NL8603289A - PROCESS FOR THE MANUFACTURE OF HIGH ANISOTROPY CARBON FORMS. - Google Patents

Description

* NL 33.897-dJ / vdM ώ =. ^ - 1 -

Process for the production of high anisotropy carbon moldings.

The present invention relates to an improved process for the production of articles of carbon or graphite in the form of fibers or films, which have a high anisotropy, by choosing a substance as carbon precursor, which has a certain chemical structure and certain properties. (Hereafter, the carbon and graphite objects are commonly referred to as carbon-form bodies.)

Various processes are already known for the production of carbon-shaped bodies, in particular of carbon fibers. In one, fibers from natural or artificial high-polymer materials, such as polyacrylonitrile, polybenzimidazole, cellulose, etc., are carbonized, while in another pitch fiber is melt-spun and then fusible and carbonization is subjected.

The second method is suitable for the manufacture of products having uniform quality and sufficient strength. On the other hand, carbon fibers produced by this method typically have an isotropic structure, from which the growth and orientation of graphite crystals are difficult only when operating at high temperatures. As a result, it has hitherto been difficult to manufacture carbon fibers with a high modulus of elasticity without subjecting them to heat treatment at graphitization temperatures or. in a temperature range close to it, at the same time allowing strong tensile forces to act.

One reason for this is that the molecular weight of the starting product pitch, which is suitable for spinning, compared to that of high polymers, such as eg polyacrylonitrile, etc., is extremely low and, moreover, the molecules as a whole are not flat enough so that, using traditional methods, it is hardly possible to obtain pitch fibers with a high molecular orientation * Moreover, the infusibility at lower temperature causes a three-dimensional cross-linking between the molecules, so that the pitch fibers are poor affordability 5, which is a further difficulty.

DE Offenlegungsschrift 20 15 175 describes a process for the production of carbon-shaped bodies. The process is characterized in that a starting material is formed into the desired shape, which consists of the following compounds: a) condensed polycyclic compounds, which are formed as a basic skeleton by condensation of at least seven rings and have a highly flat molecular structure b) compounds in which units of said condensed polycyclic structure are joined together by a single bridge, c) compounds in which units of condensed rings consisting of more than two rings are connected by two bridges, which have at least one of the elements contain carbon, nitrogen, oxygen or sulfur, are joined to form a new ring system and d) from a mixture of the compounds mentioned under a) to c), which has a highly flat condensed ring structure, an even melt , as well as a melt viscosity of 0.4-700 poise at the deformation temperature, are selected, and the char and graphitization of the n the shaped body without applying a tensile stress to the shaped bodies during these treatments.

The average molecular weight of the carbon fiber precursor is reported as 400-3000 and its viscosity at temperatures between 320-480 ° C as 0.04-70 Pa.s. These routes are taken very broadly. Usually, the average molecular weights for spinnable mesophase pitches are below 1000 and have viscosities between 1-20 Pa.s.

The modulus of elasticity (E) of the carbon fibers made from these 8 § 0 3 2 8 9 - 3 precursors is between 137-314 kN / mm2. The fibers can therefore be classified in the class of the very stiff carbon fibers. High modulus carbon fibers have an E modulus between 350-450 kN / mm 2 and are made almost exclusively of polyacrylonitrile (PAN). In contrast to the linear structure of the PAN molecules, pitch mesophases have a flat molecular structure. This can be seen as a reason for the lower elasticity of the carbon fibers from pitch precursors.

The present invention aims to develop a process for the production of carbon shaped bodies, in particular of carbon fibers from polycyclic aromatics, which have an E-modulus which is at least as high as that of fibers of PAN and to this end, the process is characterized in that linear condensed polycyclic compounds, obtainable by the polymerization of 0-position substituted linear fused aromatics with no more than six rings, optionally after distilling off the mono- and polymers with less than five rings are subjected to fractional extraction with an supercritical gas, the precursor of which is a mixture of polycyclic aromatics with a narrow molecular weight distribution with molecular weights in the range between 500-1200, which is known per se is processed into carbon moldings.

The starting materials are only linearly fused aromatics at the β-position with the general formula of the formula sheet, where n is a value between 0 and 4, which is at one or more β-positions .0, β ', β ", β'1 ") Can be arbitrarily substituted. It has been found that these aromatics polymerize exclusively to linearly condensed compounds. Particularly preferred are the aromatics substituted with alkyl, hydroxy or amino groups, in particular those at the β or β1 position and β or β '*' position at least 35 bipartyl substituted aromatics, such as e.g. 2,6-dimethyl-naphthalene, 2,7-dimethylnaphthalene, 2-hydroxy-6-methyl-naphthalene, 2,7-dimethylanthracene, 2,6-dimethylanthracene, 2,3-dimethyl anthracene, 2-amino-6-methylnaphthalene, the aromatics may be 8603289.-A ..

- 4 - can be polymerized individually or as a mixture, but it is, however, especially in the case of higher condensed aromatics to polymerize compounds having an equal number of rings, since the higher jump in molecular weight facilitates fractionation .

The polymerization is generally carried out at temperatures between 350-470 ° C. An elevated pressure is advantageous, especially for compounds whose boiling point is below or only slightly above the polymerization temperature. After completion of the polymerization, the low-boiling mono- and polymers can be removed from the reaction product by flash distillation.

The residue is extracted with a supercritical gas of low boiling aliphatic hydrocarbons, optionally using a drag agent, and the extract is separated from the liquid phase by stepwise temperature increase or pressure reduction. At least three fractions are recovered, the middle of which preferably contains no more than four successive polymerization steps of the introduced aromatics and is used as a precursor for the production of carbon moldings.

EXAMPLE

A mixture of 500 g of 2,6-dimethylanthracene and 500 g of 2,7-dimethylanthracene is polymerized for 3 hours at 450 ° C in an autoclave under nitrogen at a pressure of 5 bar. This results in about 10% by weight, based on the starting mixture, of methane-rich gas. The pressure in the autoclave is then reduced to 50 mbar via a condenser.

About 5% by weight of an oil is obtained, which mainly consists of anthracene. The residue (85% by weight of the starting mixture) is extracted with propane at 150 ° C under a pressure of 180 bar and three pitch-like fractions are recovered from the loaded extractant by stepwise relaxation. The middle fraction obtained in a yield of 65% by weight, based on the starting mixture, has a molecular weight distribution in the range between 550-1100 at an average molecular weight of 800. The viscosity at 350 ° C

8603289 - 5 - amounts to 8.2 Pa.s. When the polished surface of the cooled fraction is viewed under a polarization microscope, the complete anisotropy of the substance is visible.

It is spun at 350 ° C with a draw-off speed of 5 m / s by means of an extruder and a spinning head to fibers with a diameter of 8 µm, without creating fiber creases. The fibers are then oxidized at about 200 ° C in air for 2 hours and then for 1 hour at 300 ° C. The fibers thus rendered meltable are heated in a nitrogen atmosphere at 2 K / min to 600 ° C, at 10 K / min to 1400 ° C and subsequently at 20 K / min to 3000 ° C.

The elastic modulus of the graphite fibers thus obtained is 410 kN / mm2 and the tensile strength is 2900 N / mm2. 15 8603289

Claims (5)

1. A process for the production of a carbon-shaped body by deforming highly polymerized polycyclic aromatics mixtures into foils or fibers and subsequently rendering the carbon body infusible, carbonizing and graphitizing, characterized in that linear condensed polycyclic compounds are available by the polymerization of linearly fused aromatics substituted at the β-position with no more than six rings, optionally after fractionation of the mono- and polymers with fewer than five rings, subjected to a fractional extraction with an supercritical gas, where as precursor a mixture of polycyclic aromatics with a narrow molecular weight distribution with molecular weights in the range between 500-1200 is obtained, which is processed into carbon-shaped bodies in a manner known per se. 2. Process according to claim 1, characterized in that the linearly condensed polycyclic compounds have been prepared by polymerization of the β-position with alkyl groups, hydroxyl groups or amino groups, mono- or multiply substituted linear fused aromatics with 2-4 rings. 3. Process according to claims 1 and 2, characterized in that linearly fused aromatics with an equal number of rings are polymerized to form linearly condensed polycyclic compounds. 4. Process according to claims 1-3, characterized in that the linear condensed compounds are extracted with an supercritical gas of low-boiling aliphatic hydrocarbons, optionally using a drag agent, and by stepwise temperature increase or pressure reduction in at least three fractions are distributed, whereby the precursor for the carbon-shaped bodies is obtained as the middle fraction. 35 Process according to claim 4, characterized in that the precursor contains no more than four successive polymerization steps of the aromatics used. 8603289 ________ i $ L 33897-dJ / cs Belongs to 0.A. in the name of Rütgerswerke Aktiengesellschaft in Frankfurt / Main, B.R.D. FORMULA SHEET r ^ ^ j3. \ n 8603289