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Pressure Quench of flow-induced crystallization

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### Pressure Quench of flow-induced crystallization

Putting values to a model for Flow Induced Crystallization (DPI #714,VALFIC)

Zhe Ma, Luigi Balzano, Gerrit WM Peters

Materials Technology

Department of Mechanical Engineering

Eindhoven University of Technology

- Z. Ma, G.W.M. Peters
- Materials Technology
- Department of Mechanical Engineering
- Eindhoven University of Technology

structure

flow strength

depending on the molecular mobility

strong

mild

quiescent

(no flow)

oriented nuclei

point-like nuclei, f(T)

more point-like nuclei

nuclei

[1] Swartjes F.H.M (2001) PhD thesis, Eindhoven University of Technology, NL

[2] Hsiao B.S et al. (2005) Physical Review Letter, 94, 117802

How to observe nuclei:

Small Angle X-ray Scattering (SAXS)

Wide Angle X-ray Diffraction (WAXD)

……

flow

SAXS electron density difference

Limitation: precursors without electron density difference

(or very little concentration)

WAXD crystalline structure

Limitation: non-crystalline precursors

observable

point-like

nuclei

No

crystallization after flow

row nuclei -- No

oriented nuclei

formation during flow

shish nuclei – Yes

observable

point-like

nuclei

crystallization after flow

(kinetics)

No

row nuclei -- No

oriented nuclei

shish nuclei – Yes

develop a method which is (more) reliable, simple, also works with flow.

suspension-based model[1]

?

space fillingf

nucleation density N(T)

measure G*(T)

Avrami Equation

linear viscoelastic three dimensional generalized self-consistent method[2]

Relative dynamic modulus,f*G=G*/G*0

A*, B* and C*determined by ratio of the complex moduli of the continuous phase and dispersed phase, Poisson ratio of both phases: all known,

A*, B* and C* then depend on space filling only.

[1] R.J.A. Steenbakkers et al. Rheol Acta (2008) 47:643

[2] R.M. Christensen et al. J.Mech.Phys.Solids (1979) 27:315

iPP and U-Phthalocyanine(145oC)

method suitable for combined effect of NA and flow

Z Ma et al. Rheol Acta (2011) DOI 10.1007/s00397-010-0506-1

observable

point-like

nuclei

No

crystallization after flow

(orientation and kinetics)

row nuclei -- No

oriented nuclei

shish nuclei – Yes

crystallization:

1. morphology (isotropic or oriented)

2. kinetics (compared with quiescent case)

Undercooling is expected to start crystallization

decrease Texp by fast cooling --- Temperature quench

difficult for large devices

increase Tequilibrium by pressure

--- Pressure quench!

Set-up

Multi-Pass Rheometer (MPR)

Protocol

Erase history at 190oC and cool to 134oC

A apparent wall shear rate: 60 1/s

shear time: 0.8s

300bar

reference 50bar

b

50bar

a

c

a

b

Pressure-quench

Pressure Quench

t=0s

t=17s

flow

highly oriented

crystals

twisted lamellae

row nuclei

Set-up

Multi-Pass Rheometer (MPR)

Protocol

Erase history at 190oC and cool to 134oC

A apparent wall shear rate: 60 1/s

shear time: 0.8s

300bar

reference 50bar

annealing after flow, ta=22min

relaxation of orientation

experimental

theoretical (tube model)

For HMW tail (1,480,000 g/mol) at 134 oC

Long lifetime of orientation

Besides molecular mobility, other effect exists.

relaxation of orientation

theoretical (tube model)

For HMW tail (1,480,000 g/mol) at 134 oC

iPP[1]

Long lifetime of orientation

Besides molecular mobility, other effect exists.

[1] H An et al. J. Phys. Chem. B 2008, 112, 12256

relaxation of orientation

theoretical (tube model)

For HMW tail (1,480,000 g/mol) at 134 oC

iPP[1]

Long lifetime of orientation

Interaction between PE chains (or segments) at 134oC

[1] H An et al. J. Phys. Chem. B 2008, 112, 12256

average nuclei density

specific (200) diffraction

(equatorial, off-axis or meridional)

no annealing

annealing (ta=22min)

randomization of c-axes

content of twisting overgrowth

(nuclei density)

average nuclei density

specific (200) diffraction

(equatorial, off-axis or meridional)

no annealing

annealing (ta=22min)

randomization of c-axes

content of twisting overgrowth

(nuclei density)

some nuclei relax within annealing

lower nuclei density

Pressure Quench with annealing (ta=22min)

orientation

0s 8.5s 34s 93.5s

kinetics – apparent crystallinity

Using Pressure Quench,

it is found that nuclei orientation survives but average nuclei density decreases within annealing.

Z Ma et al. to be submitted

flow field in the slit

X-ray

WAXD results after flow the whole sample

in situ characterization the first formation outer layer (strongest flow)

observable

point-like

nuclei

No

row nuclei -- No

oriented nuclei

formation during flow

shish nuclei – Yes

combining rheology (Multi-pass Rheometer ,MPR) and X-ray

Pilatus

MPR

(30 frame/s)

to track shish formation during flow

combining rheology and X-ray

X-ray

Pilatus

MPR

flow time 0.25s

(30 frame/s)

Pressure difference and shish during flow

For ≥ 240 , pressure difference deviates from the steady state and shows an “upturn”.

results

rheology

“upturn”

wall stress

iPP (HD601CF) at 145oC

rheology

birefringence

0.03

MPa

iPP (PP-300/6) at 141oC[1]

iPP (HD601CF) at 145oC

approach steady state after start-up of flow

[1]G Kumaraswamy et al Macromolecules 1999, 32, 7537

rheology

birefringence “upturn”[1]

“upturn”

0.06

MPa

oriented precursors

iPP (PP-300/6) at 141oC[1]

iPP (HD601CF) at 145oC

∆P “upturn” precursory objects

form faster at higher shear rate

[1]G Kumaraswamy et al Macromolecules 1999, 32, 7537

apparent shear rate of 400s-1 and T = 145oC

1). formation of precursor

flow

∆P “upturn” precursors during flow.

time for precursor formation is around 0.1s

streak

results

apparent shear rate of 400s-1 and T = 145oC

2). from precursor to shish

2D SAXS

time

0.10s

0.20s

0.23s

flow stops at 0.25s

0.26s

0.40s

apparent shear rate of 400s-1 and T = 145oC

2). from precursor to shish

SAXS

2D SAXS

flow

flow

shish

SAXS equatorial Intensity

shish formation around 0.23s

apparent shear rate of 400s-1 and T = 145oC

rheological response

SAXS

flow

flow

shish formation around 0.23s

∆P “upturn” around 0.1s

Precursors develop into shish

apparent shear rate of 560s-1 and T = 145oC

t = 0.13s

t = 0.17s

shish

t = 0.20s

Shish forms during flow, faster at 560s-1 than 400s-1.

apparent shear rate of 320s-1 and T = 145oC

t = 0.26s

t = 0.33s

shish

t = 0.37s

Shish precursors form during flow and shish forms after flow.

SAXS results linked to the FIC model

Nucleation and growth model[1]

growth rate number of nuclei

length growth

total length of shish

[1] F. Custodio et al. Macromol. Theory Simul. 2009, 18, 469

conclusions

innovation

observable

point-like

nuclei

Suspension-based model

- The combined effect of nucleating agent and flow on the nucleation density can be assessed.

No

Pressure Quench

- Formation of row nuclei is visualized.
- Stable nuclei can survive within 22-min annealing.
- Unstable ones relax within 22-min annealing.

row nuclei -- No

oriented nuclei

Combining rheology and synchrotron X-ray

- Shish formation is tracked during flow.
- The shish precursors are formed during flow and further develop into shish.
- Formation times of shish precursors and shish both depend on the flow conditions.

shish nuclei – Yes

Prof. Gerrit Peters

Dr. Luigi Balzano

Ir. Tim van Erp

Ir. Peter Roozemond

Ir. Martin van Drongelen

Dr. Giuseppe Portale

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