DE2124636C3 - Process for the production of carbon fibers - Google Patents

Description

The present invention relates to a method for producing carbon fibers from coal tar pitch or other strongly aromatic distillation residues.

Carbon fibers with excellent mechanical properties by oxidation are already available and thermal conversion of filaments of organic polymers such as polyacrylonitrile and Rayon, preserved. Due to the cost of the raw materials and the low carbon yield however, the fibers obtained in this way have a high cost price. One also has fibers out Coal tar pitch obtained by 'nan the tar pitch a thermal treatment at a moderate temperature and, if necessary, other treatments or subjected to conditioning and then the tar pitch treated in this way at a temperature in of the order of 300 ° C has spun into threads. The threads thus obtained underwent oxidation subjected in order to make them infusible and then charred in the air (see, for example, FR-PS 1465 030). However, these processes yield fibers of a quality similar to that obtained from textile thread Fibers is very inferior.

The present invention now includes a method that allows the qualities of a Coal tar pitch or a strongly aromatic substance similar to coal tar pitch Improve fibers.

According to the process of the invention, these highly aromatic tar pitches are used during or a polymeric hydrocarbon before the thermal treatment phase preceding the spinning to. Among the polymers that have shown good results can be natural or synthetic Hydrocarbon polymers such as polyethylene. Polypropylene, polystyrene, polybicyclo [2.2.1] hepten-2, the rubbers, etc. name.

According to a variant of the process, the strongly aromatic tar pitch, which has only been filtered, is heated under such temperature, time and stirring conditions that the material obtained has little or no ■ does not contain any anisotropic material. The presence of this anisotropic material can be easily identified by testing be detected in the optical microscope in polarized light (M. Ihnatowicz, P. C hi ehe, J. Deduit; S. Pregermain and R. Tournant, Carbon, 4, 41, [1966]). This thermal treatment can be carried out in one with an agitator and gas purging equipped reactor.

The mixture can be heated to a much lower temperature, but not so much Extensive liberation of the material thus obtained from volatile components makes the Preservation of the infusibility of the fibers prior to charring, necessary oxidation treatments more difficult.

The product obtained by this treatment is then spun onto it by any means oxidized and charred in a manner known per se.

The following examples illustrate the invention.

example 1

A high-temperature coal tar pitch with the following characteristics was used:

Kraemcr-Sarnow point 80 "C density 1.32 g / cm ¹ volatile components in accordance with the ATIC-02-60 standard) 64.3% Elemental analysis in wt.% carbon 93.02 hydrogen 4.45 oxygen 1.5 nitrogen 0.7 sulfur 0.3

This tar pitch was previously at 190 ° C over a Bronze filter with a mean pore opening of 2 μ has been filtered to remove the naturally contained solid and pseudo-solid particles.

After adding K)% by weight of high-density polyethylene with a melt index of 4, this mixture became brought to 420 ° C with constant stirring at a heating rate of 3 ° C per minute; the Volatile substances released were removed with a stream of nitrogen with a throughput of 3 l / min.

The product obtained became a thread at 204 "C with a drawing speed of 450 m / min drawn.

The whole thing was in an oven and was subjected to the following working conditions:

"from room temperature to 250" C in
Presence of air at 0.5 ° C / min
from 250 ° to 700 ° C in the presence
of nitrogen without oxygen
0.5 ° C / min

^bü from 700 ° to 1000 ° C at 2 ° C / min

all in all

7.5 h

15 h

2.5 h

25 h

The oven is then allowed to cool naturally.

The mechanical properties of the obtained carbon fibers were measured using an Instroni tester measured under the following conditions

Length of the specimen
Drawing speed

50 mm
0.05 cm / min

An average tensile strength of 55 kg / mm ^: and an average Young's modulus of 4200 kg / mm for an average diameter of 30 μ were measured.

These values are mean values from seven measurements on different threads. The overall yield of the including filtration, devolatilization, spinning, oxidation and char Operations was 65%.

Example 2

The working conditions were identical to those in Example 1, except that the polyethylene was replaced by polybicyclo [2.2.1] -hepten-2 replaced (F. W. Michelotti and W. P. Keaveney, J. Polymer Sci., A, 3, | 1965], 895).

A tensile strength of 150 kg / mm and a Young's modulus of 11,960 kg / mm ² for a diameter of 30 μ were measured for the carbon fibers produced in this way.

The overall yield from the operations mentioned in Example 1 was 66%.

Example 3

The working conditions were identical to those in Example 1, only the polyethylene was replaced by polystyrene replaced.

The carbon fibers thus produced had a tensile strength of 60 kg / mnv and a Young's modulus of 4600 kg / mm ² for a diameter of 30 μ.

The overall yield from the operations described in Example 1 was 64%.

Example 4

The working conditions were identical to those in Example 1, but here the tar pitch did not contain any Additive.

The carbon fibers thus produced had a tensile strength of 24 kg / mm ^: and a Young's modulus of 3300 kg / mm "for a diameter of 30 μm.

The overall yield from the operations carried out as described in Example 1 was 61%.

The comparison of the above properties with those of the invention, as in Examples 1 to 3 obtained fibers shows clear advantages of the invention.

Claims (3)

Patent claims: 1. Process for the production of carbon fibers from a strongly aromatic distillation residue, such as Steink-ihlenteerpech, whereby one subjecting the distillation residue to thermal treatment at a moderate temperature, then the product treated in this way is spun and the threads obtained are oxidized and then one Subjecting to charring, characterized in that a hydrocarbon polymer is added to the starting material before or during the thermal treatment phase preceding the spinning clogs. 2. The method according to claim 1, characterized in that the hydrocarbon polymers are Polyethylene, polypropylene, polystyrene, polybicyclo [2.2.1] hepten-2 or a natural one or artificial rubber is used. 3. The method according to claim 1 or 2, characterized in that the thermal treatment, which precedes the spinning, before the occurrence of the anisotropic phase or at the beginning the occurrence of the anisotropic phase stops.