JP2856545B2 - Production method of new cellulose nitrate - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a novel method for producing cellulose nitrate, and more particularly, to a method of treating a liquid mixture comprising cellulose and an aqueous alkali solution with a nitric acid-based mixed acid. A method for producing the same.

(Prior art)

Cellulose nitrate (hereinafter abbreviated as CN) is the oldest of cellulose derivatives and is a classic substance discovered before the concept of polymer chemistry was established (1831, Braconnot). However, it is one of the long-established materials used in fields that take advantage of its characteristics.

The basis of this CN production method is to immerse cellulose in concentrated nitric acid. At present, improvements have been made from the viewpoints of reaction rate, reaction amount (degree of substitution) and required performance, and a mixed acid system of nitric acid and sulfuric acid has been developed. The method of using a nitrifying agent is dominant.

The nitration reaction is a solid-liquid reaction between a solid (cotton, pulp, linter) and a liquid (sulfuric acid / nitric acid / water system) similarly to the industrial production method of cellulose acetate (acetate ester), and has a problem in uniform reaction. Having. In particular, it is almost impossible to uniformly produce a derivative having a low degree of substitution by a one-step method. In order to enhance the uniformity of the obtained material, a derivative having a high degree of substitution is once prepared and then desubstituted to obtain a low degree of substitution. A method for producing a derivative has been adopted. In some cases, it is used as a highly substituted derivative without desubstitution.

On the other hand, in recent years, dimethyl sulfoxide / paraformaldehyde, dimethylformamide / nitrogen tetroxide, sulfur dioxide / amine, dimethylformamide / chloral, N-methylmorpholine-N-oxide, dimethylacetamide / lithium chloride, etc. Numerous organic solvents that dissolve cellulose have been found, and studies on derivatization of cellulose using homogeneous reactivity in these solvents have been extensively conducted. However, these methods have practical problems due to the stability, toxicity, and price (recoverability) of the organic solvent, and remain at the stage of academic research. Further, to the knowledge of the present inventors, there is no example in which these organic solvent systems have been applied to the conversion of cellulose to CN.

[Problems to be solved by the invention]

The present inventors have in view of such a situation, as a result of intensive studies, by using a mixture obtained by previously dissolving or highly swelling cellulose in an aqueous solution of an alkali metal hydroxide as a reaction base, The inventors have found that cellulose can be nitrated more uniformly and more quickly than the conventional method, and have reached the present invention.

The main object of the present invention is to provide a method for preparing cellulose nitrate more uniformly and quickly than in the conventional method, and moreover, to provide a new method for producing a CN molded product that is simultaneously nitrated during the molding of cellulose. Is what you do.

[Means for solving the problem]

The main component of the method for producing cellulose nitrate according to the present invention is to prepare cellulose nitrate by dissolving cellulose at 16 ° C. or lower in an aqueous solution containing 5 to 15% by weight of an alkali metal hydroxide. And treating the resulting mixture with a nitric acid-based mixed acid.

Here, “highly swelled” means that when the state of cellulose in an aqueous solution of an alkali metal hydroxide is observed with a polarizing microscope (crossed Nicols), when the cellulose is fibrous, its diameter (thickness) ) Is 3 times or more of the original, and when the cellulose is in the form of powder, it means that the diameter is 3 times or more of the original. Further, the “dissolved” state is recognized as a dark field in the same observation with a polarizing microscope. Also,
Those that do not even swell at all can clearly observe the shape as it is.

The nitric acid-based mixed acid is a sulfuric acid, hydrochloric acid, mineral acids such as phosphoric acid,
It is preferably composed of at least one or more acid components selected from organic acids such as formic acid, acetic acid and lacnic acid, and acid anhydrides such as phosphoric anhydride and acetic anhydride, nitric acid and water.

Further, when the mixture is treated with a nitric acid-based mixed acid, the mixture is formed into a film, a thread, or a powder while being immersed in a nitric acid-based mixed acid, or a nitric acid-based mixed acid is added to the mixture and mixed. It is also preferable to do so.

The most important feature of the constitution of the present invention is that when preparing cellulose nitrate, 5 to 15% by weight as a reactive base is used.
A solution obtained by dissolving or highly swelling cellulose in an aqueous solution containing an alkali metal hydroxide at a low temperature (16 ° C. or lower).

As described above, in the conventional method, since solid cellulose is used as a reaction base, the diffusion rate of the reaction agent into the solid is limited, or the diffusion rate between the crystalline region and the amorphous region is different. Non-uniformity due to differences is a problem. In contrast, in the method of the present invention, a mixture obtained by previously 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 higher than in the solid state, and In addition, there is an advantage that the non-uniformity of the reactivity based on the difference between the crystalline and amorphous structures is eliminated.

Regarding the use of the above mixture as a reaction base, if a person having ordinary chemical knowledge applies an alkali to a strong acid such as a nitric acid mixed acid, a violent neutralization reaction occurs and a practical reaction cannot be expected. Although the present inventors have experimentally found that these systems react relatively mildly, and their mechanism of action is not clear at present, alkali metal hydroxides are considered. Has realized the possibility of acting as a catalyst during the reaction, thereby realizing the development of a realistic manufacturing method.

As the alkali metal hydroxide used in the present invention,
Sodium hydroxide, lithium hydroxide, potassium hydroxide,
Cesium hydroxide and the like can be mentioned. The alkali concentration of the aqueous alkali solution is 5 to 15% by weight. In particular, a 7 to 10% by weight solution of sodium hydroxide is preferably used.

Cellulose that can be used in the present invention is not limited 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 of alkali hydroxide. Preferably, cellulose having a high degree of breaking of intramolecular hydrogen bonds described in Japanese Patent Application No. 58-149149 is used.

The concentration of cellulose in a mixture with an aqueous alkali metal solution is a problem to be determined by the degree of polymerization of cellulose,
It should contain at least 3% by weight from an economic point of view. Cellulose having a polymerization degree of about 400 can dissolve 5 to 7% by weight, and can swell uniformly up to about 9% by weight. Dissolution
It 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, in treating the mixture with a nitric acid mixed acid, the mixture is immersed in a nitric acid mixed acid while being formed into a film, a thread, or a powder, or a nitric acid mixed acid is added to the mixture and mixed. It is preferable that the treatment be performed. That is, when the mixture is a solution in which cellulose is uniformly dissolved, by using a nitric acid-based mixed acid in a coagulation bath, it is possible to simultaneously nitrate while forming into a film, a yarn, a powder, etc. And the advantage that derivatization is achieved. On the other hand, when the mixture is a highly swollen mixture, a powdery derivative can be prepared by adding a nitric acid-based mixed acid thereto, mixing and treating the mixture, and by controlling the amount of the nitric acid-based mixed acid added. Derivatives with a low degree of substitution can be prepared in one step. These features are not found in conventional methods.

Nitric acid-based mixed acids that can be used in the present invention include sulfuric acid, hydrochloric acid, mineral acids such as phosphoric acid, formic acid, acetic acid, organic acids such as lactic acid,
It is a composition comprising at least one or more acids selected from acid anhydrides such as phosphoric anhydride and acetic anhydride, nitric acid and water. The composition is a matter to be determined by the required performance (for example, the degree of substitution of the derivative) and the manufacturing conditions / process.
If the concentration of water is 75% by weight or more, the reactivity is extremely lowered, which is not preferable. Further, when reacting simultaneously during molding, the sulfuric acid concentration is desirably 85% by weight or less, and if it exceeds 85%, cellulose is dissolved, which is not preferable for molding other than powder.

Specific embodiments will be described in detail in Examples below.Films, yarns, and when immersed in a nitric acid-based mixed acid while being formed into a powder, by using a film forming apparatus or a spinning apparatus. A nitric acid-based mixed acid may be used as a coagulation bath to complete the reaction during molding. In addition, when a nitric acid-based mixed acid is added to a mixture in which cellulose is dissolved or highly swollen to be mixed and treated, a predetermined amount of a nitric acid-based mixed acid is added to the mixture under stirring and reacted while dropping. Can be achieved.

The obtained degree of substitution of cellulose, for certain of the solvent the resulting CN is uniformly dissolved, the absolute method ¹³ C
-It can be calculated by NMR spectrum measurement. For those which are difficult to dissolve uniformly, the ratio of the absorbance calculated from FT-IR (the ratio between the absorption based on the nitro group (1647 Kaiser) and the absorption as an internal standard (2911 Kaiser)) and ¹³ C
-It can be calculated from a calibration curve with a value obtained by NMR spectrum analysis.

〔The invention's effect〕

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 as a reaction base, that is, a liquid mixture is used. In addition, the reaction can proceed uniformly. (2) A derivative with a low degree of substitution can be easily prepared. (3) It has the advantage that a CN-formed product can be prepared in one step at the time of molding.

 Hereinafter, the present invention will be specifically described with reference to examples.

Example 1 100 parts of softwood pulp (Alaska pulp) having a polymerization degree of 1300 was immersed in 1000 parts of water for 3 hours, and then dehydrated with a dehydrator to obtain 220 parts of hydrous cellulose. This hydrous cellulose was subjected to a steam treatment at 235 ° C. for 20 seconds using an explosion treatment apparatus (manufactured by Nippon Kagaku Kikai) to obtain cellulose soluble in an alkaline aqueous solution having a polymerization degree of 390.

10 g of the cellulose was dissolved in 190 g of an 8% by weight aqueous sodium hydroxide solution at 5 ° C. to obtain a homogeneous solution. This solution was cast on a glass plate using a casting applicator, and immersed in a sulfuric acid / nitric acid / water-based mixed acid having a composition (% by weight) shown in Table 1 for 30 seconds to form a nitrated cellulose. A film was obtained. Table 1 shows the degree of substitution of the obtained cellulose film. FIGS. 1 and 2 show the ¹³ C-NMR spectrum and the FT-IR spectrum of the cellulose film obtained in Experiment No. 1, respectively.

Example 2 10 g of alkali-soluble cellulose prepared in the same manner as in Example 1 was treated with a 6% by weight aqueous solution of lithium hydroxide 19.
Dissolved at 0 ° C. at −5 ° C. to obtain a homogeneous solution. Using a plunger-type extruder, this solution was passed through a spout provided with 100 holes of 0.1 mm in diameter and sulfuric acid (50%) / nitric acid (30%).
%) / Water (20%)-based mixed acid was extruded into the bath as a coagulation bath (temperature of 10 ° C.) and wound up at a speed of 12 m / min.

The obtained fiber was cut into small powders with scissors, and the degree of substitution was found to be 1.4 by FT-IR measurement using a diffuse reflection method.

Example 3 Softwood pulp (Alaska pulp) having a polymerization degree of 1300 was treated with sulfuric acid of 20% by weight at 60 ° C. for 30 minutes to obtain cellulose having a polymerization degree of 470. 9% by weight of 12 grams of this cellulose
Was dissolved in 188 g of sodium hydroxide at 10 ° C., but did not result in uniform dissolution, but a mixture in which the diameter (thickness) of the pulp fiber was swollen about four times was obtained. The mixture was reacted while stirring at 10 ° C. while gradually adding 200 g of an acetic acid (30%) / nitric acid (50%) / water (20%) mixed acid.

The reaction aggregate was sufficiently washed with a large amount of water and purified. The degree of substitution of the reaction purified product determined by ¹³ C-NMR measurement was 1.7.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a typical ¹³ C-NMR spectrum of cellulose nitrate obtained by the method of the present invention, and FIG. 2 is an FT-IR spectrum of the same CN.

Claims (3)

(57) [Claims] (1) dissolving or highly swelling cellulose at 16 ° C. or lower in an aqueous solution containing 5 to 15% by weight of an alkali metal hydroxide, and treating the resulting mixture with a nitric acid-based mixed acid; Production method of cellulose nitrate. 2. The method according to claim 1, wherein said nitric acid-based mixed acid comprises nitric acid and water, and at least one selected from mineral acids, organic acids and acid anhydrides. 3. The treatment of the cellulose mixture with a nitric acid mixed acid, the mixture being formed into a film, a thread or a powder while being immersed in the nitric acid mixed acid, or the nitric acid mixed acid is added to the mixture. The method according to claim 1, wherein the mixture is processed.