structure development
and
mechanical performance
of oriented isotactic polypropylene
15th International Conference on DYFP
1-5 April 2012, Rolduc Abbey, The Netherlands
T.B. van Erp, L.E. Govaert, G.W.M. Peters
introduction: polymer crystallization
quiescent
melt
pressure
fast cooling
with flow
introduction: injection molding
typical cross section of injection
molded semi-crystalline polymer part
skin layer
shear layer
core layer
rapid cooling flow induced pressure induced
(~100 °C s-1) crystallization crystallization
(~1000 s-1)
(~1000 bar)
beamspot 10μm, ID13 @ ESRF
introduction: influence of processing
deformation kinetics: influence of processing
constant strain rate
constant applied stress
factor 500 in lifetime for different directions
motivation
rapid cooling flow induced pressure induced
(~100 °C s-1) crystallization crystallization
(~1000 s-1)
(~1000 bar)
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 history (T ,T, p, , )
on specific volume of (semi-crystalline) polymers
sample weight: ~75 mg
extended dilatometry (2)

Pirouette: a dedicated dilatometer that can perform experiments
near processing conditions

Quantify influence of thermal-mechanical history (T ,T, p, , )
on specific volume of (semi-crystalline) polymers
Ts=193 °C
Ts=133 °C
M.H.E. van der Beek et al., Macromolecules (2006)
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)
effect of shear
effect of pressure
higher pressure enhances the effect of shear
analysis crystallization kinetics
dimensionless
transition temperature

Tc,onset
TcQ,onset
analysis crystallization kinetics
Weissenberg number
(‘strength of flow’)
Wi  aT ap
WLF Temperature shift
log  aT  
dimensionless
transition temperature

c1 Tshear  Tref 
c2  Tshear  Tref 
Pressure shift
ap  exp    p  pref  
Tc,onset
TcQ,onset
J. van Meerveld et al., Rheol. Acta (2004); M.H.E. van der Beek et al., Macromolecules (2006)
flow regimes (1)
dimensionless
transition temperature

Tc,onset
TcQ,onset
flow regimes (1)
dimensionless
transition temperature

Tc,onset
TcQ,onset
flow regimes (2)
from spherulitic morphology to oriented structures
classification of flow regimes
I) No influence of flow
II) Flow enhanced (point-like) nucleation
III) Flow induced crystallization of oriented structures
modeling quiescent crystallization
space filling
Schneider rate equations
Avrami equation
nucleation density
growth rate
3  8
(3  8 N )
‘number’
2  G3
(2  4 Rtot )
‘radius’
1  G2
(1  Stot )
‘surface’
0  G1
(0  Vtot )
‘undisturbed volume’
 ln 1    0
‘real volume’
N T , p   Nmax exp  cN T  TNref  p  
2
Gi T , p   Gmax,i ( p)exp cG,i T  TGref ,i  p   


flow-induced crystallization model
total nucleation density
(flow-induced) nucleation rate
Ntot  Nq  Nf


4
Nf  g n  hmw
1
shish length (L) growth
rate equations
‘length’
‘surface’
‘undisturbed volume’
Avrami equation
‘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
total nucleation density
(flow-induced) nucleation rate
shish length (L) growth
rate equations
Ntot  Nq  Nf


4
Nf  g n  hmw
1


4
L  g l  avg
1
gn  gn T , p 
gl  gl T , p
‘length’
‘surface’
‘undisturbed volume’
Avrami equation
‘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
total nucleation density
(flow-induced) nucleation rate
shish length (L) growth
rate equations
Avrami equation
Ntot  Nq  Nf


4
Nf  g n  hmw
1


4
L  g l  avg
1
 2  4 Nf L
 1  G 2
 0  G 1
 ln 1    0  0
gn  gn T , p 
gl  gl T , p
‘length’
‘surface’
‘undisturbed volume’
‘real volume’
prediction of number, size, type and orientation of crystalline structures
for 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., J. Polym. Sci., Part B: Polym. Phys., (2009)
T.B. van Erp et al., Macromol. Mater. Eng. (2012)
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-structureproperty relations
structure development
and
mechanical performance
of oriented isotactic polypropylene
T.B. van Erp, L.E. Govaert, G.W.M. Peters
Mechanical Engineering Department
Eindhoven University of Technology