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. AbstractThe 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

shear

Dir

ecti

on

of

sh

ear

Random coil molecules in melt

Orientation of molecules giving the ‘shish’ after shear providing primary nucleation sites

Oriented folded chain crystals growing from nuclei perpendicular to shear direction

Final lamellar morphology of stacked oriented crystals ‘kebabs’

Some loss of orientation due to splaying of lamellae Growth from shear- induced nuclei

ExperimentalQuiescent 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

Temperature profile

Time

Shear profile

Tm + 30oC

Tc

Experimental shear regime followed prior to crystallization

shear cell with sample on X-ray plates

beamstopsample

Bragg : = 2d sin

i.e. small, d large large, d small

X-ray beam

SAXS detector

WAXS detector (CCD)

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.

tape

beam

x-rays

tape guides

extruded tape

Rheotens haul-off

MaterialsThe 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.

Sample Mw/kg mol-1 Mw/Mn

Lupolen PE 250 13.5

Daplen iPP 622 5.5

Linear A 52.8 1.01

Comb10 Backbone53.8Arm (8)

14.8

1.02

Table 1: Molecular parameters of samples used to investigate crystallization kinetics using polymer processing techniques

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

1.10

0 50 100 150 200 250 300 350 400 450 500 550 600

Time /sec

No

rmalized

in

vari

an

t /A

rb

370K iso370K373K375K373K iso

Lamella stacking

Amorphous block

Crystalline block0.00

0.100.200.300.400.500.600.700.800.901.001.101.20

0 200 400 600 800 1000 1200 1400Time /sec

No

rmal

ised

in

ten

sit

y /

Arb

363K iso368K iso363K shear368K shear370K shear

363K 1020 sec

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

1.10

1.20

0 100 200 300 400 500 600 700 800

Time /sec

No

rm

alised

in

ten

sit

y /A

rb

377K iso

375K shear

377K shear

379K shear

377K 400sec375K 480sec 379K 400sec

370K 400sec 375K 400sec373K 400sec

GRAPH A

GRAPH B

GRAPH C

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

Results from Linkam shear cell

Results and DiscussionUsing 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.

Comb sample architecture

Linear monodisperse sample architecture

WAXSSAXS

Dis

tan

ce f

rom

die

hea

d

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 1000mm, screw 3.0Hz, mass flowrate 5.06g/min

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

Conclusions and further workHere 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.

AcknowledgementsELH 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).  ReferencesRyan, AJ, Fairclough, JPA, Terrill, NJ, Olmsted, PD and Poon, WCK, Faraday Discussions., v.112, pp. 13-30 (1999)

Heeley, EL, Morgovan, AC, Bras, W, Dolbnya, IP, Gleeson, AJ and Ryan, AJ, Phys. Chem. Comm., v.5(23), p. 158 (2002).

Fernyhough, CM, Young, RJ, Poche, D, Degroot, AW and Bosscher, F., Macromolecules, v.34, pp. 7034-7041 (2001).Heeley, EL, Maidens, A, Olmsted, PD, Bras, W, Dolbnya, IP, Fairclough, JPA, Terrill, NJ and Ryan, AJ, Macromolecules, v.36, p. 3656 (2003).

Terrill, NJ, Fairclough, JPA, Towns-Andrews, E, Komanschek, BU, Young, RJ and Ryan, AJ, Polymer, v.39, 2381 (1998).

Heeley, EL and Gough, T, CCLRC Synchrotron Radiation Department Annual Report, 2003-2004 (2004).