Mechanical properties of semicrystalline polymers: Foundation in microscopic structure and molecular dynamics

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The characteristic morphological feature of semicrystalline polymers is a nanoscopic two-phase structure of thin lamellar crystals separated by disordered amorphous layers. Tie chains and entanglements mechanically link neighboring crystals. The crystals often contain mobile conformational defects, which entail a certain mobility of the chains in the crystal. The mechanical properties of semicrystalline polymers on the other hand are complex and are intimately related to the semicrystalline morphology. While the crystalline fraction is responsible for the high stiffness at small deformation, plastic flow and fibrillation set in for intermediate deformation and for large deformation strain hardening is generally observed, caused by the entanglement network trapped by the crystalline scaffold. Building on recent progress in the characterization and understanding of the semicrystalline morphology as well as of the above mentioned intracrystalline chain dynamics, the aim of the project is to work out the relation between the morphology resp. the chain dynamics and the mechanical properties in a quantitative way. For this purpose, we combine structural analysis by X-ray scattering with mechanical deformation experiments in tensile deformation and under compression. Deformation at constant rates will be complemented by stress relaxation and creep experiments for a number of model samples with different structural and dynamics properties as well as for complimentary common commercial materials.