Mechanical properties of semi-crystalline polymers : understanding and modelisation of creep response

Proposition de stage M2 2020-2021

Laboratoire Sciences et Ingénierie de la Matière Molle, (SIMM)

Adresse: ESPCI, 10 Rue Vauquelin 75005 Paris

Directeur du laboratoire: Etienne Barthel

Responsables du stage: Helene MONTES (helene.montes (arobase) espci.fr), Francois Lequeux (francois.lequeux (arobase) espci.fr) Sabine Cantournet (sabine.cantournet (arobase) mines-paristech.fr)

Scientific description:

The structure of semi-crystallized polymers is complex (see figure1 –a). Micrometric sized spherulites are compactly arranged. Inside spherulites, lamellar stacks of crystalline and inter-lamellar amorphous phases are found. The lamellar stacks are isotropically dispersed in an amorphous phase called the inter-fibrillar phase. The arrangement of the crystalline and amorphous phases that have different intrinsic mechanical properties results in mechanical couplings that control the macroscopic mechanical response of such materials.
Combining experiments on model samples and numerical simulations, we aim at understanding the relation between microstructure and mechanical properties of semi crystalline polymers both in the linear and non linear regime.
First mechanical properties will be measured on model semi-crystalline polymers (for instance PEKK/PEI miscible blends) for which the intrinsic mechanical properties of the crystalline, interlamellar and interfibrillar phases are known and can be varied. Measurements will be then compared to simulations based on a multi scale mechanical model we already developed for linear condition (PhD A. Beguise (2020)).
The model takes into account the dynamical properties of polymer chains in the different amorphous phases, the arrangement and the morphology of phases. (see figure 1-b). The model will be extended to non linear conditions. The question of the effect of connections between the 3 kinds of phases will be addressed more specifically, in particular how the mechanical properties are modified in the glass transition domain by connections between crystalline lamellae both inside and between the lamellar stacks. We will thus study the effect of secondary crystals that appear when a crystallization isotherm is applied to the polymer material. Mechanical measurements will be performed on materials for which the fraction and the localization of secondary crystals can be varied in a controlled manner.

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Figure 1. a) schematic representation of the morphology of semi crystalline polymer materials
b) 2D modélisation using finite elements at the scale of the sherulite . In green : the interlamellar amorphous phase, in red, the interfibrillar amorphous phase in white, the crystalline phase.

Keywords: semi-crystalline polymer, mechanical properties, experiment, simulations
Techniques/methods in use: rheology, Finite element simulations
Internship location: SIMM - ESPCI
Possibility for a Doctoral thesis: Yes

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Practical information

Sciences et Ingénierie de la Matière Molle

Soft Matter Enginering and Science Laboratory - UMR 7615

10 rue Vauquelin
75231 PARIS CEDEX 05
FRANCE

  • Chair : E. Barthel
  • Vice Chairs : J.B. d’Espinose & G. Ducouret
  • Administration : F. Decuq, M.-T. Mendy & M. Hirano-Courcot
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