Authors:C. Ramírez, M. Abad, L. Barral, J. Cano, F. Díez, and J. López
Using differential scanning calorimetry (DSC) we have studied the physical aging of an epoxy resin based on the diglycidyl
ether of bisphenol A (DGEBA) modified by two different contents of an acrylonitrile-butadiene-styrene (ABS) and cured with
1,3-bisaminomethylcyclohexane (1,3-BAC). Samples fully cured were annealed at temperature of 125C for periods of time of
72 and 120 h, to determine the process of physical aging. The apparent activation energy for the enthalpy relaxation, Dh*, is determined as the sample is heated at 10C min-1 following cooling at various rates through the glass transition region. DSC studies suggested that the presence of thermoplastic
inhibits the process of relaxation.
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-Tg 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.
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<xGPS<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 xGPS=0.45. GPS showed a slightly higher enthalpy relaxation rate than isomalt.
enthalpyrelaxation 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
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 enthalpyrelaxation. Goff et al . [ 23 ] also concluded for a 40% sucrose solution that the higher temperature transition is a glass transition as the lower
Gallino , I , Shah , MB , Busch , R . 2007 . Enthalpyrelaxation 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
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 enthalpyrelaxation or crystallization). We use the phase