Department of Biomaterial SciencesThe University of Tokyo

A. Isogai, T. Saito, M. Hirota, T. Isogai, Y. Okita, H. Fukuzumi, S. Fujisawa,S. Iwamoto, T. Iwata

TEMPO-oxidized cellulose nanofibersprepared from chemical wood pulps

Outline

1. Background of TEMPO-oxidized cellulose nanofibers (TOCNs)

2. TEMPO-mediated oxidations of wood cellulose to prepare individualized TOCNs

3. Characterization and modification of TEMPO-oxidized celluloses

4. Nano-dispersion of TOCNs in organic solvents

5. Quite high oxygen barrier properties of TOCN films

6. NEDO nanotech challenge program of TOCN for production of environmentally friendly and high-performance packaging materials

Individualization of cellulose microfibrils from abundant wood biomass resources by downsizing with green chemistry

Abundant wood biomass

Individualizedcellulose microfibril

Width 3 - 4 nm

Length > 5 µm

Crystallinity 70 - 90 %

By downsizing processing

Bottom-upprocessing

Cellulose molecules

with green chemistry

100 nm

ChemistryChemistry--assisted individualization of wood assisted individualization of wood cellulose fibrilscellulose fibrils

Mild disintegration

TEMPO-oxidizedpulp fibers in water

Highly viscous andtransparent dispersion

ZetaZeta--potential potential –– 80mV80mV

Differences in morphology between MFC, TOCN and NCC

Micro-fibrillated cellulose (MFC)

Only partial nano-fibrillation,disintegration

energy > 200 kwh / kg

TEMPO-oxidizedcellulose nanofibers

Disintegrationenergy < 2 kwh / kg,large aspect ratio,

mostly individualized

100 nm100 µm 100 nm

50-64% H2SO4-hydrolyzedcellulose nanocrystals

Low yields, spindle-like shape, some bundles

(Gray et al., Cellulose, 1998)

Isogai et al., Nanoscale (2010)

Washing by filtrationFibrous form

TEMPO-oxidized pulp

Wood cellulose fibers are the most suitable resources for preparing TEMPO-oxidized cellulose nanofibers

Fibrous formTEMPO-mediated oxidation in the presence of ca. 0.4% salt (NaCl + NaBr)

N

OH

N

O

Glucose unitGlucuronate unit–COO¯

Disintegration in water

ζ-potential : – 80 mV

Individual nanofiber

Hemicellulose &disordered region

Wood cellulose microfibrils Fibrous form

Nanofiber length (nm)0 500 1000 1500 2000

Rat

io (%

)

0

10

20

30

40

50NaClO added: 10 mmol/gNaClO added: 5 mmol/gNaClO added: 3.8 mmol/gNaClO added: 2.5 mmol/g

Relationships between the amount of NaClO added and average length of TEMPO-oxidized cellulose nanofibers

■ Nanofiber length becomes short, as the amount of NaClO added in TEMPO oxidation is increased, but has still large distribution.

Filler (%)0 10 20 30 40

E / E

m

1

2

3

4

Potential applications of TEMPO-oxidized cellulose nanofibers

■ Nano-electronics■ Separators for fuel cell, filters for capacitor■ High-performance membranes■ Cosmetic applications■ Bioactive, medical and healthcare materials■ Nano-composites

Composite reinforcementGas-barrier propertiesElectro-optical propertiesImprovement of thermal stability

Paul & Robeson, Polymer (2008)

Nano-clay / Nylon 6composite

Glass fiber / Nylon 6composite

100 nm

ExfoliatedImmiscible IntercalatedNo particular “nano-effect” was observed in the nano-clay / polymer composites, or all the obtained results were explainable by the conventional fiber-reinforcement theory.

Only aspect ratio, volume fraction ratioand elastic modulus of the filler affect the resultant mechanical properties.

100 nmAsAspect ratio > 100pect ratio > 100

TEMPOTEMPO--oxidized cellulose nanofibersoxidized cellulose nanofibers

TEMPO / NaBr / NaClO oxidation of wood cellulose at pH 10

Advantages points :■ Aqueous media at pH 10■ Highly regioselective reaction at C6-OH■ Proceeds under mild conditions

(at room temp, atmospheric pressure, < 2 h)■ Formation of some aldehyde groups

pH 10

Glucose unit

Glucuronicacid unit

N O

N OH

N O

NaCl NaBrO

NaBrNaClO

OCH2OH

OH

OH

O

OCOOH

OH

OH

O

OCHO

OH

OH

O

OCOONa

OH

OH

O

NaOH

■ TEMPO-mediated oxidation proceeds similarly to enzymatic reactions butmore rapidly like chemical reactions.

Isogai et al., Nanoscale (2010)

Cellulose fibers (1 g) : bleached kraft or sulfite pulp

Cellulose fibers / water slurry at pH 10

Water (100 mL)TEMPO (0.0125 g)NaBr (0.125 g)

TEMPO-oxidized celluloses with fibrous morphologies

Washing with water by filtration

NaClO / water

dil. NaOH additionto keep pH 10

Stirring at room temp.for <2 h

●

N

O●

N

O

TEMPO / NaBr / NaClO oxidation of wood cellulose at pH 10

TEMPO

NaCl, NaBr

TEMPONaCl, NaBr

NaClO added (mmol/g-pulp)0 2 4 6 8 10C

arbo

xyla

te o

r ald

ehyd

e co

nten

t(m

mol

/g)

0.0

0.5

1.0

1.5

2.0

Deg

ree

of p

olym

eriz

atio

n

0

500

1000

1500

TEMPO / NaBr / NaClO oxidation of softwood BKP at pH 10

Transparency at 600 nm light > 95%

■ Individualization of cellulose microfibrils can be achieved for TEMPO-oxidized celluloses with carboxylate content > 0.9 mmol / g.

Isogai et al., Nanoscale (2010)

13

24

115

6

9

10

87

10 20 30 40 50 60 70Nanofiber yield (%)

00

0.2

0.4

0.6

0.8

1.0

1.2

1.4

Car

boxy

late

con

tent

(mm

ol/g

)N

O

N

O

HN

O

CH3

N

O

OCH3

N

O

O OH

N

O

NH2

N

O

O

PHO OH

O

N

O

OH

N

O

O

N

O

OOH

N

O

ONH2

N

O

ONH2

1 2 3 4 5 6 7 8 9 10 11

Iwamoto et al., Polym. Degrad. Stab. (2009)

TEMPO / NaBr / NaClO oxidation of softwood BKP at pH 10

TEMPO / NaClO / NaClO2 oxidation of cellulose at pH 3-7

Advantages :■ Aqueous media at pH 3-7■ Highly regioselective reaction at C6-OH■ No aldehydes are present

in the oxidized products■ Proceeds under mild conditions

(at 20-80˚C, 2-24 h)■ Depolymerization by β-elimination

is avoidable.

N O

N O

NaCl

NaClO2

OCH2OH

OH

OH

O

OCHO

OH

OH

O

OCOONa

OH

OH

O

NaClO

R

R

Glucose unit

Glucuronic acid unit

Reaction time (h)0 10 20 30 40 50 60C

arbo

xyla

te o

r ald

ehyd

e co

nten

t(m

mol

/g)

0.0

0.5

1.0

1.5

2.0

Deg

ree

of p

olym

erzi

atio

n

0

500

1000

1500

AldehydeCarboxylate

DP

TEMPO / NaClO / NaClO2 oxidation of softwood BKP at pH 3-7

Transparency at 600 nm light > 95%

■ Individualization of cellulose microfibrils can be achieved for TEMPO-oxidized celluloses with carboxylate content > 0.6 mmol / g, because no aldehyde groups are present.

Saito et al., Biomacromolecules (2009)

TEMPO electro-mediated oxidation of cellulose without anyCl-containing oxidant at pH 7

AnodeCathode

e 2e

e

H+

H2

H+

N

O

N

O

N

OH

N

OH

N

O

+N

O

+

Nafion®

OOH

OH

CHOO

OOH

OH

CHOO

OOH

OH

CH2OHO

OOH

OH

CH2OHO

OOH

OH

COOHO

OOH

OH

COOHO

OOH

OH

COOO

OOH

OH

COOO

ee 2e2e

ee

H+H+

H2

H+H+

N

O

N

O

N

O

N

O

N

OH

N

OH

N

OH

N

OH

N

O

+N

O

+N

O

+N

O

+

Nafion®

OOH

OH

CHOO

OOH

OH

CHOO

OOH

OH

CH2OHO

OOH

OH

CH2OHO

OOH

OH

COOHO

OOH

OH

COOHO

OOH

OH

COOO

OOH

OH

COOO

0.1 M Phosphate buffer at pH 6.8

Isogai et al., Biomacromolecules (2010)

Summary of TEMPO-mediated oxidation of wood cellulose

■ TEMPO / NaBr / NaClO oxidation at pH 10

Carboxylate content : > 1.2 mmol/g, Aldehyde content : < 0.1 mmol/gDP : > 600Reaction time & temp. : < 2 h at room temp

■ TEMPO / NaClO / NaClO2 oxidation at pH 7

Carboxylate content : < 1.0 mmol/g, Aldehyde content : 0.00 mmol/gDP : > 1,100Reaction time & temp. : > 2 h at 60 °C

■ TEMPO electro-mediated oxidation at pH 7 without Cl-containing oxidant

Carboxylate content : < 1.2 mmol/g, Aldehyde content : > 0.2 mmol/gDP : > 800Reaction time & temp. : > 6 h at room temp

Others

■ TEMPO-peroxidase-H2O2

■ TEMPO-laccase-O2

Carboxylate content : < 0.3 mmol/gReaction time : > 4 days

X-Ray diffraction patterns of wood cellulose before and after TEMPO-mediated oxidation

■ The same X-ray diffraction patterns before and after the oxidation indicatethat carboxylate groups are selectively formed on cellulose I crystallite surfaces.

Original 0.01 mmol/g

Oxidized 1.70 mmol/g

Carboxylatecontent

Saito et al., Biomacromolecules (2004)

Diffraction angle 2θ (degree)

10 15 20 25 30

(110), (110)

(200)

Original woodcellulose microfibril

Structural model of TEMPO-oxidized cellulose nanofiber

－CH2OH

3 - 4 nm

Glucose unit

TEMPO-oxidizedcellulose nanofiber

Glucuronate unit

－COO-

1.7 Carboxylate groups / nm2

13C-NMR spectrum of alkali-extracted product of TEMPO-oxidized cellulose: Glc/GlucA alternating copolysaccharide

ppm6080100120140160180200

–C6OONaC6

C1

C4

C2,3,5

Cellouronic acid, oxidation degree 50%

Extraction with aq. NaOH

■ This NMR result justifies the anticipated structure of TEMPO-oxidized cellulose nanofibers: Position-selective oxidation of cellulose microfibril surfaces.

Hirota et al., Angew. Chem. Int. Ed. (2010)

Relationships between structure of carboxyl groups of TEMPO-oxidized cellulose and its thermal degradation point

TEMPO-oxidized cellulose-COONa TEMPO-oxidized cellulose-COOM

■ Thermal degradation point of TEMPO-oxidized cellulose is controllable to some extent by controlling the structure of carboxyl groups.

Structure of carboxyl groups of TEMPO-oxidized cellulose

Der

ivat

ive

TG (°

C)

0

50

100

150

200

250

300

350

Originalcellulose Na+ H K+ Ca2+Fe3+ CH3

Fukuzumi et al., Polym. Degrad. Stab. (2010)

Dispersion of individualized TEMPO-oxidized cellulose nanofibers in organic solvents

Okita et al., submitted (2010)

■ Compositing with organic solvent-soluble polymers is available.■ Chemical modifications of COOH & OH groups of TOCN in organic solvents

are possible.

Oxygen permeability of TOCN-coated transparent PLA filmat 0% and 70% relative humidity

■ Positron annihilation lifetime spectroscopic (PALS) analysis revealed the average vacancy size: d = 0.47 nm. c.f. O2 size: d = 0.34 nm.

PLA basefilm

TOCN-coatedPLA film #1

TOCN-coatedPLA film #2

PE

PET

EVOH

Metalized EVOH

Oxy

gen

perm

eabi

lity

(mL/

m2 ·d

ay·k

Pa)

0.0001

0.0010

0.0100

0.1000

1.0000

10.0000

TOCN film (0.8 µm)

PLA film (25 µm)

0% RH

0% RH

70% RH

70% RH

Kumamoto et al., in preparation

■ Oxygen barrier properties of PLA film at 0% R.H. were extremely improved by thin TOCN coating.

Mechanism of high oxygen barrier properties of TOCN films

Necessary points for TOCN films to have high oxygen barrier properties■ Wood TOCNs with 3-4 nm widths and shorter lengths

Tunicate TOCNs with 10 nm width and lengths > 2 µm ■ Wood TOCNs with COONa groups Wood TOCNs with COOH groups

Self-assembly by electrostatic repulsion

TOCN dispersion in water

Short TOCN

Highly dense structure with small pores

Tunicate TOCNLong TOCN

SEM images of freeze-dried TEMPO-oxidized wood cellulose nanofiber aerogels

Saito et al., in preparation

Development of environment compliant high-gas-barrier & highly functionalized packaging materials using TEMPO-oxidized cellulose nanofibers

Organizations: Nippon Paper Ind., Kao Corp., The University of Tokyo, andTOPPAN Printing. Co. Ltd.

NEDO Nanotech Challenge ProgramsStages I and II from 2007 to 2013

NEDO: New Energy and Industrial Technology Development Organization of Japan, and is an affiliated organization of Ministry of Economy, Trade and Industry

Project Title

UTThe University of Tokyo

NEDO Nanotech Challenge Program Stage II from 2010 to 2013

Goals■ Development of more efficient nanofiber

production process with a new TEMPO- related chemical

■ Safety issues of TEMPO and TOCN■ Development of super high-gas barrier films■ Efficiently TOCN-reinforced composites with

bio- and conventional petro-polymers■ Development of practical packaging films-

production process with TOCN

100 nm

200 nm

Moisture permeability(g / m2 for 1 day at 1atm, 40°C & 90% R.H.)

0.1 1 10 100 1000

Oxy

gen

perm

eabi

lity

(mL

/ m2 fo

r 1da

y at

1at

m, 2

3 °C

& 7

0% R

.H.)

0.01

0.1

1

10

100

1000

10000

50µm thickness

PLA

PHB

PBS

EVOH

PET

HD-PE

LD-PE

O-PP

Bio-plastics

Petro-plastics

Aluminum-metalizedfilms

Moisture permeability(g / m2 for 1 day at 1atm, 40°C & 90% R.H.)

0.1 1 10 100 1000

Oxy

gen

perm

eabi

lity

(mL

/ m2 fo

r 1da

y at

1at

m, 2

3 °C

& 7

0% R

.H.)

0.01

0.1

1

10

100

1000

10000

50µm thickness

PLA

PHB

PBS

EVOH

PET

HD-PE

LD-PE

O-PP

Bio-plastics

Petro-plastics

Aluminum-metalizedfilms

Acknowledgement

UTThe University of Tokyo

Thank you for your kind attention.