Using Synchrotron Radiation to Follow Structure Development in Commercial and Novel Polymer Materials During Processing

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Using Synchrotron Radiation to Follow Structure
Development in Commercial and Novel Polymer
Materials During Processing  T Gough (a), EL
Heeley(b), W Bras (c), AJ Gleeson (d), PD Coates
(a) and AJ Ryan (b) (a) IRC in Polymer
Engineering, School of Engineering, Design and
Technology,University of Bradford, Bradford,
UK. b) Polymer Centre, University of Sheffield,
Western Bank, Sheffield, UK. (c) Dubble, European
Synchrotron Research Facility, Grenoble,
France. (d) CCLRC, Daresbury Laboratory,
Daresbury, Warrington, UK.
Abstract The crystallinity of a polymeric
material imposes a direct influence on a
product's aesthetic and mechanical properties.
Understanding the crystallization process is
essential for the prediction of these properties.
Here, the use of time-resolved synchrotron
radiation is shown to be an invaluable technique
in probing real industrial processes using
instruments mounted on x-ray beamlines. Both
quiescent and shear-induced crystallization of
polymers has been studied using time-resolved
scattering techniques with in-situ processing
instrumentation. Quiescent crystallization of
polyolefins has been performed with a
differential scanning calorimeter while
shear-induced crystallization has been
investigated using a Linkam shear instrument and
a lab-scale extruder. Such shear instrumentation
along with simultaneous data collection provides
new insights into the crystallization process
under the influence of flow during industrial
processing conditions. Orientation and
crystallinity of polymer films and moulded
products plays a crucial role in determining end
properties.

• Nearly 1 km circumference
• Electron energy 6 GeV

Growth from shear- induced nuclei
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Experimental Quiescent crystallization studies
were performed using a Linkam DSC as an in-situ
device, where the sample is heated to 180oC and
then cooled at 50oC/min to the selected
crystallization temperature. Then SAXS/WAXS
measurements were used to follow the
crystallization kinetics and structure
development. In comparison, commercial and
synthesised PE samples were also subjected to
shear induced crystallization using a Linkam
CSS450 shearing instrument. Here, a fast shear
pulse is given to the sample once it has been
cooled to the crystallization temperature and
SAXS used to follow the crystallization process.
Typical experimental set-ups for DSC and shear
devices on the ESRF Dubble (BM26b) beamline are
shown opposite.
(A) Linkam DSC , (B) Linkam shear cell and (C)
Dubble CRG beamline at the ESRF
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Lupolen 1840H LDPE was also extruded using an
Axon BX18 single screw extruder fitted with a
simple slot die. Set temperatures of 150C and
180C were studied - the results here were all
achieved using the lower temperature. The
extruder was raised and lowered using a hydraulic
stage allowing a range of states of crystallinity
to be studied using the beam. The real time
extrusion process has been followed by using 2D
SAXS and WAXS techniques to follow the structure
development in the extruded polymer tape. The
figures show the extruder system on the Dubble
beamline at the ESRF. A Gottfert Rheotens system
(kindly loaned by BASF) was utilised to provide
constant haul off speed and measurements of
force. These techniques have been used to
successfully gain insight into the
crystallization of the selected polymer systems.
Materials The polymers used in these experiments
were either commercial Basell Lupolen 1840H LDPE
(kindly supplied by BASF), or Daplen isotactic
polypropylene (PCD Polymer GmbH) and polyethylene
type samples (linear and comb architectures)
which have been synthesised by anionic
polymerisation methods. The commercial LDPE is
an analogue of the well-documented IUPAC Melt A.
The table below gives the molecular
characteristics for all samples utilised.
Table 1 Molecular parameters of samples used to
investigate crystallization kinetics using
polymer processing techniques
Rheotens haul-off
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Results from Linkam shear cell
Graph A, SAXS of Comb 10 pre-sheared and
crystallized at several temperatures Graph B,
SAXS of blended sample 90 linear 50k and 10
comb 10, pre-sheared at several
temperatures Graph C, SAXS of Blended sample 90
linear 112k and 10 comb 10, pre-sheared at
several temperatures
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Results and Discussion Using these on-line
processing techniques it has been possible to
investigate the development of crystallization
and thus macro-structure of a polymer system and
some brief results are presented here. On the
previous page, shear induced crystallization is
investigated using samples with novel
architectures. A schematic of the linear and comb
architectures is shown opposite. It is seen that
addition of a few percent of comb polymer to
linear systems can produce oriented features in
the SAXS patterns and increase the rate of the
crystallization kinetics considerably. This has
enabled information to be obtained on how the
architecture, Mw and polydispersity of polymers
influence the crystallization kinetics.
The results on the following page show the effect
of haul off rate on the small angle x-ray
scattering data for the LDPE tapes produced using
the extruder at two heights above the x-ray beam.
It can be clearly observed that the orientation
imposed on the crystal structure increases
significantly with the haul off rate. By
measuring samples taken 'downstream' of the
Rheotens it was possible to calculate the stress
imposed on the tape during processing. However,
note that the dimensions are those from cooled
tape which is not quantitatively of the same
dimensions as that seen at the beampipe. More
detailed analysis of the x-ray data is required
prior to further conclusions being made. The
growth of equatorial streaks indicative of the
'shish' of the typical 'shish-kebab' structure
can clearly be observed at the higher haul off
rates for all the tests with the extruder mounted
at both heights above the x-ray beampipe.
Further analysis of this SAXS data in conjunction
with the simultaneously measured WAXS data will
provide us with quantitative insights into the
effect of haul off on final structure.
Distance from diehead
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Set T 150C, die height 1000mm, screw 3.0Hz, mass
flowrate 5.06g/min
Run Tape T (C) Rotation (rpm) Force (N) Width (mm) Thickness (mm) XSA (mm2) Stress (MPa)
E04.425 64.5 60.1 0.2233 3.48 0.377 1.24 0.180
E05.425 70.0 120.2 0.3306 2.43 0.269 0.62 0.534
E06.425 71.5 180.0 0.3668 2.05 0.197 0.37 0.992
E07.425 74.4 239.8 0.3982 1.68 0.178 0.29 1.393
E08.425 75.0 299.8 0.4277 1.44 0.150 0.21 2.049
E09.425 - 359.8 0.4550 1.35 0.128 0.16 2.806
E10.425 - 420.3 0.4720 1.37 0.132 0.17 2.749
Set T 150C, die height 1250mm, screw 3.0Hz, mass
flowrate 5.06g/min
Run Tape T (C) Rotation (rpm) Force (N) Width (mm) Thickness (mm) XSA (mm2) Stress (MPa)
E12.425 61.0 60.0 0.2162 2.97 0.331 0.96 0.224
E13.425 65.9 120.3 0.3148 2.51 0.247 0.56 0.558
E14.425 67.1 180.1 0.3583 1.98 0.208 0.38 0.953
E15.425 75.8 239.8 0.3932 1.63 0.178 0.27 1.465
E16.425 75.3 299.9 0.4077 1.49 0.161 0.22 1.881
E17.425 - 360.0 0.4285 1.32 0.140 0.19 2.241
E18.425 - 420.6 0.4472 1.22 0.127 0.14 3.188
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Conclusions and further work Here we have
discussed and shown examples of how
crystallization of various polymers can be
followed during processing with synchrotron
radiation. Importantly, the techniques used
mimic industrial processing and allow us to
relate structure development in the material with
both the processing parameters and the molecular
structure of the polymer. The use of synchrotron
radiation and high flux beamlines has enabled
these fast time- resolved processes to be
followed successfully. Further developments in
processing methods and X-ray beamlines will
continue to allow great insight into this highly
debated topic of polymer crystallization in the
future and lead to a greater understanding of the
process throughout the stages of structure
development. Acknowledgements ELH was supported
by the EPSRC grant (GR/M60415) which provided the
beamtime at the Daresbury SRS. TG was supported
by the University of Bradford and the EPSRC. The
authors would like to thank all beamline staff at
the SRS and ESRF. Samples were kindly provided
by PCD Polymer GmbH, BASF / Basell and CM
Fernyhough (Sheffield Chemistry).
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