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

Background & Objective

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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