This invention relates to a method of carbonizing polyacrylonitrile fibers by exposing the fibers at an elevated temperature to an oxidizing atmosphere; then exposing the oxidized fibers to an atmosphere of an inert gas such as nitrogen containing a carbonaceous material such as acetylene. The fibers are preferably treated with an organic compound, for example benzoic acid, before the exposure to an oxidizing atmosphere. The invention also relates to the resulting fibers. The treated fibers have enhanced tensile strength

Cagliostro, D. E.

Lerner, N. R.

English

NASA Technical Reports Server

United States Patent 1191 
Cadliostro et d. 
4,385,043 
[45] May 24, 1983 
[54] METHOD OF CARBONIZING 
POLYACRYLONITRILE FIBERS 
[75] Inventors: Domenick E. Cagliostro, Berkeley; 
Narcinda R. Lerner, Woodside, both 
of Calif. 
[73] Assignee: The United States of America as 
represented by the Administrator of 
the National Aeronautics and Space 
Administration, Washington, D.C. 
[21] Appl. No.: 282,129 
[22] Filed: Jul. 10,1981 
[51] Int. C l . 3  ................................................ DQlF 9/22 
[52] US. Cl. .............................. 423/447.6; 423/447.2; 
423/447.7 
[58] Field of Search ............... 423/447.1, 447.2, 447.4, 
423/447.6, 447.7; 2W29.2; W115.5 
[561 References Cited 
U.S. PATENT DOCUMENTS 
3,412,062 11/1968 Johnson et al. .................. 423/447.6 
3,552,923 1/1971 Carpenter et al. ............... 423/447.6 
3,167,773 10/1973 Turner et ai. .................... 423/447.4 
4,100,004 7/1978 Moss et al. ....................... 423/447.2 
4,295,844 10/1981 Warner ............................. 423/441.4 
Primary Examiner-Edward J. Meros 
Attorney, Agent, or Firm-Darrelil G. Brekke; John R. 
Manning; Robert D. Marchant 
[571 ABSTRACT 
This invention relates to a method of carbonizing poly- 
acrylonitrile fibers (PAN fibers) by exposing the fibers 
at an elevated temperature to an oxidizing atmosphere, 
then exposing the oxidized fibers to an atmosphere of an 
inert gas such as nitrogen containing a carbonaceous 
material such as acetylene. The fibers are preferably 
treated with an organic compound, for example benzoic 
acid, before the exposure to an oxidizing atmosphere. 
The invention also relates to the resulting fibers. The 
treated fibers have enhanced tensile strength. 
5 Claims, No Drawings 
https://ntrs.nasa.gov/search.jsp?R=19830017518 2020-03-22T01:01:22+00:00Z
4,3 85,043 
2 
fuel gas and aliphatic hydrocarbons generally, provided 
they can be used in gaseous form; benzene and other 
aromatic hydrocarbons; also nonhydrocarbon organic 
materials such as carbon disulfide. In general any carbo- 
5 naceous material that is gaseous at the temperature 
involved and which decomposes at temperatures below 
looo" C. within a reasonable period of time, of the order 
does not react destructively with the PAN fibers. 
In place of benzoic acid other aromatic carboxylic 
acids may be used such as phthalic acid, terephthalic 
acid and naphthoic acid. Hydroquinone may also be 
used. They may be used in liquid, 1e.g. molten state or in 
The examples below will serve further to illustrate 
materials. It is desirable that the fibers have a high ten- ing out the experimental work, a standard procedure 
sile strength and for certain purposes that they also have and a modified procedure were 
STANDARD PROCEDURE a high electrical resistance. 
air at a relatively low temperature, typically about 260" Of 2.3 denier PAN was Oxidized c., and are then subjected to carbonization in an inert at 260" C. over a contact time of about 3 hours under a 
tion is typically carried out in an atmosphere of nitrogen ter to Produce a fiber with less than 5% shrinkage or 
and it may be carried out at a relatively low tempera- 25 extension. The sample was then heated at a rate of 20" 
ture, for example 1 2 ~  to 1 5 0 ~ 0  C. or at a higher C./min to temperatures within a range of 450"-1100" C. 
perature, for example about 2500" to 30000 c. The car- in a flow of20 cc/min nitrogen atmosphere under a load 
bonized fibers resulting from the lower temperature of about 50 g in a tubular reactor of about 1.9 cm diame- 
carbonization have higher tensile strength than those ter. 
MODIFIED PROCEDURE prepared at the high temperature. 
OBJECT O F  THE INVENTION In Examples 2,4, 5 and 6 the same PAN tow was first 
It is an object of the present invention to improve passed through a molten benzoic acid bath at 175" with 
upon the methods of producing carbonized PAN fibers g loading Over a contact time Of about hours to 
and to produce PAN fibers of higher tensile strength, 35 produce fibers with less than 10% shrinkage or exten- 
electrical resistance. benzoic acid in Examples 2,4,5 and 6) the samples were 
oxidized at the control conditions under a load of 50 g 
to produce fibers with less than 5 percent shrinkage or 
accordance with the invention PAN fibers, after 40 extension. The oxidized fibers were then carbonized at 
the control conditions, except for the presence, as indi- 
BOLYACWYLQNITWPLE FIBERS 
ORIGIN O F  THE INVENTION 
The invention described herein was made by an em- 
of the United States Government and may be 
governmental purposes without the payment of any 
royalties thereon or therefor. 
This invention relates to the carbonization of poly- 
acrylonitrile (PAN) fibers. 
manufactured and used by or for the Government for Of minutes, may be for this purpose provided it 
10 
BACKGROUNDART the gaseous state. 
as reinforcement in 15 Carbonized PAN fibers find 
various materials of construction, principally plastic the practice and advantages of the invention. In carry- 
as 
Such fibers intended as reinforcement are oxidized by 2o * tow Of 96 
atmosphere at an elevated temperature. The carboniza- load of l5  g in a tubular reactor of about 2.45 cm 
30 
and higher modulus than heretofore and/or of higher sion. In each Of Examples 2 to (after tKatment with 
SUMMARY OF THE INVENTION 
the oxidation step described above, are carbonized, 
above, in the presence of a gaseous active carbon sub- 
stance, such as, for example, acetylene and/or others The are set forth in It be 
mentioned hereinbelow. As will be apparent from the 45 seen that substantial improvement in tensile strength 
obtained by pre-treatment with benzoic acid followed 
preferably at an even lower temperature than indicated cated$ of a mixture Of acetylene-nitrogen as the atmo- 
sphere (5.34% 94.66% nitrogen). 
examples and data presented hereinbelow, tensile 
strength is greatly improved. Preferably, prior to the 
from carbonizing 3, in an atmosphere 
of nitrogen and acetylene and that the best results were 
oxidation step, the PAN fibers are subjected to contact 
at a relatively low temperature, typically at about 140" by oxidation and carbonization in an atmosphere of 
to 200" C., with molten benzoic acid or other similar 50 nitrogen and (Example 4). Example 5 shows 
liquid or gaseous conditioning material. that treatment with benzoic acid, carbonizing in an 
atmosphere of nitrogen, cooling and then carbonizing in 
an atmosphere of nitrogen and acetylene substantially 
improves tensile strength but not as much as in Example 
any one or a mixture of the 55 4 where the initial (and only) carbonization is carried 
Out in an atmosphere Of nitrogen and 
DETAILED DESCRIPTION O F  THE 
INVENTION 
following may be used: Methane, acetylene, ethylene, 
active carbon 
TABLE 1 
Effect of Processes on Tensile Strength of Final Carbon Fiber Product 
Sample Treatment 175" C , hr 260"C,hr "C at "C. % Eloneation 
Benzoic Acid, Air Oxidation at 100% N2. at 5.34% C2Hz/Nz 
I Oxidized and carbonized In 
N2 (standard process) 
2 Treated with benzoic acid, 
oxidized and carbonized 
In N2 
3 Oxidized and carbonized in 
4 Treated with benzoic acid, 
~ 2 ~ 2  
- 
3 
- 
3 
3 700 
3 700 
- 3 
3 - 
- 0.76 
- 0.77 
700 0.90 
700 1.22 
4,385,043 
3 4 
TABLE 1-continued 
Effect of Processes on Tensile Strength of Final Carbon Fiber Product 
oxidized and carbonized 
In C2H2 
oxidized and carbonized 
in N2. cooled and 
carbonized in C2H2 
and carbonized in C2H2 
5. Treated with benzoic acid, 3 3 700 700 - 
6. Treated in benzoic acid 3 - - 700 - 
Tensile % Change in 
Modulus Resistance Strength Tensile Strength 
Sample Treatment (psi x 10-6) (0 cm) (psi) From (A) 
I. 
2. 
3. 
4. 
5. 
6. 
Oxidized and carbonized in 11.9 4.18 90596 0.00 
N2 (standard process) 
Treated with benzoic acid, 12.4 9.10 95160 + 5.04 
oxidized and carbonized 
In NZ 
Oxidized and carbonized in 13.8 1.32 124400 +37.30 
Treated with benzoic acid, 12.6 3.18 154170 f70.20 
oxidized and carbonized 
In C2H2 
Treated with benzoic acid, - - 129980 +43.50 
oxidized and carbonized 
in N2, cooled and 
carbonized in CzHz 
Treated in benzoic acid - - 103100 + 13.70 
and carbonized in C?H? 
C2H2 
- -  
Note: Figures in Columns I and 2 are approximate 
In Table I1 the effects of acetylene concentration and 
temperature on tensile strength are set forth. The modi- 
tied procedure was used in all cases. 
the gas flow decreased to 0.5-1.0 cc/min during the 
5-minute hold period, and the system purged with 90 
30 cc/min pure N 2  on cooldown. 
TABLE I1 
Effect of Acetylene Concentration and Temperature on Tensile Strength during Carbonization 
of a PAN Sample Treated in Benzoic Acid at 175' C. for 3 hr and Air-Oxidized at 260' C. for 3 hr. 
Sample Concentration, % Temperature, 'C. (psi) ohm-cm % Elongation (psi x 
Acetylene Tensile Strength, Resistance, Modulus 
1 5.34 647 122,730 44.1 n.a. n.a. 
2 5.34 705 154,170 3.18 1.22 12.6 
3 5.34 800 19 1,180 ,058 0.74 25.8 
4 5.34 845 169,550 .019 0.70 24.2 
1 11.3 610 73,590 254.7 - - 
2 11.3 705 124,450 1.54 - - 
3 11.3 750 136,320 ,212 
4 11.3 805 116,860 .054 
1 14.02 500 68,370 18300 - - 
2 14 02 590 116,930 657.6 - - 
3 14.02 655 144,900 9.52 
4 14.02 703 133,280 n.a. 
- - 
- - 
- - 
- - 
Standard 
process 0.00 705 90.590 4.18 0.76 11.9 
TABLE I11 
The Effect of Variation of Carbonization Procedure 
on Tensile Strength 
Acetylene Tensile Strength, Resistance Modulus 
Procedure Temperature, "C. Concentration, % psi ohm-cm % Elongation (psi x 
1. Straight 845 5.34 171,500 0.0191 0.71 24.2 
heat-up at 
20" C./min 
in CzH2 
2. Modified 840 5.34 235,200 .0199 0.93 25.3 
3. " 2.0 256,433 - 1.01 25.4 
4. ' I  1 .o 225,400 - 1 .00 22.5 
5. " 0.0 104,920 - 0.61 17.2 
Table I11 illustrates the effect of varying the proce- 
dure. In the first case there was a straight heating in an 
atmosphere of acetylene and nitrogen. In the other 65 
cases the fiber was heated to 500" C. in 20 cc/min flow 
of pure N2, held for 10 minutes while the acetylene 
mixture replaced the N2, heated to the set temperature, 
What is claimed is: 
1. A method of treating polyacrylonitrile fibers to 
enhance their tensile strengths which comprises the 
following steps: 
4,3 85,043 
5 6 
(a) subjecting the fibers to oxidation by exposure to 2. The method of claim 1 wherein step (a) is preceded 
molecular oxygen at a temperature of about 220" to by treatment of the fibers at a temperature not exceed- 
350" C. for a period of time not exceeding about 3 ing about 190" C. with a liquid or gaseous organic com- 
hours, pound capable of enhancing the effect of the active 
(b) then exposing the thus treated fibers to a carboniz- 5 carbon component on tensile strength. 
ing temperature not greater than about 1100" C. in 3. The method of claim 2 wherein the organic com- 
a non-oxidizing atmosphere containing an added pound is molten benzoic acid. 
gaseous active carbon component in sufficient 4. The method of claim 3 wherein the active carbon 
amount to enhance the tensile strength of the car- component is a hydrocarbon. 
bonized fiber as compared to the same fibers car- 10 5. The method of claim 4 wherein the atmosphere 
bonized similarly in an inert atmosphere, said ac- used in step (b) is a gaseous mixture of inert gas and such 
tive carbon compound being one which undergoes active carbon component. 
decomposition at a substantial rate below looo" C. * * * * I t  
15 
20 
25 
30 
35 
40 
45 
50 
55 
60 
65 


Method of carbonizing polyacrylonitrile fibers

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server