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
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
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
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