Stability of cellulose nanocrystal dispersions and aerogels

Jeremiah Kelley, Melissa Taylor, Dibyaranjan Mekap, John Simonsen

Oregon State University

Bruce AreyPNNL

Coming attractions: Preparation of carboxylated cellulose

nanocrystals (C.CNXLs) Preparation of C.CNXL aerogels Stability of aerogels Ester formation Evaluation

SEM FTIR XRD

Carboxylated CNC prepcellulose

Reflux2 hr

Dilute, settleand decant

N2 blanketstir

Filter, rinse

TEMPONaOClNaBr1 M NH4OHpH ~10MeOH quench

Filtersolids

Centrifuge,rinse

diafiltrationVacuum filtrationdialysis sonicationC.CNC

suspension

2.4 M HCl

Carboxylated CNCsTypical size 7 X 140 nm1.4 mmol CO2H/g CNC~ 2.4 acid groups/nm2

Zeta potential ~ -50Conductivity of 2%

dispersion ~ 1 mS/cm

AFM by A. Mangalam

~ 7 nm

~150 nm

Surface charges 1β unit cell has a surface area of 3.32 nm2

neglecting the longitudinal ends and contains two cellulose chains with a cellobiose repeat unit

Thus 1.2 C6 groups/nm2

1.038 nm

0.82 nm

0.778 nm

Not consistent with measured value of 2.4 groups/nm2

Assumes a 7 X 7 nm crystal

Nishiyama, et al, J. AM. CHEM. SOC. 2002, 124, 9074-9082

Fabrication

Layer acetone over aqueous suspension of C.CNCs

Gel forms in < 1 day Replace the acetone layer at least three

times Dry in supercritical dryer Densities to 30 mg/cm3 have been

achieved

http://www.teamonslaught.fsnet.co.uk/co2%20phase%20diagram.GIF

54

5

Supercritical drying

Flush cell to exchange solvent

C.CNC aerogels

ORGANOGEL/LYOGEL

C.CNC aerogels

AEROGEL

C.CNC aerogels

REFLECTED LIGHT TRANSMITTED LIGHT

Protocol

Add water

Wait at least one day before next addition

Evaluate visually

No addition of water

39% H2O

47% H2O

60% H2O

70% H2O

80% H2O

Control ~ 25 nm cross section

Heat treated110 °C/~2 hr

~40 nm cross section

Butyl ester ~50 nm cross section

Butyl ester

Reacted aerogel – butyl ester?Starting material

Reacted aerogelStarting material

Octyl ester

Octyl ester

Average cross section ~ 80 nmOctyl ester

2-3 nm

Octyl ester

57 14 nm

Octyl ester dried from hexane

Octyl ester dried from hexane

Reacted aerogel – octyl ester?Starting material

Reacted aerogelStarting material

Control Butyl ester

200 nm

200 nm

Butyl ester Octyl ester

-100

0

100

200

300

400

500

600

700

800

900

1000

5 10 15 20 25 30

Cou

nts

2 theta

Aerogel butyl ester

Controlbutyl ester 1butyl ester 3

Octyl ester

-100

0

100

200

300

400

500

600

700

800

900

1000

5 10 15 20 25 30

Cou

nts

2 theta

control

Octyl ester

Octyl ester hexane dried

-100

0

100

200

300

400

500

600

700

800

900

1000

5 10 15 20 25 30

Cou

nts

2 theta

control

aerogel HCl

control HAc

Effect of acidification in acetone

-100

0

100

200

300

400

500

600

700

5 10 15 20 25 30

Cou

nts

2 theta

control HClButyl esteroctyl ester

Acidification is the problem

Poly(allyl amine)PAAm

?

Acidified cellulose aerogel

PAAm

Coated (reacted?) aerogel

Carbonyl region

Celluloseaerogel

PAAm

combined

-100

0

100

200

300

400

500

600

700

800

900

1000

0 5 10 15 20 25 30 35

Cou

nts

2 Theta

Poly(allyl amine)/C.CNXL mixture

Control

PAAm mix

controly = 1.3677x - 0.0064

R² = 0.9985

PAAm-1y = 1.5689x - 0.0226

R² = 0.9996PAAm-2

y = 1.5701x - 0.0327R² = 0.9995

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.00 0.05 0.10 0.15 0.20 0.25 0.30

-str

ess,

Mpa

- strain

control

PAAm-1

PAAm-2

15% increase in bulk modulus

Conclusions

CNC aerogels have a different diameter than that observed for dried suspensions using AFM or TEM

The aerogel can be chemically modified Acidification in acetone with

trifluoroacetic acid or HCl can hydrolyze the cellulose crystal