Combined extensional rheometry, SAXS and WAXS


Enrico Troisi and colleagues from the Technische Universiteit Eindhoven have combined extensional rheometry with SAXS and WAXS on BM26B to follow the isothermal crystallization of isotactic polypropylene at 135°C. They are able to follow the crystallization kinetics using the WAXS data, evolution of polymer morphology from the SAXS data and can correlate this information with the polymer flow characteristics measured simultaneously.

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SAXS and WAXS measurements provide detailed data describing the microscopic structure of polymers, but are not available outside research settings. The ability to characterise the microscopic behavior of polymers during common industrial processes involving elongational flow, such as fibre spinning, using simple laboratory rheology measurements would represent an important advance for manufacturing industry. The work of Enrico Troisi and colleagues aims to correlate polymer rheology to polymer crystallization behavior using the detailed microscopic information provided by the SAXS and WAXS data. Validation of their theoretical model would allow them to use subsequent rheology measurements in the absence of SAXS-WAXS data.

In this experiment an Anton Paar extensional rheometer was mounted inside an oven on the BM26B beam line mimicking both industrial processes involving shear and laboratory-based polymer characterization.

extension.png Anton Paar rheometer.JPG



The SAXS patterns demonstrated the evolution of a “shish-kebab” polymer morphology, where the “shish” represents extended polymer chain crystals aligned along the flow direction and the “kebab” are folded chain lamellae growing perpendicularly to the “shish” cores.








WAXS.pngThe degree of crystallinity is extracted from the WAXS data.






The crystallization during flow is also recognisation  by the deviation from linear viscoelastic behaviour in the rheology data.


In this system flow times are extremely short (less than 0.2s in some cases) so the availability of the high speed Pilatus detectors on DUBBLE was essential in order to be able to monitor the system in real time.  This is the first time crystallization during flow at such short times and high elongation rates has been measured.

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Top image: Anton Paar rheometer installed on BM26B