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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.

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Abstract  

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.

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The 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 ΔH m 0 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.

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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.

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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(T g) at the glass transition according to the definition proposed by Solunov. However, z(T g is a dimensionless quantity and then only allows a comparative study between different samples. To calculate the average number of monomer units by CRR noted N α, 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(T g and N α values have the same evolution in function of filler content.

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The effect of ageing temperature (belowT g) 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.

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Two different poly(urethane acrylate) resins (one with a trimer: PUA1, the second with a dimer: PUA2) prepared [1] 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 [1]. 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.

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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.

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Polymorphism of progesterone

Influence of the carrier and of the solid dispersion manufacturing processes. A calorimetric and radiocrystallographic study

Journal of Thermal Analysis and Calorimetry
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 [4]. 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.

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