JPS6197312A - Highly absorptive material - Google Patents

Abstract

PURPOSE:To heighten the water absorptivity of a material both for pure water and for isotonic solution to a level higher than that of the conventional, by partially hydrolyzing a graft polymer comprising hydroxyethylcellulose and a specified olefin monomer. CONSTITUTION:An olefin monomer having a substituent which forms a carboxylate salt (preferably, acrylate ester or acrylamide) upon hydrolysis is graft-polymerized, at about 30-50 deg.C with hydroxyethylcellulose (abbreviated as HEC) having an average molar degree of substitution of 1.2-8 and a viscos ity (as measured in a 2% aqueous solution) of about 20-100,000cP (with a Brookfield viscometer, 60rpm, 25 deg.C). This graft polymer is partially hydrolyzed by a usual process. The optimum degree of hydrolysis can be selected from a wide range of about 2-98% though it varies with the properties of HEC and the kind of a branch polymer used. The partially hydrolyzed graft polymer is useful as a material for disposable absorptive products such as diapers and sanitary napkins.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention is a highly absorbent polymer comprising a graft polymer having hydroxyethyl cellulose as a backbone polymer, which has high absorbency and particularly excellent absorbency for salt-containing aqueous solutions. It concerns sexual materials.

BACKGROUND OF THE INVENTION In recent years, the market for disposable absorbent products such as diapers, sanitary napkins, and surgical dressings has grown rapidly. The raw materials for manufacturing these products need to have a high degree of water absorption as well as excellent absorption of saline aqueous solutions such as body fluids. Conventionally, paper, pulp, nonwoven fabric, etc. have been mainly used, but their absorption performance has been low (and not very satisfactory).

Recently, as such highly absorbent materials, various new water-absorbing resins that utilize the water-retaining and water-absorbing properties of water-soluble polymers have been proposed and put into practical use.

For example, Japanese Patent Publication No. 49-43395 discloses a method of graft polymerizing acrylonitrile onto starch using a cerium salt as a polymerization catalyst, followed by saponification with an aqueous alcoholic solution of an alkali base to obtain a water-absorbing material. but,
The absorption performance of the graft polymer thus obtained is 25 to 144 m/g for water and 22 to 55 m/g for urine.
It is extremely low at nl/g.

In addition, in Japanese Patent Publication No. 53-46199, starch,
Cellulose is the main polymer, and water-soluble monomers such as acrylic acid and acrylamide, monomers that become water-soluble by hydrolysis such as methyl acrylate and acrylonitrile, and crosslinking agents such as N, N-methylenebisacrylamide are essential. A water-absorbing agent or water-retaining agent comprising a resin obtained by graft polymerization as a component and hydrolysis if necessary is disclosed. However, in this case as well, the liquid absorption capacity is j ゛°～°゛°′
8.%jikj to 0.5! Water 9 to ″3°～゛.

ml/g, 30-80+nZ/g for urine, which is still not satisfactory.

Furthermore, JP-A-56-70011 discloses that an aqueous solution containing at least 40% by weight of at least one monomer selected from acrylic acid and alkali metal salts of acrylic acid,
This patent discloses a method for producing a water-absorbing graft polymer in which multi-Ti compounds such as cellulose, starch, and guar gum are present and reacted using a water-soluble radical polymerization initiator. This article also shows an example in which a mixed monomer of acrylic acid and sodium acrylate was graft-polymerized on hydroxyethyl cellulose using potassium persulfate as a polymerization initiator.
The absorption performance of the obtained graft polymer was 450 g/g for ion-exchanged water and 71 g for 0.9% saline.
/g and 52 g/g of urine, and although the absorption capacity for pure water has been considerably improved, the absorption capacity for physiological saline is still low.

(Problems to be solved by the invention) As mentioned above, various types of super absorbent resins such as starch-based, cellulose-based, and synthetic polymer-based resins have been proposed and developed. Water-absorbing resin has a water absorption capacity of about 100 to 600g/g for pure water, but its water absorption capacity for solutions containing salts and ions such as physiological saline and urine is extremely low at about 30 to 100g/g. There was a drawback that it decreased.

The purpose of the present invention is to improve this drawback and provide a highly absorbent material that has an extremely high water absorption capacity for pure water, and also exhibits an unprecedentedly high absorption capacity for physiological saline, exceeding 120 g and 7 g. It's about doing.

(Means for Solving the Problems) That is, the present invention involves graft polymerizing hydroxyethylcellulose with an olefinic monomer having a substituent that produces a carboxyl group by hydrolysis, and then subjecting it to partial hydrolysis. The present invention provides a highly absorbent material made of a graft polymer obtained by.

Hydroxyethylcellulose (hereinafter abbreviated as HEC) used as the backbone polymer in the present invention is manufactured using a known method for producing -S by reacting ethylene oxide with alkali cellulose obtained by reacting cellulose with an alkali such as sodium hydroxide. However, in order to obtain high absorption performance, the average molar substitution degree (hereinafter abbreviated as MS), expressed as the average number of moles of ethylene oxide added per anhydroglucose unit, must be 1.2 to 8.0. And,
and the viscosity of 2% aqueous solution is 20 to 100,000 cps
(Type B viscometer, 60 rpm, 25°C).

If HEC, which has a viscosity higher than 100,000 cps, is used as the backbone polymer, the viscosity will be too high and graft polymerization will be difficult, and the obtained polymer will only have poor absorption performance for partial hydrolyzate. Conversely, HE with a low viscosity of 20 cps or less
Even when C is used, a graft polymer with high absorption performance cannot be obtained.

If the MS of HEC used is less than 1.2, it becomes water insoluble, graft polymerization does not proceed uniformly, and the resulting polymer has poor absorption performance for partial hydrolyzate. On the other hand, MS is 8
．． HEC with a high MS of 0 or more is difficult to economically produce industrially.

Examples of the olefinic monomer having a substituent that generates a carboxyl group upon hydrolysis, which is grafted as a technical polymer to HEC in the present invention, include methyl acrylate, ethyl acrylate, butyl acrylate, and 2-acrylic acid. Acrylic esters such as ethylhexyl, methacrylic esters such as methyl methacrylate, ethyl methacrylate, butyl methacrylate, and 2-ethylhexyl methacrylate, monomers with nitrile groups such as acrylonitrile and methacrylonitrile, amides such as acrylamide Examples include monomers having groups.

The graft polymerization method may be any conventionally known method, such as irradiation with radiation, electron beams, ultraviolet rays, ceric salt, hydrogen peroxide, benzoyl peroxide, azobisbutyronitrile, ammonium persulfate, etc. Graft polymerization using a ceric nitrate salt as a polymerization catalyst in water or a mixed solvent of water and a hydrophilic organic solvent such as alcohol This method is preferable because a graft polymer having a high polymerization rate and excellent absorption performance can be obtained.

The polymerization temperature varies depending on the polymerization catalyst used, but is usually 10
-100°C, preferably 30-50°C. After polymerization, a solvent such as methanol, isopropyl alcohol, or acetone is added to precipitate the polymer. The obtained polymer is used as it is, or after extracting and removing unreacted NEC with water, or extracting and removing the homopolymer of monomers that generate carboxyl groups by hydrolysis with water or acetone or other organic solvent, Perform partial hydrolysis.

In the present invention, partial hydrolysis of the graft polymer is an essential requirement for obtaining high absorption performance. Graft polymers that are not hydrolyzed and graft polymers that are completely hydrolyzed do not provide high absorption performance, so it is important that they are partially hydrolyzed. The hydrolysis rate is 2
It can be selected within a wide range of ~98%, but the optimum hydrolysis rate varies depending on the HEC properties of the backbone polymer used and the type of technical polymer.

For example, when acrylamide is grafted, a hydrolysis rate of 40 to 80%, preferably 50 to 70%, has a high absorption capacity.

The partial hydrolysis may be carried out by any known method, but it is usually carried out using sodium hydroxide, potassium hydroxide, etc. in water or a mixed solvent of water and alcohol.
It is carried out at a temperature of °C.

After partial hydrolysis, the graft polymer may be neutralized to form an alkali metal salt, dried and pulverized as it is to produce a product, or the following post-treatment may be performed. That is, the partial hydrolyzate is precipitated by adding a non-solvent such as methanol or isopropyl alcohol, and after separation, it is dissolved again in pure water and neutralized with hydrochloric acid or other acid to convert the carboxyl group into acid form (-COOH).
). After precipitation with methanol, isopropyl alcohol, etc. again, and furnace separation, it is neutralized with sodium hydroxide or potassium hydroxide to obtain an alkali metal salt. Next, after reprecipitation with methanol, isopropyl alcohol, etc., separation,
Dry and crush to make products.

Drying can be done at a temperature between room temperature and 200°C using any known method such as air drying, ventilation drying, reduced pressure drying, or heat drying, but in order to obtain high absorption performance, it is best to dry at the lowest possible temperature and in the shortest possible time. desirable.

In the present invention, a crosslinking agent is not necessarily required depending on the type of technical polymer used. For example, when graft polymerizing acrylic esters, methacrylic esters, etc., a water-insoluble graft polymer is obtained by self-crosslinking, so no crosslinking agent is particularly required. On the other hand, when graft polymerizing acrylamide or the like produced by a water-soluble graft polymer, it is desirable to use a crosslinking agent.

The crosslinking agent may be any known crosslinking agent, including bisacrylamides such as N,N-methylenebisacrylamide, as long as it reacts with the graft polymer to crosslink it. Further, crosslinking can be carried out by adding a crosslinking agent during graft polymerization, but a crosslinking agent may be reacted with the graft polymer after graft polymerization.

(Examples) The present invention will be explained in more detail by examples below.
The present invention is not limited to these examples. Note that parts and percentages in the examples are parts by weight and percentages by weight.

Examples 1-6 3 parts of HEC, 15 parts of methyl acrylate, and 8.3×10. -'mol/1, nitrate 610.0
6 mol/l and water were added to make the total solution amount 120 parts, graft polymerization was carried out at 40° C. in a nitrogen stream, and then precipitation was performed with methanol. From this total polymer, HEC is extracted with water.
Polymethyl acrylate (hereinafter abbreviated as PMA) with acetone
0.5N-Na01
Partial hydrolysis was carried out using an aqueous solution of 1 at 100° C. for 5 to 400 minutes.

The partial hydrolyzate was redissolved in the precipitated water with methanol, neutralized with hydrochloric acid using phenolphthalein as an indicator,
0 was reprecipitated with methanol, then made into a sodium salt with sodium hydroxide, precipitated with methanol, separated by IP, and dried under vacuum at room temperature.

It was pulverized to obtain a partial hydrolyzate of the graft polymer.

Table 1 shows the results of measuring the absorption performance of the partial hydrolyzate of the graft polymer obtained by the above method for various HEC backbone polymers with different MS and viscosity.

To measure absorption performance, add pure water or physiological saline with a concentration of 0.85% to 0.1 to 0.2 g of the sample, leave it at room temperature for 24 hours to allow sufficient absorption, and then heat it in a furnace with a 200-mesh wire mesh. A filtration method was used in which the amount of filtrate was measured and the water absorption capacity was calculated from the amount of pure water or physiological saline added initially.

Table 1 Examples 7 to 9 2 parts of HEC, 4 parts of acrylamide, and 0.3% of N,N'-methylenebisacrylamide based on the acrylamide.
, cerium ammonium nitrate 8.3 Xl0-'mol/
1, add 0.06 mol/l nitric acid and water to bring the total solution volume to 80
After graft polymerization at 40'C in a nitrogen stream, the mixture was precipitated with isopropyl alcohol. After removing unreacted HEC and water-soluble homopolymer from the obtained polymer with water, 0.
Partial hydrolysis was carried out using a 5N-NaOH aqueous solution at 100°C for 5 to 120 minutes. This was precipitated with methanol, separated in a furnace, dried under vacuum at room temperature, and pulverized to obtain a partial hydrolyzate of the graft polymer.

Table 2 shows the results of measuring the absorption performance in the same manner as in Example 1 for the partial hydrolysates of the graft polymers obtained by the above method, with various HEC MS and viscosities of the trunk polymers.

Table 2 Example 1O 2 parts of HEC, 8 parts of acrylonitrile, 1.0 x 10-' mol/It of cerium ammonium nitrate, nitrate #0.0
6 mol/I! and 8 parts of water and heated at 40°C in a nitrogen stream.
After time graft polymerization, it was precipitated with methanol. After extracting and removing unreacted HEC with water and acrylonitrile homopolymer with dimethylformamide from the obtained polymer,
．． Partial hydrolysis was carried out in a 5N-Na011 aqueous solution at 100°C for 8 hours. The partial hydrolyzate was precipitated with methanol.
After separating the tP, it was vacuum dried at room temperature and pulverized.

The graft ratio of the obtained graft polymer was 254°2%,
The hydrolysis rate was 82.2%. Table 3 shows the results of measuring the absorption performance in the same manner as in Example 1.

Table 3 Comparative Examples Regarding commercially available starch-based and cellulose-based absorbents,
Table 4 shows the results of measuring the absorption performance of pure water and physiological saline using the method described in Example 1.

Table 4 (Effects of the invention) The superabsorbent material of the present invention has an amazing water absorption capacity of about 1000 to 3000 g/g, whereas conventional water absorbent resins only exhibit a water absorption capacity of about 100 to 600 g/g for pure water. It has a water absorption capacity of 120 to 400g for physiological saline.
/g, which overcomes the drawback that conventional water-absorbing resins have a reduced ability to absorb physiological saline to about 30 to 100 g/g.

Therefore, the superabsorbent material of the present invention having such excellent properties is extremely effective as a raw material for products for absorbing saline aqueous solutions such as body fluids, such as diapers, sanitary napkins, and surgical bandages.

Claims (1)

[Scope of Claims] 1. Consisting of a graft polymer obtained by graft polymerizing hydroxyethylcellulose with an olefinic monomer having a substituent that generates a carboxyl group by hydrolysis, followed by partial hydrolysis. Highly absorbent material. 2 Average molar degree of substitution of hydroxyethyl cellulose (M
S) is 1.2 to 8.0, and the viscosity of a 2% aqueous solution is 20
~100,000 cps (B-type viscometer, 60 rpm, 2
5°C). 3. The superabsorbent material according to claim 1 or 2, wherein the olefinic monomer having a substituent that generates a carboxyl group upon hydrolysis is at least one selected from acrylic esters and acrylamide.