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 pressure fast cooling with flow melt

typical cross section of injection molded semi-crystalline polymer part beamspot 10 μm, 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 rateconstant 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 history on specific volume of (semi-crystalline) polymers sample weight: ~75 mg

extended dilatometry (2) M.H.E. van der Beek et al., Macromolecules (2006) T s =193 °CT s =133 °C  Pirouette: a dedicated dilatometer that can perform experiments near processing conditions  Quantify influence of thermal-mechanical history on specific volume of (semi-crystalline) polymers

processing protocol Annealing °C Compressed air ~1°C/s Isobaric mode Pressures: 100 – 500 – 900 – 1200 bar Short term shearing of t s = 1s Shear rates: – 30 – 100 – 180 s -1 T s = T m (p) – ∆T s with ∆T s = °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 sheareffect of pressure

analysis crystallization kinetics dimensionless transition temperature

Weissenberg number (‘strength of flow’) WLF Temperature shift Pressure shift analysis crystallization kinetics J. van Meerveld et al., Rheol. Acta (2004); M.H.E. van der Beek et al., Macromolecules (2006)

dimensionless transition temperature flow regimes (1)

dimensionless transition temperature flow regimes (1)

from spherulitic morphology to oriented structures flow regimes (2)

I)No influence of flow II)Flow enhanced (point-like) nucleation III)Flow induced crystallization of oriented structures classification of flow regimes

modeling quiescent crystallization space filling Schneider rate equations Avrami equation nucleation density growth rate ‘number’ ‘radius’ ‘surface’ ‘undisturbed volume’ ‘real volume’

flow-induced crystallization model total nucleation density (flow-induced) nucleation rate shish length (L) growth rate equations Avrami equation ‘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 total nucleation density (flow-induced) nucleation rate shish length (L) growth rate equations Avrami equation ‘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 total nucleation density (flow-induced) nucleation rate shish length (L) growth rate equations Avrami equation ‘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

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 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