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Abstract  

Composites of poly(vinyl pyrrolidone)/hydroxyapatite (PVP/HA), at variable proportions (100/0; 80/20; 50/50; 20/80 wt%) were prepared and characterized by Fourier transformer-infrared spectroscopy (FT-IR), wide angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), and thermogravimetry/differential thermogravimetry (TG/DTG). PVP carbonyl stretching was slightly shifted to lower frequency in composites indicating the formation of hydrogen bonding with HA hydroxyl groups. At the first cycle of heating, the calorimetric curves revealed a broad peak the intensity of which was reduced insofar as the amount of PVP decreased in the composites. This peak was attributed to the PVP enthalpy relaxation. According to the TG/DTG curves, PVP degraded into two steps sharply perceivable in the composites. The first decay was ascribed to the release of the pyrrolidone pendant groups and the following one concerned the burning of the hydrocarbon chains. The HA molecules seem to exert a catalytic action on the PVP degradation.

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Abstract  

A DSC study has been carried out on isomalt, a commercial sugar alcohol derived from sucrose and widely used as a sweetener in the food industry. Isomalt is a mixture of two isomers:α-D-glucopyranosyl–1-6-mannitol (GPM) and α-D-glucopyranosyl–1-6-sorbitol (GPS). Release of the water of crystallisation (around 100C)and melting (around 150C) have been phenomenologically characterised using different scanning rates and heat treatments. The effect of dehydration/re-hydration on the melting has been investigated. The isomalt glass transition, at about 60C, was studied on samples cooled after melting. The dynamic aspect of structural relaxation of isomalt has been quantified by its fragility parameter. Glassy state stability has been evaluated by performing ageing experiments at sub-T g temperatures. During ageing, apart from the expected enthalpy relaxation effects, isomalt showed a peculiar behaviour, due to its isomeric composition. These preliminary and phenomenological results have been interpreted in terms of isomer structure and of carbohydrate-water interactions in the mixture.

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Abstract  

Isomalt, a commercial sugar alcohol widely used as a sweetener, is approximately a 1:1 mixture of two diastereomers, -D-glucopyranosyl-1-6-mannitol (GPM) and -D-glucopyranosyl-1-6-sorbitol (GPS). A calorimetric investigation has been carried out on mixtures of isomalt with GPS, in the (molar) composition range 0.45<x GPS<1, for both crystalline and amorphous states.The GPS-rich portion of the solid-liquid GPM/GPS phase diagram was established and discussed in light of the existing literature. New evidence was given for the non-ideality of GPM/GPS mixtures, by indicating excess interactions in the melt and/or in the solid state. The commonly accepted hypothesis of a simple GPM/GPS eutectic forming isomalt was refuted in favour of more complicated mixture behaviour with possible formation of a complex.Glass transition and physical ageing of isomalt and GPS were re-visited, with peculiar attention given to the measurement conditions. Standard thermal histories were adapted to each sample and the fictive temperature was used for the characterisation of the structural glass states. A linear increase of the fictive temperature was found upon passing from pure GPS to x GPS=0.45. GPS showed a slightly higher enthalpy relaxation rate than isomalt.

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enthalpy relaxation in the GTR was analyzed by Svoboda et al. [ 9 ]. The finding that the activation energy of viscous flow in the glass-transition range was identical with the effective activation energy for relaxation process. This subject received

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. 3. Zelkó , R , Orbán , Á , Nagy , J , Csóka , G , Rácz , I . Coating polymer–plasticizer interaction in relation to the enthalpy relaxation of polymer . J Therm Anal Calorim . 2002 ; 68 : 531 – 537 . 10.1023/A

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Dynamic and sub-ambient thermal transition relationships in water–sucrose solutions

Differential scanning calorimetry and neutron scattering analysis

Journal of Thermal Analysis and Calorimetry
Authors: D. Champion, C. Loupiac, D. Russo, D. Simatos, and J. M. Zanotti

exhibited non-fully reversing heat flow on cooling and heating, similar to a glass transition with enthalpy relaxation. Goff et al . [ 23 ] also concluded for a 40% sucrose solution that the higher temperature transition is a glass transition as the lower

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enthalpy relaxation: the effect of experimental conditions . J Therm Anal Calorim 81 : 125 – 129 10.1007/s10973-005-0755-x . 10. Chromčíková , M , Dej , P 2006 Structural relaxation of NBS

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structural analogues using MTDSC . Int J Pharm . 2001 ; 213 : 163 – 173 . 10.1016/S0378-5173(00)00662-1 . 37. Vasukumar , K , Bansal , AK . Enthalpy relaxation studies on celecoxib

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Journal of Thermal Analysis and Calorimetry
Authors: Javier Tarrío-Saavedra, Carlos Gracia-Fernández, Jorge López-Beceiro, Salvador Naya, and Ramón Artiaga

than the C p change when the amorphous fraction is relatively small, as it happens in crystalline polymers, what makes TMDSC more useful in this case (in addition to separating the effects of enthalpy relaxation or crystallization). We use the phase

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.04.072 . 28. Gallino , I , Shah , MB , Busch , R . 2007 . Enthalpy relaxation and its relation to the thermodynamics and crystallization of the Zr 58.5 Cu 15.6 Ni 12.8 Al 10.3 Nb 2.8 bulk metallic glass

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