1. November 2013

New Challenges in the Development

of Carbon Fibers

Institut für Textilchemie und Chemiefasern

D. Ingildeev, F. Hermanutz, M. R. Buchmeiser

Properties and applications of carbon fibers

High tensile strength,

high modulus and low density,

electrical conductivity, biologically

inert

Light weight construction (automotive,

aerospace, sporting goods, …),

antistatic materials, medical

implants,…

C-Fiber Steel

density [g/cm³] 1.8 7.8

tensile strength [GPa] 3.5 – 7 0.8

E modulus [GPa] 230 – 400 200

elongation at break [%] 1.5 - 2

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E. Frank, F. Hermanutz, M. R.

Buchmeiser, Macromol. Mater. Eng.

2012, 297, 493–501.

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Manufacture of PAN-based carbon fiber precursor

Precursor

PAN-copolymer-derived precursors

Comonomers: acrylic acids and acrylic acid esters

Wet spinning process

Conventional wet spinning, air gap spinning

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Manufacture of PAN-based carbon fiber precursor

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Manufacture of PAN-based carbon fibers

Oxidation and Carbonization

Oxidative stabilization in air at 200 – 300 °C

Carbonization in nitrogen at 400 – 1500 °C

Optionally: graphitization in nitrogen at 1500 – 2500 °C

Major cost elements in the manufacture of carbon fiber:

51% 16% 23% 4% 6%

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Synthesis of precursor polymers by free radical polymerization:

Precursor characteristics:

Molecular weight (MW): 100,000 –160,000 g/mol

Polydispersity index (PDI, 𝑀 𝑤/𝑀 𝑛): 2 - 4

Broad MW distribution due to termination reactions:

poor control over MW and broad PDIs arise from the high reactivity of

acrylonitrile

High MW fraction aggravates processability (fiber spinning)

Comonomers necessary to facilitate processing

State of the art PAN precursors

acrylonitrile polyacrylonitrile

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Aim of the study

Determination of the influence of Mw and PDI on precursor and carbon fiber

processing and properties

PAN-copolymers with high Mw and low PDI produced by means of a new

polymerization technique:

Controlled Radical Polymerization (CRP)[1]

Principle: repelling of terminating

reactions by reducing the

concentration of the active species

dormant species active species

polymerization

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[1] a) K. Matyjaszewski, Macromolecules 2012, 45, 4015-4039; b) Fundamentals of Controlled/Living Radical Polymerization, B. Z. Tang, N. V.

Tsarevsky, B. S. Sumerlin (Eds.), 2013, RCS Publishing, Cambridge; c) H. Fischer, J. Polym. Sci. A Polym. Chem. 1999, 37, 1885–1901; d) C.J.

Hawker, A. W. Bosman, E. Harth, Chem. Rev. 2001, 101, 3661-3688; e) M. R. Buchmeiser, M. G. Marino, Macromolecular Mater. Eng. 2012, 297,

894–901.

RAFT polymerization

Reversible Addition Fragmentation Chain Transfer Polymerization

Introduced 1998 by Moad, Rizzardo and Thang[1]

Dormant species are formed by a chain transfer agent which is a

thiocarbonyl thio compound[2]:

[1] J. Chiefari, Y. K. Chong, F. Ercole, J. Krstina, J. Jeffery, T. P. T. Le, T. A. Roshan Mayadunne, G. F. Meijs, C. L. Moad, G. Moad, E. Rizzardo, S.

H. Thang, Macromolecules, 1998, 31, 5559-5562.

[2] a) G. Moad, E. Rizzardo, S. H. Thang, Aust. J. Chem., 2005, 58, 379–410; b) Aust. J. Chem., 2006, 59, 669–692 ; c) Aust. J. Chem., 2009, 62,

1402–1472. d) E. Rizzardo, G.Moad, S. H. Thang, RAFT Polymerization in Bulk Monomer or in (Organic) Solution in: Handbook of RAFT

Polymerization, C. Barner-Kowollik (Ed.) 2008, Wiley-VCH, Weinheim, 6/189–234.

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RAFT polymerization of acrylonitrile

Advantage:

No transition metal ions such as Fe(II) or Cu(I) are present

Avoiding of expensive polymer purification prior to carbonization

Challenge:

Synthesis of PAN with high Mw and low PDI by CRP

CRP works well for low molecular weight PAN[1], but higher molecular

weights are needed for fiber spinning

Synthesis of low PDI precursor polymers of different molecular weights

[1] a) C. Tang, T. Kowalewski, K. Matyjaszewski, Macromolecules, 2003, 36,8587-8589. b) Q. An, J. Qian, L. Yu, Y. Luo, X. Liu, J. Polym. Sci. A:

Polym. Chem., 43, 2005, 1973-1977. c) X.-H. Liu, G.-B. Zhang, X.-F. Lu, J.-Y. Liu, D. Pan, Y.-S. Li, J. Polym. Sci. A: Polym. Chem., 44, 2006, 490-

498. d) X.-H. Liu, Y.-G. Li, Y. Lin, Y.-S. Li, J. Polym. Sci. A: Polym. Chem., 45, 2007, 1272-1281. e) X.-H. Liu, G.-B. Zhang, B.-X. Li, Y.-G. Bai, D.

Pan, Y.-S. Li, Eur. Polym. J., 44, 2008, 1200-1208. f) A. Aqil, C. Detrembleur, B. Gilbert, R. Jerome, C. Jerome, Chem. Mater., 2007, 19, 2150-2154.

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Synthesis of precursor polymers

Synthesis of homo- and copolymers: batch size 2 L

Yellow color arises from chromophoric RAFT end-groups

incorporated into the polymer

Determination of molecular weight and molecular

weight distribution via SEC

PAN-co-PMMA, Mn = 114,000 g/mol, PDI = 1.31

Advantage:

No transition metal ions such as Fe(II) or Cu(I) are present

Avoiding of expensive polymer purification prior to

carbonization

RAFT precursor polymer

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MW distribution

Wet spinning of precursor fibers (1-3k)

Coagulation of the fiber at the spinneret

Start of spinning

Wet fiber on godet

Winding on spool RAFT-derived PAN-based

precursor on spool - 11 -

Textile-mechanical properties:

in the range of standard PAN-based

precursor fibers[1]

RAFT-derived PAN-based precursor fibers

- properties

Morphology (SEM):

round cross-sections, dense

fibers, no voids; fibril

structure for highly

stretched fibers

Fineness [dtex] 1.1

Elongation [%] 13.1

Tenacity [cN/tex] 47.9

E-modulus [cN/tex] 1022

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[1] Z. Wangxi, L. Jie, W. Gang, Carbon 2003, 41, 2805-2812.

Wide-angle X-ray diffraction (WAXS)

[1] A. K. Gupta, R. P. Singhal, J. Polym. Sci. Polym. Phys. Ed. 1983, 21, 2243-2262.

Possibility to determine crystallite

dimensions and lattice spacings[1]

RAFT-derived PAN-based precursor fibers

- supramolecular structure

Crystallinity (WAXS) [%]: 75

Density by gradient column [g/cm3]: 1.178

Crystallinity (determined via density) [%]: 72

Preferred orientation (100) [%] 90

Meas. data:JS004 80/Data 1

Inte

nsity (

co

un

ts)

0

500

1000

PAN, 0

2-theta (deg)

20 40 60 80

Amorphous, 0

Values fit very well

no micro-voids

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(100)

(110) curve fitting

Thermal behavior of precursor fibers

DSC-, TG/MS-Analysis

DSC and TG/MS analysis to mimic oxidation and carbonization process

Oxidation Carbonization

TGA and MS traces of pre-oxidized

precursor in He, 10 K/min

DSC of RAFT-derived PAN-based

fibers in air, 5 K/min

Properties of RAFT-derived PAN-based carbon

fibers

Textile-mechanical properties of the fibers carbonized at 1350 °C:

Morphology:

Fineness [dtex] 0.6 – 0.8

Tensile strength [GPa] ≤ 2.5

E-modulus [GPa] ≤ 145

Elongation [%] 1.4

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J. M. Spörl, A. Ota, R. Beyer, T. Lehr, A. Müller, F. Hermanutz, M. R. Buchmeiser, submitted (2013).

Modification of wet and air gap spinning

technology for PAN

Development of supermicro precursor fibres based on polyacrylonitrile

New wet spinning technology has to be developed: superfine spinnerets for

manufacture of titer below 0.3 dtex required

Key to success: new laser technology available for drilling of tiny micro holes

for manufacture of superfine spinnerets

Advantages:

- Increase in tenacity of precursor and carbon fibers

- Cost reduction at the stabilization and carbonization

- Increase in fiber-matrix interaction

Helical Laser Drilling

IFSW/FGSW Helical Drilling Optics Circulating Focused Laser Beam

Helical Drilling

f = 50 mm

df = 5,8 µm

DF = 1°

Laser drilled spinneret 2000 x 25 µm

Outlet Inlet

10 µm 10 µm

1 µm

Testdüse 2000 x 25 µm – Geometrie und Qualität

Testdüse 2000 x 25 µm – Geometrie und Qualität

100 µm

Cellulose-2.5-acetate Supermicro Fibres

Continuous spinning of supermicro fibres (filament process)

Fibres wound on bobbins

Different yarn sizes (f.i.: 200 dtex /1000f; 300 dtex /2000f)

Cross section of super-

micro fibres (0.2 dtex)

Surface of supermicro

fibres

Comparison of supermicro

fibres and standard

cigarette filter tow

(1.0 dtex = 1.0 g/10.000 m)

20 µm 10 µm 5 µm

Cellulose as a carbon fiber precursor

Motivation:

Formation of carbon fibers from cellulose:

pulp spinning finishing oxidation carbonization

Development of high quality precursor

fibers based on cellulose from wood

Application of novel solvent systems

- Ionic Liquid technology

An increase in carbon yield Pyrolysis in reactive atmosphere or in the

presence of flame retardants

Wet and air gap spinning

e.g. novel solvents,

superfine spinnerets

Cellulose, derivatives Optimization of

carbon yield by

chemical

modification

? Formation of

graphite layers

Pyrolysis of rayon in the presence of flame

retardants

Pyrolysis of high-tenacity rayon filament yarn

Thermogravimetric analysis between 20° and 1400 °C

in He atmosphere, heating rate of 10 K/min

flame retardant 1.0 %

flame retardant 1.5 %

flame retardant 0.5 %

unmodified precursor

temperature [°C]

1 Bacon, R., Tang, M.; Carbon, 2, 211, 1964

Cellulosic carbon fiber precursors

Application of both wet spinning and air gap spinning using ILs

Figures: a.) Regular viscose , b.) IL spun fibre , c.) Tencel fibre

a.) b.) c.)

2 µm Figures: a.) Regular viscose , b.) IL spun fibre , c.) Tencel fibre

Cellulosic carbon fibres

Figures: Pyrolysis of cellulosic precursor und resulting carbon fibres

2 µm

10 µm

1 µm

50 µm

Lignins as a carbon fiber precursor

Inexpensive and renewable bypolymer

Recovered as waste products during the

manufacture of carbohydrates for paper,

sugars, and for biofuels production

Complex polymers containing three main

monomer units such as syringyl, guaiacyl

and p-hydroxyphenyl

No demonstration has yet been made of

suitable lignins being processed into carbon

fiber that satisfy both strength requirements

and cost objectives

27

3D non-linear molecules

Amorphous supramolecular structure

No preferred orientation

lignin modification spinning oxidation carbonization

Purification

Refining

Chemical modifications

Soft wood,

Hard wood

- Kraft

- Sulfite

- Organosolv

Melt spinning Cross-linking

- Thermostablization

- Plasma irradiation etc

Formation of

graphite layers

Figure: Lignin-based carbon precursor fibers at ITCF

MOPAC2009-Simulation of hardwood lignin

Lignin as a carbon fiber precursor

Thank You for Your Attention!