Physical aging of polyetherimide (PEI) was studied using a bellows dilatometer based on Zoller's design. A linear variable
differential transformer (LVDT) is used to measure the displacement of the bellows. The voltage output of the LVDT is interfaced
to a computer for automated data collection. Isothermal aging experiments were carried out at temperatures near the glass
temperature (206–209 ‡C) using a constant temperature oil bath maintained at the desired aging temperature. The time required
to reach equilibrium and the reduced curve produced by aging time-temperature superposition are given. The results compare
well with data obtained by capillary dilatometry for the same material.
The physical aging characteristics of maltose glasses aged at two temperatures below the glass transition temperature, Tg, (Tg-10C and Tg-20C) from 5 to 10 000 min were measured by standard differential scanning calorimetry (SDSC) and modulated differential
scanning calorimetry (MDSC). The experimentally measured instrumental Tg, the calculated Tg, and the excess enthalpy values were obtained for aged glasses using both DSC methods. The development of excess enthalpy
as a function of aging time, as measured by both SDSC and MDSC, was fit using the Cowie and Ferguson and Tool-Narayanswamy-Moynihan
models. The change in the Tg values and the development of the excess enthalpy resulting from physical aging measured by the two DSC methods are discussed.
Authors:L. Barral, J. Cano, J. López, I. López-Bueno, P. Nogueira, M. Abad, and C. Ramírez
The physical aging of a system containing tetraglycidyl-4-4′-diaminodiphenylmethane (TGDDM), with a multifunctional novolac
glycidyl ether resin hardened by 4,4′-diaminodiphenylsulphone (DDS) has been investigated by differential scanning calorimetry
(DSC) and dynamic mechanical analysis (DMA). Samples fully cured were aged at temperatures between 200 and 250C, during periods
of time from 1 to a maximum of 336 h. Furthermore, the dynamic mechanical relaxation behaviour annealed at temperature of
220C, was studied, aging during 24 and 168 h. The effect of the enthalpy relaxation during DSC heating scan is shown by the
presence of an endothermic peak whose position and intensity depends on the aging conditions, both temperature and time. DSC
studies suggest that enthalpy relaxation increases gradually with aging time to a limiting value for each temperature where
structural equilibrium is reached. DMA results show that the effect of aging is to cause chain stiffening and a decrease in
the height of the peak value of the loss factor.
Authors:R. Golovchak, O. Shpotyuk, A. Kozdras, B. J. Riley, S. K. Sundaram, and J. S. McCloy
the heavier chalcogen atoms (S, Se, Te), which are the main constituents of their covalent networks. However, chalcogen-rich glasses possess a pronounced physicalaging effect under ambient conditions hindering their wide use for several applications
Authors:A. Farahnaky, A. Guerrero, S. Hill, and J. Mitchell
Glass transition temperature of red crayfish flour (moisture 3.56%) was determined using a phase transition analyser (Wenger
Technical Centre, USA). Due to the importance of physical ageing in functional properties of red crayfish flour (with 65%
protein) the possible occurrence of physical ageing in dry powder of crayfish flour was studied at different temperatures
below and close to the glass transition.
Endothermic peaks that corresponded to relaxation enthalpy were observed for a commercial crayfish flour with 4.5% moisture.
Enthalpy and peak temperature increased on storage of crayfish flour when it was held in the glassy-state at different temperatures
(5, 15, 25°C).
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.
Vitrification phenomena and further structural relaxation processes or physical ageing occurring in the isothermal curing reaction of an epoxy resin are studied by Differential Scanning Calorimetry (DSC). The vitrification time,tv, the limiting conversion degree and the limiting glass transition temperature (Tg) are evaluated at curing temperatures (Tc) between 30 and 100‡C. The dependence of limitingTg withTc permits the determination of the maximumTg of the resin (109‡C). The physical ageing, which appears as the the last step of curing reaction for curing times above to vitrification, is analyzed through the endothermic peak superposed to the glass transition temperature. The results obtained in partially reticulated resin show the kinetics of the physical ageing to slow down asTc increases, as a consequence that the segmental mobility is reduced.
The physical ageing characteristics of glucose, fructose, and their mixtures were studied using standard differential scanning calorimetry (DSC). The inflection, onset, midpoint,half-height, and endpoint glass transition temperature (Tg), fictive temperature (Tf), and relaxation enthalpy (
H) were measured as a function of ageing time. The relationship between
H and Tf was evaluated. The time dependence of
H was fit using the Cowie and Ferguson model. The ageing rate was expressed in terms of the average relaxation time (<>) and the entropy production (P). It was found that the fructose component decreased the rate of ageing of the mixtures.
We report the results of an investigation by differential scanning calorimetry (DSC) of two mobility controlled processes
in the amorphous phas e of semicrystalline PEEK — enthalpy relaxation below the glass transition (Tg) and secondary crystallization aboveTg. Both result in the observation of an endothermic peak just above the annealing temperature in the DSC scan of the polymer
— the enthalpy recovery peak and the low temperature melting peak, respectively. There is a striking similarity in the time
and temperature dependence of the endothermic peak for these two processes. These results are reminiscent of those obtained
from small strain creep studies of “physical aging” of semicrystalline PEEK below and aboveTg.