Morphological Design of Highly Porous Nanocellulose Structures · - Rettenmaier & Söhne GmbH (JRS) - Marko Peura (University of Helsinki, X-Ray microtomography) Title: Morphological

Morphological Design of Highly Porous Nanocellulose Structures

Jenni Sievänen Hans-Peter Hentze Tuomo Hjelt

7/14/2009Keskuslaboratorio Oy

Agenda

1) Introduction – NFC Aerogels

2) Morphology Control by Cryoprotectants

3) Morphology Control by Hydrophobization

4) Summary & Outlook

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1) Introduction – NFC Aerogels

Nanocellulose (Nanofibrillated Cellulose = NFC)

Nanocelluloses are cellulose fibers characterized by

- diameter in the nm-range (~100 nm)- high aspect ratio (length ~10s μm)- high specific surface area- high mechanical strength

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NFC & wood fiber

10 μm

NFC 100-5 (Rettenmaier & Söhne)Ground wood-fibersd ~ 100 nm l ~ 10s microns

Introduction – NFC Aerogels

Materials made from nanocelluloses

Pure nanocelluloses can be assembled into different types of new cellulosic materials, e.g.:

NFC Aerogels: Nanocellulose-based porous solids,which combine high porosity & high mechanical stability

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Dense & transparent films

Porous & opaque films

Porous bulk materials

Introduction – NFC Aerogels

Preparation of NFC aerogels

A) Preparation of a homogeneous NFC suspensionB) Freezing of the suspensionC) Sublimation of the water by freeze-drying

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A: B: C:

Liquid NFC suspension

Frozen NFC suspension

NFC aerogel

AB

C

Introduction – NFC Aerogels

The morphology of NFC aerogels

- Open pore structure- High mechanical stability- High surface areas

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X-ray microtomography:

Introduction – NFC Aerogels

Motivation & Hypotheses

• The mechanical properties of NFC aerogels aredetermined by the pore structure

• The pore structure of NFC aerogels prepared by freeze-drying is controlled by ice crystal formation

• The morphological and mechanical properties of NFC aerogels can be adjusted by:

- Control of ice crystal formation by use of cryoprotectants (→ homogenity of the pore morphology)

- NFC hydrophobization (→ screening fiber-fiber interaction)

- NFC concentration of the suspension (→ overall porosity)

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2) Morphology Control by Cryoprotectants

Cryoprotectants – A biomimetic approach

Cryoprotectants suppress ice crystal growthand enable the vitrification of water (amorphous ice)

An example from nature – The arctic wood frog

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Glucose as a natural cryoprotectant

Morphology Control by Cryoprotectants

Glucose as a cryoprotectant additive:Homogenity of the NFC aerogel morphology

NFC aerogels with and without cryoprotectant

→ Cryoprotectants enable a homogenous pore morphology

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Morphology Control by Cryoprotectants

Glucose as a cryoprotectant additive:Homogenity of the NFC aerogel morphology

Examples of sample compositions:

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Sample c (NFC) c (glucose) porosity

JNF44 3wt% - 98.0%

JNF45 3wt% 0.15wt% 97.9%

JNF43 5wt% 0.25wt% 96.5%

Morphology Control by Cryoprotectants

Comparison of microstructure:

Addition of glucose (JNF44: 0wt%, JNF 45: 0.15wt%)c(NFC)=3wt%

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100 μm100 μm

JNF 44 JNF 45

Morphology Control by Cryoprotectants

Comparison of microstructure:

Addition of glucose (JNF44: 0wt%, JNF 45: 0.15wt%)c(NFC)=3wt%

→ No change in microstructure: Sheet-like morphology

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10 μm

JNF 44 JNF 45

10 μm

Morphology Control by Cryoprotectants

Comparison of mechanical properties:

Addition of glucose (JNF44: 0wt%, JNF 45: 0.15wt%)

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→ Increase in mechanical strength, E-modulus (10% strain): 40 kPa (JNF44) → 69 kPa (JNF45)

c (NFC)=3wt%

Morphology Control by Cryoprotectants

Comparison of mechanical properties:

Effect of increasing NFC concentration (JNF43: 5wt%, JNF45: 3wt%)

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→ Increase in mechanical strength, E-modulus (10% strain): 69 kPa (JNF45) → 173 kPa (JNF43)

c(glucose)/c(NFC)=0.05

3) Morphology Control by Hydrophobization

NFC Hydrophobization

Sizing agents are commonly used in papermakingfor hydrophobization of cellulose wood-fibers, e.g.

Alkenyl-succinic anhydride (ASA)

→ Hydrophobization of NFC by 2wt% ASA

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+Esterification

NFC NFC-ASAASA

R=C12-C20

Morphology Control by Hydrophobization

Preparation of NFC-ASA Aerogels

Examples of sample compositions:

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Sample c (NFC-ASA) c (glucose) porosity

JNF46 5wt% - 96.7 %

JNF47 5wt% 0.25wt% 96.5%

Morphology Control by Hydrophobization

Comparison of microstructure:

Effect of hydrophobization: JNF44: 0% ASA, JNF 46: 2wt% ASA

→ Screening of fiber-fiber interaction by hydrophobizationsuppresses sheet-like microstructure formation

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100 μm100 μm

JNF 44 JNF 46

Morphology Control by Hydrophobization

Comparison of microstructure:

Effect of hydrophobization: JNF44: 0% ASA, JNF 46: 2wt% ASA

→ Screening of fiber-fiber interaction by hydrophobizationsuppresses sheet-like microstructure formation

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20 μm

JNF 44 JNF 46

20 μm

Morphology Control by Hydrophobization

Comparison of mechanical properties:

Addition of glucose (JNF46: 0wt%, JNF 47: 0.25wt%)

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→ Only slight increase in mechanical strength, E-modulus (10% strain): 88 kPa (JNF46) → 95 kPa (JNF47)

JNF 46

c (ASA-NFC)=5wt%

Morphology Control by Hydrophobization

Comparison of mechanical properties:

Effect of hydrophobization: JNF43: 0wt%ASA / JNF47: 2wt%ASA

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→ pure NFC: higher mechanical strength (E-modulus)hydrophobization: higher elasticity, higher stress at high strain

Morphology Control

Macro- and micromorphology control

Morphology-Properties-Map

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c (ASA)

c (NFC): E-modulus

NFC sheets NFC bundles

Potential Applications

Potential applications of NFC aerogels

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Insulation Materials

Composite Materials

Packaging(Cellulosic Styrofoam)

Filters & Membranes

Biomedical - Tissue Engineering

Summary

- Freeze-drying of NFC suspensions:Highly porous aerogels with high mechanical stability

- Use of glucose as cryprotectant:- homogeneous sample morphology

- Increase of NFC concentration:- increase in mechanical stability (E-modulus)

- Hydrophobization of NFC:- screening of fiber-fiber-interaction- softening of the gel structure (lower E-modulus)- increase in elasticity

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Outlook

- Variation of NFC qualities (e.g. aspect ratios)

- NFC functionalization (e.g. fiber bonding)

- Different types of cryoprotectants

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Acknowledgements

- KCL Owner Companies

Metsäliitto Group: M-real, Metsä-Botnia, Myllykoski Group, Stora Enso and UPM-Kymmene

- Rettenmaier & Söhne GmbH (JRS)

- Marko Peura (University of Helsinki, X-Ray microtomography)