(Présentation EPNOE Kevin Le Goff)
Transcript of (Présentation EPNOE Kevin Le Goff)
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
5
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)
6
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
7
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%
8
1. Context & introduction 2. Materials & methods 3. Results 4. Conclusion
Nanocomposite hydrogels
Structural characterization
Transmission Electron Microscopy (JEOL JEM-1230)
Determination of CNW geometry
9
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’’
11
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
13
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
14
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
16
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!