DYFP Tim van Erp 4 april 2012

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