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Shear-Induced Crystallization of Polyethylene: Insights from Small-Angle and Wide-Angle X-Ray Scattering Studies

This study delves into the shear-induced crystallization of polyethylene, investigating changes in crystallization kinetics and morphology due to shear flow. Examining the development of shear-induced macrostructure in PE via synchrotron radiation, the research uncovers insights into chain alignment and the formation of the 'shish kebab' structure. Results highlight the stacking of lamellae along the shear direction and the impact on molecular weight and orientation. Additionally, the study explores the pore-orientation periodicity in porous polymer and carbon materials, with a focus on banded spherulites and carbon foams crystallized from a blend of maleic anhydride (MA) and polyacrylonitrile (PAN).

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Shear-Induced Crystallization of Polyethylene: Insights from Small-Angle and Wide-Angle X-Ray Scattering Studies

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  1. Shear-induced crystallization of polyethylene (see Heeley, Morgovan, Bras, Dolbnya, Gleeson, & Ryan, Phys. Chem. Comm. (2002) 5, 158-160. Shear-induced crystallization of polyethylene studied by small- and wide-angle X-ray scattering (SAXS/WAXS) techniques) In situ study of development of shear-induced macrostructure of PE injection molding ––> shear flow in polymer changes crystallization kinetics & morphology chain alignment ––> 'shish kebab' structure

  2. Shear-induced crystallization of polyethylene (see Heeley, Morgovan, Bras, Dolbnya, Gleeson, & Ryan, Phys. Chem. Comm. (2002) 5, 158-160. Shear-induced crystallization of polyethylene studied by small- and wide-angle X-ray scattering (SAXS/WAXS) techniques) In situ study of development of shear-induced macrostructure of PE synchrotron radiation using shear cell & heating stage 5 sec/frame – after shear (100 pulses/sec for 5 & 10 sec) crystallization temperature

  3. Shear-induced crystallization of polyethylene Results stacking of lamellae along shear direction shear direction lower MW - less orientation

  4. Shear-induced crystallization of polyethylene More results invariant vs crystallization time lower MW - less orientation

  5. Pores in polymers & carbons (see Olivier, Lagasse, Schaeffer, Barnes, & long, Macromolecules (1996) 29, 8515-8621. SA small-angle-scattering study of the pore-orientation periodicity in porous polymer and carbon materials) Banded spherulites ––> carbon foams crystallized blend of maleic anhydride (MA) & polyacrylonitrile (PAN) bands are ~ 3.5 mm in width in this system (can use SAXS) sublimate MA & pyrolyze ––> carbon foams (98% void volume)

  6. Pores in polymers & carbons (see Olivier, Lagasse, Schaeffer, Barnes, & long, Macromolecules (1996) 29, 8515-8621. SA small-angle-scattering study of the pore-orientation periodicity in porous polymer and carbon materials)

  7. Pores in polymers & carbons (see Olivier, Lagasse, Schaeffer, Barnes, & long, Macromolecules (1996) 29, 8515-8621. SA small-angle-scattering study of the pore-orientation periodicity in porous polymer and carbon materials) q–4 averages of intensity data around azimuth - not on absolute scale

  8. Pores in polymers & carbons (see Olivier, Lagasse, Schaeffer, Barnes, & long, Macromolecules (1996) 29, 8515-8621. SA small-angle-scattering study of the pore-orientation periodicity in porous polymer and carbon materials) q–4 sharp polymer/void interface averages of intensity data around azimuth - not on absolute scale

  9. Pores in polymers & carbons

  10. Pores in polymers & carbons Plots of intensity differences from intensity averages over 22 positions

  11. Pores in polymers & carbons Plots of intensity differences from intensity averages over 22 positions Plots repeat at 3 – 4 mm translation interval

  12. Pores in polymers & carbons Plots of sector averages of intensity vs translation position

  13. Pores in polymers & carbons Before pyrolysis After pyrolysis

  14. Pores in polymers & carbons Observation in as-crystallized blend: bands move when sample is rotated around growth direction indicates rotation of crystal orientations substantiated by high-angle x-ray studies orthorhombic MA cells

  15. Pores in polymers & carbons Observation in as-crystallized blend: bands move when sample is rotated around growth direction indicates rotation of crystal orientations substantiated by high-angle x-ray studies band motion observed in pyrolyzed mat'l ––> anisotropic pore rotation orthorhombic MA cells

  16. Pores in polymers & carbons band motion observed in pyrolyzed mat'l ––> anisotropic pore rotation pore shape assumed ellipsoidal

  17. Pores in polymers & carbons band motion observed in pyrolyzed mat'l ––> anisotropic pore rotation substantiated by oscillation in Porod data plots pore shape assumed ellipsoidal

  18. Pores in polymers & carbons Porod constant, KP, for isotropic case For anisotropic case Also, for average chord length, <LV>, inside pore vol. fact.

  19. Pores in polymers & carbons Porod constant, KP, for isotropic case For anisotropic case

  20. Pores in polymers & carbons Porod constant, KP, for isotropic case For anisotropic case

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