history dependent specific volume of (semi- crystalline...

Dutch Polymer Institute (DPI), Materials Technology (MaTe)Eindhoven University of Technology

history dependent specific volume of (semi-crystalline) polymers

Gerrit W.M. Peters,www.mate.tue.nl

outline

1. introduction

2. crystallization of polymers- Modelling- pVT-behavior

3. how to measure the influence of flow

4. results

5. conclusions

Shrinkage characterization of polymers

3

introduction

Shrinkage characterization of polymers

4

Mold

(Product Cavity)

Screw

Heated Cylinder

Raw material input

introduction

• During cooling:

– thermal contraction– phase changes

Decrease of volume per unit mass

( = specific volume)

Shrinkage / Warpage

introduction

dimensional stability & accuracy of injection moulded productsamorphous polymers

dimensional stability of PS stored @ 70 0 CPhD Thesis Leo Caspers, 1995

introduction

dimensional stability & accuracy of injection moulded productssemi-crystalline polymers

introduction

evolution of yield stress with time: physical ageing

Tom A.P. Engels,Leon E. Govaert, Gerrit W.M. Peters, Han E.H. Meijer

introductionpredicting mechanical performance of polymers

directly from processing conditions

product

simulation of filling and cooling using MoldFlowTM

processing induced property development

thermal history over thickness

introduction

resulting yield stress distribution dependence on mold temp.

yield stress varies over thickness!

processing induced property developmentintroduction

processing induced property development

validation

90 cc/s, melt 285 oC, cooling time 60 s

check mechanical performance

introduction

both short-term and long-term deformation kinetics are captured !

rate dependent yield stress long-term failure

introductionprocessing induced property development

experimental numericalvalidation

‘complex’ geometry predict thermodynamic state Sa from IM process

Tm=30˚C Tm=130˚C

mechanical evaluation

Introductionprocessing induced property development

deformation kinetics also captured for more complex geometries!

rate dependent maximum load long-term failure

introductionprocessing induced property development

mechanical performance and influence of flow of injection moulded productssemi-crystalline polymers (non solved problem)

introductionprocessing induced property development

outline

1. introduction

2. crystallization of polymers- Modelling- pVT-behavior

3. how to measure the influence of flow

4. results

5. conclusions

modelling of crystallizationquiescent and flow-induced crystallization

quiescent crystallization: Schneider’s equations

modelling of crystallization

quiescent crystallization: kinetics

modelling of crystallization

flow-induced crystallization: viscoelastic modelling

modelling of crystallization

flow-induced crystallization: results of viscoelastic modelling

modelling of crystallization

outline

1. introduction

2. crystallization of polymers- Modelling- pVT-behavior

3. how to measure the influence of flow

4. results

5. conclusions

‘Spherulite’

‘Crystals’

Introduction: specific volume

• Asymptotic pVT-data:– ‘slow cooling’ experiments– empiric

• Coupled crystallization kinetics: – Schneider + Eder– impingement: Avrami– 1 crystalline phase

theory

crystallization of polymers: pVT-behavior

crystallization of polymers: pVT-behavior

crystallization of polymers: pVT-behavior

crystallization of polymers: pVT-behavior

pressure: 0.1 MPa

predictions for different cooling rates and high pressures

crystallization of polymers: pVT-behavior

0.1 [ºC/s] 100 [ºC/s]

crystallization of polymers: pVT-behavior

outline

1. introduction

2. crystallization of polymers- Modelling- pVT-behavior

3. how to measure the influence of flow

4. results

5. conclusions

• Observations:– slow developments in modeling specific volume– present models deserve better experimental validation– influence ‘flow’ ?

• Problem definition:– general lack of experimental data for model validation– commercially available equipment not relevant to industrial

processing conditions– no technique present to investigate influence ‘flow’

influence of flow: problem definition

Shrinkage characterization of polymers

33

• Design and building of a dedicated dilatometer to measure specific volume as a function of thermal-mechanical history

• To quantify the influence of thermal-mechanical history ( P,T,T,γ,γ ) on the specific volume of semi-crystalline polymers

• To perform experiments near industrial processing conditions

• •

a new design: objectives

••

experimental methods

Shrinkage characterization of polymers

35

A)

B)

C)

experimental methods- design-

experimental methods- final design-

experimental methods

- prototype dilatometer-

• Correction for thermal gradients:

– conduction + crystallization heat

– N homogeneously cooled layers, ∂T/∂x ≤ 1 [°C]

– Over-all specific volume to compare with experiments

– viscous heating neglected

experimental methods- thermal issues-

Shrinkage characterization of polymers

39

• Procedure

– A) Heating ~ 10 oC/min

– B) Holding Tmax ~ 10 min

– C) Pressurizing

– D) Isobaric cooling

– E) Shear flow

T

tP

t

t

.γ

[s-1]

[Pa]

[ºC]A)

B)

D)

C)

E)

experimental procedure

shearing cooling

experimental methods- testing -

• Confined Compression(Δx ~ ΔV)

• shear rate ≤ 80 [1/s]• shear ≤ 110 [-]• P ≤ 100 [MPa]• T ≈ 101 - 102 [K/s]

• MTS 858 Mini Bionix(axial-torsional)

(we broke already a few pressure cells)

·

·

experimental methods- summary -

a new dilatometer

features of the dilatometer: p

features of the dilatometer: V

features of the dilatometer: T

features of the dilatometer: T●

features of the dilatometer: Y●

control software

control software

sample preparation

• Density Gradient Column– reference specific volume

• Optical Microscopy– morphology (10 - 100 μm)

• WAXD– degree of crystallinity– orientation of crystallites

characterization: experimental methods

computer (automate)manualControl

300 ºC300 ºCTemperature

100 ºC/s100 ºC/sCooling rate

100 MPa100 MPaPressure

200 s-180 s-1Shear rate

no limit (g=135/ round)270º (g=104)Rotation angle

New DesignPrototype

features

outline

1. introduction

2. crystallization of polymers- Modelling- pVT-behavior

3. how to measure the influence of flow

4. results

5. conclusions

• Materials:

– iPP-K2XMOD: Mw = 365 [kg/mol], Mw/Mn = 5.4 (Borealis )

• CF- Dilatometer (Gnomix) – (Moldflow)

validation of the set-up

validation of the set-up

• Materials:

– iPP-1: Mw = 365 [kg/mol], Mw/Mn = 5.2 ( HD120MO, Borealis )

– iPP-2: Mw = 500 [kg/mol], Mw/Mn = 6.0 ( Stamylan P13E10, DSM )

influence of cooling rate and shear flow

Shrinkage characterization of polymers

57

T

R~130 μm

R~10 μm

R~75 μm

Δν

ΔT

P = 40 MPa

part 1: influence of cooling rate

Shrinkage characterization of polymers

58

- Morphology analysis

• WAXD– ESRF, Grenoble (France)– Materials Beamline ‘ID11’– λ = 0.4956 Å– Beam area = 0.2 x 0.2 mm

• ESEM– Philips XL30 ESEM

‘Prepared’ Sample

influence of shear flow

Shrinkage characterization of polymers

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influence of shear flowWide Angle X-ray Diffraction (WAXD) patterns (iPP)

Shrinkage characterization of polymers

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Influence of pressure during flow

P = 20 MPa P = 40 MPa

P = 60 MPa

Material: iPP-1 (Mw = 365 kg/mol)

P = 20 - 60 Mpa

Cooling rate = 1.4 oC/s

Shear rate = 78.0 1/s for 1.5 s

Tγ = 140 oC

T = 140 oC

influence of shear flow

Shrinkage characterization of polymers

61Measurements: M.E.H.v.d.Beek

influence of shear flowInfluence of temperature during flow

Shrinkage characterization of polymers

62Measurements: M.E.H.v.d.Beek

influence of shear flowInfluence of temperature during flow

Shrinkage characterization of polymers

63

Influence of temperature during flow

193 oC 154 oC 139 oC

193 oC 154 oC 139 oCiPP-1

iPP-2

influence of shear flow

Shrinkage characterization of polymers

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0 50 100 150 200 250 3000,0

0,2

0,4

0,6

0,8

1,0

v* [-]

T [C]

P = 20 MPa P = 40 MPa

0 50 100 150 200 250 3000,0

0,2

0,4

0,6

0,8

1,0

P = 40 MPa

v* [-]

T [C]

quiescent T = 250C T = 260C

influence of pressure: nylon 6.6

influence of pressure & shear flow: HDPE

Temperature of flow

outline

1. introduction

2. crystallization of polymers- Modelling- pVT-behavior

3. influence of flow

4. conclusions

Shrinkage characterization of polymers

67

– a fully automated dilatometer was built to measure the influence of cooling rate and shear flow on specific volume

– quantitatively measured the influence of thermal-mechanical history on specific volume at (near-) industrial processing conditions

– crystallization kinetics enhanced with: P ↑, T ↓, Mw ↑

– near future: isothermal measurements:

conclusions