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Rheological study of reinforcement of agarose hydrogels by cellulose nanowhiskers Kevin Jacques Le Goff , Cédric Gaillard*, Catherine Garnier*, Thierry Aubry EPNOE 2013 *INRA NANTES BIA-ISD

Rheological study of reinforcement of agarosehydrogelsby ... · Rheological study of reinforcement of agarosehydrogelsby cellulose nanowhiskers Kevin Jacques Le Goff, Cédric Gaillard*,

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Rheological study of reinforcement of

agarose hydrogels by cellulose nanowhiskers

Kevin Jacques Le Goff, Cédric Gaillard*, Catherine

Garnier*, Thierry Aubry

EPNOE 2013

*INRA NANTES BIA-ISD

2

Outline

1. Context & introduction

2. Materials & methods

3. Results

4. Conclusion

3

«Green» innovative nanocomposite hydrogels

Tridimensional polymeric networks in aqueous media

Increasing development since the sixties in biomedical, cosmetic, food industries

What is a

hydrogel?

A lot of physical hydrogels are based on polysaccharides (Carrageenan, Pectins…)

Why adding fillers?

To improve the matrix properties (mechanical, electrical, magnetic…)

Carbon Nanotubes Microfluidic application

Context1. Context & introduction 2. Materials & methods 3. Results 4. Conclusion

Example:

Agarose

Song, Carbon (2012)

4

Objective: Understanding the reinforcement effect of the cellulose nanowhiskers

(CNW) on hydrogels

Approach: Study of the structure/rheology relationships

Originality: A lot of studies on thermoplastics reinforced by CNW

but few studies on hydrogels filled with CNW

Very few studies on the effect of adding CNW into an agarose matrix

Mechanical properties and orientation of CNW

Localization of the nanowhiskers using optical studies

Ozario-Madrazo & al., Biomacromolecules (2012)

Bica & al., Macromolecules (2001)

Our system: Agarose matrix filled by tunicate CNW

In literature:

Samir & al., Biomacromolecules (2005)

Bica & al., Macromolecules (2006)

1. Context & introduction 2. Materials & methods 3. Results 4. Conclusion

Introduction

OriginNeutral galactose based-polysaccharide

Extracted from red algae

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Provider

Eurogentec (Belgium)

Hydrogel preparation

Agarose + water heated at ~ 90°C

Mechanical stirring during 10 min

Cooling

Rochas and Lahaye, Carbohydrate Polymers (1989)

Gelling mecanism

The temperature induces a conformational transition (ramdom coils to helices)

At a critical concentration, the helices aggregate and form a gel

1. Context & introduction 2. Materials & methods 3. Results 4. Conclusion

Agarose

Mesh size: ~ 450 nm at 0.2 wt%Bica & al., Macromolecules (2001)

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Cellulose

Most abundant biopolymer on earth

Linear glucose based polysaccharide

Hierarchical structure: fibers, microfibers (amorphous and cristalline regions)

CNW origin: Tunicate (marine animal)

Characteristics

Insoluble in water

Very good mechanical properties

Young modulus E~ 120-140 GPa (Glass fibers : E ~ 70 GPa)

Provider: Roscoff biology station

CNW

1. Context & introduction 2. Materials & methods 3. Results 4. Conclusion

Cellulose nanowhiskers (CNW)

CNW Elaboration– Extraction and purification of the cellulose

• Degradation with KOH 5%

• Purification/whitening with chlorite

– Acid hydrolysis• Slow addition of sulfuric acid (T° < 32°C)

• Mixture heated at 70°C

– Dialysis of the cellulose nanowhiskers suspension

– Sonication

– Elimination of non-covalent ions with ions exchange resins

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1. Context & introduction 2. Materials & methods 3. Results 4. Conclusion

Cellulose nanowhiskers (CNW)

Elaboration of nanocomposite hydrogels – Sonication of the aqueous CNW suspension

– Suspension heated at 90°C

– Addition of agarose

– Mechanical stirring during 10 min (800 rpm/min)

– Cooling in Petri dishes

CompositionAgarose concentration: 0.2 wt%

CNW volume fractions: 0.013 , 0.032 , 0.065 , 0.13 and 0.2%

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1. Context & introduction 2. Materials & methods 3. Results 4. Conclusion

Nanocomposite hydrogels

Structural characterization

Transmission Electron Microscopy (JEOL JEM-1230)

Determination of CNW geometry

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Simple plane oscillatory shear in parallel plate geometry at 20°C with sandpaper

• Oscillatory shear

Determination of linear viscoelastic properties

σ* = G*γ* G* = G’ + iG ’’G’ : storage modulus stored energy (elastic contribution)

G’’ : loss modulus dissipated energy (viscous contribution)

• Stress relaxation

Stress as a function of time at constant strain

Rheological characterization

Rheometer: Gemini (Bohlin Instrument)

1. Context & introduction 2. Materials & methods 3. Results 4. Conclusion

Characterization methods

Mean length

L ~ 950 ± 475 nm

Mean diameter

d ~ 15 ± 4 nm

Mean aspect ratio

L/d = p ~ 60

10

~ 400 nanofibers

High length polydispersity

TEM image

1. Context & introduction 2. Materials & methods 3. Results 4. Conclusion

CNW geometry

CNW mean length is 2 times higher than the agarose mesh size (same order of magnitude)

Determination of the linear domain characterized by the critical strain γγγγc

- γγγγc of nanocomposite hydrogels close to that of pure agarose hydrogel:

slight perturbation of the agarose structure by CNW (rheological properties governed by agarose)

- γγγγc independent of CNW volume fraction:

absence of interactions between CNW

At low strains γγγγ < γγγγc :

G’and G’’ constant

At strains γγγγ > γγγγc :

G’ and G’’

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Volume fraction Φ of CNW (%) 0 0.013 0.032 0.065 0.13 0.2

Critical strain γc (%) 4 1 1 1 1 1

1. Context & introduction 2. Materials & methods 3. Results 4. Conclusion

Strain sweep test

0.2 wt% agarose gel filled with 0.13 vol% CNW

0,1 1 10 10010

100

1000

γγγγc

Φ = 0.13%

G' G''

G';G

" (P

a)

Strain (%)

G’>>G ’’ ; G’ and G’’ are slightly dependent on frequency

Solid like viscoelastic behaviour

Nota bene: When Φ increases, G’ becomes more frequency-dependent

CNW induce slight perturbations of the agarose structure12

1. Context & introduction 2. Materials & methods 3. Results 4. Conclusion

Frequency sweep testViscoelastic behaviour of 0.2 wt% agarose gel filled w ith 0.13 vol% CNW

1E-3 0,01 0,1 1

100

1000

Φ = 0,13%

G' G"

γ = 1%

G';G

" (P

a)

Frequency (Hz)

Volume fraction Φ of CNW (%) 0 0.013 0.032 0.065 0.13 0.2

Storage modulus G’(Pa)

at 0.1 Hz80 200 320 590 940 830

Loss modulus G’’(Pa)

at 0.1 Hz7 15 40 60 125 150

Loss angle Tan δ (=G’’/G’)

at 0.1 Hz 0.09 0.075 0.12 0.1 0.13 0.18

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For 0.13 vol% CNW, G’ is 12 times higher than for pure agarose gel

1. Context & introduction 2. Materials & methods 3. Results 4. Conclusion

Reinforcement effect

For 0.2 vol% CNW, G’ decreases: stronger perturbation of agarose structure by CNW ?

Nota Bene: Tan δ increases withΦCNW

confirmation of agarose structure perturbations

0,01 0,1

500

1000

0.1 Hz

G' (

Pa

)

Φ(%)

y=axb

a=4870 b=0,7

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0,01 0,110

100

0,1 Hz

G''

(Pa)

Φ (%)

y=axb

a=730 b=0,9

G’ ~ Φ 0.7 G’’ ~ Φ 0.9

1. Context & introduction 2. Materials & methods 3. Results 4. Conclusion

Reinforcement effect

Agarose is a strong gel that governs the viscoelastic behavior of the system15

Φ (%) 0 0.013 0.032 0.065 0.13 0.2

S (Pa) 30 140 270 480 1015 1150

n 0.06 0.1 0.06 0.07 0.06 0.1

Winter & Chambon, Journal of Rheology (1986)

The relaxation exponent n is low and very close to that of the agarose at all Φ < 0.2 vol%

Results well fitted by critical gel

model:

Critical gel: scale invariance (self–similar structure) of the structure at the gel point

S: gel strength (Pa) n: relaxation exponent

1. Context & introduction 2. Materials & methods 3. Results 4. Conclusion

Stress relaxation test

10 100 1000

500

1000

1500

Φ = 0.13%

G γ = 1%

G (

Pa)

Time (s)

S=1015

G(t)=St-n

n=0,06

Rheological behaviour of agarose hydrogels filled with cellulose

nanowhiskers:

– governed by the agarose matrix (strong gel at 0.2 wt%)

– In the range of volume fractions ΦCNW <0.2%

• Significant reinforcement effect

Even if no percolation network is formed by the nanowhiskers

• Slight (but significant) CNW perturbation effect on the structure of agarose

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Ongoing studies

Stuctural characterization on different scales by various optical techniques

and rheological characterization of nanocomposite hydrogels atΦCNW > 0.2%

1. Context & introduction 2. Materials & methods 3. Results 4. Conclusion

Conclusion

Thanks toRégion Bretagne et Région Pays de la Loire

(for financial support)

GlycoOuest Network

LIMATB Rheology team

INRA ISD team

William Helbert/CERMAV Grenoble (CNW elaboration)

I thank you for your attention!