PROBING POLYMER CRYSTALLIZATION IN PROCESSING CONDITIONS

(using synchrotron radiation)

D. Cavallo, L. Balzano, G. Portale, G.W.M. Peters, G.C. Alfonso

Synchrotron Radiation in Polymer Science 5 San Francisco, 30th March – 2nd April 2012

Crystallization of polymers in “unperturbed” conditions

Unit cell ~1-10 Å

Chain folded lamellae ~10 nm

Spherulites ~10-100 μm

Hierarchical organization

Crystallization of polymers in “unperturbed” conditions

Crystallization kinetics

Growth of PLLA spherulites,

Optical Microscopy

Polymer processing

Combined application of:

HIGH COOLING RATES

( 101-103 K/s )

FLOW FIELDS

( 10-1-103 s-1 )

Crystallization of polymers in “real” conditions

Injection molded sample

Final structure depends on local

thermo-mechanical history

Outline

Crystallization under fast cooling conditions

Effect of flow on crystallization

Structure formation during real processing

“Model” experiments

Fast cooling: Continuous-Cooling-Transformation

diagrams

Very important for steel technology, (almost) neglected for semicrystalline

polymers

DUBBLE@ESRF, March 2010

Acq. time 0.05 s

Experimental method

Quenching devicecooling rate up to

≈200°C/s

Case 1: Polymorphism of quenched isotactic polypropylene

D. Mileva, et al. Polymer 2009, 50, 5482

Q. Zia et al.Polym. Bull. 2008, 60, 791

An actual experiment

Continuous-Cooling-Transformation diagram of i-PP

Prevailing mesophase

Prevailing alpha phase

Mixed structure

Effect of comonomer on CCT diagrams

Effect of comonomer on CCT diagrams

Case 2: Polymorphism of quenched polyamide 6

a-phase

mesophase

• monoclinic• themodynamically stable• sheet-like hidrogen bonding

• pseudo-hexagonal• metastable• irregular hidrogen bonding

a-phase

mesophase

amorphous

Continuous – Cooling –Transformation diagrams of PA6

PA6 18kDa

Flow induced crystallization:consequences

Flow induced crystallization:causes

melt

FLOW

dissolution of flow induced structures

nucleating effect on crystallization

cluster of (locally) oriented chain

segments

X-raydiamond windows

(30 frame/s)Multi-pass rheometer @ DUBBLE, ESRF

Flow induced crystallization: experimental methods

Pilatus

Rotational shearing device Linkam CSS 450 coupled with SAXS at Beamline A2 HASYLAB/DESY

Flow induced crystallization: experimental methods

i-PP, “apparent” shear rate of 560s-1 ; T = 145 °C

shish

SAXS WAXD

(110)(040

)(130)

(110)

(110)

time

0.17s

0.20s

0.27s

0.13s

What happens during flow

FLOW STOPS

Crystallization onset time in flow

10-1sQuiescient onset time

103s

Effect of flow induced structures on rheologyRheology

iPP , T = 145 °C

wall stress

DP = P bottom - P top

Huge increase in viscosity during shear: “suspension” of shishes

Dissolution of shear-induced nucleation precursors: indirect

evidencesRelaxation effect on

crystallization kineticsRelaxation effect on crystal orientation

Dissolution of shear-induced nucleation precursors: mechanism

Relaxation temperature

increases

Rate controlling step:detachment of segments from

the surface of oriented clusters

X-ray beam (fixed height)

Die exit

Take-up direction

2D WAXD detector

(fixed position)

Crystallization during real processing : in-situ study of film

blowing

X-ray beam (fixed height)

Die exit

Take-up direction

2D WAXD detector

(fixed position)

Crystallization during real processing : in-situ study of film

blowing

Film blowing at synchrotron facilities : experimental setup

Collin Blown Film Unit type 180

Die-extruder on a manually operated hydraulic lifter

Film blowing at synchrotron facilities : experimental setup

Data analysis: WAXD patterns vs. axial position

b

a

c

Results

BUR= final bubble

diameter/bubble diameter at the die

TUR= take-up

velcoity/velocity at the die exit

Bubble kinematics

Video tracker technique

Machine direction

Velocity profiles

“Corrected” results

Elongation in both machine and

transverse direction affects crystallization

kinetics

Acknowledgments(this work would not have been possible without...)

Wim Bras, BM26/DUBBLE - ESRF, Grenoble (France)

Daniel Hermida-Merino, BM26/DUBBLE - ESRF, Grenoble (France)

Florian Ledrappier, BM26/DUBBLE - ESRF, Grenoble (France)

Sergio Funari, A2 - HASYLAB, DESY (Germany)

Daniela Mileva, University of Halle (Germany)

Renè Androsch, University of Halle (Germany)

Zhe Ma, Eindhoven University of Technology (The Netherlands)

Roberto Floris , University of Genova (Italy)

Lorenza Gardella, University of Genova (Italy)