tailoring the molecular weight distribution of
polyethylene for flow-enhanced self-nucleation
L. Balzano, S. Rastogi, G.W.M. Peters
Dutch Polymer Institute (DPI)
Eindhoven University of Technology
polyolefins
high
dielectric
properties
barrier,
transparency
lightweight
mechanical
properties, durability
breakthroughs
1930s
branched PE
1950s
linear PE and isotactic PP
polyethylene (PE)
1980s
metallocene
polypropylene (PP)
2000s
explore the ultimate properties of
existing polymers by controlling:
• additives
• processing conditions
process
morphology
properties
without flow
a
with flow
b
cooling rate
c
pressure
d
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
physical processes
 crystallization
 glass formation
 physical aging
processing conditions
properties
process
morphology
properties
without flow
a
with flow
b
cooling rate
c
pressure
d
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
self-nucleation: introduction
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, 289-302
Blundell, D. J. et al. J. Polym. Sci., Polym. Letters 1966, 4, 481-486
self-nucleation: introduction
iPP
crystal fragments, obtained with partial melting, are used as
nucleating agents
Fillon, B. et al Journal of Polymer Science Part B: Polymer Physics 1993, 31, (10), 1383-1393
Banks, W. et al Polymer 1963, 4, 289-302
Blundell, D. J. et al. J. Polym. Sci., Polym. Letters 1966, 4, 481-486
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)?
our goal: self-nucleation with flow
coils
deformation
fibrillar crystallites
relaxat ion t im e scale
D eS =
deform at ion t im e scale
g = g&t s > g c
= t S g&> 1
our goal: self-nucleation with flow
coils
deformation
fibrillar crystallites
relaxat ion t im e scale
D eS =
deform at ion t im e scale
g = g&t s > g c
= t S g&> 1
preparation of bimodal PE blends
synthetic route
Cr catalyst
→ low Mw
Fe catalyst
→ high Mw
Kukalyekar, N. et al. Macromolecular Reaction Engineering 2009, 3, (8), 448 - 454
preparation of bimodal PE blends
synthetic route
Cr catalyst
→ low Mw
Fe catalyst
→ high Mw
Kukalyekar, N. et al. Macromolecular Reaction Engineering 2009, 3, (8), 448 - 454
preparation of bimodal PE blends
synthetic route
Cr catalyst
→ low Mw
[Cr catalyst]
Fe catalyst
→ high Mw
[Fe catalyst]
Kukalyekar, N. et al. Macromolecular Reaction Engineering 2009, 3, (8), 448 - 454
specimens
Cr
Cr+Fe
Mw=7.0·104 g/mol Mw/Mn=3.5
LMW Mw=5.5·104 g/mol Mw/Mn=3.4
HMW Mw=1.1·106 g/mol Mw/Mn=2.3
7 wt% (C*=0.5 wt%)
Balzano L et al., Macromolecules 2011, ASAP
Kukalyekar, N. et al. Macromolecular Reaction Engineering 2009, 3, (8), 448 - 454
T effect on crystallization
isothermal crystallization after pulse of shear
30s-1 for 2s
unimodal
bimodal
with HMW molecules, crystallization can take place at higher T
(under the influence of flow)
Linkam Shear Cell (CSS-450)
Balzano L et al., Macromolecules 2011, ASAP
flow induced crystallization near T0m
120s-1 for 1s at 142ºC
HM W
D eS
> 1
Balzano L. et al. Physical Review Letters 2008, 100, 048302
flow induced crystallization near T0m
120s-1 for 1s at 142ºC
HM W
D eS
> 1
fibrillar scatterers only
Balzano L. et al. Physical Review Letters 2008, 100, 048302
size-dependent dynamics of fibrils
• fibrillar scatterers
• decreasing equatorial SAXS
• increasing crystallinity
dissolution
crystallization
melt
melt
precursor
precursor
nucleation
propagation
(1 D)
shish
self-nucleation with flow
120s-1 for 1s at 142ºC
HM W
D eS
> 1
shishes are excellent for heterogeneous nucleation
 increase Tc
 template orientation
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
shear at 142ºC
g = g&t s
shear
rate
shear
time
100s-1
50s-1
25s-1
5s-1
1s
2s
4s
20s
50s-1
25s-1
10s-1
5s-1
1s
2s
5s
10s
25s-1
5s-1
2s-1
1s
5s
12.5s
because of the high concentration of long molecules,
the formation of shishes is governed by strain
Balzano L et al., Macromolecules 2011, ASAP
self-nucleation with flow
strain 100 at 142ºC
inverse space
cooling at 5°C/min
real space
Balzano L et al., Macromolecules 2011, ASAP
self-nucleation with flow
strain
shish-kebab
isotropic
F
SA X S
H
 (3 cos   1) / 2
2
strain
more oriented ↔ higher Tc
cooling at 5°C/min
Balzano L et al., Macromolecules 2011, ASAP
room temperature morphology
more oriented ↔ higher Tc ↔ thicker lamellae
Balzano L et al., Macromolecules 2011, ASAP
room temperature morphology
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
Balzano L et al., Macromolecules 2011, ASAP
room temperature morphology
specimen sheared at 142°C
with 100s-1 for 1s and cooled at 5°C/min
0.5μm
distance between shishes between 300 and 800 nm
Balzano L et al., Macromolecules 2011, ASAP
room temperature morphology
specimen sheared at 142°C
with 100s-1 for 1s and cooled at 5°C/min
0.2μm
0.5μm
distance between shishes between 300 and 800 nm
Balzano L et al., Macromolecules 2011, ASAP
conclusions
MWD can be tailored for flow-enhanced self-nucleation with
incorporation of HMW molecules
• 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
X-ray scattering experiments
Linkam CSS-450
performed at the beamlines ID02 and BM26
self-nucleation: rationale
nucleation is the limiting step in polymer crystallization kinetics
crystal growth only possible when ΔG<0
surface
 G tot  V  G v 
 A
i
i
i
negative
positive
critical size!
σi
volume
self-nucleation: rationale
nucleation is the limiting step in polymer crystallization kinetics
crystal growth only possible when ΔG<0
surface
 G tot  V  G v 
 A
i
i
i
negative
positive
σi/2
critical size!
heterogeneous
nucleation
σi
volume
smaller critical size
self-nucleation: rationale
nucleation is the limiting step in polymer crystallization kinetics
crystal growth only possible when ΔG<0
surface
 G tot  V  G v 
 A
i
i
i
negative
positive
σi/2
critical size!
heterogeneous
nucleation
σi
volume
smaller critical size
higher Tc
melting of shish-kebabs
shishes melt at higher temperature
increased stability result of the ECC structure