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Abstract  

The response of temperature-modulated differential scanning calorimetry (TMDSC) to irreversible crystallization of linear polymers was investigated by model calculations and compared to a number of measurements. Four different exotherms were added to a typical modulated, reversible heat-flow rate in order to simulate irreversible crystallization. It was found that the reversing heat-flow rate of the TMDSC in response to such irreversible crystallization exotherms is strongly affected by tbe shape of the transition and the phase-angle where the exotherm occurs. A comparison with the experimental data gave valuable insight into the transitions, as well as the nature of the TMDSC response which is usually limited to an analysis of the first harmonic term of the Fourier series that describes the heat-flow rate.

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Abstract  

Adiabatic calorimetry is a technique that has been introduced as an important approach to hazard evaluation of exothermically reactive systems. In this paper the free radical polymerization of methyl methacrylate (MMA) has been studied. One of the most important aspects of MMA polymerization is its exothermicity and autoaccelerating behaviour, these characteristics can generate the occurrence of a runaway reaction.In a runaway situation the reacting system is close to adiabatic behaviour because it is unable to eliminate the heat that is being generated. An even worse situation can be reproduced in the laboratory with the Phi-Tec pseudo-adiabatic calorimeter. Process design parameters that are usually calculated from thermodynamic data or using semiempirical rules, such as adiabatic temperature rise or maximum attainable pressure, can be directly determined.The existence of the ceiling temperature has been experimentally demonstrated.

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Confinement of the glass-forming regions in the nanometer range influences the α-relaxation which is associated with the glass transition. These effects were investigated for semicrystalline poly(ethylene terephthalate) by dielectric spectroscopy and differential scanning calorimetry. The results are discussed within the concept of cooperative length, i.e. the characteristic length of the cooperative process of glass transition. Both experiments showed a dependence of the glass transition on the mean thickness of the amorphous layers. For the dielectric relaxation, the loss maximum was found to shift to higher temperatures with decreasing thickness of the amorphous layers, but no differences were observed in the curve shape for the differently crystallized samples. For the calorimetric measurements, in contrast, there was no correlation for the glass transition temperature, whereas the curve shape did correlate with the layer thickness of the mobile amorphous fraction. From the structure parameters, a characteristic length of approximately (2.5±1) nm was estimated for the unconfined glass relaxation (transition).

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Abstract  

40% w/w sucrose/water solutions were analyzed by Modulated Differential Scanning Calorimetry [1] in the sub-ambient temperature region. At these temperatures, the solutions exhibit a complex, two-step thermal event. The lower-temperature event is believed to be the glass transition of the amorphous sucrose phase. The nature of the higher-temperature event is the subject of controversy. This event has been shown to have distinct second-order characteristics, and as such is believed to be a second T g. Others feel that this event is the onset of melting. The temperature region between these events contains a devitrification exotherm. Through the use of MDSC, both in scanning and stepwise quasi-isothermal modes, improved sensitivity and resolution of MDSC provides new insight into the nature of these transitions.

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Abstract  

The glass-forming tendency and specific heat in ice cold water-quenched Ge1−xSnxSe2.5 glassy alloys with 0<x<0.6 were investigated by means of differential scanning calorimetry. The heat of fusion ΔH f, the heat ΔH c associated with the crystallization of an amorphous phase and the glass transition temperatureT g were deduced from the DSC curves. The composition dependence of glass forming ability,T g and crystallization behavior has been discussed.

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The modulated differential scanning calorimetry (MDSC) technique superimposes upon the conventional DSC heating rate a sinusoidally varying modulation. The result of this modulation of the heating rate is a periodically varying heat flow, which can be analysed in various ways. In particular, MDSC yields two components (‘reversing’ and ‘non reversing’) of the heat flow, and a phase angle. These each show a characteristic behaviour in the glass transition region, but their interpretation has hitherto been unclear. The present work clarifies this situation by a theoretical analysis of the technique of MDSC, which introduces a kinetic response of the glass in the transition region. This analysis is able to describe all the usual features observed by MDSC in the glass transition region. In addition, the model is also able to predict the effects of the modulation variables, and some of these are discussed briefly.

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Abstract  

The application of differential scanning calorimetry (DSC) for purity determination is well documented in literature and is used amongst others in the analysis of pure organic crystalline compounds. The aim of this work is to examine whether the DSC method for purity determination consistently produces values for the purity of polycyclic aromatic hydrocarbons (PAHs) which are sufficiently accurate as required for the certification of reference materials. For this purpose, 34 different existing PAH certified reference materials were tested. The DSC results are shown to be consistent with the results obtained by other methods assessing the organic impurities content in PAHs, like gas chromatography (GC), high performance liquid chromatography (HPLC) and mass spectrometry. Significant differences between the measured values and the certified purity values were observed only in a limited number of cases.

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Abstract  

The physical stability of amorphous drug in solid dispersion was estimated using differential scanning calorimetry (DSC). Tolbutamide (TB) and flurbiprofen (FBP) were selected as insoluble drugs in water. Polyvinylpyrrolidone (PVP) was selected as a polymer for solid dispersion. Solid dispersions of various ratios of TB or FBP and PVP-K25 were prepared by solvent evaporation method and the induction period of crystallization from amorphous drug in solid dispersion was measured by DSC. Compared with FBP, the induction period of crystallization from TB was delayed by an addition of PVP. The improvement of the physical stability by the addition of PVP-K25 was estimated from the activation energy of diffusion of drug molecules and the interfacial free energy between drug crystal and supercooled liquid of drug in solid dispersion. From thses results, the hindrance of the diffusivity of the drug molecule might be mainly affected the delay of the induction period of crystallization of TB and FBP.

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Abstract  

This paper describes some examples of the use of differential scanning calorimetry (DSC) in providing information for advanced solidification processing of metals and alloys. Spray forming, squeeze casting, grain refinement and crystallization of amorphous alloys are all discussed. DSC measurements are shown to be valuable for testing kinetic theories of nucleation and growth, and validating solidification process models.

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Abstract  

In this study, polycardanol, which was synthesized by enzymatic oxidative polymerization of thermally treated cashew nut shell liquid (CNSL) using fungal peroxidase, was partially or fully cured using methyl ethyl ketone peroxide (MEKP) as initiator and cobalt naphthenate (Co-Naph) as accelerator. The curing behavior of polycardanol was extensively investigated in terms of curing temperature, curing time, concentration of initiator and accelerator, and the monomer-to-polymer conversion of polycardanol by means of differential scanning calorimetry (DSC). The curing behavior significantly depends on the thermal condition given and it was monitored with the change of the exotherms as a function of temperature. The optimal conditions for fully curing polycardanol are 1 wt% MEKP, 0.2 wt% Co-Naph, curing time 120 min, and curing temperature 200 °C. This study suggests that a polycardanol with high monomer-to-polymer conversion would be useful for processing a polycardanol matrix composite under the optimal conditions of curing.

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