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53rd Man-Made Fibers Congress, Dornbirn 2014

Dr. Nina Köhne - Kelheim Fibres GmbH

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Absorbency

Food

filtration

Surfacemodification

Reactivemodification

Intrinsic

modification

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Electrical Conductive Viscose Fibres and their Applications

- Dr. Nina Köhne

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Overview

• Design of Viscose Fibres

• Electrical Conductive Additives

• Production of Electrical Conductive Viscose Fibres– Characteristics of Electrical Conductive Additives– Characteristics of Intrinsically Modified Viscose Fibres

• Application of Electrical Conductive Materials

• Summary

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Design of Viscose Fibres – Modifications

Cutting

Removal of CS2 & Sx

Stretching

Spinning

Bleaching, Washing, Finishing

Baling

CS2-Recovery

SpinbathRecovery

Additives

Spinning conditions

Jets

Cellulose

Cellulose

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Design of Viscose Fibres – Fibre Modification

Standard

round Danufil®

Variation of Cross Sectiontrilobal Galaxy® hollow flat Bramante flat Leonardo

Tailor made solutions

Modification:Surface Chemical Intrinsic

OH

OHO

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Electrical Conductive Additives

modifications of carbon conductive polymersmetals

10-9 10-6 10-3 100 10+3 10+6 10+9 10+12 10+15 [Ω • cm]

copper

silver

steel

polyaniline (undoped)

polyaniline (doped)

polypyrrole (doped)

polypyrrole(undoped)

graphite

CNT carbon black

conductor semiconductor isolator

spec. resistivity

Challenge: Transfer of electrical conductivity of additive to fibre Achievement of percolation threshold, formation of current paths

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Electrical Conductive Additives

carbon fibre (Toho Tenax)

modifications of carbon conductive polymersmetals fibres

steel fibre (Bekaert)

silver plated polyamide fibre (Statex)

10-9 10-6 10-3 100 10+3 10+6 10+9 10+12 10+15 [Ω • cm]

copper

silver

steel

polyaniline (undoped)

polyaniline (doped)

polypyrrole (doped)

polypyrrole(undoped)

graphite

CNT carbon black

conductor semiconductor isolator

spec. resistivity

standard viscose fibre

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Motivation for the Development

• Although many electrically conductive products are already available onthe market, further developments in the following areas are desirable

– Wearing comfort

– Washability– Processability– Manufacturing costs

• After intrinsic modification of standard viscose fibres above mentionedrequirements should be achieved

Approach: Production of viscose fibres with different conductiveadditives and characterisation of fibre properties and electric resistance

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Production of Electrical Conductive Viscose Fibres

Carbon nanotubeGraphiteAmorphous carbon

Carbon black

not testedpoorgoodSpinnability

tube-shaped

length: µm-scale

diameter: nm-scale

flaky

µm-scale

round

nm-scale

Shape

Size

poor, expensivevery good, good valuevery good, good valueAvailability

10-4 – 10-5 Ω•cm8,0 • 10-4 Ω•cm1,0 • 10-1 Ω•cmResistivity

Images: „Eight Allotropes of Carbon“ von Created by Michael Ströck (mstroeck) - Created by Michael Ströck (mstroeck).

Lizenziert unter Creative Commons Attribution-Share Alike 3.0 über Wikimedia Commons –

http://commons.wikimedia.org/wiki/File:Eight_Allotropes_of_Carbon.png#mediaviewer/Datei:Eight_Allotropes_of_Carbon.png

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Additive: Characteristics of Carbon Black

• Primary particle size, structure and surface area are essential for propertiesof carbon black

• Highest electrical conductive properties are available with carbon black withsmall primary particle sizes, high structure and high surface area

pri

mary

part

icle

siz

e

structure

lowest viscositylowest electrical conductivity

highest viscosityhighest electrical conductivity

most difficult dispersibilitymost intensive colour strength

easiest dispersibilitylowest colour strength

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Additive – Characteristics of Carbon Black

• Primary particle is globular

• In dispersions primary particlesform branched, chain-likeaggregates and agglomerates

• Effective, stable dispersionsfor spinning process have to be prepared no standardproduct

primary particlesize: 10 – 60 nm

aggregatesize: < 1 µm

agglomeratesize: >> 1 µm

primary particle

structure

outer surface

total surface

chemical surface

Images: Product information of carbon black, Co. Harold Scholz

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Additive: Percolation Threshold

• Electrical conductivity has to betransferred from additive to fibre

• Contact of conductive particles

– critical content of particlesmust be achieved

– current paths are formed

• If threshold is passed, an increaseof conductive particles causes no significant reduction in resistivity

content of conductive additive [%]

Sp

ecif

icre

sis

tivit

y[ Ω

Ω

Ω

Ω

•cm

]

thresholdinsulating conducting

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Additive: Percolation Threshold

• Percolation threshold and specific

resistivity of fibres are dependenton

– Manufacturing method of

carbon black

– Specific surface/structure of carbon black

– Content of carbon black

– Dispersant

– Spinning conditions

5 10 15 20 25

extra conductive carbon blackconductive carbon blackcolour carbon black

content of conductive additive [%]

Sp

ecif

icre

sis

tivit

y[ Ω

Ω

Ω

Ω

•cm

]

Images: Product information of carbon black, Co. Harold Scholz

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Characterisation of Intrinsically Modified Viscose Fibres

Determination of volume resistivitywith annular electrode

Determination of sheet resistance

with ʹfour point methodʹ

• Measurement of sheet resistance of thin layers with four point method(mainly used in semiconductor industry)

• Measurement of surface or volume resistivity with annular electrode (e.g. EN1149 for protective clothing)

Image left: Wikipedia, „Fourpointprobe GMR“ von Maciej UMacieju - Eigenes Werk. Lizenziert unter Public domain über Wikimedia

Commons - http://commons.wikimedia.org/wiki/File:Fourpointprobe_GMR.png#mediaviewer/Datei:Fourpointprobe_GMR.png

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Characterisation of Intrinsically Modified Viscose Fibres

• Carbon black is distributed equally all-over viscose fibre matrix, currentpaths are formed

• Additivs like graphite and graphene were tested spinning of fibres was not possible

• Additivs like CNTs and conductive polymers were not tested rawmaterials and resulting fibre are too expensive

2 µm2 µm

SEM image of standard viscose fibre SEM images of carbon black loaded viscose fibre

2 µm

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0

4

8

12

16

20

24

0% 5% 10% 15% 20%

0

1

2

3

4

5

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Characterisation of Intrinsically Modified Viscose Fibres

• Experimental results confirm that fibre tenacity decrease with higher content and with type of carbon black in fibre matrix

• After passing of percolation threshold fibre resistivity decrease significantly

• Challenge: achievement of favoured fibre resistivity with good processibility/adequate fibre tenacity

Fib

re re

sis

tivity

[ ΩΩ ΩΩ•

cm

]Fib

re t

en

ac

itiy

[cN

/tex

]

Carbon black content [%]

5 10 15 20

1024

12 106

101020

0

18Image left: „Static slide“ von Ken Bosma from Green Valley, Arizona, USA - Electric SlideUploaded by Pieter Kuiper.

Lizenziert unter Creative Commons Attribution 2.0 über Wikimedia Commons –

http://commons.wikimedia.org/wiki/File:Static_slide.jpg#mediaviewer/Datei:Static_slide.jpg

Application of Electrical Conductive Materials

conductive propertiessmart textiles: heatable or luminescent fibres and textiles, sensors

< 1low specific resistance

anti-static propertiesshielding textiles: e.g. clean room fabrics, protective apparel and work-wear

103 – 106middle specific resistance

anti-static propertiesstatic dissipative textiles: e.g. protective clothingagainst electrical shocks, filter materials

106 – 109high specific resistance

Field of application[Ω Ω Ω Ω • cm]Resistance range

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Application of Electrical Conductive Materials

Wearing comfort

Washability

Processibility

Fibre tenacity

Conductivity

Conductive viscose fibresMetal fibres

Conclusion:• Both materials have pros and cons• No fibre could be used for several applications further developments

are inevitable

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Application of Electrical Conductive Materials

• Advantages of modified viscose fibres are washability and comfort

• Application needed where absolute value of resistivity is not crucial, only a

change of resistivity must be detected humidity sensor

• Electrical resistivity of carbon black loaded viscose fibre is dependent on humidity reversible effect

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Summary

• Carbon black is suitable for the production of

electrical conductive viscose fibres

• Challenging parameters in the production of

conductive viscose fibres are

– Manufacturing method of carbon black

– Specific surface/structure of carbon black

– Stability of dispersions for spinning process

– Conductivity transfer from additive to fibre

• Application of electrical conductive fibres

competes with metallic wires

– Advantage of fibres are washability and comfort

– Electrical resistivity of fibres is dependent on

humidity (absolute value is not crucial)

For what application may you need electrical conductive viscose fibres?

Image above: Product information of carbon black, Co. Harold Scholz

1 µm

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Thank you for your attention

Please visit our stand in the exhibition area

in the foyer at the Dornbirn MFC 2014!

nina.koehne@kelheim-fibres.com