J. Perez

Microstructure and mechanical properties of isotactic polypropylene (iPP)/polyamide 12 (PA12) blends

The microstructure and mechanical properties of polyamide 12/isotactic polypropylene blends with different compositions are studied. It is shown that the injection moulding technique used to process all samples results in a more or less pronounced orientation of macromolecular chains, which in its turn is responsible for a preferential orientation of polymer crystals. At a larger scale, the injection technique is also responsible for the deformation of polyamide domains into ellipsoides when polypropylene is dominant. In contrast, when polyamide is dominant, domains of both polymers are co-continuous in the materials. This feature is discussed on the basis of dynamic mechanical measurements.

Non-linear creep behaviour of PET

The non-linear creep behaviour has been studied on PET films at room temperature. A particular value of the stress, σc, was used to characterize the change between the linear to the non-linear domain. The variations of the elastic modulus, the relaxed modulus and σc revealed great sensitivity to the morphology of the crystallization. A molecular model of non elastic deformation, assuming (i) hierarchical correlated molecular motion, and (ii) nucleation and expansion of sheared-microdomains, was used to analyse the role of stress on anelasticity. To take into account the two-phase structure of semicrystalline films, a phenomenological series/parallel model was applied to express the mechanical coupling between amorphous and crystalline phases. Quantitative agreement was found between theoretical predictions and experimental data for low and high stresses. However, there was a discrepancy in the rate of recovery because the model predicts a strain recovery slower than the experimental behaviour. Consequently, it is proposed to develop further the molecular model mentioned above by specifying the energy profile of a sheared-microdomain and its stress dependence. Then, the difference between creep and recovery strain rate could be explained.

Anelastic Behaviour of Ice at Low Temperature Due to Quenched Point Defects

ABSTRACT At low frequencies (~ 1 Hz) and under some conditions, the internal friction peak associated to the relaxation of water molecules in Ice exhibits an irreversibility with the temperature variation rate. This phenomena is described in terms of quenched rotationnal defects out of thermodynamic equilibrium. As a consequence of our results the anomalies observed by several authors on physical properties near 100-130 K are discussed in terms of evolution of defects out of thermodynamic equilibrium.