Process for the preparation of fine-particle, water-swellable polysaccharide graft copolymers

Fine-particle, water-swellable polysaccharide graft copolymers by prepared inverse suspension polymerization of 5 to 40 parts of polysaccharide and 95 to 60 parts of an olefinically unsaturated carboxylic acid, in which an aqueous phase which contains the olefinically unsaturated carboxylic acid, polymerization initiator and 100 to 75 wt. % of the polysaccharide is metered into a hydrophobic solvent which contains 0 to 25 wt. % of the polysaccharide at 40.degree. to 100.degree. C., exhibit improved absorptivity properties and particle size distribution.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a novel process for the preparation of 
fine-particle, porous and rapidly water-swellable polysaccharide graft 
copolymers. These polymers are prepared by inverse suspension 
polymerization and crosslinking. The present invention also relates to the 
polysaccharide graft copolymers prepared by the present process. 
2. Discussion of the Background 
Water-absorbing polymers are used for a wide variety of purposes in the 
sanitary and hygiene sectors as water-absorbing agents in disposable 
diapers and paper towels, as tampons, undersheets for patients, 
electrolyte thickeners in dry batteries, as moisture retainers or water 
stores in agriculture, and as desiccants. 
Suitable polymers are derivatized polysaccharides, usually grafted with 
water-soluble vinyl monomers, such as carboxymethyl cellulose, hydrolyzed 
starch/acrylonitrile graft copolymers, acrylic acid/starch graft 
copolymers, or completely synthetic, slightly crosslinked polymers such as 
partially crosslinked polyacrylic acid salts or partially crosslinked 
polymaleic acid derivatives. 
Incorporation of starch in water-soluble graft copolymers makes it 
possible, compared with completely synthetic polymers, to adjust 
particular product properties. Thus, the porosity of the polymer particles 
is raised, the absorption is increased, and the biodegradability is 
improved. 
Preparation of graft copolymers by direct grafting of starch with acrylate 
in aqueous solution is not straightforward industrially. Previous swelling 
of the starch is necessary in order to obtain the maximum homogeneity of 
dispersion, which is necessary for the grafting, of starch in the aqueous 
monomer solution. This considerably increases the viscosity of the monomer 
solution, and a paste-like consistency is obtained when more than about 
10% starch is used. 
DE-C 26 12 846 discloses the preparation of water-absorbing graft 
copolymers by grafting water-soluble monomers, such as acrylic acid, onto 
starch in the presence of a crosslinking agent. The grafting reaction is 
carried out in aqueous solution or in aqueous/alcoholic medium as 
so-called precipitation polymerization. This process results, in the case 
of grafting in aqueous solution, in rubber-like gels which cannot be 
stirred and from which final products in the form of powders are obtained 
only after drying and milling. By contrast, if a grafting is carried out 
as precipitation polymerization in the presence of an approximately 
20-fold excess of alcohol as precipitant, the resulting fine-particle 
products have only moderate liquid absorption capacity. 
According to Japanese Patent Specification 80/139 408, a graft copolymer 
can be prepared by polymerization of acrylonitrile in aqueous medium in 
the presence of starch and can subsequently be hydrolyzed and crosslinked. 
The result is a powder with a water absorption capacity of 150 to 180 
ml/g. 
Fine-particle water-absorbing polymers can be prepared by polymerization of 
partially neutralized acrylic acid in inverse suspension, also called 
reverse phase suspension. This entails a water-soluble monomer in the form 
of an aqueous solution being emulsified in a hydrophobic medium in the 
presence of a dispersant and polymerized to a fine-particle final product. 
In the presence of a polysaccharide such as starch, it is possible in this 
way to obtain water-soluble or water-insoluble, swellable graft 
copolymers. 
A graft copolymerization in inverse suspension is indicated in Japanese 
Patent Specification 80/161 813. This entails initially making up a 
mixture of n-hexane with sorbitan monostearate, starch, water, acrylic 
acid, sodium hydroxide solution and water-soluble initiator, before 
initiating the polymerization by heating. However, in this case, the 
reaction product tends to aggregate during the polymerization and does not 
give a fine-particle product. 
According to DE-C-28 40 010 it is possible to prepare water-soluble 
polysaccharide graft copolymers by inverse suspension polymerization, 
preferably in a batch process. This entails a polysaccharide being 
initially suspended in a solvent which is immiscible with water in the 
presence of a surface-active agent. Subsequently, an aqueous monomer 
solution which contains predominantly acrylamide or a cationic monomer, 
and can also have small amounts of acrylic acid, is added at room 
temperature. Addition of an initiator is followed by heating and 
polymerization. The solids contents, based on the aqueous polymerization 
mixture, are above 50%. 
In this case, no crosslinking agents are employed and no water-swellable 
gel-like polymers are obtained. The indicated batchwise preparation 
process leads at the start of the polymerization to temperature peaks 
which are difficult to control in large batches. 
In EP-B-0 083 022, acrylic acid is polymerized in the presence of starch in 
aqueous solution. The products can then be crosslinked in an inert solvent 
in the presence of 0.01 to 1.3 parts of water per part of resin. The 
preparation of the starch graft copolymer takes place at a solids content 
of only 20%. In addition, these starch graft copolymers - crosslinked or 
uncrosslinked-have only a low water absorption capacity. 
According to DE-A-38 01 633, polysaccharide graft copolymers are prepared 
by inverse suspension polymerization, partial removal of water and 
crosslinking. The inverse suspension polymerization is carried out in one 
stage and batchwise by first mixing all the reaction components and then 
initiating the polymerization by heating in the presence of an initiator. 
In this case there is violent evolution of heat at the start of the 
polymerization. In industrial production reactors it is often possible 
only with difficulty to ensure sufficiently rapid dissipation of the heat 
of polymerization. 
Thus, there remains a need for a process to produce fine-particle, 
water-swellable polysaccharide graft copolymers, which is free of the 
above-described drawbacks. There also remains a need for polysaccharide 
graft copolymers with improved particle fineness and absorptivity and 
liquid-retention properties. 
SUMMARY OF THE INVENTION 
Accordingly, one object the present invention is to provide a novel process 
for the preparation of polysaccharide graft copolymers, which are prepared 
from 5 to 40 parts by weight of polysaccharide and 95 to 60 parts by 
weight of an olefinically unsaturated carboxylic acid, which yields 
polysaccharide graft copolymers exhibiting improved particle fineness and 
absorptivity for urine. 
It is another object of the present invention to provide a process for the 
preparation of polysaccharide graft copolymers, which are prepared from 5 
to 40 parts by weight of polysaccharide and 95 to 60 parts by weight of an 
olefinically unsaturated carboxylic acid, which possess a high level of 
liquid-retention capacity. 
It is another object of the present invention to provide the improved 
polysaccharide graft copolymers prepared by such processes. 
These and other objects, which will become apparent in the course of the 
following detailed description, have been achieved by carrying out an 
inverse suspension polymerization in which an aqueous phase which contains 
the olefinically unsaturated carboxylic acid, polymerization initiator and 
100 to 75 percent by weight of the polysaccharide is metered into a 
hydrophobic solvent which contains 0 to 25 per cent by weight of the 
polysaccharide as dispersion at 40.degree. to 100.degree. C. 
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Thus, the present invention relates to processes in which 5 to 40 parts by 
weight of polysaccharide are graft copolymerized with 95 to 60 parts by 
weight of an olefinically unsaturated carboxylic acid, by inverse 
suspension polymerization. An aqueous phase containing the olefinically 
unsaturated carboxylic acid, polysaccharide (100 to 75 wt. %), and 
possibly a polymerization initiator is metered into a hydrophobic solvent 
in which 0 to 25 wt. % of the polysaccharide is dispersed. 
Preferably used for the inverse suspension polymerization are 10 to 20 
parts by weight of polysaccharide and 90 to 80 parts by weight of the 
olefinically unsaturated carboxylic acid, with preferably 2 to 20 percent 
by weight of the polysaccharide being dispersed in the hydrophobic 
solvent, and 98 to 80 percent by weight of the polysaccharide being added 
in the aqueous phase. 
Polysaccharides suitable for the process according to the present invention 
are starches, starch derivatives and cellulose derivatives. Starches are 
preferred in this connection. It is possible to use natural starches from 
potatoes, maize, wheat, rice or tapioca roots, as well as wax maize or 
high amylose starch, and derivatives thereof, such as, for example, ethers 
and esters of starch. Also suitable are thin-boiling starches, which 
usually consist of starches which have undergone slight hydrolytic or 
oxidative breakdown. Preferred in this connection are starches with a 
viscosity of 20 to 25,000 mPa.s, preferably 30 to 20,000 mPa.s, measured 
for a 10 wt. % strength aqueous paste at 20.degree. C. 
Hydrophobic solvents which can be used for the organic phase are ethers, 
halogenated hydrocarbons or hydrocarbons with 6 to 12 C atoms. Preferably 
used are aliphatic or alicyclic hydrocarbons such as cyclohexane, 
n-hexane, C.sub.8 -isoparaffins or industrial petroleum fractions such as 
petroleum spirit, ligroin, white spirit or solvent-naphtha, with an 
aromatic content up to 20 wt. % and a boiling point in the range from 
50.degree. to 200.degree. C. The ratio of organic phase to aqueous 
solution is usually 1.3:1 to 4:1 by weight, preferably 1.5:1 to 3:1 by 
weight. 
Preferably used as dispersant is a non-ionic surfactant with a 
hydrophilic/lipophilic balance (HLB) of 0.5 to 10, which ought to be at 
least partially soluble in the organic solvent. Suitable examples are 
lipophilic sorbitan esters such as sorbitan monolaurate, sorbitan 
monopalmitate or sorbitan monooleate. 
It is also possible to use satisfactorily polyetheresters such as 
polyethylene glycol (200) monooleate, polyethylene glycol (200) 
monolaurate or polyethylene glycol (300) oleate. It is also possible to 
use cellulose ethers such as ethylcellulose, or 
ethylhydroxyethylcellulose. 
It is advantageous also to use a non-ionic dispersant which is 
predominantly water-soluble and has an HLB of 10.5 to 20. Examples of such 
substances are water-soluble polyethylene glycols with a molecular weight 
of 200 to 20,000, in particular of 400 to 5,000, also polyethylene glycol 
ethers composed of an aliphatic monohydric alcohol with 6 to 20 C atoms 
and a polyethylene glycol with 3 to 30, in particular with 4 to 20, 
ethylene oxide units. 
Also suitable are commercially available C.sub.12 -fatty alcohol polyglycol 
ethers with 7 to 19 ethylene oxide units and an HLB of 13 to 18. 
Furthermore suitable are polyoxyethylenesorbitan fatty acid esters such 
as, for example, polyoxyethylene sorbitan monolaurate or polyoxyethylene 
sorbitan monooleate. 
In a preferred embodiment, the dispersant is a mixture consisting of 50 to 
90 percent by weight of non-ionic surfactant with an HLB of 0.5 to 10 and 
of 10 to 50 percent by weight of non-ionic surfactant with an HLB of 10.5 
to 20. 
The content of dispersant mixture is 1 to 10 percent by weight based on the 
weight of the olefinically unsaturated carboxylic acid. It is preferable 
in this connection for 10 to 60 percent by weight of the dispersant 
mixture to be present in the organic phase and for 90 to 40 percent by 
weight to be metered in with the aqueous phase. 
The olefinically unsaturated carboxylic acids have 3 to 10 carbon atoms. 
Examples of these are acrylic acid, methacrylic acid, crotonic acid, 
tiglic or angelic acid. Acrylic and methacrylic acids are preferably used. 
The acids can be neutralized or partially neutralized with alkali metal or 
ammonium hydroxide solutions. Sodium hydroxide solution is preferably used 
for this purpose. Acrylic acid and methacrylic acid which are 50 to 90% 
neutralized are very particularly preferred. The aqueous solutions of the 
unsaturated carboxylic acids usually have a solids content, including the 
polysaccharide content, in the range from 20 to 80 wt. %, preferably 30 to 
70 wt. %, based on the total weight of the solution. 
Besides the unsaturated carboxylic acids, it is possible to use up to 20 
parts by weight of other olefinically unsaturated monomers such as 
acrylamide, methacrylamide, Na salt of 
2-acrylamido-2-methylpropanesulphonic acid, 2-methacryloylethanesulphonic 
acid, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 
N,N-dimethylaminoethyl acrylate or methacrylate, or the quaternary 
ammonium salts thereof, in the form of their aqueous solution for the 
polymerization. 
The aqueous phase which is added to the polysaccharide suspension for the 
polymerization can also contain up to 2 parts by weight of completely or 
predominantly water-soluble crosslinking agents. Suitable are vinyl 
compounds such as N,N-methylenebisacrylamide, 1,4-butanediol 
di(meth)acrylate, ethanediol di(meth)acrylate, diallyl maleate, glycidyl 
(meth)acrylate, allyl methacrylate, polyethylene glycol(450) 
dimethacrylate, or polyepoxides such as, for example, ethylene glycol 
diglycidyl ether, polyethylene glycol diglycidyl ether, glycerol 
triglycidyl ether or diglycerol tetraglycidyl ether. 
The aqueous phase can also contain up to 20 parts by weight of hydrophobic 
solvent. 
Conventional polymerization initiators are used for the graft 
copolymerization. Suitable examples are ammonium, sodium or potassium 
peroxodisulfate and corresponding peroxomonosulfates, dibenzoyl peroxide, 
dilauroyl peroxide, di-2-ethylhexyl peroxodicarbonate, dicyclohexyl 
peroxodicarbonate, tert-butyl perpivalate, tert-butyl perbenzoate, 
tert-butyl permaleate, tert-butyl hydroperoxide, di-tert-butyl peroxide, 
hydrogen peroxide and redox catalysts, suitable reducing components being 
ascorbic acid, sodium methylsulphinate, disodium sulphite and sodium 
bisulphite. Also suitable are azo initiators such as 
azobisisobutyronitrile, 2,2-azobis(2-amidinopropane) dihydrochloride, 
2,2'-azobis(4-cyanopentanoic acid) and 2-carbamoylazoisobutyronitrile. 
The initiators can be added in the aqueous phase of the unsaturated 
carboxylic acid to the polysaccharide suspension. However, it is also 
possible, and has advantages, to meter them in as separate aqueous 
solutions. It is also possible for part of the initiator to be present in 
the organic phase and another part to be added with the aqueous phase of 
the unsaturated carboxylic acid. In general, 0.005 to 5 parts by weight of 
initiator, based on the weight of the unsaturated carboxylic acid, are 
introduced via an aqueous phase and 0 to 1 part by weight of initiator, 
based on the weight of the unsaturated carboxylic acid, is introduced via 
the organic phase. It is preferable for 0.05 to 1.5 parts by weight of 
initiator to be metered in in an aqueous phase, and 0.03 to 0.5 part by 
weight of initiator to be present in the organic phase. 
Potassium and ammonium peroxodisulfates are preferably used. 
The polysaccharide suspension and aqueous phase can additionally contain 
conventional auxiliaries and additives such as foam suppressants and 
complexing agents. Thus, for example, nitrilotriacetate, 
ethylenediaminetetraacetate or diethylenetriaminepentaacetate can be added 
in order to complex traces of iron. Suitable antifoaming agents are 
described in Ash et al, Handbook of Industrial Chemical Additives, VCH 
Publishers, New York (1991), which is incorparated herein by reference. 
The polymerization is preferably carried out at 50.degree. to 75.degree. C. 
This then entails the hydrophobic phase being heated to 50.degree. to 
75.degree. C., while the aqueous phase with the unsaturated carboxylic 
acid usually has a temperature of 15.degree. to 40.degree. C. The reaction 
is generally complete after 0.5 to 5 hours. 
The metering of the aqueous phase into the hydrophobic solvent may be 
carried by any conventional metering method using any conventional 
apparatus, such as dropwise or portionwise addition of the aqueous phase 
to the hydrophobic solvent. Typically, the aqueous phase is added to the 
hydrophobic solvent over a period of time of from 0.5 to 4 hrs., 
preferably 0.5 to 2 hrs., while constantly stirring the hydrophobic 
solvent. After the metering of the aqueous phase is complete, the reaction 
mixture may be maintained at the reaction temperature with continued 
stirring for an additional 0.1 to 1 hr. 
The inverse suspension polymerization results in a suspension of separate 
water-swollen polymer particles which preferably have a solids content of 
30 to 60% based on the total weight of polymer and water. 
Crosslinking can be carried out before, during or after the polymerization. 
It is preferable to carry out a partial removal of water and a subsequent 
crosslinking after the polymerization is complete. The partial removal of 
water preferably establishes a residual water content of 10 to 50% based 
on the total of polymer and water. Residual water contents of 10 to 30% 
are very particularly preferably established thereby. The partial removal 
of water is generally carried out at 50.degree. to 100.degree. C. by 
azeotropic distillation during which it is also possible to apply a 
vacuum. It is possible in this connection to use conventional 
water-removal apparatus in which the organic phase is recycled. 
During or after the partial removal of water it is possible to carry out a 
subsequent crosslinking by the addition of, preferably, 0.005 to 5 percent 
by weight, most preferably 0.01 to 1 percent by weight, of crosslinking 
agent based on the weight of the graft copolymer. It is preferable to 
carry out first the partial removal of water and then the subsequent 
crosslinking. Epoxides are preferably used for the subsequent 
crosslinking. Suitable in this connection are, inter alia, polyglycidyl 
ethers such as, for example, ethylene glycol diglycidyl ether, 
polyethylene glycol diglycidyl ether, glycerol triglycidyl ether and 
diglycerol tetraglycidyl ether. It is also possible to use polyaldehydes 
such as glyoxal, or halo epoxy compounds such as epichlorohydrin. These 
crosslinking agents are expediently added in aqueous or organic solution. 
The subsequent crosslinking is carried out by heating at 50.degree. to 
100.degree., with heating at 60.degree. to 80.degree. C. being preferred. 
The crosslinking reaction is complete after 0.5 to 4 hours. 
The starch graft copolymers resulting after the crosslinking take the form 
of porous particles in the form of a free-flowing powder. The particles 
can easily be separated from the continuous organic phase, for example by 
filtration or centrifugation. They can subsequently be dried by 
conventional processes, for example in vacuo or by use of a fluidized-bed, 
tumbler or paddle dryer, to give the product in the form of a powder. The 
filtrate can be reused in the next polymerization batch. Solvent and water 
can also be separated from the polymer powder by distillation. 
No temperature peaks and no high viscosities occur during the 
polymerization according to the present invention. The preparation process 
can therefore be carried out satisfactorily on the pilot plant and 
production scale. 
The present polymerization results an a uniformly fine product with a 
narrow particle size distribution. The formation of coarse-particle 
agglomerates and deposits is very low. 
The term fine-particle is defined, within the meaning of this invention, as 
products with particle sizes below 2 mm, and more than 85 percent by 
weight of the products ought to have particle sizes below 1,000 .mu.m. 
The products display rapid and high liquid absorption. The liquid retention 
capacity is very high even under pressure. On incorporation of the 
polymers in hygiene articles such as, for example, diapers, only little 
rewetting occurs. 
The products are especially suitable for incorporation in 
cellulose-containing absorbent hygiene articles such as disposable 
diapers, sanitary towels, wiping towels and undersheets for patients. They 
can be used as desiccants, as swelling agents in sealing compositions, as 
thickening agents and as water stores or moisture retainers in 
agriculture. 
The process according to the present invention is carried out in a 
preferred embodiment in such a way that a portion of the polysaccharide is 
dispersed by stirring in the hydrophobic solvent in a stirred vessel with 
the aid of a non-ionic surfactant and heated to the required 
polymerization temperature. Subsequently an aqueous monomer solution which 
contains the unsaturated carboxylic acid, the remaining polysaccharide, 
non-ionic surfactant, polymerization initiator, where appropriate a 
crosslinking agent and minor amounts of a hydrophobic solvent is metered 
in. Polymerization with grafting takes place during this. After the 
polymerization, part of the water is removed by azeotropic distillation 
with a water trap. Subsequent crosslinking is then carried out, and it is 
then possible to separate the polymer as fine-particle product. 
Other features of the invention will become apparent in the course of the 
following descriptions of exemplary embodiments which are given for 
illustration of the invention and are not intended to be limiting thereof.

EXAMPLES 
Liquid retention capacity 
0.500 g of polymer is mixed with 70 ml of synthetic urine (mixture of 3,883 
g of distilled water, 33.2 g of NaCl, 4.0 g of MgSO.sub.4.7H.sub.2 O, 2.4 
g of CaCl:, and 77.6 g of urea) in a 100 ml centrifuge tube and stirred 
gently while swelling for one hour. The gel phase is then removed from the 
sol phase by centrifugation at 4,500 rpm, for 0.5 hour and weighed. 
##EQU1## 
Absorptivity 
0.100 g of polymer is spread on a glass frit (type G3, diameter 3 cm) which 
is connected to a burette filled with synthetic urine and is levelled at 
the level of the glass frit. The absorbed amount of liquid is measured o 
the burette after 0.5 and 5 minutes. 
##EQU2## 
The initial value after 0.5 minute characterizes the absorption rate. The 
final value after 5 minutes is a measure of the absorption capacity. 
The highest possible values are generally desirable. For absorption 
capacity, the term "moderate" is applied to a range from 10 to 19 g/g, 
"high" to a range from 20 to 24, and "very high" to a range from 25 to 30 
g/g. 
A model diaper test is carried out as follows for testing the products in 
cellulose-containing hygiene articles: 
Liquid spread and rewetting in a model diaper 
as described in Edana Nordic Nonwovens Symposium, June 1988, page 242. 
Rectangular pieces 14.times.38 cm in size are cut out of an incontinence 
pad (Caducee Slipad, supplied by Molnlycke GmbH, D-4010 Hilden) consisting 
of two layers of cellulose fluff. The covering nonwoven (coverstock) 
consisting of polypropylen is replaced by a cellulose nonwoven. 5.0 g of 
polymer is scattered in a uniform distribution over the entire 
cross-section between the two layers of fluff. 
Into the middle of the model diaper are initially placed 60 ml and on two 
occasions, after 30 minutes each time, a further 30 ml of red-stained 
synthetic urine. 30 minutes after the last dose of liquid, 80 sheets of 
paper towels (Apura Ecotex), whose dry weight has been determined 
beforehand, are placed on the model diaper and loaded with a weight of 
21.3 kg (=4 kg/dm.sup.2) for 10 minutes. The wet paper towels are then 
reweighed. 
##EQU3## 
The better the liquid retention capacity the lower the measurements for the 
rewetting. The following classification is undertaken: 
______________________________________ 
Rewetting 40 to 45 g: very good 
46 to 50 g: good 
51 to 60 g: moderate 
70 (blank): no effect 
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The yields in g indicated in the examples always relate to products which 
have been dried in a vacuum drying oven (15 mbar vacuum) at 50.degree. C. 
for 24 hours to a residual moisture content&lt;7 per cent by weight. 
The indicated viscosities of the starches relate to 10% strength aqueous 
pastes at 20.degree. C. 
EXAMPLE 1 
2,400 ml of cyclohexane are placed in a 4 l glass reactor equipped with 
stirrer, nitrogen inlet, metering devices, and water trap and heated to 
70.degree. C. While stirring at 400 rpm, 
______________________________________ 
4 g of natural maize starch (supplied by Cerestar, 
D-4150 Krefeld), 
4 g of sorbitan monolaurate (SPAN .RTM. 20 supplied by 
Atlas, Wilmington, Del., USA), 
2 g of polyethylene glycol with a molecular weight 
of 1,550 (POLYDIOL 1550 supplied by Huls AG, 
D-4370 Marl), 
0.25 g of ammonium peroxodisulfate in 30 ml of water, 
and 
50 mg of ethylenediaminetetraacetate (Na salt) are 
dispersed. 
______________________________________ 
Oxygen is then displaced by nitrogen, and a mixture of 
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312 g of acrylic acid, 
480 g of 25 wt. % strength sodium hydroxide solution, 
42 g of natural maize starch, 
12 g of sorbitan monolaurate, 
0.1 g of trimethylolpropane triacrylate, 
0.5 g of ammonium peroxodisulfate in 15 ml of water, 
and 
20 ml of cyclohexane 
______________________________________ 
is metered in over 45 minutes. The mixture is then stirred for half an 
hour. Then 280 ml of water are removed by azeotropic distillation at 
75.degree. C., after which, at 70.degree. C., 0.25 g of ethylene glycol 
diglycidyl ether in 5 ml of water is added. The mixture is then stirred 
for 2 hours, and the product in the form of a powder is obtained by 
filtration. 
Yield: 402 g of product with a solids content of 96%. 
The particle distribution determined by screening analysis and the 
absorption properties are shown in Table 1. 
EXAMPLE 2 
The process of Example 1 is carried out but no native maize starch is 
introduced into the cyclohexane. Instead, 46 g of natural maize starch are 
metered in with the acrylate solution. The progress of polymerization and 
the particle structure corresponds to the product prepared as in Example 
1. 
Yield: 406 g of product with a solids content of 96% by weight. 
COMATIVE EXAMPLE A 
The process of Example 1 is carried out. However, the total amount of 
natural maize starch (46 g) is initially dispersed in the cyclohexane. 
After the metering in of the aqueous solution is complete, the reactor 
contents are highly viscous, hardly stirrable and partially agglomerated. 
The stirrability improves during the azeotropic removal of water, during 
which 280 ml of water are removed by distillation. 
416 g of a highly porous product which is composed of loosely packed fine 
particles and has a high coarse particle content (cf. Table 1) are 
obtained. 
EXAMPLE 3 
1,800 ml of cyclohexane are introduced into the polymerization apparatus 
used in Example 1 and heated to 70.degree. C. While stirring at 400 rmp, 
______________________________________ 
4 g of natural maize starch, 
5 g of sorbitan monolaurate, 
2.5 g of polyethylene glycol with a molecular weight 
of 1,550, 
0.25 g of ammonium peroxodisulfate in 30 ml of water, 
and 
50 mg of ethylenediaminetetraacetate (Na salt) 
______________________________________ 
are dispersed. Oxygen is then displaced by nitrogen, and a mixture of 
______________________________________ 
312 g of acrylic acid, 
80 g of 25 wt. % strength sodium hydroxide solution, 
42 g of natural maize starch, 
10 g of sorbitan monolaurate, 
0.1 g of pentaerythritol triacrylate, 
0.3 g of ammonium peroxodisulfate in 15 ml of water, 
and 
20 ml of cyclohexane 
______________________________________ 
is metered in over 45 minutes. The mixture is then stirred for half an 
hour. No adhesion of the polymer particles is found during the 
polymerization. Then 280 ml of water are removed by azeotropic 
distillation at 75.degree. C., and 0.25 g of ethylene glycol diglycidyl 
ether in 5 ml of water is added The mixture is then stirred at 70.degree. 
C. for 2 hours. 404 g of a fine-particle, compact polymer powder, 95% of 
which consists of the useful fraction from 90 to 800 .mu.m, are obtained. 
EXAMPLE 4 
The process of Example 1 is carried out. However, thin-boiling starch with 
a viscosity of 127 mPa.s (AMISOL.RTM. 05515 supplied by Cerestar) is used. 
409 g of a fine-particle product, 96% of which consists of the useful 
fraction from 90 to 800 .mu.m, are obtained. 
COMATIVE EXAMPLE B 
The process of Example 4 is carried out. However, the total amount of 
starch (46 g) is initially introduced into the cyclohexane phase. The 
acrylate solution is metered without starch. After addition of acrylate is 
complete, the reaction mixture is highly viscous, and the polymer 
particles agglomerate. 
396 g of a coarse-particle product, 100% of which consists of agglomerated 
particles&gt;2 mm in size, are obtained. The product is comminuted by milling 
to a particle size&lt;800 .mu.m to determine the absorption properties. 
EXAMPLE 5 
2,000 ml of cyclohexane are introduced into a 4 l glass reactor equipped 
with stirrer, nitrogen inlet, metering device, and water trap and heated 
to 70.degree. C. While stirring at 400 rpm, 
______________________________________ 
5 g of natural maize starch, 
5 g of sorbitan monolaurate, 
2.5 g of polyethylene glycol with a molecular weight 
of 1,550, 
0.25 g of ammonium peroxodisulfate in 8 ml of water, 
and 
50 ml of ethylenediaminetetraacetate (Na salt) in 8 ml 
of water 
______________________________________ 
are dispersed. Oxygen is then displaced by nitrogen, and a mixture of 
______________________________________ 
312 g of acrylic acid, 
480 g of 25 wt. % strength sodium hydroxide solution, 
70 g of natural maize starch, 
10 g of sorbitan monolaurate, 
0.1 g of pentaerythritol triacrylate, 
0.3 g of ammonium peroxodisulfate in 15 ml of water, 
and 
20 ml of cyclohexane 
______________________________________ 
is metered in over 45 minutes. The mixture is then stirred for half an 
hour. Then 330 ml of water are removed by azeotropic distillation at 
75.degree. C., after which, at 70.degree. C., 0.25 g of ethylene glycol 
diglycidyl ether in 8 ml of water is added. The mixture is then stirred 
for 2 hours, and the product, which is in the form of a powder and 
consists of compact, porous particles, is isolated by filtration. 
Yield: 455 g of product. 
EXAMPLE 6 
The process of Example 5 is carried out. However, the total amount of 
starch (75 g) is metered in with the acrylate phase. The starch content in 
the dried polymer powder (yield 460 g) is 16 per cent by weight, as in 
Example 5. 
COMATIVE EXAMPLE C 
The process of Example 5 is carried out. However, the total amount of 
starch (75 g) is employed in the cyclohexane phase. After the metering in 
of the aqueous solution is complete, the reaction mixture is highly 
viscous and only partly mixed. The polymer particles agglomerate. The 
agglomeration diminishes during the azeotropic removal of water. After 
removal of 330 ml of water by distillation and crosslinking with 0.25 g of 
ethylene glycol diglycidyl ether, 440 g of a product in the form of a 
powder are obtained. 
EXAMPLE 7 
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620 kg of cyclohexane, 
1.3 kg of natural maize starch, 
1.4 kg of sorbitan monolaurate, 
0.7 kg of polyethylene glycol with a molecular weight 
of 1,550, 
20 g of ethylenediaminetetraacetate, dissolved in 1 l 
of water, and 
50 g of ammonium peroxodisulfate, dissolved in 1 l of 
water, 
______________________________________ 
are introduced into a stainless steel polymerization vessel which has a 
capacity of 1,200 l and is equipped with a two-blade Intermig stirrer, 
reflux condenser, water trap and introduction devices. The contents of the 
vessel are heated to 68.degree. C. while stirring and flushed with 
nitrogen. Over the course of one hour the mixture obtained by 
neutralization of 95 kg of acrylic acid with 147 kg of 25 wt. % strength 
sodium hydroxide solution and addition of 25 1 of cyclohexane, 4.2 kg of 
sorbitan monolaurate, 13 kg of natural maize starch and 30 g of 
trimethylolpropane triacrylate are added while the reaction mixture is 
stirred at 80 rpm. Also added, metering separately, is an activator 
solution of 150 g of ammonium peroxodisulfate in 4.5 l of water. After the 
metering of the acrylate phase and of the activator solution is complete, 
the mixture is then stirred at 70.degree. C. for half an hour. Then 95 kg 
of water are removed by azeotropic distillation under 600 hPa, and 78 g of 
ethylene glycol diglycidyl ether dissolved in 2.5 l of water are added. 
The mixture is then stirred for 2 hours and then 1,400 g of pyrogenic 
silica (AEROSIL.RTM. 200 supplied by Degussa, D-6000 Frankfurt) in the 
form of a suspension in 25 l of cycloheaxane are added. 
The polymer is isolated by filtration from the cyclohexane and dried at 
60.degree. C. in a paddle dryer to a residual moisture content of 4.8%. 
138 kg of a fine-particle polymer which contains 10.4 percent by weight of 
starch and 100% of which has a particle size of the useful fraction from 
90 to 800 .mu.m. 
EXAMPLE 8 
The process of Example 5 is carried out. However, 
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16 g of natural maize starch, 
5 g of sorbitan monolaurate, 
2 g of polyethylene glycol with a molecular weight 
of 1,550, 
0.25 g of ammonium peroxodisulfate in 8 ml of water, 
and 
66 ml of ethylenediaminetetraacetate (Na salt) in 8 ml 
of water 
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are dispersed in 2,000 ml of cyclohexane in this case. Oxygen is then 
displaced by nitrogen, and a mixture of 
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312 g of acrylic acid, 
480 g of 25 wt. % strength sodium hydroxide solution, 
144 g of natural maize starch, 
10 g of sorbitan monolaurate, 
0.1 g of trimethylolpropane triacrylate, 
0.3 g of ammonium peroxodisulfate in 15 ml of water, 
and 
20 ml of cyclohexane 
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is metered in over 50 minutes. The mixture is then stirred for half an 
hour. Then 330 ml of water are removed by azeotropic distillation at 
75.degree. C., after which, at 70.degree. C., 0.50 g of ethylene glycol 
diglycidyl ether in 8 ml of water is added. The mixture is then stirred 
for 2 hours, and the product, which is in the form of a powder and 
consists of compact, porous particles, is isolated by filtration. 
Yield: 545 g of product. 
It is evident from Table 1, which follows, that the products according to 
the present invention are distinguished from the comparative products by a 
finer particle size, more narrow particle size distribution, smaller 
content of coarse particles, a distinctly higher final absorptivity and by 
a distinctly better liquid retention in cellulose-containing diapers, 
expressed by lower measurements for rewetting. 
TABLE 1 
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Screening analysis 
Absorption 
% by weight capacity 
Absorptivity 
Coarse Useful 
g/g of 
g/g of synthetic urine 
Model diaper test 
particles 
fraction 
synthetic 
After Rewetting 
Ex. 
&gt;800 .mu.m 
90-800 .mu.m 
urine 30 sec. 
300 sec. 
Assessment 
(g) Assessment 
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1 8 92 34 16 29 very high 
41 very good 
2 10 90 34 13 27 very high 
43 very good 
A 67 33 33 17 21 high 52 moderate 
3 5 95 44 7 30 very high 
42 very good 
4 4 96 37 7 19 moderate 
50 good 
B 100 0 31 10 16 moderate 
54 moderate 
5 2 98 36 18 28 very high 
46 good 
6 3 97 33 13 25 very high 
50 good 
C 6 94 31 19 21 high 53 moderate 
7 0 100 36 14 26 very high 
47 good 
8 1 99 28 21 25 very high 
50 good 
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Obviously, numerous modifications and variations of the present invention 
are possible in light of the above teachings. It is therefore to be 
understood that, within the scope of the appended claims, the invention 
may be practiced otherwise than as specifically described herein.