Melt Spinning of Polyacrylonitrile

Carbon Fiber Precursors

1

J. Huang1, D. G. Baird1 , J. E. McGrath2, S. Mecham2, and F. L.

Paulauskas3

1Departments of Chemical Engineering and 2Chemistry, Virginia Tech

3Carbon and Composites Group, Oak Ridge National Laboratory

American Chemical Society-Polymer Chemistry Division: Meeting in

Honor of J. E. McGrath, Cetraro, Italy, June 29 to July 2, 2014

Cooperative Research with Jim

McGrath

2

Title: High Performance Elastomer and Other Multiphase

Organic Composites

Sponsor: Army Research Office

Amount: $800,000 ($160,000 my share)

Duration: September 1, 1980 to February 28, 1984

Title: Lower Cost Carbon Fiber for H2

Storage for Vehicle Fuel Cells

Sponsor: Department of Energy/ORNL

Amount: $785,000

Duration: 10/14/13 to 10/13/16

Total cooperative funding from 1980 to 2016:

$29,580,000

Total number of bottles of wine consumed: ?, ∞ (Not in

resume)

3

Outline of Presentation

•Motivation: Lower cost carbon fiber

•Background: Conversion of PAN fiber to carbon fiber;

solution spinning of precursors; melt spinning of

precursors; water as a plasticizer; patents.

• Reduction of melting point: water; water plus a

miscible substance (azeotrope)

•Rheology of plasticized PAN

•Laboratory spinning process and fiber production

•Precursor fiber properties

•Summary of progress

•Status and future direction

Production of carbon fibers from

PAN precursors

1000 to 1700C in N2

200 to 300C in air

The ideal precursor fibers should have high AN contents (~95 mol% AN),

high strength, high modulus, size of about 10 microns in diameter and free of

voids and other defects.

PAN Precursor Fibers

Carbon Fibers

4

Advantages of melt spinning over

wet spinning process

5

Cost savings by using melt-spun

precursor fibers

Factory cost is the manufacturer’s cost to produce finished CF’s. These cost estimates are

derived primarily from the 2007 Kline reports and are based on petrochemical prices in

CY2007Q1. Estimates based on oil at $60/bbl.

6

Dependence of Melting Point for PAN

Copolymers on Water Content

Frushour, B. G. Polymer Bulletin 7, 1-8 (1982)

Acrylonitrile

(AN)

Vinyl Acetate

(VA)

CH

O

CH2

C

CH3

O

CHCH2

C N

7

8

Melt-spinning of PAN fibers with

water as a plasticizer

Porosoff H., US 4,163,770 (1979)

American Cyanamid Company (ACC)

Kreahling, R.P. et al, US 4,301,107 (1981)

American Cyanamid Company

Steam, 20-32

psiSteam, 40-55

psi

9

Research Objectives

Establish the melting and rheological behavior of

polyacrylonitrile (PAN) copolymers with various plasticizers.

Develop a melt-spinning system and process to generate

precursor fibers from PAN plasticized with water and/or other

plasticizers.

Determine the fiber spinning and drawing conditions.

Evaluate the structure and properties of melt-spun fibers and

compare them with that of commercial wet-spun fibers.

Optimize the MW and AN/MA ratio for best fiber properties.

132.46°C

103.87°C

158.91°C

133.52°C

-1.0

-0.5

0.0

0.5

1.0

1.5

Heat F

low

(W

/g)

-50 0 50 100 150 200 250

Temperature (°C)

PAN-VA-25+25wtpc-water+acn.001––––––– PAN-VA-50-wtpc-water.001–––––––

Exo Down Universal V4.5A TA Instruments

10

DSC of PAN/VA (Vinyl Acetate) with

plasticizers

PAN/VA + H2O +

Acetonitrile

PAN/VA + H2O

11

DSC of PAN/MA (Methyl Acylate)

with plasticizers

PAN/MA+H2O+Acetonitrile

PAN/MA+H2O

167.99°C

135.93°C105.20°C

138.87°C

-1.0

-0.5

0.0

0.5

1.0

1.5

Heat F

low

(W

/g)

-50 0 50 100 150 200 250

Temperature (°C)

pan-ma-50wtpc-water.001––––––– pan-ma-25+25-wtpc-water+ACN.001– – – –

Exo Down Universal V4.5A TA Instruments

Melting of PAN/Vinyl Acetate (VA)

with plasticizers

12

Heating at 10C/min

Melting of PAN/Methyl Acrylate (MA)

with plasticizers

13

Heating at 10C/min

Instron Capillary Rheometer

with Pressure ChamberA

B

C

D

E

F

J

I

G

H

A Rheometer plunger with O-ring

B Rheometer barrel

C Polymer melt

D Capillary die

E Pressure chamber assembly

F Capillary sealing block

G Sealing block holding/releasing

mechanism

H Inlet of compressed gas or steam

I Pressure gauge

J Bleeding valve

(a) (b)

(a) The capillary is

sealed until test starts

(b) The sealing block F

is released once test

starts

Rheology data is very useful in fiber

spinning. It is noticed that there is no

such data available for PAN-water

melt in literature and the commercial

rheometer is not applicable to PAN-

water system. So we tried to modify

the rheometer and turn it into one that

can test PAN-water systems.14

Preparation of PAN-H2O Samples

PAN

Sample

P

1 2 3 4

H2O

1. Mix and stir PAN and water with desired ratio

2. Transfer the mixture to rheometer barrel at room temp

3. Compress the mixture with plunger until P=3000 psi

4. Open the barrel bottom and extrude the sample out

15

16

Viscosity of PAN/VA with

Plasticizers

10

100

1000

10000

1 10 100 1000 10000 100000

Vis

cosi

ty (

Pas

)

Shear Rate (s-1)

20%H2O, 180 C

20%H2O, 185 C

20%H2O, 190 C

14%H2O+14%AC, 155 C

Die: D=0.0303”, L/D=33.18, AC = Acetonitrile

The viscosity converges when the shear rate is higher than 1000 s-1

The viscosity of PAN plasticized with water at 190C is about the same as that

plasticized with water and acetonitrile at 155C.

17

VT lab spinning system for

generating melt-spun PAN fibers

Plunger

Barrel

N2

Pressure

Gauge

Pressure Chamber

PAN Fibers

Spinneret

Spool

PAN Melt

18

Continuous fiber drawing system

Steam Bath Winder

Drawn Fibers

As-spun Fibers

VT melt-spun PAN/VA fibers

Inlet for

CO2

Spool

4” SS Tee

19

VT 04-13

Fiber diameter =17.4 m

AN: Acrylonitrile, VA: Vinyl Acetate

Polymer: PAN/VA with 93 mol% AN

Plasticizer: Water and acetonitrile

As spun fiber diameter: ~ 35 micron

Post-spinning stretch:

Heating media: Saturated steam

Steam pressure: 18 psi

Steam temperature: 124C

Draw ratio (second stretch): 5~6

Fiber diameter: 17 m

Filament number: 14

VT PAN/VA drawn fibers

Inlet for

CO2

Spool

4” SS Tee

Fiber diameter =13 m

Polymer: PAN/VA with 93 mol% AN

Plasticizer: Water and acetonitrile

As spun fiber diameter: ~ 35 micron

Heating media: Saturated steam

Steam pressure: 18 psi

Steam temperature: 124C

Draw ratio (second stretch): 6

Fiber diameter: 13 m

Filament number: 8

Filament length: 125’

20

SEM images of PAN fibers

Motor

Present Work

Melt-Spun Fibers after Stretch

Fiber Diameter = 17 µm

Commercial Product

Wet-Spun Fibers

Fiber Diameter = 12 µm

21

22

Mechanical properties of PAN

precursor fibers

Motor

0

100

200

300

400

500

600

700

VT-M Spun GT-M Spun FISIPE-1 FISIPE-2 COMMODITY AEROSPACE

Pe

ak S

tre

ss (

MP

a)

Name Producer Process Component Diameter (µm)

VT-M Spun Virginia Tech Melt-Spun AN/VA 17.4

GT-M Spun* Georgia Tech/BASF Melt-Spun AN/MA 10.9

FISIPE-1/2 FISIPE Wet-Spun AN/VA 14.1/13.7

COMMODITY Industry Wet-spun AN/MA 11.7

AEROSPACE Industry Wet-spun AN/MA 12.9

* From Dale Grove et al., Carbon, 26(3), 1988, pp.403-411.

23

Mechanical properties of PAN

precursor fibers

Motor0

5

10

15

20

VT-M Spun GT-M Spun FISIPE-1 FISIPE-2 COMMODITY AEROSPACE

Mo

du

lus

(GP

a)

24

Mechanical properties of PAN

precursor fibers

Motor0

5

10

15

20

VT-M Spun GT-M Spun FISIPE-1 FISIPE-2 COMMODITY AEROSPACE

Stra

in a

t B

reak

(%

)

Summary

Studied melting behavior of PAN copolymers plasticized with water

and other plasticizers by DSC. The presence of water can lower

the melting point of PAN and make it melt-processable. The use of

second plasticizer can lower the melting point of PAN further.

Measured the viscosity of PAN plasticized with water or water and

second plasticizer with a modified capillary rheometer. The

viscosity of PAN-water at 190C is about the same as that of PAN-

water-acetonitrile at 155C.

Designed and constructed a novel pressurized spinning system

consisting of an Instron capillary rheometer with modified extrusion

die and a pressure chamber with fiber taking-up device.

The SEM images showed that the melt-spun fibers had surfaces

as smooth as those of commercially wet-spun PAN fibers.

25

Summary

Our melt-spun PAN/VA precursor fibers have mechanical

properties similar to that of wet-spun commercial precursors and

higher than that of melt-spun precursors reported in the literature.

The melt-spun PAN/VA precursor has been converted to carbon

fibers at Oak Ridge National Laboratory. The evaluation of the

carbon fibers and optimization of carbonization process are

currently in progress.

Will try PAN copolymers plasticized with water or water and benign

second plasticizer to produce precursor fibers.

Will move to fiber spinning with 5/8” screw extruder to generate

larger quantity of fibers for carbon fiber conversion.

26

27

Acknowledgements

DOE and Oak Ridge National Laboratory (ORNL) for financial

support

Thank You Jim!

28

132.46°C

103.87°C

158.91°C

133.52°C

-1.0

-0.5

0.0

0.5

1.0

1.5

Heat F

low

(W

/g)

-50 0 50 100 150 200 250

Temperature (°C)

PAN-VA-25+25wtpc-water+acn.001––––––– PAN-VA-50-wtpc-water.001–––––––

Exo Down Universal V4.5A TA Instruments

29

Determination of melting point of

plasticized PAN by DSC

PAN/VA + H2O + Acetonitrile

PAN/VA + H2O

Heating at 10C/min

Cooling at 10C/min

VA: Vinyl Acetate