JP2000297101A - Manufacture of crosslinked carboxyalkyl cellulose and absorber therefrom - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing crosslinked carboxyalkyl cellulose having excellent water absorbing capacity even in the case a recycled pulp from used paper is used, and also provide a method of manufacturing absorbent therefrom. SOLUTION: A recycled pulp is microfibrilated beforehand in a method of manufacturing the crosslinked carboxyalkyl cellulose by carboxyalkylating and crosslinking the recycled pulp. It is preferable to microfibrilate the recycled pulp, and then to form the crosslinked carboxyalkyl cellulose by carboxyalkylation and crosslinking.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a crosslinked carboxyalkylcellulose from recycled pulp made from waste paper or the like and a method for producing an absorbent comprising the crosslinked carboxyalkylcellulose.

[0002]

2. Description of the Related Art Waste paper consumed in Japan is high-quality waste paper, and most products made from waste paper are paper products. 87.8% of paperboard (corrugated cardboard, paperboard for cardboard, construction paper, etc.) and paper (newspaper, print information paper,
27.2% of such paper (wrapping paper, sanitary paper, etc.) uses waste paper as a raw material (according to a survey of the Waste Paper Recycling Promotion Center in 1996). The average number of times of recycling as a paper product is 3 to 5 times, and there are no reused waste papers that are difficult to recycle, and those collected with great care are often incinerated. Paper is 200
Since it is subject to the Containers and Packaging Recycling Law that will be enforced in fiscal year 0, it is certain that the amount of recovered waste paper, especially miscellaneous waste paper, will increase, and development of products that use waste paper other than paper is desired.

[0003] Use methods other than waste paper include pulp mold, paper mold pallet, paper sheet pallet, cellulose fiber, concrete form, recycled paper mulch, livestock litter, solid fuel, hot-press molding material, soil substitute material, etc. There is.
The usage of non-paper is small compared to the usage rate of paper, and there is a demand for increased sales of used paper. As one of the reuse destinations of the used paper, it is conceivable to prepare a carboxyalkylcellulose crosslinked material used for a water absorbing material or the like. The water absorbing material can be used in various fields, such as disposable diapers, agricultural and horticultural water retention agents, artificial snow, chemical warmers, and sealing agents for civil engineering and construction. Becomes

Conventionally, as a method for producing a crosslinked carboxyalkylcellulose, a method of directly carboxyalkylating cellulose as a raw material has been known (Japanese Patent Publication No. 47-17965, Tetsuo Koshijima, Akira Kai, See "Development of Functional Cellulose", edited by Kenji Kamiide and Kunihiko Okajima, etc., published by CMC Co., Ltd., 1985). on the other hand,
Microfibrillated cellulose having a high suspension stability (showing stable dispersibility even at a very low solid content) and a high viscosity by making pulp fibers into fine fibers is known. This is useful as a humectant, dispersant and thickener, but there is no example of carboxyalkylation and use as a water absorbing agent.

[0005]

The recycled pulp obtained from waste paper has been subjected to at least one drying step in the papermaking process, and therefore contains a large amount of fine fibers such as keratinized fiber pieces and binding fibers. Also, through the recycling process,
Fibers are damaged or fiber lengths are irregular. For this reason, the reaction is likely to be non-uniform, and there is a problem that the same water-absorbing effect cannot be obtained even by using the conventional method for producing a carboxyalkylated crosslinked product.

An object of the present invention is to provide a method for producing a crosslinked carboxyalkylcellulose having excellent water absorbing ability even when recycled pulp obtained from waste paper is used, and a method for producing a water-absorbing material comprising the same. Is what you do.

[0007]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve such problems. As a result, the crosslinked carboxyalkylcellulose produced from the regenerated pulp can be obtained by appropriately microfibrillating the regenerated pulp. The present inventors have found that a conventional water absorbing effect can be obtained, and have reached the present invention.

That is, the present invention provides a method for producing a crosslinked carboxyalkylcellulose, which comprises preliminarily microfibrillating the regenerated pulp when producing a crosslinked carboxyalkylcellulose by carboxyalkylating and crosslinking the regenerated pulp. And a method for producing an absorbent comprising the crosslinked carboxyalkylcellulose thus produced.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
Recycled pulp used in the present invention is cardboard, tea imitation paper, magazines, mounts, ground tickets, balls, newspapers, white paper, cards,
It is obtained from used paper such as special white, medium white, white manila, ticket, imitation, etc. through a general recycled paper manufacturing process. The outline of the recycled paper manufacturing process is as follows: first, a defibration process using a pulper, etc.
Dewatering is performed as necessary after a selective cleaning step and a deinking step by a flotation method or the like, and these steps may be appropriately selected and adjusted according to the type and quality of the used paper.

In the present invention, it is necessary that the recycled pulp obtained from the used paper be appropriately microfibrillated before being subjected to carboxyalkylation and treatment with a crosslinking agent. As a method for microfibrillation, various conventionally known methods for microfibrillating pulp fibers can be applied. For example, a medium stirring mill treatment, a vibration mill treatment, a treatment with a high-pressure homogenizer, a colloid mill treatment and the like can be mentioned.

In the medium stirring mill treatment, a recycle pulp fiber is stirred by rotating a stirrer inserted into a fixed crushing vessel at a high speed to agitate a medium such as glass beads or alumina beads placed in the vessel and the regenerated pulp fiber. This is a method of microfibrillation. Vibration milling is a method in which a crushed container is vibrated at a high speed, and the regenerated pulp fibers are microfibrillated by beads, balls, rods and the like in the container. The treatment by a high-pressure homogenizer is a method in which regenerated pulp fibers are slurried, and high pressure is applied to the pulp fibers to pass between small-diameter orifices to be pulverized and dispersed. Colloid mill processing uses a stone mill type pulverizer composed of a pair of whetstones, at least one of which rotates, and applies an impact, centrifugal force, and shear force generated when the processing object passes through the opposing gap between the whetstones, thereby processing the processing target object. In this method, the fibers of the recycled pulp are cut and microfibrillated when passing through the opposing gap of the grinding wheel.

Although any method can be used to microfibrillate the regenerated pulp, a method using a millstone-type pulverizer is preferable. The method using a medium stirring mill and a vibration mill requires a medium such as glass beads, alumina beads, balls, or the like. Further, in the method using the high-pressure homogenizer, the pulp needs to be slurried, so that the pulp must be once ground as a pretreatment. According to the method using a millstone-type pulverizer, it is possible to treat the recycled pulp in a state of being disintegrated with water without pulverizing the regenerated pulp, and even after the pulverization, there is no need to separate the medium from the medium only by dewatering.

In the present invention, the regenerated pulp is microfibrillated as described above. At this time, the regenerated pulp preferably has a viscosity of 200 mPa · s or more and the stability of the suspension is 70 or more, Viscosity 400mPa ・
More preferably, the stability of the suspension is 95 or more. Here, the viscosity is a value measured at a concentration of 2% by weight in a water suspension at a room temperature of 25 ° C. and a rotor rotation speed of 30 rpm using a B-8L type viscometer of Tokimec Co., Ltd. The stability was determined by preparing a 0.5% by weight suspension, placing the suspension in a 100 mL graduated cylinder, degassing by decompression, and allowing the suspension to stand at 25 ° C. for 1 hour. It is a value expressed as a percentage. Viscosity less than 200 mPa · s, suspension stability 70
If it is less than this, microfibrillation becomes insufficient, and as a result, the water absorption of the obtained crosslinked carboxyalkylcellulose is inferior, which is not preferable.

Next, the microfibrillated regenerated pulp fiber is dehydrated by a centrifuge or a filter press, and the moisture content is measured, followed by carboxyalkylation and crosslinking. The dehydration may be performed so that the moisture content required in the method for performing the carboxyalkylation reaction is attained. When the carboxyalkylation reaction described below is a water-based method, the water content is about 40%.
About 0% is desirable.

For carrying out carboxyalkylation and crosslinking, conventionally known methods can be similarly applied. The carboxyalkylation method is roughly classified into an aqueous medium method and a solvent method (refer to the above-mentioned “Development of functional cellulose”). In the aqueous medium method, for example, after pulp and monochloroacetic acid, which is an inexpensive carboxymethylating agent, are sufficiently immersed at 10 ° C. or less, crushing and mixing are performed while cooling, and then 18%
In this method, sodium hydroxide is added, crushing and mixing are performed in the same manner while cooling, and the mixture is reacted at 60 ° C. for about 2 hours to obtain crude carboxymethyl cellulose. The carboxymethylating agent used is not limited to sodium monochloroacetate, but may be another alkali metal salt or a monobromoacetic acid alkali metal salt. In the solvent method, for example, an aqueous solution of sodium hydroxide and isopropanol are added to the pulp, and the mixture is sufficiently stirred to obtain alkali cellulose. This is a method for obtaining carboxymethyl cellulose.

When preparing a crosslinked carboxyalkylcellulose other than carboxymethylcellulose, an alkali metal salt of halocarboxylic acid, such as alkali metal salt of α-chloropropionic acid or alkali metal salt of β-chloropropionic acid, is used instead of sodium monochloroacetate. An alkali metal salt of α-bromopropionic acid, an alkali metal salt of β-bromopropionic acid and the like may be used. In addition, halogenated polycarboxylic acids such as monochlorosuccinic acid and monochloromalonic acid can be used.

The degree of substitution of the carboxyalkyl group is 0.5
It is preferable that this is the case. For this reason, it is preferable that the carboxyalkylating agent be used in one reaction in a molar ratio of 1 to 2 with respect to the hydroxyl group of the glucose residue. If the molar ratio is less than 1, the degree of substitution will be low, while if the molar ratio exceeds 2, the degree of substitution will not increase in one reaction. In order to obtain a high degree of substitution, the reaction may be performed twice or more.

For crosslinking of carboxymethylcellulose,
A known crosslinking agent such as epichlorohydrin, ethylene glycol dicricidyl ether, divinyl sulfone, formaldehyde, etc. may be reacted.

The smaller the degree of crosslinking, the higher the water absorption.
Gel strength decreases. An appropriate degree of crosslinking may be determined depending on the application, and the degree of crosslinking may be adjusted by increasing or decreasing the rate of addition of the crosslinking agent.

The carboxyalkylation and cross-linking may be performed after the carboxyalkylation is performed first, the carboxymethylation may be performed after the cross-linking is performed first, or the cross-linking and the carboxyalkylation may be performed. May be performed simultaneously. The carboxyalkylation reaction may be performed repeatedly, for example, the first time, the degree of substitution is decreased, and the second time, the degree of substitution is increased.

The crosslinked carboxyalkylcellulose thus obtained may be sufficiently washed with methanol or the like and then sufficiently dried by drying under reduced pressure. Further, the obtained carboxymethylated crosslinked product is preferably swelled in a mixed treatment solution of water, a hydrophilic organic solvent, an ammonium salt, and an alkali metal salt as a post-treatment, so that the water absorption can be increased. The crosslinked carboxyalkylcellulose may be of a sodium salt type or an acid type.

The crosslinked carboxyalkylcellulose obtained as described above is useful as a water absorbing material because of its excellent water absorbing power. The method for producing a water-absorbing material of the present invention,
After the regenerated pulp is microfibrillated as described above, carboxyalkylation and cross-linking are performed to produce a cross-linked carboxyalkyl cellulose.

In the present invention, it is considered that fine fibers such as keratinized fiber pieces of regenerated pulp fibers and binding fibers are removed or unraveled through the microfibril process. Further, the fibers are damaged or the fiber lengths become irregular during the recycling process, but it is considered that the fiber lengths themselves become uniform. Further, it is known that microfibrillated fibers themselves have high water retention capacity. For this reason, in the present invention, since the reaction becomes uniform by the uniformity of the quality of the recycled pulp and the water retention capacity is improved by microfibrillation, the water absorption capacity is improved even when recycled pulp from waste paper is used. It is thought that it was done.

[0024]

The present invention will be described in more detail with reference to the following examples. The moisture content of the microfibrillated regenerated pulp is Y
The measurement was performed using an infrared drying electronic moisture meter IB-30 manufactured by MC Corporation. The water absorption and the degree of carboxyalkyl substitution of the crosslinked carboxyalkylcellulose were measured by the following methods. The viscosity and suspension stability of the regenerated microfibrillated pulp were measured by the methods described above.

Reference Example 1 [Measurement of Water Absorption] A sample (0.2 g) was placed in a 9.5 cm × 7 cm, 250 mesh nylon bag and immersed in 1 L of pure water. 3
After a period of time, this was lifted up, lifted and drained for 10 minutes, and then the weight of the sample was measured. The weight (g) of pure water absorbed per gram of the sample was defined as the water absorption.

Reference Example 2 [Measurement of degree of carboxyalkyl substitution] A 0.5 g sample was placed in a beaker, 25 mL of a 70% methanol solution containing 1 mol / L hydrochloric acid was added, and the mixture was allowed to stand for 1 hour. After washing hydrochloric acid with methanol, it was dried under reduced pressure. Next, the dried sample was placed in a 100 mL beaker, and about 15 mL of 0.1 N sodium hydroxide and 5 mL of pure water were added.
After adding 0 mL and stirring for 1 hour, the mixture was titrated with phenolphthalein indicator using 0.1 N hydrochloric acid. The degree of substitution was calculated by the following equation. Y = 0.1A-0.1B ... Expression Substitution degree = 162Y / (1000W-80Y) ... Expression A: Amount of 0.1N sodium hydroxide solution (mL) B: 0.1N hydrochloric acid Amount (mL) Y: Amount of carboxyalkyl group (milliequivalent) W: Weight of carboxyalkyl cellulose (g)

Example 1 Waste paper was refined through a pulper and a deinking process and used as recycled pulp. 10L of 100g of recycled pulp
And left for 1 hour after boiling in deionized water. After returning to room temperature, a stone mill type pulverizer (Serendipita MKCA)
6-3 type: manufactured by Masuyuki Sangyo Co., Ltd.), using a 150 mm diameter grinding wheel made of silicon carbide, and a grinding wheel rotation speed of 1600 rpm
m, and the processing was performed under the conditions of a grinding wheel gap of 0.05 mm. By this treatment, the viscosity of the pulp obtained was 600 mPa ·
s, and the suspension stability was 98. The obtained pulp slurry was supplied to centrifugal separation, and dewatered to a moisture content of about 80%.

The obtained microfibrillated recycled pulp 1
g., a solvent prepared to be 89.7% isopropanol and 10.3% pure water based on the measured moisture content.
7 mL was added and stirred until the solution became homogeneous. After stirring, 0.55 g of sodium hydroxide was dissolved in 968 μL of pure water, and then added little by little to the reaction solution. After sufficiently alkalizing the pulp fiber, 0.59 g of monochloroacetic acid was dissolved in 2.1 mL of isopropanol,
The reaction solution was added in small portions. After raising the temperature of the reaction solution to 72 ° C., a carboxymethylation reaction was performed for 3 hours.

Next, 103 μL of epichlorohydrin was added as a crosslinking agent, and the mixture was further reacted for 3.5 hours. After the reaction,
The reaction solution was neutralized with acetic acid, washed with 80% methanol, and then with 100% methanol. The crosslinked carboxymethylcellulose that had been sufficiently washed was dried under reduced pressure. With respect to the crosslinked carboxyalkylcellulose thus obtained, the water absorption in pure water and the degree of carboxymethylation substitution were measured. Water absorption is 83.3
g / g and the degree of substitution was 0.54. Table 1 shows the results
Shown in

[0030]

[Table 1]

Example 2 A microfibrillated regenerated pulp was obtained in the same manner as in Example 1 except that the gap between the grinding wheels was 0.15 mm. The viscosity of the obtained pulp was 400 mPa · s, and the suspension stability was 95. This pulp was subjected to carboxymethylation and crosslinking in the same manner as in Example 1. With respect to the crosslinked carboxyalkylcellulose thus obtained, the water absorption in pure water and the degree of carboxymethylation substitution were measured. The water absorption is 62.6 g / g,
The substitution degree was 0.58. Table 1 shows the results.

Comparative Example 1 A crosslinked carboxyalkylcellulose was obtained without performing microfibrillation in the examples. That is, 100 g of pulp regenerated from used paper was boiled in 10 L of ion-exchanged water and left for one hour. The viscosity of the obtained pulp dissociated solution could not be measured because the value was not constant because it was fibrous. The suspension stability was 50. Pulp was recovered from the pulp disintegration solution by vacuum filtration. After measuring the weight and calculating the amount of water, 19.7 g of recycled pulp was treated with 89.7% isopropanol and 10.3% based on the measured water content.
49.7 mL of a solvent prepared to become pure water was added, and the mixture was stirred until the solution became homogeneous. Thereafter, the same treatment as in Example 1 was performed to obtain a crosslinked carboxyalkylcellulose. This water absorption was 28.7 g / g, and the degree of substitution of the carboxymethyl group was 0.47.

Comparative Example 2 1 g of cellulose powder was boiled in 100 mL of ion-exchanged water and left for 1 hour. The viscosity of the cellulose powder sample was 10 mPa · s, and the suspension stability was 5. Thereafter, the same treatment as in Comparative Example 1 was performed to obtain a crosslinked carboxyalkylcellulose. This water absorption is 69.7 g / g.
And the degree of substitution of the carboxymethyl group was 0.55. .

As can be seen from Table 1, the crosslinked carboxymethylcellulose of the regenerated pulp fiber which had been microfibrillated using a millstone type mill (Examples 1 and 2) was crosslinked with carboxymethylcellulose obtained without microfibrillation. The water absorption was higher and the degree of substitution was higher than that of the body (Comparative Example 1). These values were almost the same as the water absorption and the degree of substitution of the crosslinked carboxymethylcellulose of the cellulose powder.

[0035]

According to the present invention, the regenerated pulp obtained from waste paper is microfibrillated as a pretreatment to improve the water absorbing power of the crosslinked carboxyalkyl cellulose of the regenerated pulp.

Claims (2)

[Claims] 1. A method for producing a crosslinked carboxyalkylcellulose, wherein the regenerated pulp is preliminarily microfibrillated when producing a crosslinked carboxyalkylcellulose by carboxyalkylating and crosslinking the regenerated pulp. 2. A method for producing an absorbent material, wherein a recycled pulp is microfibrillated, then carboxyalkylated and crosslinked to form a carboxyalkylcellulose crosslinked product.