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Journal of Thermal Analysis and Calorimetry
Authors: A. Danch, W. Osoba, D. Chrobak, G. Nowaczyk, and S. Jurga

Abstract  

The study presents properties of polyethylene commercial products with special attention to properties of a ‘semi-ordered’ amorphous phase. Although, one can hardly prove the existence of such an interphase, the results description based on the idea of coexistence of two amorphous fractions (‘real’ and ‘semi-ordered’) in one system gives a broader understanding of the relationship between product history and morphology of the resultant engineering products. Their supermolecular structures were explored using positron annihilation lifetime spectroscopy (PALS), calorimetry (DSC) and mechanical spectroscopy in a tensile and a torsion mode (DMTA). The stability of these structures is also discussed based on a simple statistical analysis of the thermodynamic and structural parameters. The study exhibited that chalk did not disturb too much the crystalline domains of PE-LD whereas it influenced the interphase. Mechanical study showed that such a product is not stable during long time storage. The comparison with previous results, obtained for PE-carbon black composites, revealed differences in the morphologies and the αc relaxations of PE chains, observed in the composites including various fillers.

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Abstract  

The first experimental evidence of the existence of the rigid amorphous phase was reported by Menczel and Wunderlich [1]: when trying to clarify the glass transition characteristics of the first main chain liquid crystalline polymers [poly(ethylene terephthalate-co-p-oxybenzoate) with 60 and 80 mol% ethylene terephthalate units] [2], the absence of the hysteresis peak at the lower temperature glass transition became evident when the sample of this copolymer was heated much faster than it had previously been cooled. Since this glass transition involved the ethylene terephthalate-rich segments of the copolymer, we searched for the source of the absence of the hysteresis peak in PET. There, the gradual disappearance of the hysteresis peak with increasing crystallinity was confirmed [1]. At the same time it was noted that the higher crystallinity samples showed a much smaller ΔC p than could be expected on the basis of the crystallinity calculated from the heat of fusion (provided that the crystallinity concept works). Later it was confirmed that the hysteresis peak is also missing at the glass transition of nematic glasses of polymers. When checking other semicrystalline polymers, the sum of the amorphous content calculated from the ΔC p at the glass transition, and the crystallinity calculated from the heat of fusion was far from 100% for a number of semicrystalline polymers. For most of these polymers, the sum of the amorphous content and the crystalline fraction was 0.7, meaning that ca. 30% rigid amorphous fraction was present in these samples after a cooling at 0.5 K min−1 rate. Thus, the presence of the rigid amorphous phase was confirmed in five semicrystalline polymers: PET, Nylon 6, PVF, Nylon 66 and polycaprolactone [1]. Somewhat later poly(butylene terephthalate) and bisphenol-A polycarbonate [3] were added to this list. In this paper we also report details on a special effect of the rigid amorphous phase (RAP) on the mobile amorphous phase (MAP): the hysteresis peak at the glass transition of the MAF disappears under the influence of the RAP, and this raises the question whether the glass transition of the MAF becomes time independent in semicrystalline polymers.

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Abstract  

Differential scanning calorimetry (DSC) is one of the most frequently used techniques for analyzing small concentrations of amorphous phases in a crystalline matrix. In recent years novel enhanced DSC approaches have been intensively looked for to improve parameters such as sensitivity, accuracy, and detection limit of the technique. Low levels of amorphous phases can be quantitatively determined in DSC by measuring the heat capacity change associated with the glass transition. In this short review the potentials provided by the HyperDSC and StepScan DSC techniques are discussed. Examples illustrate the advantages and disadvantages of the techniques and compare their abilities to detect small glass transitions and determine low contents of amorphous phases in samples which are mostly crystalline.

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Abstract  

The T and d/dTT curves of the FeCuNbSiB amorphous alloy, which are the relationship between the total saturated magnetic moment per unit mass and temperature, are investigated by magnetic thermogravimetry analysis (TG(M)) technique. It is found that the crystallization process of the samples can be divided into five stages. The studies of samples annealed in temperature range of 480–610°C for 1h show that when the annealing temperature (T a) is less than 540°C, the quantity of nanocrystalline -Fe(Si) phase increases evidently with T a, and the Curie temperature (T C) of residual amorphous phase also increases linearly with T a, i.e. T C=0.52T a+91.7°C, with correlation coefficient =0.98. The variation of volume fraction of -Fe(Si) nanocrystalline phase or residual amorphous phase with T a is measured by TG(M) technique.

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Journal of Thermal Analysis and Calorimetry
Authors: N. Delpouve, C. Lixon, A. Saiter, E. Dargent, and J. Grenet

Abstract  

Temperature modulated differential scanning calorimetry (TMDSC) and dynamic mechanical analysis (DMA) are used to calculate cooperative rearranging region (CRR) average sizes for drawn poly(ethylene terephthalate) (PET) with different draw ratios (λ) ranging from λ=1 to 4, according to Donth’s approach. It is shown for both studies that the CRR size decreases when increases, due to the amorphous phase confinement by the crystals generated during the drawing. However, differences observed between the values calculated from TMDSC and DMA investigations are explained by the differences between a mechanical uniaxial dynamic solicitation (DMA) or a thermal solicitation (TMDSC) in terms of cooperative rearrangements at the glass transition.

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Abstract  

A new approach for determining the activation energy of amorphous alloys is developed. Setting the second order differential coefficient of heterogeneous reaction rate equation of non-isothermal heating as zero at extreme points of DSC curve, we obtain the new correlation taking form:

\documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{upgreek} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} $$\gamma_{1} = Lambertw\left( {\gamma_{3} e^{{ - \gamma_{2} }} } \right) + \gamma_{2}$$ \end{document}
where γ 1, γ 2 and γ 3 are symbols comprising parameters, and Lambertw(…) is the Lambert W function symbol. Through this function, the activation energy can be calculated with DSC test at single heating rate without the isoconversion assumption. To evaluate the feasibility of calculating the activation energy with the new method, the glass transition activation energy of as-cast Pd40Ni40P20 amorphous alloy is measured. The value is 1.6 eV, which agrees well with the result of viscosity measurements. Thus, it is a good possibility that the new approach can be used to determine the activation energy of amorphous phase.

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Abstract  

We report a thermal analysis study of the effect of molecular weight on the amorphous phase structure of poly(phenylene sulfide), PPS, crystallized at temperatures just above the glass transition temperature. Thermal properties of Fortron PPS, having viscosity average molecular weights of 30000 to 91000, were characterized using temperature modulated differential scanning calorimetry (MDSC). We find that while crystallinity varies little with molecular weight, the heat capacity increment at the glass transition decreases as molecular weight decreases. This leads to a smaller liquid-like amorphous phase, and a larger rigid amorphous fraction, in the lower molecular weight PPS. For all molecular weights, constrained fraction decreases as the scan rate decreases.

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those dipoles in the amorphous phase of a material. Based on what is available in the technical literature, TSDC has been much more widely applied to research in solid materials than TSPC [ 3 , 4 ]. Irrespective of this difference in the number

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Abstract  

The amorphous content of different Desferal samples was quantified by recording its recrystallization using isothermal microcalorimetry in a static as well as in a flowing humid atmosphere. Furthermore water vapor sorption gravimetry was performed for the same purpose. These analytical methods result in a quantitative signal directly dependent on the content of the amorphous phase (recrystallization, water sorption equilibrium). Their sensitivity allows the detection of amorphous content below 1%. Methods are compared and advantages and disadvantages are discussed.

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Journal of Thermal Analysis and Calorimetry
Authors: G. Bruni, C. Milanese, V. Berbenni, F. Sartor, M. Villa, and A. Marini

Abstract  

The thermodynamic properties of a new antidepressant drug are studied from room temperature to 200 °C. In this range, the sample neither decompose, nor has a significant reactivity with water. When slowly heating a “fresh” sample, we may observe the following phenomena (in the order): melting of a form (F1, ~170 °C), crystallization of a structurally different form (F2), and melting of F2 (~180 °C). In no circumstances, the direct transition from F1 to F2 can be observed. On the other hand, F2 reverts to F1 upon cooling below ~130 °C. A glassy phase is formed upon cooling from above 180 °C, as confirmed by X-ray analysis and the appearance of a glass transition when reheating. The “reversible” (e.g., melting) and “irreversible” (e.g., glass formation) contributions to the measured enthalpies are estimated with temperature-modulated DSC measurements, resulting into a consistent description of thermodynamics of the forms, their melting and their kinetics of transformation.

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