JPS6318601B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a novel method for producing chitosan-based molded products, particularly fibers, films, and membranes.

Chitosan is obtained by hydrolyzing chitin, which is widely distributed in nature such as the outer shells of shrimp, crabs, insects, and other crustaceans, with concentrated alkali [2-amino-2-deoxy-D-glucose]. ]
It is a basic polysaccharide with a molecular weight of approximately 200,000 to 300,000.

Chitin is difficult to mold because it is not soluble in water or organic solvents, whereas chitosan is soluble in dilute acid aqueous solutions and is easier to handle than chitin. In this case, chitosan has an amino group and reacts with an acidic substance to easily form a salt, which improves its water solubility and dissolves it.

On the other hand, although the use of chitosan has received widespread attention, it is currently limited to practical use as a polymer flocculant. Of course, due to its chemical structural characteristics, it can be used as a variety of functional materials, but industrially favorable molding conditions have not yet been found, and progress has been slow. In particular, problems arise in that molding operability and productivity are generally low due to the fact that the main solvent is limited to an aqueous acid solution and the chitosan salt structure has an abnormally high water swelling property.

A typical method to date is to once cast an aqueous chitosan salt solution in film molding, then distill off the water by drying under reduced pressure to form a film, and then perform an alkali treatment to desalinate to regenerate chitosan. However, this method has poor production efficiency and lacks uniformity in alkali treatment.

The present invention examines various molding methods for chitosan or its salt, and enables molding with good operability by specifying coagulation bath conditions when wet or dry-wet molding an aqueous solution of chitosan or its salt. We found a method and arrived at the present invention.

The gist of the present invention is that from an aqueous solution of chitosan or its salt, the equilibrium pH containing a basic substance is
A method for producing a molded chitosan product characterized by wet molding or dry-wet molding using an aqueous solution of 7.0 or higher as a coagulation bath.

That is, the method of the present invention involves so-called reactive coagulation in which a desalination reaction is introduced into the coagulation process. Through many experiments, it has been found that particularly when the equilibrium pH of the bath during coagulation is 7.0 or higher, good coagulation properties are obtained and a homogeneous coagulated structure can be obtained.

The present invention will be explained in detail below in accordance with its implementation.

The starting material is chitosan or chitosan salt. Chitosan salt is obtained by treating chitosan with an aqueous solution of a common acid to form a salt, which is then isolated and purified. Examples include salts of inorganic acids such as hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, and boric acid, and organic acids such as formic acid, acetic acid, sulfamic acid, and toluenesulfonic acid.

When starting from chitosan, it can be dissolved in an aqueous solution of the above-mentioned acid, and when a chitosan salt is used, it can be dissolved in water alone. The dissolution method is not particularly limited, but when using an acid aqueous solution as a solvent, care must be taken because solubility, solution viscosity, etc. vary depending on the concentration of the acid.

Solutions (referred to as dopes) that are convenient for molding generally have a high concentration, but chitosan is a relatively rigid polymer with a large molecular weight, so its solubility limit is low, usually 2 to 10 wt%, preferably 3
~8wt%. The dope thus prepared is then filtered, defoamed, and introduced into a molding process, where it is extruded through a conventional spinning nozzle into an aqueous solution in which a basic substance is dissolved to form a thread. In addition, in the case of film molding,
As is well known, a casting box equipped with a doctor knife is filled with dope, and the dope is cast to a certain thickness onto a smooth glass plate, metal surface, etc., and then
A film-like material can be obtained by immersing the material in an aqueous solution in which a basic substance is dissolved and reacting and coagulating it.

The basic substances used in the coagulation bath are those dissolved in water.
A wide variety of inorganic and organic compounds can be used as compounds that exhibit a pH of 8 or higher. Inorganic compounds include alkali metal hydroxides such as LiOH, NaOH and KOH, alkaline earth metal hydroxides such as Mg(OH) ₂ and Ca(OH) ₂ , Na ₂ (CO ₃ ) ₂ and NaHCO ₃ ，
Neutralized salts of strong bases such as Na ₃ PO ₄ and weak acids are preferred, and as organic compounds, water-soluble amino compounds such as diethanolamine and dimethylaminoethanol are effective. It has been found that particularly desirable basic substances are alkali metal hydroxides, which have excellent coagulability. The concentration of these basic substances is appropriately set, but the higher the concentration, the higher the coagulation rate. In particular, it was found that when the equilibrium pH during the solidification operation was set to 7.0 or higher, solidification proceeded sufficiently, resulting in a uniform structure throughout the molded product and improved physical properties. This means that when chitosan salt, which is stable in the dope, reacts with the basic substance in the bath and regenerates water-insoluble chitosan, it deswells, precipitates and coagulates, and the presence of an excess of the basic substance, which is more than the reaction equivalent, actually occurs. It has been shown to be useful in the above. On the other hand, although the salts produced by the reaction coexist in the coagulation bath, they do not pose a particular problem, and in some cases, they have a dehydrating effect and are therefore superfluous in promoting coagulation. For this reason, for example, mirabilite or common salt may be actively added to the coagulation bath. especially
Adding thiocyanate such as NaSCN, KSCN, _NH4SCN , Ca(SCN) ₂ to the coagulation bath promotes coagulation and is effective.

The temperature of the coagulation bath is not particularly limited, but is usually 0 to 90.
℃ range. Furthermore, elongation conditions during solidification affect the mechanical properties of the molded product, so they are adjusted as appropriate; however, in the case of fiber formation, a spinning draft of 0.5 to 10 can be adopted.
In addition, during such molding, a so-called dry-wet method in which the dope is once extruded into air or an inert gas and then immediately immersed in a coagulation bath is also employed, and is effective depending on the purpose.

When producing a fibrous product, the chitosan coagulate thus formed is then thoroughly washed and dried. In order to further improve the drying properties, the water in the cleaned molded product may be replaced in advance with an organic solvent having high drying properties and then dried.

As described above, the method of the present invention has developed a new method of reaction coagulation as a solution molding method for chitosan, and as described above, the desired molded product can be produced extremely easily and through simple steps. In addition, any form of molded product can be produced, including fibrous, hollow fiber, tube-like, and film-like products, and can be used as fibers in the clothing field and as semipermeable membranes in the medical field. .

The present invention will be explained in more detail with reference to Examples below.

Example 1 Chitosan flakes (Kyowa Yushi Chemical Industry Co., Ltd.)
After suspending (manufactured by Fronac N) in water and stirring uniformly, add a predetermined amount of acetic acid aqueous solution and heat at 40°C.
to make a homogeneous solution with a chitosan concentration of 3.0 wt%.

The acetic acid concentration in the dope is 0.5wt%. Then
The temperature was raised to 60°C, defoamed and filtered under a reduced pressure of 15 mmHg, and the mixture was kept at 50°C to obtain a dope for spinning. The dope viscosity was 400 poise at 50°C.

This dope was wet-spun into a 5% NaOH aqueous solution maintained at a temperature of 30°C at a rate of 13ml/min through a spinning nozzle with a hole diameter of 0.15mmφ and a number of holes of 50.
It was immersed in a coagulation bath for 200 cm and taken off at a speed of 30 m/min (spinning draft approximately 2.0). The equilibrium pH of the bath in this case was adjusted to 10.2.

Next, the first stage was washed in warm water at 40° C. under constant length conditions, and then thoroughly washed in boiling water. The physical properties of the fiber obtained by air-drying the washed yarn are fineness of 3.05 denier, strength of 2.44 g/d, elongation of 10.8%, and knot strength of 1.75 g/d.
d, showing sufficient filament quality. The cross-sectional shape of the fiber was circular and the side surface was smooth.

Example 2 Chitosan acetate (Fronac #250, manufactured by Kyowa Yushi Kogyo Kagaku Co., Ltd.) was dissolved in water to prepare a dope with a concentration of 4%. The apparent pH of the dope was 4.0, and the viscosity of the dope was 780 poise at 50°C. this dope
Wet spinning was carried out in a saturated aqueous solution of Rodan soda which was maintained at 25°C and whose pH was adjusted to 8.0 by adding a small amount of NaOH.

It was drawn from a nozzle with a hole diameter of 0.1 mm and 100 holes at a speed of 30 m/min, thoroughly washed with water, and then passed through an acetone bath to dry.

The fiber thus obtained has a fineness of 3.1 denier,
The strength was 2.7 g/d and the elongation was 11.4%.

On the other hand, the swollen yarn before passing through the acetone bath was dehydrated under Nipprol, cut into stable lengths of 5 mm, uniformly dispersed in water, and made into paper.
Then, it was dried at 110°C to obtain a chitosan nonwoven fabric with a thickness of about 100 μm. This nonwoven fabric had a supple texture and sufficient strength.

Example 3 Using the same method as in Example 1, chitosan concentration was 4wt%.
A homogeneous solution of was prepared. The concentration of acetic acid in the dope is
It is 1.0wt%. After passing through a cloth, the defoamed dope was filled into a casting box kept at 40° C., and the casting thickness was adjusted to 400 μm using a doctor knife, and the dope was cast onto a smooth glass plate. After being left in an atmosphere of 25°C and 65% relative humidity for 2.0 seconds, it was immersed in a KOH aqueous solution whose temperature was adjusted to 30°C to cause reaction and coagulation to obtain a transparent film. In this case, the coagulation bath was kept at pH 11.

The obtained film had a uniform thickness of 50 μm. It is a strong film with a wet strength of 2.6Kg/ ^mm2 , and when the water permeation rate was measured at an operating pressure of 760mmHg, the water overrate was 3.78 (ml/ ^m2 , hr,
mmHg).

Claims (1)

[Claims] 1. Production of a chitosan-based molded product characterized by wet or dry-wet molding of an aqueous solution of chitosan or a salt thereof in a coagulation bath containing an aqueous solution containing a basic substance and having an equilibrium pH of 7.0 or higher. Law. 2. The method for producing a chitosan-based molded product according to claim 1, wherein the basic substance is an alkali metal hydroxide. 3. The method for producing a chitosan-based molded article according to claim 1, wherein the aqueous solution containing a basic substance contains a thiocyanate.