RU2541473C2 - Method of obtaining solution of copolymer based on acrylnitrile in n-methylmorpholine-n-oxide - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to method of obtaining solution of copolymer, based on acrylnitrile (PAN), suitable for obtaining polyacrylnitrile fibres-precursors of carbon fibres. Method of obtaining copolymer solution consists in the following: solid-phase mixing of acrylnitrile-based copolymer with content of comonomers not higher than 8 wt % with hydrate of N-methylmorpholine-N-oxide, containing 5-13.3 wt %, is performed at room temperature to complete mixture homogenisation. After that, obtained mixture is heated to temperature 80-135°C. Acrylnitrile-based copolymer is taken in amount 20-50 wt %, the remaining part is hydrate of N-methylmorpholine-N-oxide.

EFFECT: invention makes it possible to increase concentration of PAN solution with its preparation by ecologically pure method.

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Description

The invention relates to chemical technology, in particular to a method for producing a solution of a copolymer based on acrylonitrile in N-methylmorpholine-N-oxide (MMO), suitable for obtaining

polyacrylonitrile fibers - carbon fiber precursors. The term "acrylonitrile-based copolymer" (PAN) refers to copolymers with a prevailing acrylonitrile content and a mass fraction of various comonomers not exceeding 8% wt.

Polyacrylonitrile fibers and filaments are currently a common type of industrially developed carbochain synthetic fibers. This is due to the specifically valuable properties of PAN fiber: a low coefficient of thermal conductivity and the ability of the polymer to cyclize under certain conditions, which determines such a production range as a technical thread used as a raw material (precursor) for the production of carbon fibers. Currently, PAN thread is available in the UK, USA, Germany, Japan, Austria and other countries. Compared to staple fiber, PAN-filament is characterized by a higher linear density of the filament (425-1700 tex) and elementary fiber - 0.17 tex, and increased strength - up to 2000 mN / tex.

In the technology for producing PAN filaments, aprotic solvents were most widely used: dimethylformamide (DMF), dimethylacetamide (DMAA), dimethyl sulfoxide (DMSO), and a hydrotropic solvent — 51.5% NaSCN aqueous solution. The most popular PAN solvent systems are DMF and DMSO. However, despite the fact that these solvents are more accessible and less toxic than aqueous solutions of sodium thiocyanate, they are quite toxic, especially at the stage of molding and regeneration. Moreover, the maximum concentration of PAN spinning solutions in DMF and DMSO due to their high viscosity and phase instability does not exceed 23-24%.

In this regard, a highly polar donor solvent, N-methylmorpholine-N-oxide (MMO), is of great interest. This solvent is most effective for proton donor polymers, in particular for cellulose, and allows you to translate into solution up to 45% of cellulose (Golova L.K. Chemical fibers. No. 1, 1996. p.13-23).

With regard to hydrophobic polymers, in US patent No. 3,447,939, publ. 06/03/1969, a method for dissolving a number of polymers in IMO is described, including dissolving PAN in IMO (see Table 1). However, the author (D.L. Johnson) could not obtain solutions with a PAN concentration of more than 2% at 160 ° C. This direction has not been further developed either in scientific or in patent literature. Nevertheless, this is the only mention of the possibility of dissolving PAN in IMO, therefore, as the closest analogue (prototype) of the present invention, the method according to US patent No. 3.447.939 is adopted.

The objective of the invention is the development of a new, environmentally friendly method for producing a highly concentrated homogeneous solution of a copolymer based on acrylonitrile - PAN in MMO, suitable for forming filaments, which are the precursors of carbon fibers.

To solve this problem, a method of obtaining a solution of a copolymer based on acrylonitrile - PAN in N-methylmorpholine-N-oxide involves solid-phase mixing of PAN with a comonomer content of not more than 8% by weight. and hydrate of N-methylmorpholine-N-oxide containing 5-13.3 wt.% water, with their ratio,% wt .:

PAN 20-50 N-methylmorpholine-N-oxide hydrate rest,

at room temperature until complete homogenization of the mixture and subsequent heating to 80-135 ° C.

The following examples illustrate the proposed technical solution, but in no way limit.

Example 1

To prepare a 35% PAN solution, PAN in an amount of 35% of the total mass and N-methylmorpholine-N-oxide hydrate (hereinafter MMO) in an amount of 65% of the total mass containing 5% wt. water (T _pl. = 160 ° C). As a copolymer, a triple copolymer of acrylonitrile of industrial production with methyl acrylate and itaconic acid is used (the composition of the ternary copolymer in wt% is 92: 6: 2). The initial heterogeneous mixture is machined in a vibratory mill for 4 minutes at a frequency of 50 Hz at room temperature. The resulting homogeneous powder mixture has a T _pl. 120 ° C. At a temperature of 120 ° C, the mixture melts, forming a clear solution of light yellow color.

Studies conducted using a polarizing microscope show that the resulting solution has a high degree of homogeneity, which indicates the possibility of using the resulting solution as a spinning one.

The copolymer solution obtained according to the present example, to confirm the possibility of using it as a spinning dope, is formed by dry-wet method in an aqueous precipitation bath at a temperature of 80-135 ° C to obtain a PAN fiber. The physicomechanical properties of the PAN fibers obtained after the precipitation bath are as follows: tensile strength 410 MPa, tensile elongation 28%, elastic modulus 6 GPa. The given values are at the level of industrial nitron fibers, formed, but not subjected to plasticization and thermal drawing stages.

Example 2

The preparation of a solution of PAN in IMO of the same composition is carried out in the same way as in example 1, with the content of PAN of the same composition as in example 1, in the amount of 35 wt.% And hydrate of IMO in the amount of 65% of the total mass containing 5% water (T _pl. = 160 ° C). Mixing is carried out in a screw mixer with mechanical force on the screw shaft equal to 5 kgf · m, until a homogeneous mixture is obtained. T _pl. the resulting mixture is 120 ° C. At a temperature of 120 ° C, the mixture melts, forming a clear solution of light yellow color, characterized by high homogeneity.

The physicomechanical properties of the formed fibers from the copolymer solution obtained according to the example are similar to the fibers shown in Example 1.

Example 3

To prepare a 35% PAN solution, PAN in the amount of 35% of the total mass and MMO hydrate in the amount of 65% of the total mass, containing 8% wt., Are loaded into the working unit of the vibration mill without grinding elements. water (T _pl. = 130 ° C). As a copolymer, a ternary copolymer of acrylonitrile with methyl acrylate and itaconic acid is used (the composition of the ternary copolymer in wt% is 92: 6: 2). The initial heterogeneous mixture is subjected to mechanical mixing at a frequency of 50 Hz at room temperature. The resulting homogeneous powder mixture has a T _pl. 120 ° C.

At a temperature of 120 ° C, the mixture melts, forming a clear solution of light yellow color.

Studies using a polarizing microscope show that the resulting solution is homogeneous.

The physicomechanical properties of the formed PAN fibers from the copolymer solution obtained according to the example are similar to those described in Example 1.

Example 4

To prepare a 20% PAN solution, PAN in an amount of 20% of the total mass and MMO hydrate in an amount of 80% of the total mass containing 13.3% wt. water (T _pl. = 78 ° C). As a copolymer, a ternary copolymer of acrylonitrile with methyl acrylate and acrylic acid is used (the composition of the ternary copolymer in wt% is 92: 6: 2). The initial heterogeneous mixture is subjected to a vibration mill at a frequency of 50 Hz at room temperature. The resulting homogeneous powder mixture has a T _pl. 76 ° C. At a temperature of 80 ° C, the mixture melts, forming a clear solution of light yellow color.

Studies using a polarizing microscope show that the resulting solution is homogeneous.

The physicomechanical properties of the formed PAN fibers from the copolymer solution obtained according to the example are similar to those described in Example 1.

Example 5

To prepare a 50% PAN solution, PAN in an amount of 50% of the total mass and MMO hydrate in an amount of 50% of the total mass containing 5 wt.% Water (T _pl. 160 ° C) are loaded into the working unit of the vibration mill. As a copolymer, a ternary copolymer of acrylonitrile with methyl acrylate and acrylic acid is used (the composition of the ternary copolymer in wt% is 95: 3.8: 1.2). The initial heterogeneous mixture is subjected to a vibration mill at a frequency of 50 Hz at room temperature. The resulting homogeneous powder mixture has a T _pl. 120-125 ° C. At a temperature of 125 ° C, the mixture melts, forming a clear yellow solution.

However, studies using a polarizing microscope show that the resulting copolymer solution is characterized by a low degree of homogeneity, which does not allow it to be used as a spinning one.

Example 6

To prepare a 40% PAN solution, PAN in an amount of 40% of the total mass and MMO hydrate in an amount of 60% of the total mass containing 5 wt.% Water (T _pl. 160 ° C) are loaded into the working unit of the vibration mill. As a copolymer, a ternary copolymer of acrylonitrile with methyl acrylate and acrylic acid is used (the composition of the ternary copolymer in wt% is 95: 3.8: 1.2). The initial heterogeneous mixture is subjected to a vibration mill at a frequency of 50 Hz at room temperature. The resulting homogeneous powder mixture has a T _pl. 115-117 ° C. At a temperature of 120 ° C, the mixture melts, forming a clear yellow solution.

Studies conducted using a polarizing microscope show that the resulting solution has a high degree of homogeneity.

The physicomechanical properties of the formed PAN fibers from the copolymer solution prepared according to the example are as follows: tensile strength 400 MPa, tensile elongation 30%, elastic modulus 5.6 GPa.

Example 7

The preparation of the PAN solution in IMO of the same phase composition is carried out in the same way as in Example 5, with the PAN content in the solution in the same amount as in Example 5, i.e. in the amount of 40 wt.% and MMO hydrate in the amount of 65% of the total mass containing 5% water (T _pl. = 160 ° C). Mixing is carried out in a screw mixer with mechanical force on the screw shaft equal to 5 kgf · m, until a homogeneous mixture is obtained. T _pl. the resulting mixture is 110 ° C. Subsequent melting of the mixture is carried out at 115 ° C. The resulting solution is characterized by high homogeneity and has a light yellow color.

The physicomechanical properties of the formed PAN fibers from the copolymer solution prepared according to the example are similar to those described in Example 6.

Example 8

To prepare a 25% solution of PAN, PAN in an amount of 25% of the total mass and MMO hydrate containing 13.3 wt.% Water (T _pl. = 78 ° C) are loaded into the working unit of the vibration mill. As a copolymer, a ternary copolymer of acrylonitrile with methyl acrylate and acrylic acid is used (the composition of the ternary copolymer in% is 97: 2: 1). The initial heterogeneous mixture is subjected to a vibration mill at a frequency of 50 Hz at room temperature. The resulting homogeneous powder mixture has a T _pl. 80 ° C. At 80 ° C, the mixture melts, forming a clear yellow solution.

Studies using a polarizing microscope show that the resulting solution is homogeneous.

The physicomechanical properties of the formed PAN fibers from the copolymer solution prepared according to the example are similar to those described in Example 6.

Example 9

To prepare a 35% PAN solution, PAN in the amount of 35% of the total mass and MMO hydrate in the amount of 65% of the total mass containing 8 wt.% Water (T _pl. 130 ° C) are loaded into the working unit of the vibration mill. As a copolymer, a double copolymer of acrylonitrile with acrylic acid is used (the composition of the copolymer in wt% is 97.4: 2.6). The initial heterogeneous mixture is subjected to a vibration mill at a frequency of 50 Hz at room temperature. The resulting homogeneous powder mixture has a T _pl. 95-125 ° C. At a temperature of 130 ° C, the mixture melts, forming a clear, dark yellow solution.

Studies conducted using a polarizing microscope show that the resulting solution has a high degree of homogeneity.

The physicomechanical properties of the formed PAN fibers from the copolymer solution prepared according to the example are similar to those described in Example 6.

Example 10

Prepare a solution of PAN in an MMO of the same phase composition as in Example 8, with a PAN content of 35% and an MMO hydrate in an amount of 65% of the total mass containing 8 wt.% Water (T _pl. 130 ° C). Mixing is carried out in a screw mixer with mechanical force on the screw shaft equal to 5 kgf · m, until a homogeneous mixture is obtained. T _pl. the resulting mixture is 120 ° C. At a temperature of 120 ° C, the mixture melts, forming a clear solution of light yellow color.

Studies using a polarizing microscope show that the resulting solution is homogeneous.

The physicomechanical properties of the formed PAN fibers from the copolymer solution prepared according to the example are similar to those described in Example 6.

Example 11 (comparative)

The preparation of the PAN solution is carried out in the same way as in example 5, with the content of PAN of the same composition as in example 5, in an amount of 55 wt.% And MMO hydrate in an amount of 45% of the total mass containing 6% water (T _pl. 150 ° C). The initial heterogeneous mixture is subjected to a vibration mill at a frequency of 50 Hz at room temperature. The resulting homogeneous powder mixture has a T _pl. 110-160 ° C. When heated to 160 ° C, the mixture melts, but it darkens intensively, which is caused by the active occurrence of destructive processes. However, even at 170 ° C, according to polar microscopy, an undissolved polymer phase is present in the isotropic field of the resulting solution.

Example 12 (comparative)

To prepare a 40% solution of PAN, PAN in an amount of 40% of the total mass and MMO hydrate containing 5 wt.% Water (T _pl. 160 ° C) are loaded into the working unit of the vibration mill. As a copolymer, a ternary copolymer of acrylonitrile with methyl acrylate and acrylic acid is used (the composition of the ternary copolymer in% is 97: 2: 1). The initial heterogeneous mixture is subjected to mechanical treatment at a vibration mill without grinding elements for 4 minutes at a processing frequency of 50 Hz at room temperature. The resulting powdery mixture has a T _pl. 160 ° C.

When heated, the mixture melts, and due to the active occurrence of destructive processes, the mixture darkens intensively and even at 170 ° C in the isotropic field of the resulting solution, according to polar microscopy, under-dissolved polymer particles are present in the sample.

Example 13 (comparative)

The preparation of a solution of homopolymer of polyacrylonitrile in MMO is carried out in the same way as in example 1, with the content of polyacrylonitrile equal to 15% of the total mass, and hydrate of MMO in the amount of 85% of the total mass. When heated, the resulting mixture does not completely go into a viscous-flowing state; an optically transparent heterophase of an insoluble polymer is present in the molten sample, which does not disappear even at a temperature of active thermal degradation of the mixture - at a temperature above 160 ° C.

Thus, the proposed method is an environmentally friendly way to obtain a solution of a copolymer based on acrylonitrile in MMO, suitable for forming filaments, which are the precursors of carbon fibers, and provides an increase in the concentration of the PAN solution and the spinning solution compared to the traditional method up to 20-30% of the mass. (see table).

Table The method of obtaining solutions of PAN The maximum concentration of the PAN solution,% wt. The concentration of the dope,% wt. Conventional Dissolution (DMF, DMSO) NaSCN 20-32 18-20 The proposed method of dissolution (MMO) 20-50 20-40

Claims (1)

A method of obtaining a solution of an acrylonitrile-based PAN copolymer in N-methylmorpholine-N-oxide, characterized in that the acrylonitrile copolymer with a comonomer content of not more than 8 wt.% Is used as a PAN, and the solution is prepared by solid-phase mixing with N- hydrate methylmorpholine-N-oxide containing 5-13.3 wt.% water, with their ratio, wt.%:
PAN 20-50 N-methylmorpholine-N-oxide hydrate rest,
at room temperature until complete homogenization of the mixture and subsequent heating to 80-135 ° C.