NASA CASE NO. LAR 15526-1-SB

PRINT FIG. N/A

The invention disclosed in this document resulted from research in aeronautical

and space activities performed under programs of the National Aeronautics and Space

Administration. The invention is owned by NASA and is, therefore, available for

licensing in accordance with the patent licensing regulations applicable to U.S.

Government-owned inventions (37 CFR 404.1 et seq.).

To encourage commercial utilization of NASA-owned inventions, it is NASA

policy to grant licenses to commercial concerns. Although NASA encourages

nonexclusive licensing to promote competition and achieve the widest possible

utilization, NASA will provide the necessary incentive to the licensee to achieve early

practical application of the invention.

Address informational requests for this invention to the Technology

Applications Team, NASA Langley Research Center, Code 200, Hampton, Virginia

23681-0001.

Address applications for license to the Patent Counsel Office, Mail Stop 212,

3 Langley Boulevard, Hampton, Virginia 23681-0001.

Serial No.: 08/689,760

Filed: 08/13/96 LaRC
LAR 15526-1-SB -14-

POLYIMIDE FIBERS

PATENT APPLICATION

Ah._trac.t nf thA r)i._eln._urA

5 A polyimide fiber having textile physical property characteristics

and the process of melt extruding same from a polyimide powder.

Polyimide powder formed as the reaction product of the monomers 3,4'-

ODA and ODPA, and endcapped with phthalic anhydride to control the

molecular weight thereof, is melt extruded in the temperature range of

10 340°C to 360°C and at heights of 100.5 inches, 209 inches and 364.5

inches. The fibers obtained have a diameter in the range of 0.0068 inch

to 0.0147 inch; a mean tensile strength in the range of 15.6 to 23.1 ksi;

a mean modulus of 406 to 465 ksi; and a mean elongation in the range

of 14to 103%.

15

LAR 15526-1-SB

_ r n._._- R AfP.r A n o.P.

-1-

POLYIMIDE FIBERS

PATENT APPLICATION

This application claims the benefit of U.S. Provisional Application No.

60/021,206, filed July 3, 1996.

Orinin nf thP. InvP.ntinn

10

The invention described herein was jointly made by an employee of

the United States Government and contract employees in the performance

of work under NASA contracts. In accordance with 35 USC 202, the

contractors elected not to retain title.

15

Field nf thP. InvP.ntinn

This invention relates generally to the extrusion preparation of fibers

and relates specifically to the preparation of polyimide fibers having

enhanced flow and high mechanical properties.

20 Bac.kgrnHnd nf thP. InvP.ntinn

25

High performance polyimides are used in the aerospace industry, for

example, in joining metals to metals, or metals to composite structures. In

addition, polyimides are rapidly finding new uses as matrix resins for

composites, molding powders and films. These materials display a number

of performance characteristics such as high temperature and solvent

resistance, improved flow for better wetting and bonding, high modulus,

chemical and hot water resistance, and the like. Another area of application

is in the manufacture of lighter and stronger aircraft and spacecraft
LAR 15526-1-SB -2- PATENT APPLICATION

structures.

U. S. Patent No. 5,147,966 (St. Clair, et al) discloses a polyimide that

can be melt processed into various useful forms such as coatings,

adhesives, composite matrix resins and film. This polyimide is prepared

5 from 3,4'-oxydianiline (3,4'-ODA) and 4,4'-oxydiphthalic anhydride (ODPA)

in various organic solvents. The use of phthalic anhydride as an

endcapping agent is also disclosed in this patent to control the molecular

weight of the polymer and, in turn, to make it easier to process in molten

form.

10 In the present invention, a polyimide fiber is produced from the

polyimide powder that is prepared from the 3,4'-ODA and ODPA monomers.

This polyimide powder was endcapped with phthalic anhydride, as

described in U. S. Patent No. 5,147,966, to control the number average

molecular weight in the range of 10,000 g/mole to 20,000 g/mole.

15 The need for polyimide fibers of this type are apparent. Since this

polyimide is fire resistant, these fibers would be useful in manufacturing

articles which might be exposed to flames/fire to prevent their burning.

These articles would range from clothing articles to aerospace components.

In addition, fibers from this polyimide, since they are thermoplastic, could

20 be co-mingled with reinforcing media such as glass fiber, graphite fiber,

inert fillers, and the like, and be subsequently melted, in-situ, to form

composite structures which would have utility in fire-resistant applications

in the automotive and aerospace industries.

A primary requirement for such fibers is that they have adequate

25 textile properties to permit processing using normal textile equipment. The

two primary measures of fiber quality are tensile strength and elongation-tobreak percentage. Adequate strength must be developed to afford handling

properties during processing and to afford adequate strength in the final

form. Additionally, the fiber must possess adequate elongation-to-break
LAR 15526-1-SB -3- PATENT APPLICATION

properties to provide the required toughness in the processing operations

and in the final components.

5

._llmmary nf thp. InvAntinn

The invention is a polyimide fiber formed from the reaction product

of 3,4'-oxydianiline (3,4'-ODA) and 4,4'-oxydiphthalic anhydride (ODPA) in

2-methoxyethyl ether (diglyme), or other suitable solvent, and endcapped

with phthalic anhydride to control the number average molecular weight in

10 the range of 10,000 g/mole to 20,000 g/mole.

It is an object of the present invention to provide a polyimide fiber

that has the textile physical property characteristics to permit processing

into useful articles using normal textile equipment.

Another object of the present invention is polyimide fiber having high

15 strength and high elongation-to-break property characteristics.

A further object of the present invention is a process for preparing

polyimide fibers via melt extrusion of a molten polyimide.

An additional object of the present invention is a process for making

polyimide fibers over a range of processing conditions which produce fibers

20 having high strength and high elongation-to-break properties.

Another object of the present invention is a process for preparing

polyimide fibers that exhibit mechanical properties that permits them to be

used in various commercial applications.

Still another object of the present invention is to provide polyimide

25 fibers having fire resistant properties.

DA._.rintinn nf the. Pr_.fArrp.d I=mhndiment._

The invention and its advantages are illustrated by the specific
LAR 15526-1-SB -4- PATENT APPLICATION

examples given below. Conditions for melt spinning/extrusion are detailed

in the individual examples and a comparison of resulting mechanical

properties are shown in the data Tables 1-3.

The polyimide powder employed in each of the specific examples was

5 the reaction product of 3,4'-ODA and 4,4'-ODPA endcapped with phthalic

anhydride to control the number average molecular weight of the polymer

powder in the range of 10,000 g/mole to 20,000 g/mole. This polyimide

powder was obtained commercially as LaRCTM-IA from IMITEC, Inc., 1990

Maxon Road, Schenectady, NY 12308.

10 In each example below, the LaRCtM-IA polyimide powder, as received,

was dried in an air oven at approximately 200°C for twenty-four hours prior

to use to drive off any residual solvent and/or moisture. The melt extrusion

was performed using a Barbender, single screw extruder, equipped with a

NASA-LaRC drive unit, and provided with a 8-filament, 0.0135 inch vertical

15 die. The extrusion rate employed was 10 revolutions per minute (rpm).

Polyimide fibers were extruded from three heights to vary the

diameter of the fiber: (1) 364.5 inches, (2) 209 inches, and (3) 100.5

inches. Three processing temperatures were also utilized: 340°C, 350°C

and 360°C.

20 The following specific Examples are provided for purposes of

illustration, and are not intended to serve as limitations of the invention.

EXAMPLES

25 Fxamnlp. I

The oven dried LaRCTM-IA powder was placed in the sample feed of

the single screw melt extruder. The extrusion temperature was 340°C with

an extrusion rate of 10 rpm. The fiber exited through the 0.0135 inch
LAR 15526-1-SB -5- PATENT APPLICATION

diameter slit and fell 30 feet, 4.5 inches (364.5 inches). The average final

fiber diameter was 0.0094 inch. Mean tensile strength, modulus, and

elongation were 22.7 ksi, 412 ksi, and 103%, respectively.

5

10

The oven dried LaRCTM-IA powder was placed in the sample feed of

the single screw melt extruder. The extrusion temperature was 350°C with

an extrusion rate of 10 rpm. The fiber exited through the 0.0135 inch

diameter slit and fell 30 feet, 4.5 inches (364.5 inches). The average final

fiber diameter was 0.0068 inch. Mean tensile strength, modulus, and

elongation were 23.1 ksi, 436 ksi, and 102%, respectively.

15

2O

The oven dried LaRCTM-IA powder was placed in the sample feed of

the single screw melt extruder. The extrusion temperature was 360°C with

an extrusion rate of 10 rpm. The fiber exited through the 0.0135 inch

diameter slit and fell 30 feet, 4.5 inches (364.5 inches). The average fiber

diameter was 0.0071. Mean tensile strength, modulus, and elongation were

20.8 ksi, 415 ksi, and 84%, respectively.

The mechanical properties of the melt-extruded fibers obtained from

a height of 364.5 inches in Examples I-III are tabulated in TABLE I.

25
LAR 15526-1-SB -6-

TABLE I

PATENT APPLICATION

5

Processing

Temperature,

oC

Average

Fiber

Diameter,

Inch

Mean

Tensile

Strength,

ksi

Mean

Modulus, ksi

Mean

Elongation,

%

340 0.0094 22.7 412 103

350 0.0068 23.1 436 102

360 0.0071 20.8 415 84

lO

15

The oven dried LaRCTM-IA powder was placed in the sample feed

of the single screw melt extruder. The extrusion temperature was 340°C

with an extrusion rate of 10 rpm. The fiber exited through the 0.0135

inch diameter slit and fell 17 feet, 5 inches (209 inches). The average

final fiber diameter was 0.0094 inch. Mean tensile strength, modulus,

and elongation were 20.9 ksi, 406 ksi, and 79%, respectively.

2O

25

ExampLe 

The oven dried LaRCTM-IA powder was placed in the sample feed

of the single screw melt extruder. The extrusion temperature was 350°C

with an extrusion rate of 10 rpm. The fiber exited through the 0.0135

inch diameter slit and fell 17 feet, 5 inches (209 inches). The average

final fiber diameter was 0.0101 inch. Mean tensile strength, modulus,

and elongation were 20.6 ksi, 448 ksi, and 65%, respectively.
LAR 15526-1-SB

l::xamnlA VI

-7- PATENT APPLICATION

The oven dried LaRCTM-IA powder was placed in the sample feed

of the single screw melt extruder. The extrusion temperature was 360°C

5 with an extrusion rate of 10 rpm. The fiber exited through the 0.0135

inch diameter slit and fell 17 feet, 5 inches (209 inches). The average

final fiber diameter was 0.0117 inch. Mean tensile strength, modulus,

and elongation were 17.7 ksi, 441 ksi, and 34%, respectively.

The mechanical properties of the melt-extruded fibers obtained

10 from a height of 209 inches in Examples IV-VI are tabulated in TABLE I1.

TABLE II

15

Processing

Temperature,

oC

Average

Fiber

Diameter,

Inch

Mean

Tensile

Strength,

ksi

Mean

Modulus, ksi

Mean

Elongation,

%

340 0.0104 20.9 406 79

350 0.0101 20.6 448 65

360 0.0117 17.7 441 34

20

25

The oven dried LaRCTM-IA powder was placed in the sample feed

of the single screw melt extruder. The extrusion temperature was 340°C

with an extrusion rate of 10 rpm. The fiber exited through the 0.0135

inch diameter slit and fell 8 feet, 4.5 inches (100.5 inches). The average

fiber diameter was 0.0147 inch. Mean tensile strength, modulus, and

elongation were 19.9 ksi, 433 ksi, and 50%, respectively.
LAR 15526-1-SB -8- PATENT APPLICATION

5

The oven dried LaRCTM-IA powder was placed in the sample feed

of the single screw melt extruder. The extrusion temperature was 350°C

with an extrusion rate of 10 rpm. The fiber exited through the 0.0135

inch diameter slit and fell 8 feet, 4.5 inches (100.5 inches). The average

final fiber diameter was 0.0118 inch. Mean tensile strength, modulus,

and elongation were 17.3 ksi, 463 ksi, and 28%, respectively.

lO Ex_a_eJX

The oven dried LaRCTM-IA powder was placed in the sample feed

of the single screw melt extruder. The extrusion temperature was 360°C

with an extrusion rate of 10 rpm. The fiber exited through the 0.0135

15 inch diameter slit and fell 8 feet, 4.5 inches (100.5 inches). The average

final fiber diameter was 0.0115 inch. Mean tensile strength, modulus,

and elongation were 15.8 ksi, 465 ksi, and 14%, respectively.

The mechanical properties of the melt-extruded fibers obtained

from a height of 100.5 inches in Examples VII-IX are tabulated in TABLE

20 II1.

TABLE III

25

Processing

Temperature,

°C

Average

Fiber

Diameter,

Inch

Mean

Tensile

Strength,

ksi

Mean

Modulus, ksi

Mean

Elongation,

%

340 0.0147 19.9 434 50

350 0.0118 17.3 463 28

360 0.0115 15.6 465 14
5

10

LAR 15526-1-SB -9- PATENT APPLICATION

The foregoing specific Examples are given to illustrate the principal

of the invention and are not intended to serve as limitations thereof.

There are many variations and modifications of the invention that will be

readily apparent to those skilled in the art in the light of the above

teachings. It is therefore to be understood that, within the scope of the

pending claims, the invention may be practiced other than as specifically

described herein.

What is claimed as new and desired to be secured by Letters

Patent of the United States is: