The usual determination of kinetic parameters of crystallization of amorphous products is based on isothermal measurements. In general the crystallization of amorphous selenium thin films is studied by non-isothermal experiments (DTA). The adaptation to non-isothermal crystallization of the Avrami transformation rate equation allows us to determine different types of crystallization. These different regions enable one to determine the variations of the growth rate and of the nucleation rate versus temperature. The influence of the wavelength of illumination during the crystallization time on these parameters is also investigated.
Behaviours of drawn semi-crystalline poly(ethylene terephthalate) films are investigated by DSC, X-ray diffraction and birefringence
measurements. The comparison of the different results confirms the coexistence of two structures into the amorphous part of
the material: a completely disordered amorphous phase and a mesomorphic amorphous one. Moreover, for the strongest draw ratio,
the calorimetric results show that the drawing effect on the strain induced crystalline structure proceeds by a better orientation
of this structure rather than by nucleation and growth of new oriented crystallites.
melting and crystallisation behaviour of poly(m-xylene
adipamide) (MXD6) are investigated by using the conventional DSC, X-ray diffraction
and polarised light microscopy. Triple, double or single melting endotherms
are obtained in subsequent heating scan for the samples after isothermal crystallisation
from the melt state at different temperatures. The lowest melting peak can
be ascribed to the melting of secondary crystals. The melting of primary crystals
causes the medium melting peak and the highest melting peak is attributed
to the melting of recrystallised species formed during heating. Following
the Hoffman–Weeks theory, the equilibrium melting temperature is equal
to 250C and the equilibrium melting enthalpy ΔHm0
to 175 J g–1. Then, using the Lauritzen–Hoffmann
theory of secondary crystallisation, the analyse of the spherulitic growth
shows that the temperature of transition between the growing regimes II and
III is equal to 176C. Finally the Gibbs-Thomson relationship allows the
determination of the distribution function of crystalline lamellae.
Thermally stimulated depolarization currents and differential scanning calorimetry are performed on thermoplastic polyesters
to characterize both a and b relaxations. The influence on the different relaxations phenomena of the chemical structure (size
of the naphthalene groups, presence of cyclohexane, length of the aliphatic group, ...) as well as the influence of the crystallinity
are discussed. The three phases model with a crystalline part, a rigid amorphous part unable to relax and an amorphous phase
able to relax at various temperatures depending on the distribution of the relaxation times is used to explain the evolution
of the main α relaxation while the standard two-phases model is sufficient to explain the variations of the β relaxation mode.
Elementary analysis of both α and β relaxations show that the β relaxation characterized by a continuous variation of activation
energies as a function of temperature follows the activated state equation with a zero activation entropy while the cooperative
a relaxation exhibits a prominent maximum of the activation energies at the glass transition temperature.
Authors:Allisson Saiter, H. Couderc, and J. Grenet
Measurements have been performed
on poly(ethylene terephthalate)glycol/montmorillonite nanocomposites with
different filler contents using differential scanning calorimetry (DSC) and
temperature modulated differential scanning calorimetry (TMDSC). According
to the strong-fragile concept proposed by Angell, we have determined the values
of the fragility index m. In a second time,
we have calculated the average size of a cooperative rearranging region (CRR) z(Tg)
at the glass transition according to the definition proposed by Solunov. However, z(Tg
is a dimensionless quantity and then only allows a comparative study between
different samples. To calculate the average number of monomer units by CRR
we have used the method developed by Donth. The results show that the presence
of montmorillonite in PETg matrice implies modifications
on structural relaxation phenomena. Furthermore, we have shown that z(Tg
and Nα values
have the same evolution in function of filler content.
Authors:J. Grenet, J. M. Saiter, C. Vautier, and J. Bayard
The effect of ageing temperature (belowTg) on physical ageing of glassy PET has been investigated by differential scanning calorimetry. The position of the glass transition endotherm was found to be strongly dependent on the annealing conditions (time, annealing temperature). A single relaxation time model is proposed for the analysis of physical ageing.
Authors:J. Ledru, B. Youssef, J. Saiter, and J. Grenet
Two different poly(urethane acrylate) resins (one with a trimer: PUA1, the second with a dimer: PUA2) prepared  by photo
curing reaction are investigated by means of thermogravimetry and thermomechanical measurements. The lack of mass loss found
up to 300C for both systems shows their good thermal stability. Beyond this temperature, two mass losses occur consecutively.
This mass loss already studied by TG-FTIR coupled measurements for PUA1 resin has been attributed to the degradation of carbonyl
groups . The extension to PUA2 and the comparison between the mass loss magnitude and the relative contain in acrylate
of the resins leads to attribute the first degradation to the degradation of the acrylate fraction. The degradation of dimer
based resin occurs earlier and with a faster kinetic than the trimer based resin. The variations of linear expansion and penetration
coefficients measured by thermomechanical analysis (penetration probe) in the glassy state and in the glass transition temperature
domain (the onset glass transition temperatures measured by DSC at 20C min–1 are respectively equal to 111 and 107C for PUA1 and PUA2, the transitions, not well defined, extending over 30C), show
that despite of a weaker compactness, the trimer based resin is more rigid than the dimer one.
Authors:J. Grenet, S. Marais, M. Legras, P. Chevalier, and J. Saiter
This work reports on the curing kinetics of unsaturated polymer resins (UPRs) cured with styrene, studied by differential
scanning calorimetry and Fourier transform infrared spectroscopy. The data lead to determination of the experimental conditions
with which to obtain a fully cured material and open the way for study of the relaxation phenomena by means of thermally stimulated
depolarization current analysis (TSDC). In relaxation studies on fully cured resins, the TSDC spectra revealed important overlapping
of the main relaxation peak with an extra upper peak. The importance of this extra peak a priori prevents further analysis
of the main relaxation. To identify the origins of this peak (space charge or other), the purity of the resin was checked
by X-ray fluorescence spectroscopy. The use of UPR specimens with different compositions (in terms of the resin/activator/initiator
ratio) demonstrated that the bulk of the impurities Cl, K, Ca, Sr, Zr and Ba are due to the promoter. Decoupling of the mixed
peaks (α-relaxation and extra) revealed that the a peak is independent of the proportion of the promoter in the resin and
that the extra peak is principally due to the presence of these impurities.
Authors:R. Duclos, J. M. Saiter, J. Grenet, and A. M. Orecchioni
Solid dispersions are used in pharmaceutical technology in order to improve solubility and/or dissolution kinetics of poorly water soluble drugs [1, 2, 3]. A preliminary study concerning progesterone structure after melting revealed the existence of a drug polymorphism after cooling, and gave the opportunity to specify the manufacturing conditions in order to obtain the stable form of this hormone . In this work, two different types of progesterone solid dispersion have been compared. The first one is obtained by a slow cooling rate of the drug in the presence of polyoxyethylene glycol 6000 and the second one after quenching in the presence of saccharose distearate.