DE2528701C3 - Hydrogel particles, processes for their preparation and their uses - Google Patents

Description

The invention relates to water-insoluble, water-absorbent hydrogel particles. It also concerns Process for their manufacture and their use.

According to US Patents 34 19 006, 36 64 343, 69 103, 36 70 731 and 37 83 872 are hydrogels, too in particulate form, known to be capable of absorbing several times their weight in aqueous liquid and retain the absorbed liquid even under moderate pressures. These hydrogels could be used as Water absorbent additive used in disposable items after use will. The known hydrogels have the disadvantage that they are relative to the aqueous liquids absorb slowly and that they are mobile in a fibrous matrix, e.g. B. when shaking fall out or settle.

The object of the invention is to provide hydrogel particles which absorb aqueous liquids at a maximum rate absorb and are practically immobile in a fibrous matrix.

This object is achieved in that the hydrogel is made of inorganic material or from a crosslinked organic polymer, the

ίο Particles have a coating of natural or synthetic Fibers with a fiber length of less than 5 mm and a ratio of fiber length to fiber diameter of at least 5: 1 with at least some fibers across the surface of the particles

is out, and the coated particles through a sieve pass with a mesh size of 4 mm.

In a preferred embodiment, the coating consists of hydrophilic and / or hydrophobic Fibers, in particular made of nylon, cotton or cellulose fibers.

Hydrogel particles in which the proportion of hydrogel makes up 20 to 75 percent by weight are very suitable.
A number of hydrogels can be used to prepare the mixtures according to the invention. An important requirement of the hydrogel selected is that it can absorb relatively large amounts of aqueous liquid. This includes both inorganic substances (silica gel) and organic compounds

} o gen (polymers that are linked to one another via covalent, ionic bonds, Van der Waals forces or hydrogen bonds).

Polymers that can be used as hydrogels include: polyethylene oxide, polyvinyl

.15 nylpyrrolidone. Polyacrylamide, partially hydrolyzed Polyacrylamide, polyvinyl alcohol, copolymers of maleic anhydride vinyl ether, Maleic anhydride-vinylpyrrolidone, polyacrylic acid, copolymers of ethylene-maleic anhydride, Polyvinyl ether, dextran, agar, gelatin, hydroxypropyl cellulose, methyl cellulose, Carboxymethyl cellulose, hydroxyethyl carboxymethyl cellulose, hydroxyethyl cellulose, propylene glycol alginate, Sodium alginate, polyethyleneimine, polyvinylalkylpyridinium halides, Polyvinylmorpholinone, Polymers and Copolymers of Vinylmorpholinone, Polymers and copolymers of vinyl sulfonic acid and its ammonium and alkali metal salts, amides and alkali metal salts or ammonium salts of the copolymers of maleic anhydride and vinyl methyl ether, with vinyl

so pyrrolidone, with vinyl morpholinone or with one mono-olefinic hydrocarbon, polymers and copolymers of acrolein, which by reaction with Alkali metal hydroxides or alkali metal bisulfites and copolymers of sulfur dioxide with

ss allyl alcohol, allyl ether of glycerol or allyl ether of ethylene glycol or a polyethylene glycol, polyvinyl-n-butylpyridinium bromide, polyproline, natural Starch, modified starch as described in U.S. Patent 3,661,815 and U.S. Patent Application

fio 4 56 911 are described, casein, proteins, polymethacrylic acid, Polyvinyl sulfonic acid, polystyrene sulfonic acid, polyvinylamine, ammonium polyacrylate, hydroxyalkyl acrylate, Hydroxyalkyl methacrylate, Hydroxyalkoxyalkylacrylat, Hydroxyalkoxyalkylmethacrylat Polyäthy-

hs lenoxide adducts with esters of acrylic acid and methacrylic acid, Alkoxyacrylates and methacrylates, alkoxyalkyl acrylates and methacrylates, partially hydrolyzed Polyacrylamides, quaternary salts of poly-4-vinylpyri-

din, polymerized monoesters of olefinic acids, polymerized diesters of olefinic acids, acrylamides and bifunctional polymerizable materials, such as B. dibasic acids, diesters or diamides and the like.

It is also possible. Blends or copolymers to use from the aforementioned compounds or substances. For example, copolymers from ethylene oxide and smaller or larger amounts of other alkylene oxides are used, ι ο In addition, salts of the aforementioned polymers can be used. It is also possible to be networked To use polymers.

A variety of natural and synthetic fibers can be used for the production of the invention Mixtures are used. Of course, cheap and readily available fibers are preferred to this include wood and wood products, such as ». B. wood pulp fibers Cellulose flakes, cotton nocks and the like; inorganic fibers, synthetic fibers, such as z. Nylon flakes, rayon flakes and the like. It is also possible. Mixtures of natural fibers or made of synthetic fibers or mixtures of synthetic and natural fibers. Preferred become hydrophilic fibers. However, hydrophobic fibers can also be used in conjunction with hydrophilic fibers are used, in particular as fibers that protrude and that serve to hold the hydrogel particles in the to fix fibrous or cellular matrix. It is also possible to modify the fiber surface with a corresponding to treat the appropriate method in order to make the fiber surface more or less hydrophilic or hydrophobic do.

The fibers serve three purposes: (a) by capillary action they increase the speed, with which the liquid is absorbed; (b) they bind the liquid near the surface of the hydrogel by swelling) they fix the hydrogel particle in the fibrous or cellular matrix in which they are embedded.

The ratio of hydrogel to fiber should be such that the hydrogel / fiber mixture is at least 20 Weight percent hydrogel. A particularly satisfactory hydrogel mixture consists of approximately equal proportions by weight of hydrogel and fibers. Hydrogel to fiber ratios from 50:50 to 75/25 show a synergistic effect on fluid absorption. When the hydrogel / fiber blends When used in a fibrous matrix, their retention capacity is greater than the sum of the so individual components.

The invention also relates to a method of making the fiber-coated hydrogel particles. The method is characterized in that the hydrogel particles soften on the surface and with the Fibers are mixed.

Softening can be caused by the action of heat or steam or by treatment with a liquid, preferably with water, water-alcohol mixtures, glycol or benzene will.

After the hydrogel particles are coated with fibers, they can be crosslinked, e.g. B. by chemical Crosslinking agents, preferably by irradiation.

In a preferred method, the liquid (^ finely divided is sprayed on while the hydrogel or the hydrogel-fiber mixture is stirred.

In most cases it will be sufficient to add a minimal amount of the liquid; H. an amount of liquid, that is enough to soften the hydrogel so that the fibers stick to it. The amount of fluid should also to be sufficient to the hydrogel essentially by irradiation or by chemical action to make insoluble. As indicated earlier, the amount of liquid should be that amount of liquid at which the mixture retains its free flowing particulate shape. For other manufacturing processes the amount of liquid can be larger or smaller than that at which the. Mix in In general, the liquid content is in the range of 15 to 80 Weight percent of the mixture of hydrogel and fiber. For some uses it can be desirable be to have a product available with a higher fluid content, and in such cases the specified figures can be exceeded. The water content can be greater than 80%, when the hydrogel and the fibers are present in a 1: 1 ratio and the hydrogel by irradiation is made insoluble

The invention further relates to the use of the coated fibers with hydrogel as water abso ^r beer forming additive in particular after use for disposal articles, preferably diapers, sanitary napkins and tampons. The hydrogel particles can be incorporated into a matrix of fibers or of a cell body, for example made of polyurethane.

The hydrogel particles are worked so firmly into the matrix that they do not settle and or cannot be shaken out during use.

The hydrogel / fiber mixtures described in the following examples were made according to four different Processes which are described below:

1. Large Lodige mixer

A solid-liquid mixer was used with the prescribed amounts of the polymeric compound and fed the fibers; Intimate mixing occurred as soon as water passed through the nozzles within the Mixing container was introduced. Mixing was continued until the specified water was added; the mixing process was also continued afterwards. Overall, the mixing process took a long time about 30 minutes. The resulting wet mixtures flowed freely and could can be moved without difficulty on conventional transport equipment. In this example Polyethylene oxide used; all mixtures were then exposed to ionizing radiation in order to obtain the Carry out crosslinking under the following conditions: using a Van de Graaff electron accelerator an energy of 1.5 MeV was used; the end Particulate, wet powder was moved under the jet at a speed of 15 m / min. The dose was approximately 0.3 Mrad. The wet irradiated mixtures then became a holding jar conveyed and dried in a drying bed through which hot air flows.

2. Small Lodige mixer

A solid-liquid mixer was used with the prescribed amounts of the polymeric substance and

the fibers loaded; once water through the inside The nozzles attached to the mixing vessel entered, intimate mixing occurred. The mixing process went like this continued long until the predetermined water was added; the mixing process was also still going on continued for some time afterwards The mixing process lasted an average of 10 to 15 minutes. The resulting moist mixtures were fairly free flowing and could be used without difficulty ι ο be promoted on conventional transport equipment. Only polyethylene oxide was used; the Mixtures were exposed to ionizing radiation to crosslink under the following conditions initiate; a Van de Graaff electron accelerator with an energy of 1.5 MeV was used; the particulate, glowing powder was under the jet moved at a speed of 50 m / min. The dose was approximately 0.3 Mrad. The irradiated wet mixtures were dried at room temperature and then in a Cumberla: id grinder crushed.

3. Vee mixer

25th

A Patterson-Kelley mixer was prescribed with the Amounts of the polymeric compound or hydrogel and fibers charged; once water entered through the nozzles mounted inside the mixing vessel, intimate mixing occurred. the Mixing was continued until the water was added; even after that the Mixing process continued for a short time. The mixing process took about 15 minutes in total.

In some cases the subsequent crosslinking was carried out by ionizing radiation. In in other cases treatment with ionizing radiation was omitted. All moist hydrogel / fiber mixtures were dried at room temperature and then a sieve with a mesh size of 1.65 mm given.

4. Manual mixing process

A prescribed amount of the hydrogel and the fibers were manually mixed in a beaker; as soon as a sufficient amount of water was added, a damp or wet mixture was created, which no longer contained any free liquid. This wet mixture was then dried at room temperature. A Waring mixer was used to break the dried material into small particles; the Particles were passed through a sieve with a mesh size of 1.65 mm.

A number of hydrogels were used in the examples to show that the improved liquid absorption of the unique hydrogel / Fiber can be attributed and not to the chemical composition of the hydrogels or the Fibers. The following hydrogels were used in the examples:

1. Polyethylene oxide (POLYOX Gel I): polymer compound with high molecular weight, cross-linked by ionizing radiation according to US patents 36 64 343 and 37 83 872.

2. Polyethylene oxide (POLYOX Gel II): polymer compound with high molecular weight, cross-linked with di- and tri-functional acrylate compounds according to Belgian patent 7 83 858.

3. Polyethylene oxide (POLYOX Gel III): polymer compound with high molecular weight, cross-linked with acrylic acid according to US Pat. No. 3,763,277.

4. Dow XD-1300: Commercially available hydrogel in Particle form made from cross-linked !, partially hydrolyzed polyacrylamide. Delivery by the Dow Chemical Corporation.

5. AA / AA'vl Hydrogel: Hydrogel, produced thereby ate sodium acrylate and acrylamide in aqueous solution with ionizing radiation be treated.

6. Polymeric compound 34-A-100: Granular hydrogel, that by saponification of a starch-acrylate copolymer is obtained in aqueous alcoholic solution.

All hydrogel / fiber mixtures based on Polyethylene oxide were compared to a starting hydrogel obtained by irradiating a 4 percent aqueous solution with a Van de Graaff electron accelerator (1.5 MeV, dose 5 Mrad) was obtained. The resulting gel was dried and crushed to a powder having approximately the same distribution as the Particle size was the same as the polymeric substance used to make the hydrogel / fiber mixtures would.

Not only the type but also the length of the fibers used is important. The preferred length the fiber ranges from 1.5 mm to 0.1 mm; however, longer or shorter fibers can also be used will. Mixtures of fibers of different lengths but of the same composition can also be used. Combinations of fibers of various compositions are also useful. The hydrophobic The character of a fiber affects the absorption of the liquid. The more hydrophobic the fiber, the more so the effectiveness is lower.

The following cellulose fibers were used in the examples. used:

Bleached sulphate pulp fibers, average fiber length »0.66 mm.

Bleached sulphite pulp fibers C-40 - average fiber length «0.50 mm,
Bleached sulphite pulp fibers C-100 ß average fiber length «0.50 mm,
Bleached sulfite pulp fibers C-200 - average fiber length <0.50 mm,
Bleached sulphite pulp fibers RB-100 - average fiber length «= 0.47 mm,
Bleached sulfithari wood fibers JBH - average fiber length «1.23 mm,
Bleached Linters CL-100 - average fiber length «0.50 mm.

example 1

The absorption values for hydrogel / fiber mixtures were determined with salt solutions in the following way: Two absorbent pads made of sulfate pulp fibers (dimension: 15.24 cm χ 20.32 cm, weight: approx. 6 g) were placed in layers around a sheet of wadding, the 0.25 g of the evenly distributed hydrogel / fiber mixture contained. 20, 30, 40 and 50 ml of a saline solution (0.3 normal NaCl solution) were slowly added to the Cast surface of the separate pillow; after 30 minutes equilibrium was established. After that

feed
with liquid wedge

was the moist, the hydrogel or the hydrogel / fiber mixture containing film is removed and separated from the upper and lower absorbent pads weighed. Corrections for the average weight of a moist sheet of cotton wool were only made in different liquid additions made. The difference in weight corresponds to that in the particles absorbed liquid. Using this number, it is possible to calculate an absorption value.

This data was used to determine the effectiveness improvement for various Fydrogel / fiber blends determined by comparison with reference substances (see numerical examples). In this example, a Mixture of polyethylene oxide and bleached sulphate pulp fibers used (weight ratio 1: 1). The The procedure and the results are explained below:

Mixing process:

Lodige mixer, great

54.5 kg POLYOX

54.4 kg of pulp fibers

136 kp water

1 kp polyethyleneimine
Radiation dose:

0.3 Mrad

Absorption values when loaded with the following amounts of liquid:

This results in an increase in the effectiveness of hydrogel / fiber particles:

g solution / g hydrogel with coating

ml 12.2

ml 13.5

ml 17.8

ml 19.8

Absorption values of the POLYOX Gel I (irradiated with 5 Mrad).

g solution / g hydrogel

20 m!
30 ml
40 ml
50 ml

7.6

8.9

12.7

15.9

Absorption values of bleached sulphate pulp fibers:

feed
with solution

g solution / g fiber

20 ml 3.9 30 ml 5.0 40 ml 6.8 50 ml 6.7

feed
with solution

g solution

g hydrogel / fiber

g solution
0.5g hydrogel g solution
0.5 g fiber

g additionally
absorbed
solution

Increase in effectiveness

20 ml 12.2 3.8 30 ml 13.5 4.45 40 ml 17.8 6.35 50 ml 19.8 7.95 Examples 2 to 5

1.95 6.45 112% 2.50 6.55 94% 3.40 8.05 83% 3.35 8.50 75%

Analogously to Example 1, the increase (%) in the effectiveness of other hydrogel mixtures was determined. the Results are shown in Table 1. Although the effectiveness of each mixture for 20, 30, 40 and 50 ml of saline solution was determined, only the range of effectiveness is given in the table. The first The number stands for the increase in effectiveness when adding 50 ml and the second number stands for the Increased effectiveness when adding 20 ml

In Examples 2 to 7, bleached sulfate pulp fibers were used used.

Table I. Hydrogel fiber ratio
Hydrogel to fiber Increase in effectiveness
ability of the mixture example Polyethylene oxide gel I cellulose 3: 2 39- 2 Polyethylene oxide gel I cellulose 3: 1 25- 3 Polyethylene oxide gel I cellulose 2.3: 1 32- 4th AA / AAm cellulose 1: 1 38- 5 Starch graft polymer
35-A-100 cellulose 2: 1 25- 6th Starch graft polymer
35-A-100 Pulp bleached 1: 1 36- 7th - 102 - 62 - 48 - 117 - 23 - 24

l-'orlsct / ung llydmgcl 25 28 701 fiber ratio
Hydrogel / u 10 - 32 9 example Polyethylene oxide gel I Sulphite Pulp (C-40) 1: 1 - 4.0 8th Polyethylene oxide gel I Bleached sulphite pulp
(C-IOO) 1: I. - (-) 8.0 9 Polyethylene oxide gel I Bleached sulphite pulp
(C-200) 1: 1 (-1) 10 Chemically cross-linked
Polyethylene oxide gel II Bleached sulphite pulp
(RU-100) 1: 1 Increase in the
l-ascr wedge of the mixture
(%) 58 Il Dow XD-1300 Bleached sulphite pulp
(RB-100) I: 1 50.2 34 12th Dow X D-1300 Bleached sulphite pulp
(RB-100) 2: 1 42.4 50 13th Polyethylene oxide gel I Bleached sulphite
Hardwood razors (JHB) 1: 1 19.0 100 14th Polyethylene oxide gel I Bleached cotton
fiber (linters) (Cl-100) 1: 1 31 - 15th 42 - 29- 48 - 106-

Examples 16-18

Mixtures with three other hydrogels were prepared analogously to Example 1 and absorption values were determined when 20, 30, 40 and 50 ml of saline solution were charged. The hydrogel used and the absorption values are given in Table II.
The following hydrogels were used:
a) Hydroxyethyl cellulose:

Commercially available high molecular weight polymeric compound. The manufacture of the Hydrogel / fiber blends were made using a Vee mixer, and the moist, powdery Mixture was crosslinked by ionizing radiation (dose 0.5 Mrad).

Table II

b) carboxymethyl cellulose:

Commercially available high molecular weight polymeric compound. The hydrogel / fiber mixture was made by means of a Vee mixer, and the moist, powdery mixture was crosslinked by ionizing radiation (dose 1.0 Mrad).

c) polyacrylamide:

Commercially available high molecular weight compound. The manufacture of the hydrogel / Fiber blends were made using a Vee mixer, and the moist, powdery Mixture was crosslinked by ionizing radiation (dose 0.3 Mrad).

Example hydrogel

fiber ratio
Hydrogel to fiber Absorption values
g solution / g hydrogel
with cover Bleached sulfate
cellulose 1: 1 7.7-7.6 Bleached sulfate
cellulose 1: 1 10.5-8.8 Bleached sulfate
cellulose 1: 1 11.3-7.6

16 hydroxyethyl cellulose

17 carboxymethyl cellulose

18 polyacrylamide

Claims (8)

Patent claims: 1. Insoluble in water. Water-absorbing hydrogel particles, characterized in that that the hydrogel a) consists of an inorganic material or a cross-linked organic polymer, b) the particles have a coating of natural or synthetic fibers with a fiber length less than 5 mm and a ratio of fiber length to fiber diameter of at least 5: 1 have, where c) at least some fibers lead out over the surface of the particles, and d) the coated particles pass through a sieve with a mesh size of 4 mm. 2. Hydrogel particles according to claim 1, characterized in that the coating is made of hydrophilic and / or hydrophobic fibers, in particular nylon, rayon, cotton or cellulose fibers. 3. hydrogel particles according to claim 1, characterized in that the hydrogel portion 20 to 75 % By weight. 4. Process for the preparation of the hydrogel particles according to claims 1 to 3, thereby characterized in that particulate hydrogel superficially softened and mixed with the fibers will. 5. The method according to claim 4, characterized in that the softening of the hydrogel by Exposure to heat, water vapor or treatment with a liquid, preferably with Water, water-alcohol mixtures, glycol or benzene is done. 6. The method according to claim 4 or 5, characterized in that the particulate hydrogel is crosslinked by irradiation after sheathing with fibers. 7. Use of the hydrogel particles according to any one of claims 1 to 3, as a water absorbent Additive in objects intended to be thrown away after use, preferably diapers, sanitary napkins and tampons. 8. Use according to claim 7, characterized in that the hydrogel particles in a Matrix made of fibers or a cell body, such as polyurethane, are incorporated.