JPH03146501A - Production of cellulose ether having high polymerization degree - Google Patents

Abstract

PURPOSE:To obtain the subject substance, capable of exhibiting a high viscosity and useful as an admixture for extrusion molding of cement-based molded bodies by etherifying anhydrous crude linter with an alkyl halide and alkylene oxide in respective specific proportions in the presence of a base and washing the resultant ether with hot water. CONSTITUTION:One pt.wt anhydrous crude linter is etherified with 0.6-1.9 pts.wt alkyl halide (e.g. methyl chloride or ethyl chloride) and 0.1 pts.wt. alkylene oxide (e.g. propylene oxide or ethylene oxide) in the presence of 0.5-1.5 pts.wt. base and the resultant ether is then washed with hot water to afford the objective compound.

Description

Detailed Description of the Invention (Field of Application of Production, 1!7) The present invention relates to a method for producing a highly polymerized cellulose ether suitable as an admixture for extrusion molding of concrete and cementitious molded bodies. .

(Prior Art) Water-soluble cellulose ether is used in a wide range of fields as a thickener, binder, etc. because it exhibits a thickening effect even when added in a relatively low amount. The degree of polymerization of industrially produced cellulose ethers varies widely, from 3 cps to 100,000 cps, expressed as the viscosity of a 2% aqueous solution, and one with an appropriate addition amount and viscosity is selected depending on the purpose of use. There is.

On the other hand, applications that have recently been considered and are being put into practical use include the civil engineering field, which focuses on extruded cementitious molded products that do not contain asbestos as reinforcing fibers and concrete that has been given viscosity.

For both products, it has been confirmed that the higher the degree of polymerization of the admixture, that is, the higher the viscosity of the aqueous solution, the more effective it is with a smaller amount added, and there is a demand for cellulose ethers that are cheaper and have a higher degree of polymerization.

In particular, alkyl cellulose ethers with a high degree of polymerization obtained by etherifying cellulose with alkyl halides are preferred as cement-based admixtures that provide excellent thickening properties.

(A! Problem to be solved by the invention) By the way, cellulose and its derivatives are generally substances that easily undergo depolymerization due to various factors such as heat, oxidation, mechanical force, acids, alkaline earth metals, etc. In the cellulose-related industry, how to lower the degree of polymerization to a desired level or how to suppress the decrease in the degree of polymerization has always been a technically important issue.

The means for producing this highly polymerized cellulose ether can be summarized into the following two methods.

1) Use a high polymerization degree cellulose raw material.

2) Etherification is performed under conditions that suppress a decrease in the degree of polymerization.

Currently, the cellulosic raw material available for the former is purified cotton linters. The degree of polymerization of the linter pulp made from this is usually determined by the viscosity of the copper ammonia solution (A, C, S
2.5% falling ball formula).

Conventionally, the viscosity was about 3,000 to 4,500 seconds, and the degree of polymerization was about 2,500 to 3,000, but with recent advances in linter refining technology, the viscosity has decreased to about 1,500 seconds.
0,000-130.000 seconds 1 degree of polymerization s, oo
It is said that this level is close to the limit for the time being. Of course, in the laboratory it is possible to obtain purified linter that maintains the degree of polymerization of the crude linter as a raw material, but this is not economically viable and is not practicable industrially.

Regarding the latter, a technology has been established to suppress the decrease in the degree of polymerization as much as possible by alkalizing and etherifying cellulose in the absence of oxygen.

In particular, for alkylcellulose ethers produced using alkyl halides whose degree of etherification is determined by the amount of alkali added to cellulose, the amount of alkali added is usually large, and the latter method is suitable for producing highly viscous alkylcellulose ethers. It is a necessary condition to obtain it. However, cellulose ethers obtained using these conventional techniques have a viscosity of about 20,000 cps when measured at 20°C as a 1% aqueous solution, even if the cellulose ether has a high viscosity.
The extent is the limit.

In view of this fact, the present inventors have found that the viscosity of a 1% aqueous solution is 20,000 ml, which is sufficient for use as an admixture for cement.
The results of a study on an inexpensive method for producing cellulose ether with a high degree of polymerization of 0 cps or more.

After cutting long hair fibers (lint) from cotton seeds, the short hair fibers (crude linter) obtained by separating them from the cotton seed shells are used as raw material for cellulose, and ether is produced by a known method for producing alkyl cellulose ethers. If it becomes
The measured viscosity of a 1% aqueous solution at 20°C is approximately 20,000.
The present invention was achieved by discovering that alkyl cellulose ether having a production capacity of cps or higher can be produced.

In other words, the α-cellulose content in crude linter is usually 90%.
After purification, the purity can be increased to about 99%. On the other hand, the degree of polymerization of cellulose in its natural state is said to be on the order of s, ooo, but after boiling with a dilute aqueous sodium hydroxide solution, followed by bleaching with a chlorine bleach such as sodium hypochlorite, and deashing with an acid. The degree of polymerization of cotton linters that are continuously depolymerized and purified through a series of treatments such as the above decreases to a maximum of about 2,500. Therefore, the present inventors focused on the fact that a cellulose ether exhibiting the highest viscosity could be obtained by etherifying it while maintaining the degree of polymerization in its natural state, and proceeded with research.

Note that the crude linter contains about 1 to 4% of impurities such as pectin and protein. Due to the presence of these impurities and the low α-cellulose content, there were concerns about a decrease in yield during production and coloration of the product, but the present inventors found that the cost of crude linter pulp was 1/2 that of ordinary refined linter pulp. /3
However, the present invention has cost advantages that outweigh the reduction in yield, and even if the product is colored, the amount of admixture added to the cement product is small, 1% or less.
The present invention was completed by discovering that the influence of coloring is not a problem.

(Means for Solving the Problems) The method for producing a highly polymerized cellulose ether according to the present invention is a method for producing a highly polymerized cellulose ether in the presence of 0.5 to 1.5 parts by weight of a base based on 1 part by weight of anhydrous crude linter. .6-1.9
It is characterized in that it is etherified using part by weight and 0 to 1 part by weight of alkylene oxide, and then washed with hot water.

To explain this in more detail, 1. The crude linter used as a raw material in the present invention is the short-hair fiber (crude linter) obtained by cutting long-hair fibers (lint) from cottonseed and then separating it from the cottonseed shell. ), and is used as is, without being purified with alkaline solutions or chlorine bleach as in the past.

The base used in the production of cellulose ether is
It is necessary to destroy the crystallinity of cellulose, and it is necessary to react without leaving any unreacted base after the reaction is completed, and to reduce the decrease in the degree of aged polymerization due to the base and oxygen in the air. Therefore, it is generally preferable to use dust in an amount of 90 mol% or less based on the amount of alkyl halide used, and in the present invention, it is used in an amount of 0.5 to 1.5 parts by weight per 1 part by weight of anhydrous crude linter. .

The present invention is based on formula (1) in which cellulose is reacted with a halogenated alkyl etherification agent in the presence of approximately equimolar base;
In formula (2), in which an activation reaction component (alkylene oxide) that can directly react with the hydroxyl group of cellulose is reacted in the presence of a catalytic amount of base, formula (1) or (1)
) is a base quantum based on the formula (L), and is based on the formula (3) which performs both formula (2).

Ce1l-OH-BOH+Hal-R1→Cel1-0
-R1+ H, 0+ B Hal- (L) BO here
H: bases such as alkali metal hydroxides, alkaline earth metal hydroxides, or quaternary ammonium salts Hal: chlorine or bromine atom R1: alkyl group R1, R3: hydrogen atom or alkyl group (1) (2 ) (3) The reaction product of (2) alone dissolves in hot water, making it necessary to use an organic solvent other than hot water to purify the reactant, which makes inexpensive production impossible.

The alkyl halide used in the present invention is either chloromethyl or chloroethyl.

Or both. Alkyl halides having more than this number of carbon atoms can also serve as etherifying agents, but as the number of carbon atoms increases, they become less water-soluble.

It becomes unsuitable as cellulose ether for use in cement, etc.

The amount of the alkyl halide added is 0.6 to 1.9 parts by weight per 1 part by weight of anhydrous crude linter. If it is less than 0.6 parts by weight, cellulose crystals remain in the cellulose ether produced by the reaction, making it difficult to dissolve in water and viscosity cannot be obtained.If it exceeds 1.9 parts by weight, the cellulose ether becomes hydrophobic. This also makes it difficult to dissolve in water, resulting in poor viscosity.

In the present invention, the etherification reaction can be carried out by adding alkylene oxide in addition to the alkyl halide.

The introduction of alkylene oxide has the advantage of further improving water solubility.

As alkylene oxide, propylene oxide,
Ethylene oxide can be used. Alkylene oxides with a larger number of carbon atoms can also be etherified, but the resulting cellulose ether tends to be hydrophobic and difficult to be water-soluble.

The amount to be added may be within a range that sufficiently promotes the water solubility of the etherified product, and it is O-1 part by weight per 1 part by weight of crude linter, and even if it is added more than this, the effect of improving water solubility will be negligible. do not have.

The reaction according to the present invention involves charging crude linter in a pressure-resistant container,
The base component is added under high vacuum with stirring, and then the alkyl halide and alkylene oxide are charged under vacuum, and the reaction is allowed to proceed at room temperature to 100°C over several hours.

Incidentally, during this reaction, an inert solvent such as dimethyl ether may be added.

To prevent the purified cellulose ether from dissolving, the product after the reaction is washed at a high temperature of 80°C or higher, then dried and pulverized with a suitable pulverizer, or used as is by dissolving it in water. The product should be able to

(Example) Hereinafter, specific aspects of the present invention will be explained using examples.
The invention is not limited to this example.

Examples 1-2. And Comparative Examples 1 to 3 First, crude linter was charged into an autoclave so that the composition ratio shown in the following table was obtained. After vacuuming, a NaOH aqueous solution was added to prevent oxygen molecules from entering. After stirring the inside, methyl chloride or Ethyl chloride and propylene oxide or ethylene oxide were charged.

After reacting at 50°C with stirring for 5 hours, the reaction was carried out at 80°C for 2 hours.
The reaction product was further stirred at 90°C for 1 hour, and the resulting reaction product was washed in excess hot water at 80°C or higher, water was separated, and then dried at 105°C.

A 1% aqueous solution of the obtained product was prepared, and the viscosity was measured at 20°C, and the results are also shown in the following table.

(Preparation Composition Double Placement Part) In the table, normal linter pulp: α-cellulose content 98.5%, crude linter pulp: α-cellulose content 989.0%.

Yield (QL) of cellulose ether obtained in Example 1 to crude linter pulp and yield (QL) of cellulose ether obtained in Comparative Example 3 to normal linter pulp
2), Q2/Ql, was 0.95.

Furthermore, no difference was observed between Example 1 and Comparative Example 3 in the reaction efficiency of the added etherification agent.

The cost of the crude linter pulp used in Examples 1 and 2 was 1% compared to the normal linter pulp used in Comparative Example 3.
/3, which shows that there is sufficient merit.

(Effects of the Invention) According to the present invention, a water-soluble cellulose ether exhibiting a high degree of polymerization and high viscosity can be provided at low cost.

Claims (1)

[Claims] 1. 1 part by weight of anhydrous crude linter, in the presence of 0.5 to 1.5 parts by weight of a base, 0.6 to 1 part by weight of alkyl halide.
A method for producing a highly polymerized cellulose ether, which comprises etherifying the cellulose ether using 9 parts by weight and 0 to 1 part by weight of an alkylene oxide, followed by washing with hot water.