Carbon Fibres from CelluloseJoining FP1205 and MP1206 “Electrospinning”

Stephen EichhornCollege of Engineering and Physical Sciences, University of Exeter

AcknowledgementsDr Libo Deng (Schenzen Institute for Advanced Technology, China)Dr Tommy Shyng (Exeter)Dr Kenny Kong (Nottingham)Professor Yanqiu Zhu (Exeter)Dr Anna Lewandowska (Exeter)Professor Robert Young (Manchester)Professor Ian Kinloch (Manchester)

EPSRC for funding “Hybrid Electrospun Fibres from Biomass-Based Carbon Nanostructures” (2008 – 2013)

EPSRC Centre for Innovative Manufacturing in Composites –follow on funding for feasibility study (2013)

Why Carbon?

Most relevant market segments for new low cost CFs and 2020 forecast per macro-area (Composites World’s annual Carbon Fibre 2011 conference, Washington, D.C., Dec. 5-7th 2011)

Various estimates on use suggest growth rates of 13%/year with a total global market worth $2.3bn by 2015

What precursors?• PAN (poly acrylonitrile) – oil based, non-renewable,

industrially proven and commercial, high modulus/strength, process produces toxins.

• Pitch – oil-based, industrially proven, high strength.• Lignin – non-oil-based, renewable, some industrial

proven technology (Oak Ridge, Innventia), low/medium modulus/strength.

• Cellulose – non-oil-based, renewable, industrially proven (Union Carbide), low-medium modulus.

• Polyethylene – oil or non-oil-based, not industrially proven yet (some activity from Oak Ridge), low strength/modulus.

Summary of Talk• Raman spectroscopy of carbon• Carbon nanostructures from cellulose• Introduction to materials

– Electrospun cellulose fibres– SiC/carbon fibres– SWNT/MWNT/cellulose

• Carbonisation of cellulose fibres• Carbonisation of electrospun fibres• Supercapacitance• Conclusions

Raman Spectroscopy - Carbon• Raman effect occurs due to inelastic

scattering of light• Two first-order Raman bands that

are present; D-band centred at ~1350 cm-1 and the G band located at ~1590 cm-1. Generally, the G band is considered to be an in-plane bond stretching motion of sp2-hybridised C atoms and the D band is related to the breathing mode of the six-fold aromatic ring near the basal edge

• At higher carbonisation temperatures (>2000°C) a G’ band is present –seen also in carbon nanotubes and graphene

• Various spectral indicators of graphitisation – one is the ID/IG ratio. Undergoes a transition for cellulose

500 1000 1500 2000 2500 3000 3500

4

G´

D´

G

Inte

nsity

, a.u

.

Raman Shift, cm-1

DB

Ferrari & Robertson (2000) PRB 61 14095

Carbon Fibres from Cellulose

Tang & Bacon (1964) Carbon 2, 211; ibid 221

Carbon Fibres from Cellulose

Zickler et al. (2006) Carbon 44 3239–3246

Data for a range of PAN and cellulose fibres

<2 nm: ID/IG=kLa2

>2nm: ID/IG=kL-1

Ferrari & Robertson (2000) PRB 61 14095

Carbon fibres from Cellulose Nanostructures

Kim et al. (2001) Carbon 39, 1051-1056

Kaburagi et al. (2012) Carbon 50, 4757-4760

Various forms of cellulose nanofibres have been converted to carbon eg. Bacterial cellulose, tunicate etc.

Electrospun Cellulose FibresCellulose acetate fibres

De-acetylated cellulose acetate fibres

• Cellulose acetate fibres electrospun in DMAc/acetone mix

• Fibres spun onto a rotating mandrel

• Mean fibre diameters were ~300 nm

Deng et al. (2013) Carbon, 58, 66-75

SiC/C Nanofibres

• Electrospun cellulose nanofibres were carbonised (grey sheet) above a bed of SiO2 beads or SiC whiskers. Pyrolysis temperature – 1500 °C for 2.5 hours under an Ar atmosphere

• After pyrolysis SiC nanostructures were observed.

• SiC structures can be formed through the carbothermal reduction of silica according to

SiO2 + 3C→SiC + 2CO

Essentially this comprises two sub-reactions with an intermediate formation of SiO

Deng et al. (2013) Carbon, 58, 66-75

Deacetylation of Fibres

3500 3000 2500 2000 1500 100040

60

80

100

Tran

smis

sion

(%)

Wavenumber (cm-1)

CA Deacetylated CA

1746 cm-1a

800 900 1000 1100 1200 1300 1400 15000

2000

4000

6000

8000

10000

12000

Inte

nsity

(arb

.uni

t)

Raman shift (cm-1)

CA Deacetylated CA

b

Both infrared and Raman spectra indicate that the fibres are de-acetylated to cellulose

5 10 15 20 25 30 35 40

0

1000

2000

3000

4000

5000

Inte

nsity

2

CA Deacetylated CA

(101)

(101)(002)

Structure Developmenta b c

d e

5 nm 5 nm 5 nm

5 nm

(a) 800 ºC(b) 1000 ºC,(c) 1200 ºC,(d) 1500 ºC (e) 2200 ºC.

Deng et al. (2013) Carbon, 58, 66-75

Structure Development

500 1000 1500 2000 2500 3000

800 C

1000 C

1200 C

1500 C

2200 C

Inte

nsity

Raman shift (cm-1)

a

0.5 1.0 1.5 2.0 2.5 7 8 9

0.6

0.8

1.0

1.2

1.4

1.6

I D/I G

La (nm)

c

Deng et al. (2013) Carbon, 58, 66-75

Universal Band Shifts - Carbon

Huang & Young (1995) Carbon 33, 97-107

Universal Band Shifts - Carbon

Frank, Tsoukleri, Riaz, Papagelis, Parthenios, Ferrari, Geim, Novoselov, Galiotis (2011) Nature Comm. 2 255

Micromechanics of carbon nanofibres

-0.1 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.72660.2

2660.4

2660.6

2660.8

2661.0

2661.2

2661.4

2661.6

G'-b

and

posi

tion

(cm

-1)

Strain (%)

-3 cm-1/%

a

-0.1 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

2660.5

2661.0

2661.5

2662.0

2662.5

G'-b

and

posi

tion

(cm

-1)

Strain (%)

-5 cm-1/%

b

1500 °C; ~ 60 GPa 2200 °C; ~ 100 GPa

Deng et al. (2013) Carbon, 58, 66-75

Fibre Density

(g cm-3)

Elongation

at break

(%)

Tensile

Strength

(MPa)

Young’s

modulus

(GPa)

Specific

Modulus GPa

cm3 g-1

E-glass 2.5 2.5 2000 – 3500 70.0 28

Carbon 1.4 1.4 – 1.8 4000+ 230.0+ 234+

Our fibres 1.4(?) ? ? 100 71

SiC/C composite fibres

500 1000 1500 2000 2500 3000 3500

-SiC

G´

D´

G

Inte

nsity

, a.u

.

Raman Shift, cm-1

5

D

600 650 700 750 800 850 900 950 1000

Inte

nsity

, a.u

.

Raman Shift, cm-1

-SiCTO

LO

5

A B

?

Pyrolysed SWNT/cellulose electrospun fibres

500 1000 1500 2000 2500 3000 3500

4RBM

Inte

nsity

, a.u

.

Raman Shift, cm-1

G´

D´

GD

500 1000 1500 2000 2500 3000 3500

4RBM

Inte

nsity

, a.u

.

Raman Shift, cm-1

3

2

1

G´D´

GDA B

Carbon nanotube fingerprint (RBMs) are still visible inside a pyrolysedcarbon fibre

Carbon Nanotubes

(8,7)

(11,4)

Carbon nanotubes have what is called chirality

Chirality of nanotubes depends on how you role up the graphene sheet in order to make a tube

Nanotubes with different chiralities have different electronic properties (metallic, semiconducting etc)

Most samples of carbon nanotubes contain a variety of tubes of different chiralities

Methods must be employed to separate nanotubes in order to generate electroninc devices etc.

Radial Breathing Modes (RBMs)

= 785 nm = 632 nm

200 220 240 260 280 3005000

10000

15000

20000

25000 272268

238232

210Inte

nsity

Raman shift (cm-1)180 200 220 240 260 280 300 320 340

0

5000

10000

15000

20000

25000

30000

292

261223

199

Inte

nsity

Raman shift (cm-1)

HiPco

• The HiPco material contains a range of different sizes of nanotubes• Different ones are in resonance with the different lasers

RBMs in our Fibres

180 200 220 240 260 280 300 320 3401,6

1,8

2,0

2,2

2,4

2,6

ESE22

EME11

ESE33

218.5

Opt

ical

Tra

nsiti

on E

nerg

y E ii, e

VRBM position, cm-1

2.33 eV274

290

264

A B

150 200 250 300 350 400 450

427

626

1216

Inte

nsity

, a.u

.

Raman Shift, cm-1

281

254

217

255

218 27

529

328

1

218

3

2

1

Prabharakaran, Eichhorn & Young (2007) Nanotechnology, 18, 235707. Prabharakaran, Young & Eichhorn (2008) Small, 4, 930-933.

Can “see” individual CNTs in fibres in resonance with the laser!

MWNTs/Cellulose Electrospun

5 m 5 m

• Cellulose fibres electropsun with/without the presence of MWNTs (0.5 -1.5%)• Fibres were de-acetylated as before• Fibres then

Stabilised (at 240 °C) in air, followed by Carbonised (at 1000 °C) in Ar, followed by Activated in steam/Ar (at 800 °C) – making ACNFs (Activated

Carbon Nanofibres)

Deng et al. (2013) – ACS Appl Mater Interf – in press

TEM of samples• Can see MWNTs inside

fibres

• Would not be able to image SWNTs – contrast not good enough in TEM between Cellulose/MWNTs

• MWNTs protude from the fibre surfaces

• Some alignment of the nanotubes noted

Preparation of SupercapacitorElectrodes

ACNFs ground & mixed with 10% of carbon black (CB) and 10% of PVDF binder. + small amount of NMP produce a paste

Paste cast onto Ni foam, dried under vacuum at 50 °C for 24 h and pressed under a pressure of 7 MPa to make electrodes.

Supercapacitor cells were built by assembling two pieces of 1.0 cm2

electrode, with a Whatman filter paper as a separator, in a coin cell containing 6 M aqueous KOH as the electrolyte.

The loading of ACNF in each electrode was 3 mg.Cyclic voltammetry (CV) and galvanostatic charge/discharge

measurements of the as-built supercapacitor cells were carried out using an Iviumstat Electrochemical Interface.

Electrochemical Impedance Spectroscopy (EIS) analysis was carried out using a Solartron 1287 Electrochemical Interface, in the frequency range from 0.1 Hz to 100 kHz at an open circuit potential with an AC amplitude of 10 mV.

CV Curves and Capacitance

Sample Crystallinitya Activationenergy (kJmol-1)b

ID/IG Specificsurfacearea(m2 g-1)

Electricalconductivity(S m-1)

RS () Rct () Specificcapacitance(F g-1)c

ACNF 60% 22920 1.210.08 86520 101095 0.380.03 0.370.03 105102%MWNT/ACNF

61% 21820 1.250.1 91023 1120104 0.350.03 0.340.03 12111

4%MWNT/ACNF

62% 20918 1.280.12 105020 1185110 0.330.03 0.320.03 13612

6%MWNT/ACNF

64% 182 17 1.310.08 112025 1255100 0.300.03 0.310.03 14511

Specific capacitances comparable with those derived from poly(acrylonitrile), poly(benzimidazole) and polyimide nanofibers

Comparable with those of cornstalk-carbon

Lower than coconut shell but critically more stable under cycling

Conclusions• We need new precursors for carbon fibre production• Some interesting and potentially useful carbon fibres can

be made from cellulose• Electrospinning offers a way to make fine structured

carbon fibres – volume production for electrospinningand shrinkage an issue

• Modulus of fibres looks promising. Lots of work to do improving processing

• Catalysis of graphitization possible using SiC/SWNTs• Potential for making new family of carbon fibres for

applications (automotive composites, batteries, supercapacitors)

Topsham (near Exeter), February 2013

Thankyou for listening

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