of substitution 0.8)
was added, and the whole was mixed thoroughly. Mixtures were
cross-linked with 0.7 mol % of BDDE at 50.degree. C. for 18 hours,
70.degree. C. for 2.5 hours, and 100.degree. C. for 1 hour,
respectively. Gels obtained were sized and, subsequently, dried in
a fluidised bed drier for 1 hour at 100.degree. C. The dried gels
were ground and re-swollen in an excess of demi water. By addition
of 2 M HCl, pH of the gel was adjusted to pH of 4.7-4.8 in demi
water. Subsequently, the re-swollen gels were washed with excess
demi water on a 80 .mu.m sieve to remove any salts present. Then
the gels were dried in the fluidised bed drier at 100.degree. C.
for 1 hour. The materials were characterised in synthetic urine
with the following results:
5 XL temp. XL time FSC CRC AUL (.degree. C.) (h) (g/g) (g/g) (g/g)
pH gel 50 18 26.5 15.5 14 4.2 70 2.5 27 14 13 3.8 100 1 27 15.5
11.5 3.9
EXAMPLE 14
Absorbent 6-carboxy Starch Crosslinked under Acidic Conditions.
[0044] Fifty g of desalted freeze-dried TEMPO-oxidised starch (TOS,
degree of oxidation 0.70) was kneaded till a fibrous structure was
obtained, and subsequently demi water (21.4 ml of demi water) was
added. The whole was kneaded for 3 minutes at 17.degree. C. to
obtain 70 wt % TOS paste (pH of paste was ca. 4.6). To this paste
0.4 mol % BDDE was added and the whole was again kneaded for 3.5
minutes at 17.degree. C. Then the paste was crosslinked for 16
hours at 50.degree. C. The gel obtained was sized and dried in a
fluidised bed drier for 1 hour at 80.degree. C. Dried gel particles
were re-swollen in 10 liters of demi water, and subsequently dried
in the fluidised bed drier for 1.5 hours at 80 .degree. C. The
material was characterised in synthetic urine with the following
results: FSC: 27 g/g, CRC: 14.5 g/g, AUL: 17.5 g/g, pH gel 4.9.
* * * * *