Crystalline Fundamental Groups I — Isocrystals on Log Crystalline ...
history dependent specific volume of (semi- crystalline...
Transcript of 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
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introduction
Shrinkage characterization of polymers
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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
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• 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
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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-
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• 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
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T
R~130 μm
R~10 μm
R~75 μm
Δν
ΔT
P = 40 MPa
part 1: influence of cooling rate
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- 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
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influence of shear flowWide Angle X-ray Diffraction (WAXD) patterns (iPP)
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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
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Influence of temperature during flow
193 oC 154 oC 139 oC
193 oC 154 oC 139 oCiPP-1
iPP-2
influence of shear flow
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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
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– 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