Francesco Farsaci

DSC and DMTA study of annealed cold-drawn PET: a three phase model interpretation

Cold-drawn poly(ethylene terephthalate) (PET) samples annealed at different undercoolings are studied by means of differential scanning calorimetry and dynamic mechanical thermal analysis. When heating from room temperature, the onset of the glass transition region in cold-drawn, un-annealed samples is found to be significantly lower than in the case of un-oriented PET. On the contrary, the presence of crystalline lamellae in oriented PET cause a shift (and spread out) of the glass transition region towards higher temperatures. The crystal thickening process caused by heating above the annealing temperature, is suggested to take place after a rigid amorphous phase linked to the basal surface of the lamellae has softened. It is found that the low-temperature (between 100 and 140 °C) annealed samples have a glass dispersion region ranging significantly above the annealing temperature itself. This circumstance leads to envisage vitrification as a possible mechanism able to limit lamellar thickening during the annealing process at these low temperatures.

Local and cooperative molecular mobilities in thermoplastic polymers

Comparative measurements of calorimetry and low-frequency mechanical spectroscopy (temperature interval between 120 and 400 K) in a thermoplastic interpenetrating polymer network based on semicrystalline poly(urethane) and a styrene–acrylic acid block copolymer show the existence of distinct calorimetric and mechanical transitions associated with the two components, as a clear indication of a multiple-phase heterogeneous structure. In contrast with the apparent thermodynamic incompatibility of the components, significant deviations in the magnitudes of local and cooperative transitions from a simple dilution effect are revealed. These findings are associated with a limited miscibility due to weak interactions (hydrogen bondings) between the functional groups of the two polymeric components.

Phenomenological and state coefficients in viscoanelastic medium of order one (with memory)

The aim of this work is to indicate a method to measure experimentally some phenomenological an state coefficients, and so to verify some inequalities that follow from principle of entropy production. In particular, we will consider the Kluitenberg-Ciancio model for a visco-anelastic medium of order one with memory and the relative rheological equation in which, neglecting cross effects between viscous and inelastic flow, four phenomenological an state coefficients appear. Assuming an harmonic deformation as cause and the stress as effect we will compare the solution of the Kluitenberg-Ciancio’s equation with a well known expression of the stress obtained, by experimentally considerations in the linear response theory, as function of the frequency of deformation at a constant temperature. This comparison will be able to determine the phenomenological an state coefficients as function of frequency dependent quantities experimentally measurable. This method will be applied to polymeric materials as Polyisobutilene.

On evaluation of electric conductivity by mean of a thermodynamical model for dieletric relaxation phenomena. An application to liver tissue

In this paper we study the electric conductivity of continuous media in the contest of the non-equilibrium thermodynamics with internal variables. Namely, we shall use some recent results that allow to infer conductivity as function of the frequency of perturbation, only by means of dielectric measurements. Although the results obtained can be applied to several materials, we have applied them to the study of electric conductivity on porcine liver tissue obtaining the spectrum frequency of conductivity (real and imaginary part).