JPH04198301A - New process for producing cellulose nitrate - Google Patents

Abstract

PURPOSE:To obtain the subject derivative having low substitution degree by dissolving or swelling cellulose in an aqueous solution containing a specific amount of an alkali metal hydroxide at a low temperature and treating the obtained mixture with a nitric acid-base mixed acid, thereby quickly and uniformly proceeding the reaction. CONSTITUTION:Cellulose is dissolved in or highly swollen with an aqueous solution containing 5-15wt.% of an alkali metal hydroxide (preferably 7-10wt.% of sodium hydroxide) at <=16 deg.C (preferably -10 to +10 deg.C) and the obtained liquid mixture is treated with a nitric acid-base mixed acid (preferably a mixed acid composed of nitric acid, water and at least one kind of substance selected from mineral acid, organic acid and acid anhydride) to obtain the objective cellulose nitrate.

Description

[Detailed Description of the Invention] [Technical Field] The present invention relates to a new method for producing cellulose nitrate, and more specifically, the present invention relates to a new method for producing cellulose nitrate. Concerning the manufacturing method.

[Prior art]

Cellulose nitrate (hereinafter abbreviated as CN) is the oldest derivative among cellulose derivatives, and was developed before the concept of polymer chemistry was established (in 1831, by Bracon.
Although it is a classic substance discovered in the 19th century, it is one of the materials with a long history and is still used today in fields that take advantage of its properties.

The basic method for producing CN is to immerse cellulose in concentrated nitric acid.Currently, improvements have been made in terms of reaction rate, reaction amount (degree of substitution), and required performance, and a mixed acid system of nitric acid and sulfuric acid has been made. The mainstream method is to use a nitrifying agent.

The nitrate reaction is a solid-liquid reaction between a solid (cotton, pulp, linter) and a liquid (sulfuric acid/nitric acid/water system), similar to the industrial production method of cellulose acetate (acetate ester), and there are problems in achieving a uniform reaction. has. In particular, it is almost impossible to uniformly produce derivatives with a low degree of substitution by a one-step method.
In order to improve the uniformity of the resulting material, a method has been adopted in which a highly substituted derivative is first prepared and then desubstituted to produce a low substituted derivative. In some cases, they are used as highly substituted derivatives without desubstitution.

On the other hand, in recent years, dimethyl sulfoxide/paraformaldehyde, dimethylformamide/dinitrogen tetroxide, sulfur dioxide/amine, dimethylformamide/chloral, N-methylmorpholine-N-oxide, dimethylacetamide/lithium chloride, etc. A large number of organic solvents that dissolve cellulose have been discovered, and extensive research has been conducted on the derivatization of cellulose by utilizing the uniform reactivity in these solvents. However, these methods have practical problems due to the stability, toxicity, cost (recoverability), etc. of the organic solvent, and are still at the stage of academic research. Further, as far as the present inventors know, there is no example in which these IQ solvent systems have been applied to CN conversion of cellulose.

[Problem to be solved by the invention]

In view of this situation, the present inventors have made extensive studies and found that by using a mixture obtained by dissolving or highly swelling cellulose in an aqueous solution of an alkali metal hydroxide as a reaction base, The present invention was achieved by discovering that cellulose can be nitrated more uniformly and more quickly than conventional methods.

The main purpose of the present invention is to provide a method for preparing cellulose nitrate more uniformly and quickly than conventional methods, and more specifically, to provide a new method for producing CN molded products that simultaneously converts cellulose into nitrate during molding. It is something to do.

[Means to solve the problem]

The main components of the method for producing cellulose nitrate of the present invention are that, in preparing cellulose nitrate, cellulose is basically melted or It consists of highly swelling and treatment of the resulting mixture with a nitric acid mixed acid.

Here, "highly swollen cell" means that when the state of cellulose in an aqueous solution of alkali metal hydroxide is observed with a polarizing microscope (nakoa stone), the diameter ( When the cellulose is in powder form, the diameter of the cellulose is swollen to three times or more the original size. Furthermore, ``the dissolved state is recognized as a dark field when observed using a similar polarizing microscope.Furthermore, if it does not even swell at all, its shape can be clearly observed as it is.

The above-mentioned nitric acid mixed acid includes: (1) mineral acids such as sulfuric acid, hydrochloric acid, and phosphoric acid;
It is preferably composed of at least one acid component selected from organic acids such as formic acid, acetic acid, and luffic acid, and acid anhydrides such as phosphoric anhydride and acetic anhydride, nitric acid, and water.

In addition, when treating the mixture with a nitric acid mixed acid, the mixture is formed into a film, thread, or powder while being immersed in the nitric acid mixed acid, or the mixture is treated by adding and mixing the nitric acid mixed acid. It is also preferable to do so.

The most important feature of the present invention is that when preparing cellulose nitrate, it is added to an aqueous solution containing 5 to 15% by weight of an alkali metal hydroxide as a reaction base at a low temperature (16").
The point is to use a mixture obtained by dissolving or highly swelling cellulose under (C and below).

As mentioned above, in the conventional method, solid cellulose is used as the reaction base, so the diffusion rate of the reactant into the solid becomes rate-limiting, and the diffusion rate between the crystalline and amorphous regions is different. One of the problems is the non-uniformity due to the difference. In contrast, in the method of the present invention, a mixture obtained by dissolving or highly swelling cellulose in an aqueous solution of an alkali metal hydroxide is used as a reaction base, so that the diffusion rate is faster than in a solid state. It has the advantage that non-uniformity in reactivity is easily eliminated due to the difference between crystalline and amorphous structures.

Regarding the use of the above mixture as a reaction base, anyone with ordinary chemical knowledge would know that when an alkali reacts with a strong acid called a nitric acid mixed acid, a violent neutralization reaction occurs, and a practical reaction cannot be expected. However, the present inventors have experimentally found that these systems react relatively mildly, and although the mechanism of action is not clear at present, alkali metal hydroxides By discovering the possibility that
This led to the development of a realistic manufacturing method.

Examples of the alkali metal hydroxide used in the present invention include sodium hydroxide, lithium hydroxide, potassium hydroxide, and cesium hydroxide.

The alkaline concentration of the alkaline aqueous solution is 5 to 15% by weight. In particular, a 7 to 10% by weight solution of sodium hydroxide is preferably used.

The cellulose that can be used in the present invention is not limited in any way by crystal type, degree of polymerization, plant species, etc., as long as it dissolves or highly swells in an aqueous solution of 5 to 15% by weight alkali hydroxide. Preferably, Japanese Patent Application No. 58-149149
Cellulose with a large degree of intramolecular hydrogen bond destruction is used, as described in the above issue.

The concentration of cellulose in the mixture with the aqueous alkali metal solution is a matter to be determined depending on the degree of polymerization of cellulose, but from an economical point of view it should be contained at 3% by weight or more. Cellulose with a degree of polymerization of 400 can be dissolved in an amount of 5 to 7% by weight, and can be uniformly swollen up to about 9% by weight. Melting is carried out at a low temperature of 16°C or lower, preferably -10°C or higher and 10°C or lower.

In the present invention, when treating the mixture with a nitric acid mixed acid, the mixture is formed into a film, thread, or powder while being immersed in the nitric acid mixed acid, or the nitric acid mixed acid is added to the mixture and mixed. It is preferable to treat it as follows. That is, cellulose is uniformly dissolved in the mixture,
By using a nitric acid mixed acid in the coagulation bath, it is possible to simultaneously form nitrate into films, threads, powders, etc., and to obtain the advantage of forming and derivatizing in one step. have On the other hand, if the mixture is a highly swollen mixture, a powdered derivative can be prepared by adding and mixing a nitric acid mixed acid to the mixture, and by controlling the amount of the nitric acid mixed acid added. Derivatives with a low degree of substitution can be prepared in one step. These features are not found in conventional methods.

The nitric acid mixed acids that can be used in the present invention include: (1) mineral acids such as sulfuric acid, hydrochloric acid, and phosphoric acid; (2) organic acids such as formic acid, acetic acid, and rough acid;
It is a composition consisting of at least one acid selected from acid anhydrides such as phosphoric anhydride and acetic anhydride, nitric acid, and water. The composition should be determined depending on the required performance (for example, the degree of substitution of the derivative) and the manufacturing conditions and process.
A water concentration of 75% by weight or more is not preferred because the reactivity is extremely reduced. In addition, when reacting simultaneously during molding, it is desirable that the sulfuric acid concentration is 85% by weight or less;
Exceeding this value is not preferable for molding other than powder, as it involves dissolution of cellulose.

The specific embodiment will be described in detail in the examples below, but when forming into a film, thread, or powder and immersing it in a nitric acid mixed acid, a film forming device or a spinning device can be used. The reaction may be completed during molding using a nitric acid mixed acid as a coagulation bath.

In addition, when treating a mixture in which cellulose is dissolved or highly swollen by adding and mixing a nitric acid mixed acid, a predetermined amount of the nitric acid mixed acid is added dropwise to the stirred mixture and mixed. It can be achieved.

The degree of substitution of the cellulose obtained is determined by the absolute method for solvents in which the obtained CN is uniformly dissolved.
C-N? It can be calculated by IR spectrum measurement. For substances that are difficult to dissolve uniformly, the ratio of absorbance calculated from FT-IR (absorbance that is easily absorbed by nitro groups (164
7 Kaiser) and the absorption as an internal standard (2911 Kaiser)) and the value obtained from ClNMR spectrum analysis.

[Effects of the Invention] In the method of the present invention, since a cellulose compound is used as a reaction base, (1) the reaction can proceed more quickly and uniformly than in the conventional method. (2) Derivatives with a low degree of substitution can be easily prepared.

(3) It has the advantage that a CN molded product can be prepared in one step during molding.

The present invention will be specifically described below with reference to Examples.

Example 1 Softwood pulp (Alaska pulp) with a degree of polymerization of 1300 10
After immersing 0 part in 1000 parts of water for 3 hours, it was dehydrated using a dehydrator to obtain 220 parts of hydrated cellulose. 20 Hydrous cellulose was heated to 235°C using a blasting treatment device W (manufactured by Nippon Kagaku Kikai).
A steam treatment was performed for 20 seconds to obtain cellulose having a degree of polymerization of 390 and soluble in an alkaline aqueous solution.

Ten grams of the cellulose was dissolved in 190 grams of an 8% by weight aqueous sodium hydroxide solution at 5° C. to obtain a homogeneous solution. This solution was cast onto a glass plate using a casting applicator, and the cellulose was nitrated by immersing it in a sulfuric acid/nitric acid/water mixed acid having the composition (wt%) shown in Table 1 for 30 seconds. Film la obtained. Table 1 shows the degree of substitution of the obtained cellulose film. In addition, Figures 1 and 2 show the C=NMR spectrum and FT-IR spectrum of the cellulose film obtained in Experiment No. 1, respectively.

Table 1 Example 2 10 grams of alkali-soluble cellulose prepared in the same manner as in Example 1 was added to a 6% by weight lithium hydroxide aqueous solution 1
A homogeneous solution was obtained by dissolving 90 grams at -5"C. This solution was mixed using a plunger type extruder to obtain a 0.1
Sulfuric acid (50%) from a spindle with 100 millimeter diameter holes.
A mixed acid of /nitric acid (30%)/water (20%) system was extruded into a coagulation bath (temperature 10°C) and wound up at a speed of 12 m/min.

The resulting fibers were cut into small powder pieces using scissors, and the degree of substitution was determined by FT-IR measurement using a diffuse reflection method and found to be 1.4.

Example 3 Coniferous pulp (Alaska pulp) with a degree of polymerization of 1300 was
Cellulose with a degree of polymerization of 470 was obtained by treatment with 0% by weight sulfuric acid at 60° C. for 30 minutes. 12 crumbs of this cellulose were added to 188 g of sodium hydroxide at 9% by weight, IOo.
When the mixture was dissolved in step C, uniform dissolution was not achieved, but a mixture in which the diameter (thickness) of the pulp fibers was swollen to about 4 times was obtained. The mixture was stirred at 10''C and reacted while gradually adding 200 grams of acetic acid (30%)/nitric acid (50%)/water (20%) mixed acid.

The reaction aggregate was thoroughly washed with a large amount of water and purified.

The degree of substitution of the purified reaction product was determined to be 1.7 by C-NMR measurement.

[Brief explanation of the drawing]

Figure 1 shows a typical cellulose nitrate "C=NMR spectrum" obtained by the method of the present invention.
The figure shows the FT-IR spectrum of the same CN.

Claims (3)

[Claims] (1) Cellulose night characterized by dissolving or highly swelling cellulose in an aqueous solution containing 5 to 15% by weight of alkali metal hydroxide at 16°C or below, and treating the resulting mixture with a nitric acid mixed acid. How to make rate. (2) The method according to claim 1, wherein the nitric acid mixed acid comprises nitric acid, water, and at least one selected from mineral acids, organic acids, and acid anhydrides. (3) When treating the cellulose mixture with a nitric acid mixed acid, the mixture is formed into a film, thread, or powder while being immersed in the nitric acid mixed acid, or the nitric acid mixed acid is added to the mixture and mixed. The manufacturing method according to claim 1, characterized in that the treatment is performed by: