L. Balzano, S. Rastogi, G.W.M. PetersDutch Polymer Institute (DPI)

Eindhoven University of Technology

tailoring the molecular weight distribution of polyethylene for flow-enhanced self-nucleation

1930sbranched PE

1950slinear PE and isotactic PP

2000s

explore the ultimate properties of

existing polymers by controlling:

• additives

• processing conditions

1980smetallocene

breakthroughs

polyolefins

polyethylene (PE) polypropylene (PP)

without flow

with flow

pressure

a

b

c

d

process morphology properties

cooling rate

a) Basset, D.C.et al. Phyl Trans Roy Soc London A 1994 b) Hobbs, J.K. et al. Macromolecules 2001 c) Androsch, R. Macromolecules, 2008

motivation

understand structure formation at molecular level

design materials that after processing have morphology (=properties) tailored for their application

polymer molecules

properties crystallization glass formation physical aging

physical processes

processing conditions

without flow

with flow

pressure

a) Basset, D.C.et al. Phyl Trans Roy Soc London A 1994 b) Hobbs, J.K. et al. Macromolecules 2001 c) Androsch, R. Macromolecules, 2008

a

b

c

d

cooling rate

process morphology properties

self-nucleation: introduction

Fillon, B. et al Journal of Polymer Science Part B: Polymer Physics 1993, 31, (10), 1383-1393

Banks, W. et al Polymer 1963, 4, 289-302Blundell, D. J. et al. J. Polym. Sci., Polym. Letters 1966, 4, 481-486

self-nucleation: introduction

Fillon, B. et al Journal of Polymer Science Part B: Polymer Physics 1993, 31, (10), 1383-1393

Banks, W. et al Polymer 1963, 4, 289-302Blundell, D. J. et al. J. Polym. Sci., Polym. Letters 1966, 4, 481-486

self-nucleation: introduction

crystal fragments, obtained with partial melting, are used as nucleating agents

iPP

our goal: self-nucleation with flow

can we generate crystal fragments (at high temperature) with flow that can be used as

nucleating agent?

what are the controlling parameters?

what is their efficiency (Tc)?

1S S

relaxationtimescaleDe

deformationtimescalet g= = >&

s ctg g g= >&

our goal: self-nucleation with flow

fibrillar crystallites

deformation

coils

deformation

1S S

relaxationtimescaleDe

deformationtimescalet g= = >&

s ctg g g= >&

coils

our goal: self-nucleation with flow

fibrillar crystallites

Cr catalyst → low Mw

Kukalyekar, N. et al. Macromolecular Reaction Engineering 2009, 3, (8), 448 - 454

Fe catalyst → high Mw

preparation of bimodal PE blendssynthetic route

Cr catalyst → low Mw

Kukalyekar, N. et al. Macromolecular Reaction Engineering 2009, 3, (8), 448 - 454

Fe catalyst → high Mw

preparation of bimodal PE blendssynthetic route

Cr catalyst → low Mw

Kukalyekar, N. et al. Macromolecular Reaction Engineering 2009, 3, (8), 448 - 454

Fe catalyst → high Mw

preparation of bimodal PE blendssynthetic route

[Fe catalyst][Cr catalyst]

Cr Cr+Fe

LMW Mw=5.5·104 g/mol Mw/Mn=3.4

HMW Mw=1.1·106 g/mol Mw/Mn=2.3

Mw=7.0·104 g/mol Mw/Mn=3.5

7 wt% (C*=0.5 wt%)

Balzano L et al., Macromolecules 2011, ASAPKukalyekar, N. et al. Macromolecular Reaction Engineering 2009, 3, (8), 448 - 454

specimens

unimodal bimodal

isothermal crystallization after pulse of shear30s-1 for 2s

T effect on crystallization

with HMW molecules, crystallization can take place at higher T (under the influence of flow)

Balzano L et al., Macromolecules 2011, ASAPLinkam Shear Cell (CSS-450)

flow induced crystallization near T0m

120s-1 for 1s at 142ºC

1HMWS

De >

Balzano L. et al. Physical Review Letters 2008, 100, 048302

flow induced crystallization near T0m

120s-1 for 1s at 142ºC

fibrillar scatterers only

1HMWS

De >

Balzano L. et al. Physical Review Letters 2008, 100, 048302

crystallizationdissolution

melt

precursor

nucleation

propagation(1 D)

shishprecursor

melt

size-dependent dynamics of fibrils• fibrillar scatterers• decreasing equatorial SAXS• increasing crystallinity

self-nucleation with flow

shishes are excellent for heterogeneous nucleation increase Tc

template orientation

120s-1 for 1s at 142ºC

1HMWS

De >

our goal: self-nucleation with flow

can we generate crystal fragments (at high temperature) with flow that can be used as

nucleating agent?

what are the controlling parameters?

what is their efficiency?

peculiarity: critical strain

Balzano L et al., Macromolecules 2011, ASAP

because of the high concentration of long molecules, the formation of shishes is governed by strain

100s-1 1s50s-1 2s25s-1 4s5s-1 20s

50s-1 1s25s-1 2s10s-1 5s5s-1 10s

25s-1 1s5s-1 5s2s-1 12.5s

stg g= & shear

rateshear time

shear at 142ºC

cooling at 5°C/min Balzano L et al., Macromolecules 2011, ASAP

inverse space real space

strain 100 at 142ºC

self-nucleation with flow

Balzano L et al., Macromolecules 2011, ASAPcooling at 5°C/minmore oriented ↔ higher Tc

isotropic

shish-kebab

strain

strain

2(3 cos 1) / 2SAXS

HF

self-nucleation with flow

room temperature morphology

Balzano L et al., Macromolecules 2011, ASAP

more oriented ↔ higher Tc ↔ thicker lamellae

room temperature morphology

Balzano L et al., Macromolecules 2011, ASAP

Dew 0.07 0.2 0.4 0.9 1.8 3.5

Dez 0.4 0.9 1.9 4.7 9.5 18.9

room temperature morphology

200 μ

m

flow

specimen sheared at 142°C with 100s-1 for 1s and cooled at 5°C/min

Balzano L et al., Macromolecules 2011, ASAP

distance between shishes between 300 and 800 nm

0.5μm

0.5μm

room temperature morphologyspecimen sheared at 142°C

with 100s-1 for 1s and cooled at 5°C/min

Balzano L et al., Macromolecules 2011, ASAP

distance between shishes between 300 and 800 nm

0.2μm

conclusions

• with HMW molecules, shishes can be formed around T0m

• shishes formed around T0m are an excellent substrate for heterogeneous

nucleation of bulk molecules

• with an excess (~10·C*) of HMW molecules, morphology during cooling (after step shear) is ruled by macroscopic strain (i.e. minimum strain/shear time for oriented morphology)

a ‘smart’ combination of materials and processing conditions can be used for self-nucleation of polymer melts

reducing the need for additives for nucleation and morphology control

MWD can be tailored for flow-enhanced self-nucleation with incorporation of HMW molecules

X-ray scattering experiments

performed at the beamlines ID02 and BM26

Linkam CSS-450

nucleation is the limiting step in polymer crystallization kinetics

crystal growth only possible when ΔG<0

self-nucleation: rationale

tot v i ii

G V G A

critical size!

negative positive

surface

volume

σi

nucleation is the limiting step in polymer crystallization kinetics

crystal growth only possible when ΔG<0

tot v i ii

G V G A

critical size!

surface

volume

σiσi/2

negative positive

self-nucleation: rationale

heterogeneous nucleation

smaller critical size

nucleation is the limiting step in polymer crystallization kinetics

crystal growth only possible when ΔG<0

σiσi/2

tot v i ii

G V G A

critical size!

negative positive

self-nucleation: rationale

surface

volume

heterogeneous nucleation

smaller critical size higher Tc

melting of shish-kebabs

shishes melt at higher temperature increased stability result of the ECC structure