JPH03275740A - Production of cellular polyamide - Google Patents

Abstract

PURPOSE:To obtain a cellular polyamide, having a large surface area and suitable as a carrier, etc., of filtration, functional materials, etc., by dissolving a polyamide in a solvent, then gelatinizing the prepared solution and removing the solvent from the resultant gel. CONSTITUTION:A polyamide (e.g. nylon 66 or nylon 6) is dissolved in a solvent (e.g. N-methyl-2-pyrrolidone) and the obtained solution is then cooled, solidified and gelatinized. The solvent is subsequently removed by a method for evaporation from the aforementioned gel or extraction thereof with other solvents. Since the weight ratio of the polyamide to the solvent has an influence on the surface area of the resultant cellular polyamide, the concentration of the polyamide is within the range of preferably 0.5-30wt.%, especially 1-15wt.%.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a method for producing porous polyamide.

More specifically, carriers such as filtration materials and functional materials,
The present invention also relates to a method for producing porous polyamide used as a prepolymer for polymerization.

[Conventional technology]

Conventionally, as a method for producing porous polyamide, as described in "Kobunshi" Vol. 23, pp. 592-596 (1974), a polymer is dissolved in a calcium chloride/methanol solvent, and then the solution is dissolved. A solution coagulation method is known in which the solution is cast on a plate, the solvent is evaporated, the solution is coagulated, and the salt is eluted in water.

Further, Japanese Patent Application Laid-Open No. 1-245035 discloses a method that is an improvement on the above method. That is, a porous membrane is prepared by dissolving a water-soluble salt together with a polymer in a calcium chloride/methanol solvent, absorbing moisture, and coagulating the solution.

However, porous polymers obtained by a solution coagulation method as described in "Polymer" are
It does not have a continuous porous structure as disclosed in Japanese Patent No. 035, but has an aggregated structure of isolated pores.

Therefore, the surface area is also 0. It can be estimated that it is very small, oi rri'/g.

Further, in the method described in JP-A-1-245035, only the portion where the salt is precipitated has a continuous porous structure, and the other portions have an aggregated structure of isolated pores. Therefore, the surface area of this film is estimated to be about 0.1rrr/g, which is a small surface area.

[Problem to be solved by the invention]

The object of the present invention is to provide a porous polyamide with a large surface area.

[Means to solve the problem]

That is, the present invention is a method for producing porous polyamide, which is characterized by dissolving polyamide in a solvent, gelling it, and removing the solvent from the gel without destroying the network structure of the gel.

The polyamide according to the present invention includes polyhexamethylene adipamide (nylon 66), polycapramide (nylon 6)
, polyundecanoamide (nylon 11), polyhexamethylene sebacamide (nylon 61O), polytetramethylene adipamide (nylon 46), polyundecamethylene adipamide (nylon 116), and other aliphatic polyamides Alternatively, it is a polyamide formed by combining two or more of these types. Moreover, this polyamide has a weight of 15wt.
It may also be a copolymer or mixture containing up to % of other polymers.

The polyamide according to the present invention may contain additives such as a heat stabilizer, an antioxidant, a light stabilizer, a pigment, a catalyst, and a matting agent, if necessary.

The number average molecular weight of the polyamide according to the present invention is not particularly limited.

Next, one of the manufacturing methods for making the polyamide of the present invention porous with a surface area of In(/g or more, preferably 1r11'/g to 100 rrr/g) will be specifically explained.

First, polyamide is heated and dissolved in a solvent to form a uniform solution.

The solvent used in the present invention may be any solvent as long as it can dissolve the polyamide. For example, the following solvents or a combination of these solvents and salts can be used.

That is, N-methyl-2-pyrrolidone, N-ethyl-2
-pyrrolidone, N-methyl-piperidone, N-ethyl-
Piperidone, N,N-dimethylacetamide, N-methyl-N-ethylacetamide, N,N-diethylacetamide, N-acetylpiperidine, N-acetylpyrrolidine, N-acetylmorpholine, N-acetylpyrrolidone, N-acetylpipe Lydone, amide solvents such as 1,5-dimethylpyrrolidinone, 1,3-dimethyl-
2-imidazolidinone, 1,3-dimethyl-4,5,6
(H)-2-pyrimidinone, urea solvents such as tetramethylurea, imide solvents such as N-methylsuccinimide and N-acetylsuccinimide, ether solvents such as tetrahydrofuran, methanol, ethanol,
Alcohol solvents such as benzyl alcohol and furfuryl alcohol, phenol, orthochlorophenol,
Phenolic solvents such as m-cresol, formic acid, sulfuric acid,
The solvent is one or more solvents selected from the group consisting of acid solvents such as trichloroacetic acid, fluorine solvents such as hexafluoroisopropanol, and hexafluoroacetone.

Among the above solvents, preferred are amide solvents, urea solvents, imide solvents, and alcohol solvents that do not easily cause decomposition of the polyamide polymer when it is dissolved therein.

Among them, N-methyl-2-pyrrolidone, N-ethyl-
2-pyrrolidone, 1,5-dimethylpyrrolidinone, N-
Acetylpiperidine, N-acetylmorpholine, 1,
A solvent system consisting of 3-dimethyl-2-imidazolidinone, 1,3-dimethyl-4,5,6(H)-2-pyrimidinone, N-methylsuccinimide, N-acetylsuccinimide, methanol, and ethanol was used. , is more preferred since it has a high ability to dissolve polyamide.

Furthermore, the most preferable one is N-methyl-2
-pyrrolidone, 1,5-dimethyl-2-pyrrolidinone,
N-acetylpiperidine, N-acetylmorpholine,
1.3-dimethyl-2-imidazolidinone and 1.3
-dimethyl-4,5,6(H)-2-pyrimidinone. More preferably, N-methyl-2-pyrrolidone, N-
Acetylpiperidine, N-acetylmorpholine and 1,3-dimethyl-2-imidazolidinone.

In addition, the salts used in the present invention include group Ia, group Ib of the periodic table,
It is a halide or perhalide of an element of the Ila group, the Nb group, the IIIa group, or the Group Ⅰ, and must also be soluble in the solvent used together with the salt.

Preferred salts are lithium, calcium, magnesium,
halides of zinc, aluminum, boron, and iron,
or perhalide.

The effects of salts include improving the solubility of polymers in solvents,
A decrease in the gelation temperature of the solution can be expected.

Therefore, the salt has O to amide groups of polyamide.
Add 100 moA/mol. Preferably 0, O
1~60 mo 12 /mo I! , more preferably 0.05 to 2 moj2/moA, most preferably 0.1 to 1 moj2/moA.

A stock solution is prepared by adding a polyamide polymer to the above solvent and dissolving it by heating at a temperature at which the polymer dissolves. On this occasion,
It is preferable that the solvent, salt, and polymer be dehydrated and dried before use to keep their moisture content as low as possible. The dissolution operation is also preferably carried out in dry nitrogen. because,
This is because if the temperature at the time of dissolution is high, the polymer will be hydrolyzed by heating, resulting in a decrease in molecular weight.

For melting, it is preferable to apply a certain amount of shear using a helical blade, a kneader, or the like. However, if the shearing force is too strong, the molecular chains of the polymer will be cut, which is not preferable.

In the method of the present invention, the weight ratio of polyamide and solvent affects the surface area of the porous polyamide, so it is preferable to adjust the ratio depending on the desired surface area. Note that the range of gelation varies depending on the molecular weight of the polyamide used, but the polyamide is usually 0.1 to 60 wt%,
Preferably it is 0.5 to 30 wt%. More preferably, it is 1 to 15 wt%.

Next, this solution is cast onto a plate such as a glass plate or sandwiched between glass plates, and then cooled to a gelling temperature and solidified. The gel thus solidified has a network structure.

The method of the invention then requires removing the solvent from this gel without substantially disrupting the network structure.

The solvent can be removed by evaporation,
Alternatively, a method of extracting this solvent system using another solvent that dissolves this solvent system is preferably used.

However, in the case of a solvent with a high surface tension, the network structure may be disrupted during evaporation. In such a case, it is preferable to first replace the solvent with a solvent having a lower surface tension and then evaporate it or dry it using a critical point.

For example, after replacing the solvent with liquid carbon dioxide, the solvent is removed while maintaining the network structure by vaporizing the liquid carbon dioxide at a temperature and pressure above the critical point, e.g., 35°C and 73 atm or above. can do.

In this way, a porous polyamide with a large surface area is obtained.

〔Example〕

The present invention will be explained below using examples. The physical properties were measured using the following method.

Measurement of surface area (BET method) Manufactured by Shimadzu Corporation, flow type automatic specific surface area measuring device (product name,
It was measured by the -point method using a Flowsorb Model 2300).

1.0 g of the sample was placed in a cell and degassed at 200° C. for XIO minutes, followed by measurement using a 30 mon% mixed gas of N2/He.

Example 1 50% hexamethylene adibate (hereinafter referred to as AH salt)
The aqueous solution was put into a reaction vessel, and after the atmosphere was sufficiently purged with nitrogen, the reaction vessel was sealed. The reaction vessel was heated to 290°C. After reacting for 1 hour while removing steam so that the pressure inside the container was 17.5 kg/ci, the pressure was gradually raised to atmospheric pressure. As a result, a polymer having a number average molecular weight of 15,000 was obtained.

15 wt% of this polymer was dissolved in N-methyl-2-pyrrolidone (hereinafter referred to as NMP) at 190°C to form a uniform solution. When this solution was cooled to room temperature, it solidified into a gel. This gel was immersed in isoamyl acetate and NMP
was fully substituted with isoamyl acetate. While being careful not to dry the gel substituted with isoamyl acetate,
It was immersed in liquid carbon dioxide at 0°C and sealed. Then 20'
C and left for 20 minutes, and after being sufficiently replaced with liquid carbon dioxide, the temperature was raised to 35°C. The pressure at this time was 73 atmospheres. Under these conditions, the critical point has already been exceeded, so the liquid carbon dioxide has vaporized.

After leaving this state for 5 minutes, carbon dioxide was discharged at a rate of 300 mon/min. In this way, a porous polymer was obtained.

The surface area of this porous polymer was measured by the BET method and was found to be 14 rrr/g.

〔Effect of the invention〕

According to the present invention, a porous polyamide having continuous pores can be obtained. Gas permeability, liquid permeability, and chemical structural characteristics of polyamide can be fully utilized. Therefore, it can be used for applications such as filters and immobilized carrier materials for functional substances.

Claims (1)

[Claims] 1. A method for producing porous polyamide, which comprises dissolving polyamide in a solvent, gelling it, and removing the solvent from the gel without destroying the network structure of the gel.