structure development and

mechanical performance

of oriented isotactic polypropylene

15th International Conference on DYFP1-5 April 2012, Rolduc Abbey, The Netherlands

T.B. van Erp, L.E. Govaert, G.W.M. Peters

introduction: polymer crystallization

quiescent

pressure

fast cooling

with flow

melt

typical cross section of injection molded semi-crystalline polymer part

beamspot 10μm, ID13 @ ESRF

skin layer

rapid cooling (~100 °C s-1)

shear layer core layer

flow induced crystallization

(~1000 s-1)

pressure induced crystallization(~1000 bar)

introduction: injection molding

introduction: influence of processing

deformation kinetics: influence of processing

factor 500 in lifetime for different directions

constant strain rate constant applied stress

rapid cooling (~100 °C s-1)

flow induced crystallization

(~1000 s-1)

pressure induced crystallization(~1000 bar)

motivation

need for controlled and homogeneous structure formation

extended dilatometry (1)

Pirouette: a dedicated dilatometer that can perform experiments near processing conditions

Quantify influence of thermal-mechanical historyon specific volume of (semi-crystalline) polymers

),,,,( pTT

sample weight: ~75 mg

extended dilatometry (2)

M.H.E. van der Beek et al., Macromolecules (2006)

Ts=193 °C Ts=133 °C

Pirouette: a dedicated dilatometer that can perform experiments near processing conditions

Quantify influence of thermal-mechanical historyon specific volume of (semi-crystalline) polymers

),,,,( pTT

processing protocol

Annealing 10 min @ 250°C

Compressed air cooling @ ~1°C/s

Isobaric mode

Pressures: 100 – 500 – 900 – 1200 bar

Short term shearing of ts = 1s

Shear rates: 3 - 10 – 30 – 100 – 180 s-1

Ts = Tm(p) – ∆Ts with ∆Ts = 30 - 60°C

evolution of specific volume (1)

effect of shear rate

evolution of specific volume (2)

effect of shear temperature

pronounced effect of shear flow at lower shear temperature

evolution of specific volume (3)

higher pressure enhances the effect of shear

effect of shear effect of pressure

analysis crystallization kinetics

,

,

c onsetQ

c onset

T

T

dimensionlesstransition temperature

,

,

c onsetQ

c onset

T

T

dimensionlesstransition temperature

T pWi a a

Weissenberg number (‘strength of flow’)

WLF Temperature shift

Pressure shift

1

2

log shear refT

shear ref

c T Ta

c T T

expp refa p p

analysis crystallization kinetics

J. van Meerveld et al., Rheol. Acta (2004); M.H.E. van der Beek et al., Macromolecules (2006)

,

,

c onsetQ

c onset

T

T

dimensionlesstransition temperature

flow regimes (1)

,

,

c onsetQ

c onset

T

T

dimensionlesstransition temperature

flow regimes (1)

from spherulitic morphology to oriented structures

flow regimes (2)

I) No influence of flowII) Flow enhanced (point-like) nucleationIII) Flow induced crystallization of oriented structures

classification of flow regimes

modeling quiescent crystallization

space filling

3

2 3

1 2

0 1

8

G

G

G

2

max, , ,, ( )expi i G i Gref iG T p G p c T T p

max, exp N NrefN T p N c T T p

Schneider rate equations

Avrami equation

nucleation density

growth rate

3

2

1

0

( 8 )

( 4 )

( )

( )

tot

tot

tot

N

R

S

V

0ln 1

‘number’

‘radius’

‘surface’

‘undisturbed volume’

‘real volume’

flow-induced crystallization model

tot q fN N N total nucleation density

(flow-induced) nucleation rate

shish length (L) growth

rate equations

Avrami equation

4 1f n hmwN g

‘length’

‘surface’

‘undisturbed volume’

‘real volume’

R.J.A. Steenbakkers and G.W.M. Peters, J. Rheol. (20011); P.C. Roozemond et al., Macromol. Theory Simul. (2011)

flow-induced crystallization model

tot q fN N N total nucleation density

(flow-induced) nucleation rate

shish length (L) growth

rate equations

Avrami equation

4 1f n hmwN g

4 1l avgL g

‘length’

‘surface’

‘undisturbed volume’

‘real volume’

,n ng g T p

,l lg g T p

R.J.A. Steenbakkers and G.W.M. Peters, J. Rheol. (20011); P.C. Roozemond et al., Macromol. Theory Simul. (2011)

flow-induced crystallization model

2

1 2

0 1

4 fN L

G

G

tot q fN N N total nucleation density

(flow-induced) nucleation rate

shish length (L) growth

rate equations

Avrami equation 0 0ln 1

4 1f n hmwN g

4 1l avgL g

‘length’

‘surface’

‘undisturbed volume’

‘real volume’

,n ng g T p

,l lg g T p

prediction of number, size, type and orientation of crystalline structuresfor pressure and flow-induced crystallization

R.J.A. Steenbakkers and G.W.M. Peters, J. Rheol. (20011); P.C. Roozemond et al., Macromol. Theory Simul. (2011)

prediction of flow regimes

effects of pressure and shear flow on crystallization kinetics captured

mechanical performance

mechanical performance

influence of orientation

T.B. van Erp et al., Macromol. Mater. Eng. (2012)

T.B. van Erp et al., J. Polym. Sci., Part B: Polym. Phys., (2009)

influence of orientation

relation between yield stress and orientation still an open issue

conclusions

rheological classification of flow-induced crystallization of polymers by incorporating in a controlled way the effect of pressure, under cooling and the effect of flow.

a molecular stretch based model for flow induced crystallization provides detailed structure information in terms of number, size and degree of orientation

promising route for determining processing-structure-property relations

structure developmentand

mechanical performance

of oriented isotactic polypropylene

T.B. van Erp, L.E. Govaert, G.W.M. PetersMechanical Engineering DepartmentEindhoven University of Technology