impact of two different cellulose nanoreinforcements on ... · impact of two different cellulose...
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Geneva, October 14th - 2010
Gilberto Siqueira, Carole Fraschini, Julien Bras, Alain Dufresne, Robert Prud’ homme and Marie-Pierre Laborie
Impact of two different Cellulose Nanoreinforcements on the Melting and
Crystallization Behavior of Polycaprolactone
Outline• Background
• Research Objective
• Materials and Methods
• Results and Discussion– Cellulose/PCL morphology
– Crystallization kinetics (Avrami and Secondary Nucleation Theory)
• Conclusions
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Nanofillers & PCL Melting Crystallization
• PCL/ nanoclay crystallization 1,2
– For low clay/carbon nanotubes content, fillers act as a nucleating agent, accelerating the crystallization of the polymer.
– At high clay content, fillers delay crystallization, possibly due to reduced mobility.
• PCL/ carbon nanotubes crystallization 3,4
– Decrease of avrami exponent n or dimensionality of the crystal growth.
– Carbon nanotubes expedited the crystallization process of PCL.
1. Jimenez G. Et al. 1997, J. of Appl. Pol. Sci. 64:2211.2. Di Maio E et al. 2004, Polymer 45:8893.
3. Wu & Chen 2006 Poly. Eng. & Sci. 46(9):1309.4. Chen & Wu 2007 Poly. Degr. & Stability 92(6):1009.
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Nanocellulose & PCL Melting Crystallization
• In PEO/ CNW nanocomposites1:– Xc constant up to 10 % loading; decreased with further loading– Smaller and more numerous spherulites were observed– The whiskers acted as nucleating agents while limiting crystal growth
• In PP/ CNW models4
– Nucleating effect – Transcrystalline layer
• In MFC reinforced PVA2 and PLA3
– slight increase in Xc with small amounts of MFC (1 to 5 wt%)– nucleating effect
1. Azizi Samir et al. 2004, Polymer 45(12):4149.2. Lu J. et al. 2008, Comp. Part A 39(5):738.
3. Suryanegara L. et al. 2009, Comp. Sci. & Techno. 69:1187.4. Grey D. , 2008, Cellulose , 15, 297.
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Objective
It is important to understand the impact of nanocellulose melting/crystallization behavior and kinetics of polymers
- Fundamental standpoint: understanding interactions, morphology, and miscibility in the melt etc.- Practical standpoint: processing of nanocomposites.
Objective:
• To evaluate the impact of different cellulose nanofillers on the melting/crystallization behavior of Polycaprolactone.
• How the shape and nature of the cellulosic filler might influence the morphology and crystallization kinetics of the matrix?
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Cellulose Nanocrystals vs MFC
MFC from Opuntia ficus-indicaMalainine et al., 2005
Individual crystals Mechanical disintegration
Herrick et al. and Tubark et al. (1983)Rånby and Ribi (1950)Terminologies: whiskers, cellulose nanowhiskers(NCW), cellulose nanocrystals (CNX or CNC),Nanocrystals of cellulose (NCC).
Terminologies: microfibrillated cellulose (MFC),microfibrils, nanofibrillated cellulose (NFC),cellulose nanofibers (CNF).
Dimensions:Length: 100 – 1000 nm;Diameter: 4 – 15 nm.
Dimensions:Length: micrometer scale;Diameter: 10 – 100 nm.
Cellulose nanocrystals from Sugar beet pulp Azizi Samir et al., 2004
Acid Hydrolysis Web-like structure
Straight Long and flexible
Materials & Methods
Polycaprolactone
Microfibrillated Cellulose (MFC) & Cellulose Whiskers (CNWs)
Chemical Modification : Isocyanate Grafting on Cellulose
Morphological Characterization and Isothermal Crystallization Studies
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Raw Materials
Sisal-based Cellulose• fibers (Agave sisalana),
originating from northeast Brazil,were purchased in Mariana(Minas Gerais, Brazil)
poly(ε-caprolactone) PCL
n
O
O
n
O
O
Mn= 42,500 g.mol-1Mw= 65,000 g.mol-1
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Raw Materials
Dimensions of WhiskersLength: 215 nm 67 nm Diameter: 5 nm 1 nm
→ L/D ∼ 43
TEM of sisal whiskers
TEM of sisal MFC
Dimensions of MFCLength: µm scale
Diameter: 52 nm 15 nm
Acid Hydrolysis with sulfuric acid Microfluidizer
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Chemical Modification
Siqueira et al. (Langmuir 2010)
Nanoparticles in acetone
Nanoparticles in toluene
Temp.50 °C30min
Temp.90 °C75 min
Add.Toluene
Method II
Nanoparticles in water
Nanoparticles in acetone
Nanoparticles in dichloromethane
Nanoparticles in toluene
SolventExchange
SolventExchange
Temp.-10 °C
Method I
IsocyanateTemp. 110 C
30 min
OO
O
HO
OHHO
OOH
OH
OHHO
NC
O
H
n
• XRD showed that the cellulose crystalline structure was not affected by grafting• Grafting was demonstrated by XPS (O/C and N/C ratios)
n-octadecyl isocyanate
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51 m².g-1
252 cellulose chains
3.1% OH accessible
533 m².g-1
25.2 cellulose chains
21% OH accessible
Fiber MFC Whiskersx10 x10
2 to 10 m².g-1
~ 2% OH accessible
(Trejo-O’reilly et al. 1997)
microfibrilFiber
Siqueira et al. (Langmuir 2010)
Chemical Modification
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Methods: DSC Analysis
• Pure PCL , 12% wt PCL/MFC, 12% wt PCL/CNW
• Isothermal crystallization studies with Perkin-Elmer DSC-7
– Heat to 90 C at a heating rate of 100 C/min
– Stay at 90 C for 20 minutes
– Quench (100 C/min) to Tc and maintain until crystallization is complete
– Tc ranged from 42-50 C with a spacing of 2 C.
– Heat at 10 C/min to 90 C
• Heat flow as a function of time during isothermal crystallization
• Melting temperature (Tm) and endotherm upon second heat
• The degree of crystallinity (Xc)
Nanocomposite Morphology
Melting and crystallization behavior
Crystalline structure analysis
Equilibrium melting point
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DSC Melting Behavioren
do
• Broadening and splitting of the melting upon addition of nanocellulose• Effect is more marked with MFC than CNW• More heterogeneous crystals, other crystalline structure and/or a melting-recrystallization phenomena in nanocomposites?
50 60 70 80 90
c
b
a
Tm2=64.5 oC
Heat
Flo
w (W
/g)
b
a
endo
Tm2=62.0 oCb
a
Tm1=62.4 oCTm2=63.5 oC
Tm1=62.4 oC
Temperature (°C)
PCL
PCL-CNW
PCL-MFC
Tc = 42 Cb
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Melting/Crystallization Behavior
• Xc increases with addition of MFC and CNWs• Effect more marked with CNWs than MFC
Sample Tc( C) Xc Tm1( C) Tm2( C)
PCL
42 0.44 62.4 -44 0.45 62.9 -46 0.45 63.7 -48 0.45 65.2 -50 0.50 65.7 -
PCL-CNW
42 0.64 62.2 63.544 0.61 62.9 *46 0.56 63.4 *48 0.56 63.9 *50 0.56 64.5 *
PCL-MFC
42 0.52 62.0 64.544 0.52 62.5 64.746 0.52 63.2 65.248 0.51 63.5 65.750 0.51 64.2 66.2
10 15 20 25 30 35 40
MFC
CNW
PCL-MFC
PCL-CNW
PCL
Inte
nsity
(a.u
.)
2θ (degree)
• No new crystalline structure
Nanofillers enhance PCL crystallization- nucleating effect?- related to surface area?
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42 48 54 60 66 72 7842
48
54
60
66
72
78
R2=0.9973
R2=0.9946
R2=0.9839
PCL - Tm0 = 79 oC
PCL-CNW - Tm0 = 70 oC
PCL-MFC - Tm0 = 69 oC
T m (o C
)
Tc (oC)Tc
Equilibrium Melting Point
Hoffman-Weeks Plot
γ : thickening coefficientl: final lamellar thicknessl*: critical nucleus size
)(1c
omm
om TTTT −=−
γ *ll
=γ
Sample Tom ( C) γ
PCL 79 2.3
PCL-CNW 70 3.6
PCL-MFC 69 3.7
• Addition of MFC and CNWs depress the Tm0 of PCL
• Suggests melt miscibility of modified nanocellulose and PCL• Nucleating effect
Isothermal Crystallization kinetics
Avrami Kinetics: Bulk Crystallization Theory
Lauritzen-Hoffman Kinetics: Secondary Nucleation Theory
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Isothermal Crystallization: Raw Data
• MFC and CNWs expedite PCL crystallization• Slightly faster with MFC than with CNW
Nanofiller enhance PCL crystallization- nucleating effect- not just related to surface area- related to surface chemistry? Confinement ?
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Avrami Modelization
( )[ ]nt tkX −=− exp1
•Xt is the relative crystallinity,• t is the crystallization time• k is the crystallization rate constant (min-1) •n is the Avrami exponent
• Increasing Tc results in slower crystallization: nucleation dominated domain;• Good fit to Avrami equation up to 70% relative crystallinity.
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Avrami Modelization
( )[ ] ktnX t lnln1lnln +=−−
• Avrami parameter varies between 2 and 3: heterogeneous growth with truncated spherulite;• No clear effect of nanocellulose on n.
42 44 46 48 501.50
1.75
2.00
2.25
2.50
2.75
3.00
n
Tc (°C)
PCL PCL-CNW PCL-MFC
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• k is increased ca. 100 fold and t1/2 decreased 10 fold by adding nanocellulose • k is larger and t1/2 is smaller with MFC than with CNW
Avrami Parameters
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3.08 3.10 3.12 3.14 3.16 3.18
-4.5-4.0-3.5-3.0-2.5-2.0-1.5-1.0-0.50.00.51.0
R2=0.9822R2=0.9859
R2=0.9981
1/n
ln(k
)
1/Tc(x10-3)
PCL PCL-CNW PCL-MFC
( )c
a
RTE
kkn
∆−= 0lnln1
Sample Ea (kJ/mol)
PCL 317
PCL-CNW 264
PCL-MFC 242
• Energetics of crystallization are facilitated with addition of CNW and MFC• Effect more marked with MFC than with CNWs
Activation Energy for Crystallization
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Secondary Nucleation Theory: Lauritzen-Hoffman
∆
−−
−=
∞ fTTK
TTRUGG
c
g
c )()(exp
*
0
G : linear lamellar growth rateG0 : growth rate constantU* : diffusional activation energy (1500 cal.mol-1 )T∞ : temperature at which motion ceases (30k below Tg)Kg : nucleation parameter or free energy necessary to form a nucleus of critical size∆T: supercoolingf: correction factor
Transport Nucleation
1.0x10-4 1.2x10-4 1.4x10-4 1.6x10-4
-3.0
-2.0
-1.0
0.0
1.0
2.0
R2=0.99589
R2=0.99937
R2=0.99742
PCL PCL-CNW PCL-MFC
ln(1
/t 1/2)
+ U* /[R
(Tc-T
∞)]
1/(Tc.(∆T).f )
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Secondary Nucleation Theory: Lauritzen-Hoffman
0
04
f
meg Hk
TbK
∆=
βσσ • Kg decreases when adding CNW
and MFC (effect of MFC>CNW)• Decrease of energy barrier of secondary nucleation (MFC>CNW)
• G0 decreases when adding CNW and MFC (effect of MFC> CNW)• Molecular chain mobility significantly reduced by nanocellulose (effect of MFC> CNW)
PCL PCL-CNW PCL-MFC
G0 (min-1) 5.307x105 1.625x104 1.170x104
Kg (K2) 1.434x105 6.381x104 6.091x104
σσe(erg2/cm4) 887.2 404.8 385.6
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Conclusions
• Surface area effect: heterogeneous nucleation effect– Overall degree of crystallinity is greater in nanocomposites (CNW than
MFC)– Energetics of bulk crystallization lowered by nanocellulose – Crystallization expedited
• Surface chemistry effect? – Compatibility (T0m depression)– Energetics of nucleation slightly favored with MFC compared to CNW
(Kg and lamellar surface energies)
• Confinement / transport effect?– Growth rate constant significantly lowered by nanocellulose– Effect more marked with MFC (entanglements) than CNW
Thank you for your attention !
AcknowledgementsALBAN Program for the financial support (PhD
fellowship) of Dr. Gilberto Siqueira Grenoble Polytechnic Institute for financial
support (sabbatical) of Dr. Marie-Pierre Laborie