Cost-Effective Production of Super-Strong Polymer FibersXudong Fang, Tom Wyatt and Donggang Yao; email: yao@gatech.edu

School of Materials Science & Engineering

Georgia Institute of Technology

Research Focuses: 1. Developing cost-effective methods for gel spinning of super-strong

polymer fibers.

Twist-Gel Spinning Process:• A majority of solvent is removed by twisting rather than by evaporation or coagulation as

used in conventional gel spinning.

• Thermal behavior of gels

Gel-Fiber before extractionTPmm 0.5TPmm 2 70%

80%90%

100%

%)polymer fibers.

2. Making super-strong polymer fibers from polar polymers, including polyoxymethylene and nylon 6.

3. Making high-strength polymer fibers from biopolymers, including protein, cellulose and polyhydroxybutyrate.

I: MixingII: Gel extrusion & twistingIII: Extraction (optional)IV: Hot drawingA: Solution or blendB: Quenching bathC: Extraction bathD Heated bath

II III

C

I

Novel twist-gel spinning process

• Reducing emission for volatile solvents and reduce production of solvent waste or coagulation byproducts for non-volatile solvents, leading to an environmentally more friendly and economically more viable solvent removal process for gel spinning.

• Improving the recyclability of solvent.• Reducing the time of solvent extraction, particularly useful for large-diameter fibers.

100 110 120 130 140 150

Hea

t Flo

w

Temperature (C)

TPmm 2TPmm 4TPmm 8Conventional extraction in hexane

DSC melting endotherms of mechanically extracted PE/paraffin gel-fibers; gel-fibers before extraction and conventionally extracted are included for reference.

0%10%20%30%40%50%60%

0 60 120 180

Wei

ght L

oss

(%

Time (min)

Conventional Extraction TPmm 4Neat Paraffin Oil

TGA weight loss curves of PE/paraffin gel-fiber and drawn fibers as a function of time. Fibers heated to 300C in N2 atmosphere for 180 min.

• X-ray diffraction of gel and drawn fibers

Methods for gel twisting

V1 V2

N2N1

Mono-filament twisting Continuous twisting with a rotating roving frame

Gel-fiber feed in, V1

N1

Significant Achievements:• A novel twist-gel spinning (TGS) process.

D: Heated bath

IV

B D

A

Twisting

W

22 ' WL

Twist drying mechanism

TPmm=4 ConventionalTPmm=0 TPmm=0.5 TPmm=2

WAXD 2-D patterns of mechanically extracted PE/paraffin gel-fibers with TPmm 0, 0.5, 2, and 4 as noted and conventional fiber extracted in hexane.

110

Conventional

Twisted

Conventional Twisted

Rotating disk

Rotating axis

Gel-fiber feed outGel-fiber feed in

False twisting by a spinning disk

Twist-drying region

Frame drive

Bobbin drive

Frame

Bobbin

To remove solvent mechanically rather than by evaporation/extraction To produce more drawable fiber precursors. To allow direct drawing in a continuous setup. To enable a process similar to melt spinning.

• New oligomer/polymer spinning dopes, allowing spinning of molecular blends with controllable miscibility and separation.

• New polymers for gel spinning: PEO, POM, and other polar polymers. Gel spun PEO and POM fibers 5-10 times stronger than melt spun fibers.

• Production of large-diameter super-strong polymer fibers for ropes, nets and armors.

Existing fibers have diameter smaller than 35 m

L W’

x

L’

222

222

22

2

2

2

414'1

RR

xLx

WW

22' xLL 22

'xL

WLW

100%

Selected Results:• Solvent removal by mechanical twisting

PE/decalin gel-fiber100%

PE/paraffin oil gel-fiber

0 30 60 90 120 150 180

0 30 60 90 120 150 180

200

Conventional

Twisted

WAXD of hot-drawn fibers. LEFT: azimuthal integrations of the [110] and [200] diffractions of the conventional and twisted fibers – offset by 1 for clarity; RIGHT: 2-D patterns of the conventional fiber and twisted fiber.

• Mechanical properties

40

50

60

3

4

5

deni

er)

GPa

) 40

50

60

3

4

5

enie

r)

GPa

)

30

40

50

60

3

4

5

deni

er)

GPa

)

• Existing fibers have diameter smaller than 35 m.• The TGS process can make fibers with diameter ~ 100 m.

Gel Spinning and Limitations:

Comparison between twist-gel spun polyethylene fibers and top-notch commercial fibers

Sample Strength(GPa) / (g/denier) Modulus (GPa) Elongation

Twist gel spun fiber 4.68 / 53 181.09 4.8%

Dyneema SK90 yarn 3.69 / 42 101.04 6.7%

Spectra S2000 fiber 3.56 / 40 140.65 4%

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

0 2 4 6 8 10

Perc

enta

ge o

f Sol

vent

Rem

oved

Applied Twist per mm (TPmm)

ExperimentalTheoretical

0%

10%20%

30%

40%50%

60%

70%80%

90%

0 2 4 6 8 10

Perc

enta

ge S

olve

nt R

emov

ed

Applied Twist per mm (TPmm)

• Twisted gel filament and drawn fiber appearance

0

10

20

30

0

1

2

0 0.01 0.02 0.03 0.04 0.05 0.06

Stre

ss (g

/d

Stre

ss (G

Strain (mm/mm)

GA Tech single filament 0

10

20

30

0

1

2

0 0.01 0.02 0.03 0.04 0.05 0.06

Stre

ss (g

/de

Stre

ss (G

Strain (mm/mm)

Spectra S2000 filament0

10

20

30

0

1

2

0 0.02 0.04 0.06 0.08

Stre

ss (g

/d

Stre

ss (G

Strain (mm/mm)

Dyneema 5-fiber bundle

Tensile properties of PE fibers: GaTech (left); Spectra S2000 (middle); Dyneema SK91 yarns.

Undrawn gel-fiber 10X drawn – before extraction

110

120032

20060X

10X

• Oligomer/polymer spinning (PEO and POM)

Acknowledgements

Gel Spinning and Limitations:

Limitations of gel spinning

• High cost, 10 times more expensive than nylon fibers and polyester fibers.

• High processing cost due to slow production and complex solvent recovery steps.

• Solvent concentration > 80% is typical for commercial gel-spun UHMWPE fiber production, making the process inherently inefficient in that for 1 kg of high strength fiber produced 4 kg spin

Coagulation or evaporation

Stretch

Melt spinning Gel spinning vs.

TPmm=1 TPmm=2 TPmm=4

TPmm=0 TPmm=0.25 TPmm=0.5

TPmm=2 TPmm=0

A B C D

Fibers prepared from PE/ paraffin oil spin dope: precursor fibers (left); drawn fibers at a draw ratio of 120 (right).

A

C

B

D

10X drawn – after extraction 60X drawn fiber

12 17 22 272 theta (degrees)

0X

120 azimuthal peak

0X10X20X

PEO and POM fibers, 5-10 times stronger than traditional melt-spun ones, were produced.

School of Materials Science and Engineering

• Resin supplied by Ticona, Mitsui and DSM.• X-ray diffraction from Prof. Satish Kumar’s group at Georgia Tech.• Related research funding from KDH Defense and Ticona.

Acknowledgementshigh strength fiber produced, 4 kg spin-solvent byproduct is created and another 400 kg solvent for extraction.

• Only applicable to very few polymers Polyethylene, PVA, PAN.

Low orientationHigh entanglementLow strength

Hot drawing

Highly extendedHigh crystallinityHigh strength

100 µm 100 µm 100 µm 100 µm

SEM of PE/decalin gel-fibers mechanically extracted using different level of twisting: A) TPmm=0; B) TPmm=2; C) TPmm=4; D) TPmm=8.