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Keywords:

  • fibrillar morphology;
  • isotactic polypropylenes;
  • molecular stretch;
  • shear flow;
  • shear induced crystallization;
  • specific work

Crystallization of isotactic polypropylene during step shear rate experiments is carried out in a plate–plate geometry by means of a Linkam shearing cell. The evolution of crystalline structures is observed during the tests at a fixed radial position. The samples are then analyzed by optical microscopy and the radial position at which a transition between the spherulitic and fibrillar morphology took place is measured. The analysis of the samples allows detecting the critical shear rate at which, after a given shearing time, the fibrillar morphology overcomes the spherulitic structure. With the aim of giving a quantitative description of the conditions for the formation of a fibrillar structure, two different models are applied: one based on molecular stretch, the other one relying on specific work.mame201400131-gra-0001