Method of polymer separation from solution in formation of pan-precursor for obtaining carbon fibres

FIELD: chemistry.

SUBSTANCE: invention relates to a technology of obtaining fibres from polymers based on polyacrylonitrile-polyacrylonitrile (PAN) and acrylonitrile (AN) copolymers, namely to a stage of a polymer separation from a solution, and can be applied in the production of materials for the textile industry and precursors for obtaining highly strong carbon fibre of a novel quality, applied in different fields of technology. The method of separating the polyacrylonitrile-based polymer from 15-22 vol% solution in the formation of a PAN-precursor for obtaining the carbon fibres includes the extraction of the polymer from its solution without the application of precipitators and the following removal of a solvent by the ventilation of the fibre by air jet. Separation of the polymer from the solution is realised under an influence of mechanical tensions at a temperature of 150°C lower than the temperature of the solvent boiling, with 8-12-time extraction until the freshly formed fibre, with a residual content of the solvent not more than 1%, is obtained.

EFFECT: considerable acceleration of the fibre formation, sharp simplification and acceleration of the polymer separation process, exclusion of a necessity of a multi-stage extraction of the fibre, simplification of the solvent regeneration process.

1 tbl, 3 ex, 2 dwg

 

The invention relates to technology for production of fibers from polyacrylonitrile (PAN) and copolymers of Acrylonitrile (an), namely the stage of separation of the polymer from solution, and can be used in the production of materials for the textile industry and precursors to obtain high-strength carbon fiber new quality used in various fields of engineering.

PAN fiber under different trade names, along with fibers from polyamides and polyesters, are one of the most common synthetic materials used in textile industry. In addition, PAN is one of the most widely used precursors in the production of carbon fibers.

Since the PAN does not melt, the mortar method is the only method of its processing in fiber. Thus, the possibility of industrial production of PAN-fibres connected with the use of suitable solvents, including dimethyl sulfoxide (DMSO).

The use of DMSO as solvent PAN in the production of fibers due to the fact that the synthesis of the starting polymer can be carried out in this solvent on the mechanism of radical polymerization, so that in the process of synthesis is obtained directly spinning solution.

Another rasprostranennymi processing PAN in fiber is associated with its solubility as monomer, and polymer in aqueous solutions of inorganic salts, of which the practical application found a solution of sodium thiocyanate.

Usually the PAN used for the production of fibers, has the molecular mass of the order of 40-60 thousand and weighted mean molecular mass of the order of 80-120 thousand, which provides the required viscosity of the spinning solution and its required predmosti.

The molding fiber PAN must be extracted from the spinning solution by removing the solvent. To date the most common method of forming a PAN-fiber is a so-called "wet" when the die is immersed in a precipitation bath containing a liquid medium in which the PAN is insoluble (usually a mixture of precipitating solvent). Thus there is a coagulation of the polymer, the formation of the gel fiber and its subsequent transformation into the finished fiber as a result of orientational drawing, washing, drying, heat treatment, avevano processing, etc. On the "wet" method currently receive about 80% of all PAN-fibers.

Alternative to the "wet" method of molding until recently served as a "dry" method in which streams of spinning solution PAN served in the mine, in which circulates the inert gas is heated above the boiling point of the solvent. As the jets of the solution along �Akhty of them gradually removes the solvent, and the output is a dry fiber, ready for final processing. For various reasons, "dry" method of forming a PAN-fibers currently almost never used.

To combine advantages of both methods was called the so-called "dry-wet" method of molding in which a die, separated from the mirror the precipitation bath by an air gap, and streams of spinning solution are part of the path forming in the air. This method has to date attention, since it allows one to increase the speed of forming textile yarns and spun PAN fiber. This leaves aside the question of rheological and phase behavior stretched in the air gap of jets of spinning solution that can dramatically affect the properties of the finished fibers. A detailed examination of this behavior led us to the concept of a new method of forming fibers from polymer solutions, including PAN fiber.

Known wet and dry-wet methods of forming unites the implementation of the separation process of polymer solution on a separate phase - polymer and solvent - by contact of the solution with the precipitant. Vzaimodeistvie molecules of the solvent and the precipitant (Pat. Of the Russian Federation No. 2265679, IPC D01F 6/18, 10.12.2005, Pat. Of the Russian Federation No. 2178815, IPC D01F 6/18, 27.01.2007) leads to the release of the concentrated solution on the polymer phase, those. obtain gel fibers.

All of these methods have serious disadvantages. In the dry method is the high energy costs for heating large quantities of air or inert gas in the volume of the mine. In the method of liquid molding with the use of precipitants significantly reduced the rate of formation and problems with subsequent stages the separation of the precipitant and solvent and cleaning them, i.e. with the processes of regeneration.

The closest to the claimed (prototype) is a method of forming fibers, comprising the initial allocation based polymer of polyacrylonitrile from a solution with a concentration of 5-30, preferably from 14 to 25, even more preferably from 18 to 23 wt.%, by forming filaments by the dry method (without the use of precipitators, or wet, or dry-wet method, when the speed of withdrawal of 0.65 to 3 mg of polymer/with 1 hole Spinneret and the maximum shear rate 2000-17000 with-1, followed by drying (see, JP 2009-270248 A, CL D01F 6/18, publ. 19.11.2009). However, this method does not exclude the disadvantages of the dry way and the need to use the precipitation bath for washing of the fundamental quantities of the solvent from the spinning solution, followed by regeneration of the mixture of solvent/precipitant in wet and dry-wet methods.

We propose to perform almost a complete elimination of the polymer from the solution is not PU�eat a diffusion interaction, both in wet and dry-wet methods, and not by evaporation of the solvent, as in a dry way (long carbon chains of synthetic fibres, ed. by K. E. Perepelkin, M., Chemistry, 1973, p. 91]), and as a result of the application to the jets of spinning solution tensile stress, creating 8-12-fold hood, which leads to mechanical squeezing of the solvent and curing of the jets, i.e. to the phase transition "liquid fiber" caused by stretching.

Brief description of the invention

A distinctive feature of this invention is to discontinue use of any precipitants and the implementation of the separation of the polymer from the solution due to changes in the phase composition of the system at strong elongation (longitudinal) currents and a high degree hoods.

In the proposed method of separating polymer on the basis of polyacrylonitrile from 15-22%. solution in spinning of PAN precursor for carbon fibers, including proper selection of the polymer from its solution without the use of precipitants and subsequent removal of the solvent by blowing fiber airflow, the proper selection of the polymer from the solution to obtain nascent fibre, with a residual solvent content of no higher than 1% is carried out under the influence of a mechanical stress at a temperature below the boiling point of the solvent at 150°C, p�and 8-12 times the hood.

Based on the performed theoretical and experimental studies of the molding PAN fibers from different solvents, we found that at high strain rate is the displacement of solvent from the jet stretch up to almost complete separation from the polymer. Thus, there is a deformation caused by the phase decay vysokoorientirovannogo fiber, which is in the form of individual droplets is solvent. This method of formation vysokoorganizovannyh fibers can be named "mechanotronics".

The principal feature of the invention is made the implementation of such a high speed of deformation and the degree of extraction, in which it becomes possible the emergence of strong radial concentration gradient of the solvent until the phase separation of the solution.

The implementation of this method of obtaining vysokoorganizovannyh fibers allows the process has the following advantages:

- the possibility of obtaining fibers at velocities substantially exceeding normal speed molding,

drastic simplification and acceleration of the process of selection of polymers (coagulation),

- the creation of a significant degree of molecular orientation on the stage mehanotronika molded�I, thereby eliminates the need for multi-stage drawing of the fiber after washing the fibers,

- simplification of the process of regeneration of the solvent.

The process mehanotronika selection of the polymer from solution with the formation of fibers either from solutions of PAN ordinary stamps used in the textile industry, or from copolymers of PAN other molecular compounds, for example, with a high content of Acrylonitrile, replacing takenaway acrylic acid, etc. Srednevozrastnoe molecular weight PAN should be from 60 to 120 thousand, according to the equation

[η]=2.685*10-4Mη0,768

corresponds to the interval of values of the characteristic viscosity of 1.25 to 2.45. Squeezing solvent from the solution under the action of tensile stresses at high strain rates occurs when macromolecules form a three-dimensional grid of links. This is achieved when the execution conditions [η]c≥5 (where c is the volumetric concentration of the polymer in solution), which for the specified range of molecular masses correspond to the concentration of the polymer in the spinning solution is not less than 6 vol.%.

To implement mehanotronika �the manual selection of the polymer from a solution by forming fibers use solutions with a concentration of PAN in the range of 15-22%, that meets the requirements of the above conditions for the formation of a three-dimensional mesh of links and corresponds to the desired range of viscosity of spinning solutions. Removal of the solvent occurs at temperatures much below the boiling point, due to phase separation of a polymer solution under the influence of mechanical loads and a high degree of stretching (orientation) of macromolecules.

Example 1 (sustainable methanotrophy" the collapse of the jets)

Sustainable long "mehanotron" fiberizing possible on solutions with high viscosity. Only under this condition it is possible to ensure the necessary balance of viscoelastic forces and surface tension.

In this example, using a highly concentrated solution of PAN 1 in DMSO composition: 23% PAN + 77% DMSO. At room temperature the solution is near the point of formation of the gel (amorphous phase decomposition) due to the high concentration of polymer.

As a starting copolymer used PAN 1 of the following composition: Acrylonitrile 92.9%, methacrylic acid 5.75%, taconova acid 1.35%. Intrinsic viscosity: 1.78 DL/g, Mw94.6 kDa. As solvents used reagent-grade DMSO.

Dissolution is carried out in a flask, heated, equipped with a stirrer, reflux condenser with chlorellas tube and a thermometer. Previously, the polymer � the solvent in the flask was stirred at room temperature until a homogeneous slurry. Then the slurry temperature was raised to 80°C, after which the polymer with continuous stirring for 6 hours completely converted into the dissolved state to form a homogeneous transparent viscous liquid straw color. The viscosity of the solutions prepared at room temperature is 350 and 380 PA·s, respectively.

"Mechanotherapy" a method of separating a polymer from a solution by forming fibers PAN is implemented on standard laboratory equipment consisting of a metering device, capillary and winding devices at room temperature, i.e. 150°C below the boiling point of the solvent at 10-fold the hood.

Methanotrophy effect - squeezing solvent from the concentrated solutions PAN is already apparent at low speeds of the stretching of the jet (1 cm/s) at practically zero velocity at the outlet of the capillary (diameter 0.5 mm, a flow rate of 0.5 ál/s). Multiplicity of extraction is 10.

Fig.1 shows a series of photographs illustrating the phase selection drops of the solvent on the surface of the jet of concentrated solution of PAN in DMSO (23% PAN + 77% DMSO. Relative humidity 30%. Interval between photos 10 s.

Chemical analysis drops (according to IR-spectroscopy) showed that they contain not more than 0.1% of the dissolved polymer.

Diameter (d) formed of fibers�isit the speed of stretching of the jet (V) and conforms to the General pattern:

Vd2=const;

So, at a speed of stretching of the jet 0.5 m/s the diameter of the filaments was 10 µm.

Example 2 (solution concentration at which it can be "mechanotherapy" collapse)

"Mehanotron" phase separation can occur in a wide range of polymer concentrations from the moment of formation of a grid of links (ce) to the concentration at which gel is formed. To prove this, determined the minimum concentration of polymer in the solution (cmin) when "mechanotherapy" the collapse of the jets, and explained how this concentration correlates with the crossover concentration (c*).

cminc*=1[η]

To this end prepare solutions of the three PAN homopolymers with different molecular weight. For dissolved using DMSO reagent-grade brand. By using a rotational rheometer Physica MCR301 measure their viscosity. From these data by linear extrapolation to zero concentration to determine their intrinsic viscosity, concentration of the crossover and the formula Mark-Kuhn-Houwink expect srednevekovoy molecular weight samples.

Low concentrated solutions were prepared by serial dilutions. At Pere�stage prepare 1% solution. The powder of the polymer is left to swell in the solvent for one hour at room temperature, then stirred on a magnetic stirrer at 50°C for 5 hours. The resulting solution was allowed to stand for hours, stirred again for one hour and then diluted to lower concentrations (dilution step is not more than 10 times). The diluted solution PAN 2, the composition of which, see table 1, stirred for one hour, allowed to stand overnight and then stirred again within the hour.

Stretching sprays up to 8 times the extraction is carried out at room temperature, i.e. 150°C below the boiling point of the solvent, the method of separation of the needle from the surface of the drop. A glass substrate coated drop of solution, immersed into the solution, a steel needle. Then raise the needle with a constant acceleration so that the average speed of the fiber drawing at a distance of 10 mm from the drops was ≈0.25 m/s.

Of fast decay phase (fractions of seconds) of jets of small diameter (a few micrometers) fixed camera Nikon D7000 with macronyssidae in the form of groups of two series-connected lenses Tokina macro 100 mm f2.8 and Tokina 12-24 mm f4, with a total increase of 8.3. As a light source using high-power led matrix white light with a luminous flux of 1000 LM.

The system used allowed us to obtain images� with a resolution of 1.7 μm/pixel when the shooting interval is 40 MS and the exposure time of the frame of 0.125 MS, and thereby to ensure reliable identification of the presence or absence of drops of the solvent on the surface of the jets.

In table 1 for three solutions of homopolymers, in addition to the crossover concentration c*and their srednevekovoi MM shown experimentally found the minimum concentration (cminin which begins "mechanotherapy" collapse.

The data obtained show the presence of a linear correlation between the minimum concentration "mehanotronika" formation of fibers and the concentration of the crossover. The proportionality factor equal to 5, indicates the region of concentrations the beginning of an "mehanotronika effect in relation to the concentration of the crossover and is consistent with theory of the phenomenon. "Mehanotron" the formation of PAN fibers is possible in the concentration range from 5c*up to concentrations of gel formation.

Example 3 (mechanical properties of the fibers obtained "mechanotronics" method)

To obtain fibers used 18% solution of a ternary copolymer PAN 3 (PAN/methyl acrylate/itaconic sodium, the quantitative composition of which is given in table 1) in DMSO. High strength fiber PAN get, separating the polymer from the solution methanotrophy way by winding strands of drops of solution on whip winding device located on a high-speed p�evade, the average velocity of the extrusion of the thread 2 m/s, relative humidity of 25% and a temperature of 20°C. the multiplicity of extraction is 12.

The average yarn diameter is 4 μm. The distance between the pins of the winding device 25 mm, the number of threads is 10.

When loading for 1 h threads load in 10 g when the angle between the force direction and floss 55° or weighing 20 g at the angle between the force direction and the filament 40° gap thread starts in 2 hours. Durable coil voltage is 1.1 GPA. Estimation of the error of this measurement given the measurement error of the diameter of the filament (optical microscope) and geometry experience is 20%.

To measure the elastic modulus and elongation at break using laboratory bench, equipped with precision force transducer, a movable crosshead and a special device for mounting ultra-thin fibers.

Fig.2 shows a plot of voltage relative deformation, which implies that "Gukovskaya" area of deformation is 4%, the elongation at break of 55% and a young's modulus of 17 GPA. For comparison, a standard staple fiber, produced by LLC "Composite" (Saratov), has a tensile strength of 0.4 GPA, the young's modulus of 8 GPA. It should be borne in mind that the high breaking elongation, suggests the possibility of additional Orient�tion of fibers, received methanotrophy way, and consequently, improving their mechanical properties.

Table 1
PolymerThe composition of the polymerc*g/DLcming/DLMη,kDa
PAN-1Acrylonitrile 92,9%, methacrylic acid 5,75%, taconova acid of 1.35%2,631013
PAN-2Acrylonitrile 97,0%, methacrylic acid 3,0%0,422,5140
PAN-3Acrylonitrile 95,1%, methacrylic acid 3,55%, itaconic sodium 1,35%0,241515

Thus, the proposed technical solution is the easiest and quickest way to select a polymer for obtaining PAN precursor for the formation of carbon fibers, characterized by the quality level is known analogues.

A method of separating polymer-based �of poliakrilonitrila from 15 to 22 vol.% solution in spinning of PAN precursor for carbon fibers includes the actual selection of the polymer from its solution without the use of precipitants and subsequent removal of the solvent by blowing fiber air stream, characterized in that the actual selection of the polymer from the solution to obtain nascent fibre, with a residual solvent content of no higher than 1% is carried out under the influence of a mechanical stress at a temperature below the boiling point of the solvent at 150°C, 8-12-fold extract.



 

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