Authors:Y. Yoshihashi, H. Iijima, E. Yonemochi, and K. Terada
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.
Authors:S. Aubuchon, L. Thomas, W. Theuerl, and H. Renner
40% w/w sucrose/water solutions were analyzed by Modulated Differential Scanning Calorimetry  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 Tg. 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.
Authors:Qun Zhou, Donghwan Cho, Bong Song, and Hyun-Joong Kim
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.
Authors:A. Vasconcelos, M. Dantas, M. Filho, R. Rosenhaim, E. Cavalcanti, N. Antoniosi Filho, F. Sinfrônio, I. Santos, and A. Souza
The influence of drying processes in the biodiesel oxidation was investigated by means of the oxidative induction time obtained
from differential scanning calorimetry data. For this purpose, corn biodiesel was dried by different methods including: chemical
(anhydrous sodium sulfate) and thermal (induction heating, heating under vacuum and with microwave irradiation). The drying
efficiency was evaluated by monitoring IR absorption in the 3,500–3,200 cm−1 range and by the AOCS Bc 2-49 method. In general, the oxidative induction times increased inversely to the heating degree,
except that of microwave irradiation, which was selective to water evaporation and caused low impact over the unsaturation
of biodiesel. The DSC technique was shown to be a powerful tool to evaluate with high level of differentiation the influence
of the drying process on the oxidative stability of biodiesel.
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).
Authors:G. Maschio, J. Feliu, J. Ligthart, I. Ferrara, and C. Bassani
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.
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.
Authors:Katarzyna Drozdzewska, V. Kestens, A. Held, G. Roebben, and T. Linsinger
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.
The phase diagram for the AgNO3−KNO3 system has been determined using differential scanning calorimetry (DSC). Eutectic point has been found at 391 K andXAg=0.580 mole fraction AgNO3. The DSC curves indicate the existence of an intermermediate compound (AgNO3·KNO3) in the KNO3-rich region of the phase diagram. This compound was identified in the solid phase by X-ray diffraction. The melting and the
crystallization processes were followed with the aid of a hot stage microscope, too.
Thermal analysis of the binary system KCl-LiCl in the composition range 0.368–0.812 mol fraction of LiCl was studied by differential
scanning calorimetry (DSC). On the basis of the DSC curves, the experimental data for the phase-diagram, the latent heat of
fusion, and the average specific heat in the liquid and solid states are presented as a function of the composition of the
mixture. The experimental results compared with literature data. The following empirical correlation between the heat of fusion
(ΔH) and of compositions of the mixture in mol fraction of LiCl (x) was obtained: ·GH=26.95−50.20x+43.06x2 with a minimum value of 11.8 kJ(g mol)−1 at the eutectic point of 0.587 mol fraction of LiCl at 354.4°C. These results are required as basic data to develop thermal
energy storage materials, based on the phase change of a molten mixture of KCl-LiCI.