CELLULOSE NANOCRYSTALS FOR LIGHTWEIGHT SHEET MOLDING COMPOUNDS COMPOSITES

Amir Asadi, Ferdinand Baaij, Robert Moon and

Kyriaki Kalaitzidou

G.W. Woodruff School of Mechanical Engineering and

School of Materials Science and Engineering

Georgia Institute of Technology

Motivation

Goal and Objectives

Background

Feasibility study of using basalt fibers

Light-weighting of sheet molding compounds

Conclusions

OUTLINE

2

Reasons for Light-Weighting:

• Governamental regulations

• Societal/customer pressure

Better fuel economy

Less green house gas emissions

Better performance

LIGHT-WEIGHTING IN THE AUTOMOTIVE INDUSTRY

3

https://obamawhitehouse.archives.gov/blog/2011/07/29/president-obama-announces-new-fuel-economy-standards ; 07/28/2017.

CREATE LIGHTWEIGHT SHEET MOLDING COMPOUND (SMC) COMPOSITES FOR AUTOMOTIVE APPLICATIONS

1. Study feasibility of using basalt fibers as alternative for glass fibers

2. Reduce weight of SMC parts by introduction of cellulose nano-crystals

GOALS AND OBJECTIVES

4

SHEET MOLDING COMPOUND -APPLICATIONS

5

SHEET MOLDING COMPOUND –PROCESS

6

Upper carrier

filmUpper doctor

box

Resin

Resin

Lower doctor

box

Lower carrier

film

Fiber rovings

Cutter

Compaction Zone SMC

collection winder

SMC PRODUCTION LINE

7

Unique SMC line:

Similar to industrial SMC machines

Smaller width

(0.3 m vs. 0.9 - 1.5 m)

SMC PROCESSING

8

(1) (2)

(3) (4)

COMPRESSION MOLDING -CURING CYCLES

9

0

10

20

30

40

50

60

70

80

90

100

110

120

Time1.5h 1h 2h 24h

Curing Post-Curing

Heat-Up

Cool-Down

Demolding

10min

Pre-Conditioning

Temperature [°C]

0

10

20

30

40

50

60

70

80

90

100

110

120

Temperature [°C]

10min

1h 2h 15min

Curing(Vacuum)

Post-Curing

Heat-Up

Cool-Down

Demolding

Time

Fiber content < 40 %

1.5h pre-conditioning increase viscosity for handling

Pressure: 125 kPA

Fiber content > 40 %

no pre-conditioning keep viscosity low for good fiber impregnation

Pressure: up to 430 kPa

• Extrusive volcanic rock

• Rapid cooling of basaltic lava

• Mixture of different silicates

• Most common rock type

• Superior hygrothermal and chemical stability

• Less energy-extensive manufacturing compared to GF

• No additives required

• High availability of basalt

Potential lower economical cost

Ecofriendly

WHAT IS BASALT?WHY USING BASALT FIBERS?

10

BASALT FIBER VS. GLASS FIBER

11

Basalt fiber Glass fiber

Density (g/cm3) 2.75* 2.54*

Filament diameter (μm) 10±1 10±1

Elastic modulus (GPa) 87±5* 75±5*

Tensile strength (MPa) 4500±400 4100±300

Price ($/lb) 1.4* 1-2*

* Data provided by suppliers

CURING BEHAVIOR

12

-0.2

0.0

0.2

0.4

0.6

-0.2

0.0

0.2

0.4

0.6

He

at

Flo

w (

W/g

)

20 40 60 80 100 120 140 160 180

Temperature (°C)

BF-epoxy––––––– GF-epoxy–– –– –

Exo Up Universal V4.5A TA Instruments

Same curing behavior for BF/epoxy and GF/epoxy

Same curing cycles can be applied for both

INTERFACIAL SHEAR STRENGTH (IFSS)

13

BF/epoxy GF/epoxy

Average Fragment Length (μm)

729.7±62.4 758.0±98.9

Interfacial Shear Strength (MPa)

42.7±6.1 39.8±8.1

Measured distance

• 25 wt% fiber content for both composite types

• Cut into test coupons for mechanical testing

SMC PLATES

14

25BF/epoxy 25GF/epoxy

MECHANICAL PROPERTIES

15

0

30

60

90

120

150

Strength(M

Pa)

0

2

4

6

8

10

Modulus(GPa)

25GF/epoxy 25BF/epoxy

Tensile propertiesASTM D638

Flexural propertiesASTM D790-02

• Theoretical density: 𝜌𝑡ℎ𝑒𝑜𝑟𝑒𝑡𝑖𝑐𝑎𝑙 =1

𝑤𝑓/𝜌𝑓 + 𝑤𝑚/𝜌𝑚

• Experimental density (ASTM D-792): water displacement method

• Void content (ASTM D2734-16 ): 𝑉𝑣𝑜𝑖𝑑 = 100 ×𝜌𝑡ℎ𝑒𝑜𝑟𝑒𝑡𝑖𝑐𝑎𝑙−𝜌exp

𝜌𝑡ℎ𝑒𝑜𝑟𝑒𝑡𝑖𝑐𝑎𝑙

DENSITY AND VOID CONTENT

16

25BF/epoxy 25GF/epoxy

Fiber density (g/cm3) 2.75* 2.54*

Theoretical composite density (g/cm3)

1.35 1.31

Experimental composite density (g/cm3)

1.29±0.04 1.25±0.01

Void content (vol-%) 5±1 5±1

* Data provided by suppliers

0

30

60

90

120

SpecificStrength

(MPa/g/cm^3)

0

2

4

6

8

SpecificModulus

(GPa/g/cm^3)

SPECIFIC MECHANICAL PROPERTIES(DIVIDED BY DENSITY)

17

25GF/epoxy 25BF/epoxy

Tensile properties Flexural properties

FRACTURE SURFACE MORPHOLOGY

18

25BF/epoxy 25GF/epoxy

100μm

100μm 100μm

100μm

IMPACT STRENGTH

19

CONCLUSIONS

20

BF-reinforced SMC composites do not show advantages in terms of lightweighting.

However, they are a potential cost-efficient and ecofriendly alternative to GF/epoxy composites.

0

30

60

90

120

SpecificStrength

(MPa/g/cm^3)

0

2

4

6

8

SpecificModulus

(GPa/g/cm^3)

WHAT IS CELLULOSE?

21

Moon et al. Chem. Soc. Rev. 2011; 40, 3941-3994.

CELLULOSE NANO-CRYSTALS

22

Length (nm) 138±22 *

Width (nm) 6.4±0.6 *

Density (g/cm3) 1.6 **

Tensile strength (GPa) 7.5 – 7.7 **

Elastic modulus in axial direction (GPa)

110 – 220 **

Elastic modulus in transverse direction (GPa)

10 – 50 **

* Girouard et al., Polymer 2015; 68: 111-121.** Moon et al. Chem. Soc. Rev. 2011; 40: 3941-3994.

LIGHT-WEIGHTING OF SMC COMPOSITES BY ADDING CELLULOSE NANO-CRYSTALS (CNC)

23

Introducing CNC to the matrix

Coating the fibers with CNC Increasing the

Interfacial Shear Strength between fiber surface and

matrix

Increasing the mechanical

properties of the matrix

Ability to reduce fiber content

( and weight) without

compromises in the properties

Or

Increased properties of the composite with no compromises

in the density

Light-weight SMC parts:

Lower density

Or

Smaller thickness

Using the CNC-epoxy matrix, how much fibers can be reduced without compromising the specific properties compared to a composite with neat epoxy?

Micromechanical Model:

𝑬𝑪𝒐𝒎𝒑𝒐𝒔𝒊𝒕𝒆 =𝟑

𝟖𝑬𝟏𝟏 +

𝟓

𝟖𝑬𝟐𝟐

𝐸11 = 𝐸𝑚

1+2𝑙𝑓𝑑𝑓𝜂𝐿𝑣𝑓

(1−𝜂𝐿𝑣𝑓); 𝐸22 = 𝐸𝑚

1+2𝜂𝐿𝑣𝑓

(1−𝜂𝐿𝑣𝑓)

Predict fiber contents for CNC-epoxy composites with same specific modulus ascomposites with neat epoxy and a fiber content of 60% (maximum fiber content)

INTRODUCING CNC TO THE EPOXY MATRIX

24

ρ (g/cm3) E (GPa)

Neat epoxy 1.15 3.0±0.3

1.4CNC-epoxy 1.15 4.4±0.5

2CNC-epoxy 1.15 4.7±0.3

𝜂𝐿 =

𝐸𝑓𝐸𝑚

− 1

𝐸𝑓𝐸𝑚

+ 2𝑙𝑓𝑑𝑓

𝜂𝑇 =

𝐸𝑓𝐸𝑚

− 1

𝐸𝑓𝐸𝑚

+ 2

0

30

60

90

120

150

180

Sp

ecif

ic Im

pa

ct

En

erg

y,

kJ

/m2(g

/cm

3)-1 (c) GF/epoxy

BF/epoxy

Fiber content (wt %)

50 60 65 70

0

4

8

12

16

0

50

100

150

0.0

0.5

1.0

1.5

0

1

2

Speicific tensile properties (g/cm3)-1

GF/epoxy BF/epoxy

W

ork

of

fra

ctu

re

(M

J/m

3)

Mo

du

lus (

GP

a)

Str

en

gth

(M

Pa)

Str

ain

at

Bre

ak

(%

)

(a)

Fiber content (wt %)

CNC content (wt %)

50 60 65 70

0

10

20

30

0

100

200

300

0

1

2

0

1

2

3

Tensile properties

GF/epoxy BF/epoxy

W

ork

of

fractu

re

(M

J/m

3)

Mo

du

lus

(G

Pa

)S

tre

ng

th (

MP

a)

Str

ain

at

Bre

ak

(%

)

(a)

Fiber content (wt %)

CNC content (wt %)

50 60 65 70

DETERMINATION OF MAXIMUM FIBER CONTENT

25

0

10

20

30

0

100

200

300

0

1

2

0

1

2

3

Tensile properties

GF/epoxy BF/epoxy

W

ork

of

fra

ctu

re

(M

J/m

3)

Mo

du

lus (

GP

a)

Str

en

gth

(M

Pa)

Str

ain

at

Bre

ak

(%

)

(a)

Fiber content (wt %)

CNC content (wt %)

50 60 65 70

0

10

20

30

0

100

200

300

0

1

2

0

1

2

3

Tensile properties

GF/epoxy BF/epoxy

W

ork

of

fractu

re

(M

J/m

3)

Mo

du

lus

(G

Pa

)S

tre

ng

th (

MP

a)

Str

ain

at

Bre

ak

(%

)

(a)

Fiber content (wt %)

CNC content (wt %)

50 60 65 70

0

5

10

15

20

25

0

100

200

300

400

0

1

2

3

0

2

4

6

Flexural properties

GF/epoxy BF/epoxy

W

ork

of

fractu

re

(M

J/m

3)

Mo

du

lus (

GP

a)

Str

en

gth

(M

Pa)

Str

ain

at

Bre

ak

(%

)

(b)

Fiber content (wt %)

CNC content (wt %)

50 60 65 70

0

10

20

30

0

100

200

300

0

1

2

0

1

2

3

Tensile properties

GF/epoxy BF/epoxy

W

ork

of

fractu

re

(M

J/m

3)

Mo

du

lus

(G

Pa

)S

tre

ng

th (

MP

a)

Str

ain

at

Bre

ak

(%

)

(a)

Fiber content (wt %)

CNC content (wt %)

50 60 65 70

0

50

100

150

200

250

300(c) GF/epoxy

BF/epoxy

Fiber content (wt %)

Imp

act

En

erg

y (10

3J

/m2)

50 60 65 70

0

5

10

15

0

50

100

150

200

0

1

2

0

1

2

3

4

Speicific flexural properties (g/cm3)-1

GF/epoxy BF/epoxy

W

ork

of

fractu

re

(M

J/m

3)

Mo

du

lus (

GP

a)

Str

en

gth

(M

Pa)

Str

ain

at

Bre

ak

(%

)

(b)

Fiber content (wt %)

CNC content (wt %)

50 60 65 70

0

10

20

30

0

100

200

300

0

1

2

0

1

2

3

Tensile properties

GF/epoxy BF/epoxy

W

ork

of

fractu

re

(M

J/m

3)

Mo

du

lus

(G

Pa

)S

tre

ng

th (

MP

a)

Str

ain

at

Bre

ak

(%

)

(a)

Fiber content (wt %)

CNC content (wt %)

50 60 65 70

Almost no performance improvement above 60 wt% fiber content

Found 60 wt% as maximum fiber content with a good fiber wetting

LIGHT-WEIGHT COMPOSITES WITH CNC

26

Etheor (GPa) ρ (g/cm3) Especific,theor

60GF/epoxy 14.38 1.71 8.40

48GF/0.9CNC-epoxy* 13.23 1.56 8.48

44GF/1.1CNC-epoxy** 12.73 1.51 8.41

60BF/epoxy 14.99 1.76 8.48

48BF/0.9CNC-epoxy* 13.41 1.58 8.47

44BF/1.1CNC-epoxy* 13.17 1.54 8.52

* 1.4 wt% CNC in the epoxy** 2 wt% CNC in the epoxy

DENSITY AND VOID CONTENTS OF THE LIGHT-WEIGHT SMC COMPOSITES

27

ρc,theoretical

(g/cm3)ρexp,wd

(g/cm3)Fiber content

(acid digestion)ρexp,ad

(g/cm3)Void content

(%)

60GF/epoxy 1.71 1.67±0.06 0.69±0.08 1.85±0.07 9

60GF/0.6CNC-epoxy* 1.71 1.74±0.06 0.66±0.05 1.80±0.08 3

48GF/0.9CNC-epoxy* 1.56 1.51±0.03 0.56±0.05 1.66±0.06 9

44GF/1.1CNC-epoxy** 1.51 1.49±0.05 0.52±0.06 1.61±0.07 8

60BF/epoxy 1.77 1.75±0.07 0.72±0.03 1.97±0.07 12

60BF/0.6CNC-epoxy* 1.77 1.73±0.05 0.71±0.08 1.96±0.1 13

48BF/0.9CNC-epoxy* 1.59 1.48±0.05 0.55±0.05 1.69±0.07 14

44BF/1.1CNC-epoxy** 1.55 1.39±0.06 0.53±0.08 1.66±0.1 19

* 1.4 wt% CNC in the epoxy** 2 wt% CNC in the epoxy

0

5

10

15

0

50

100

150

0.0

0.6

1.2

0

1

2

Speicific tensile properties (g/cm3)-1

GF/epoxy BF/epoxy

W

ork

of

fra

ctu

re

(M

J/m

3)

Mo

du

lus

(G

Pa

)S

tre

ng

th (

MP

a)

Str

ain

at

Bre

ak

(%

)

(a)

Fiber-CNC content (wt %)

CNC content (wt %)

60 60-0.6CNC 48-0.9CNC 44-1.1CNC

0

3

6

9

12

0

50

100

150

200

0.0

0.6

1.2

1.8

2.4

0

1

2

3

4

(b)

Speicific flexural properties (g/cm3)-1

GF/epoxy BF/epoxy

W

ork

of

fra

ctu

re

(M

J/m

3)

Mo

du

lus (

GP

a)

Str

en

gth

(M

Pa)

Str

ain

at

Bre

ak

(%

)

Fiber-CNC content (wt %)

CNC content (wt %)

60 60-0.6CNC 48-0.9CNC 44-1.1CNC

SPECIFIC PROPERTIES OF THE LIGHT-WEIGHTING COMPOSITES

28

0

5

10

15

0

50

100

150

0.0

0.6

1.2

0

1

2

Speicific tensile properties (g/cm3)-1

GF/epoxy BF/epoxy

W

ork

of

fractu

re

(M

J/m

3)

Mo

du

lus (

GP

a)

Str

en

gth

(M

Pa)

Str

ain

at

Bre

ak

(%

)

(a)

Fiber-CNC content (wt %)

CNC content (wt %)

60 60-0.6CNC 48-0.9CNC 44-1.1CNC

0

30

60

90

120

150

180

(c) GF/epoxy

BF/epoxy

Fiber-CNC content (wt %)

Sp

ecif

ic Im

pact

En

erg

y, kJ/m

2(g

/cm

3)-1

60 60-0.6CNC 48-0.9CNC 44-1.1CNC

0

5

10

15

0

50

100

150

0.0

0.6

1.2

0

1

2

Speicific tensile properties (g/cm3)-1

GF/epoxy BF/epoxy

W

ork

of

fra

ctu

re

(M

J/m

3)

Mo

du

lus

(G

Pa

)S

tre

ng

th (

MP

a)

Str

ain

at

Bre

ak

(%

)

(a)

Fiber-CNC content (wt %)

CNC content (wt %)

60 60-0.6CNC 48-0.9CNC 44-1.1CNC

170μm

FRACTURE SURFACE MORPHOLOGY –GF/EPOXY WITH AND WITHOUT CNC

29

110μm 110μm

170μm

GF60/epoxy 60GF/0.6CNC-epoxy

BF60/epoxy 60BF/0.6CNC-epoxy 48BF/0.9CNC-epoxy

Contact Angles between Fiber and 2CNC-epoxy matrix:

GF have better fiber wetting with 2CNC-epoxy compared to BF, possibly leading to a better fiber-matrix adhesion.

170μm

FRACTURE SURFACE MORPHOLOGY –BF/EPOXY WITH AND WITHOUT CNC

30

170μm 170μm

Void

spots

BF GF

40.7 36.4

Lightweighting Results

0

2

4

6

8

0

40

80

120

160

0.00

0.75

1.50

2.25

3.00

3.75

4.50

Mo

du

lus (

GP

a)

Tensile properties Flexural properties

25GF-C

NC0

35GF-C

NC0

25GF-C

NC1.

5

25GF-C

NC1

Str

en

gth

(M

Pa)

Str

ain

at

Bre

ak (

%)

0

20

40

60

80

100

120

Imp

act

en

erg

y (10

3J

/m2)

25GF-C

NC0

25GF-C

NC1

25GF-C

NC1.

5

35GF-C

NC0

CONCLUSIONS AND ASHBY PLOT

32

Presence of 1 wt% CNC increases mechanical performance of SMC with 44-48 wt% to the level of SMC with maximum fiber content 11% weight reduction

SMC with BF and CNC/epoxy matrix did not meet the properties of BF60/epoxy SMC composites due to high void content and lower wettability .

ACKNOWLEDGEMENT

33

Dr. Robert Moon Dr. Amir Asadi

Ferdinand Baaij

VOLKSWAGEN Group of America