DE1928194A1 - Process for the production of carbon fibers - Google Patents

Description

', ΡΛΤΕNTAMWXCTl = ί * \ *

DIPL.-ING. GÜNTHER KOCH DR. TINO HAIBACH

8 Munich 2, June 3, 1969

OUR MARK iNi 12 04-9 - K / W!

Rolls-Royce Limited, Derby, Derbyshire, England Process for making carbon fibers.

The invention relates to a method of manufacture of carbon fibers.

It has already been proposed "to produce carbon fibers by pyrolysis of various raw materials, in particular using PoIyacrylonitril and copolymers thereof. Here again, it is known to use a Voroxydationsstufe in which the output fiber in an oxidizing atmosphere to a temperature of about 25O ⁰ C is heated, and this pre-oxidation step gives the starting material at least the characteristics of cross-bonded material and thereby it becomes more resistant to depolymerization, so that the subsequent pyrolysis can be carried out more quickly Characteristic which leads to a considerable development of heat, which brings with it the risk that the reaction proceeds in the opposite direction and that the fiber explodes or charred.

The invention is based on the object of creating a method in which the exothermic characteristics the pre-oxidation can be changed so that it is much easier

909850/1452

- 2 can be controlled or monitored. -

According to the invention, the process for the production of carbon fibers is carried out in such a way that first a Paser consisting of Polyacrylonnitr ^ l is heated in an inert atmosphere to a temperature in a range from 200 ° 0 to 300 ⁰ C, that then the Paser in a Oxygen-containing atmosphere is heated to a temperature in the range between 150 ° C and 250 ⁰ C, and that finally the Paser is subjected to pyrolysis.

w Preferably, the fiber is heated in an inert atmosphere to a temperature in the range between 800 ° C and 1500 ⁰ C during pyrolysis. For example, the pyrolysis can be ^{carried out at a temperature of 1000 °} C. in an atmosphere of nitrogen.

The pre-oxidation treatment preferably consists of first heating in nitrogen and, as a second stage, heating in air. The first heating stage in nitrogen can be carried out for three hours at 210 ^° C., two hours at 220 ^° C. and two hours at 250 ^° C. in a nitrogen atmosphere, the following second stage being carried out for seven hours at 220 ^° C. in air.

In experiments carried out in practice, a technique called "differential thermal analysis" was used in the preoxygenation of fibers consisting in particular of polyacrylonitrile. In this technique, the material is heated at a constant temperature increase (6 ⁰ C per minute) up to about 500 ° C, and the temperature difference between this test object is exactly the same as an inert reference

90985 0./1452

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material measured. Any difference in temperature between the Polyaerylonitril-Versuohskörper and the Reference body indicates either an exothermic or an endothermic process, depending on whether the Folyacrylon & tril fiber is at a higher or lower temperature »than the reference body *

In carrying out this technique in a polyacrylonitrile fiber was heated in air, it was found that the resultant reaction showed two exothermic peaks at about 25O ⁰ C and 310 ⁰ O. It is clear that in the known pre-oxidation processes these two exothermic processes contributed to the final energy generation of the reaction and accordingly to a likely reversal of the process.

Further experiments were carried out using the polyacrylonitrile fiber was heated in an inert atmosphere, and it was found that the lower temperature was even remains exothermic under inert conditions. It is believed, that this lower temperature exotherm is due to the conversion of the nitrile group in the original polymer caused by cross-tie, or instead by a ring bond along the polymer molecular chain, while the higher temperature reaction, which presupposes the presence of oxygen, to dehydration and oxygen absorption runs through the fiber. These reactions are both useful and the necessary stability of the fiber to achieve and to reduce the depolymerization and to create the possibility in the following pyrolysis to be able to perform rapid heating.

This hypothesis was tested by first treating the fibers in nitrogen and then in air, and it did

909850/1452.

"■■■■■■ 'ORiGIiIAL

confirmed by the thermal differential analysis » that as expected, each treatment was a single exotherm Reaction of lesser intensity produced than the combined reaction which occurs only when heated in air.

From the above it follows that

by heating the fiber first in Stioksotff and then in an oxygen-containing atmosphere like this proposed by the invention, the two ejtthermen

Reactions are separated and so a stabilization

of the polymer can be softened, with the risk of a

Reversal of response is much smaller *

In an exemplary method of the invention Pasern a Polyacryl / i-Sohpolyraerleators, the, under

w '

known by the trade name "Courtelle", and by the

Gourtaulds Limited company is based in Sticketoff

heat treatment for three hours at 210 ^{° C.} subjected and then two hours at 220 ° 0 and then at 2 hours 250 ⁰ C. The fibers were then placed in an air atmosphere transferred, and left at 22o ° 0 for seven hours *

The resulting fibers then became one Subjected to pyrolysis by being at 1000 ⁰ C in an inert Brought to the atmosphere and in this for about 3 hours Atmosphere were left. Then the sioh became high

resulting fiber tested by the usual procedures, around the value of the Young's modulus and the final

To achieve tensile strength. These values were then combined with the Compared values obtained from a material

which was pre-oxidized by sifting it only in air

Brought to 22O ° 0 for hours and then a pyrolysis

in a nitrogen atmosphere «for the same period of time was subjected and under dike temperature conditions as with the fibers that were pretreated according to the invention.

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ORIQ! WSFECTED

In the case of the fibers pretreated according to the invention, the result was an average value for the modulus of elasticity of 2.18. 10 kg / cm (j31.10 psi) while the average ultimate tensile strength is 15.46. Was 10 x ^ kg / cm (219th ICr psi). These values, compared with the values for the fibers that were not pretreated according to the invention showed a modulus of elasticity of 1, * 97 kg / cm (260. 10 ⁵ psi). These differences in values are relatively small and are within the limits of the normal deviations observed with known methods.

From these experiments it can be seen that the heat treatment according to the invention is able to produce irons which have an equal strength and an equal Have elastic modulus like those produced by known methods, but at the same time the Risk of explosion is considerably reduced. It has also been found that when using the two-stage heat treatment according to the invention the temperature of the second stage (i.e. the heating in an oxygen-containing Atmosphere) can be carried out effectively at a lower temperature than known Pretreatments were possible, and thereby a further improvement of the controllability and controllability of the Pretreatment achieved and possibly a shortening of the total treatment time.

The invention has been described with reference to a specific Wärmebehandlung.Is wire but possible, the conditions exerts Witröeteeh-asidlung to change considerably. It is believed that “Any femptrature was within the range between 0 ° C and 3QQ ° for door

® f ^s

909850/14

expectant-en used first stage of heating in an inert atmosphere could be / as well as any temperature in the range between 150 ⁰ C and 25Q ⁰ C in the second heating step, in an oxygen-containing atmosphere ·. Of the various oxygen-containing atmospheres useful for the second stage, air has been found to be extremely useful because it is readily available and these advantages outweigh any other considerations.

The invention has also been described above with reference to a special copolymer made from polyacrylonitrile but it will be understood that the invention is useful in connection with others Polymers in which this combined cross-linking process and oxygen absorption is applicable. It is clear that other Michpolymerisate. by Polyacrylonltrile can be used and that the invention is also applicable to cellulosic material, e.g. Rayon and polyamide material such as nylon.

The subsequent pyrolysis of the fiber can take place at any temperature can be carried out in the range between 800 ° C and 1500 ° C, and a graphitization stage can follow * those at any temperature starting from the pyrolysis temperature can be carried out up to about 250 ° G, depending on the required final properties of the paser,

Fibers produced in this way can find many uses in technology. Their most common and most practical use that 1st as a reinforcing material within a made of a synthetic resin matrix, such fiber-reinforced Kuneth & rzwerkstoffe are widely used - in the manufacture von.-QasturMnens-trahltriebewerken, bearings uiiWf benutat.

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Claims (1)

t r ι ir * t · r t Pat entans prtic h et A process for preparing Kohlenstoffaeern, characterized in that initially in a first stage a polymer fiber in an inert atmosphere to a temperature in a range "wipe 200 ⁰ C and 300 ° C heated 'and is kept at this temperature for a predetermined tent duration and in that the laser an atmosphere containing oxygen in a wipe "wide step at a TenpeAur in BenLoh" 150 ⁰ C and is SGO ⁰ O exposed during a predetermined time period, and thereafter Al "fiber is subjected to pyrolysis. 2. The method according to claim Iy. characterized in that the pyrolysis of the fiber is carried out by heating it in an inert atmosphere to a temperature in the range between 600 ⁰ C and 1 ^ QO ⁰ C » 3. The method according to claim 2, characterized in that the pyrolysis of the fiber is carried out by heating the fiber to a temperature of 1000 ⁰ C, the inert atmosphere being nitrogen A method according to claim 1, characterized in that the first heating step is carried out by the fact that keeping the fiber for three hours at 210 ° C, then zwii hours at 220 ⁰ C and then swel hours at 250 ⁰ C within a group consisting of nitrogen atmosphere » 909850/1452 ^ \ SNAL itiSPcCTED 5 · The method according to claim 1, characterized in that in the second stage the fiber within air brought to a temperature of 700 C and left for seven hours. 6. The method according to claim 1, characterized in that the Paser consists of polyacrylononitrile. 9098 5 0 / U52