The nucleating efficiency and selectivity of different
β-nucleating agents was characterised and compared by differential scanning
calorimetry, (DSC) and temperature-modulated DSC (TMDSC). The nucleating agents
were the calcium salts of pimelic and suberic acid (Ca-pim and Ca-sub), linear trans-γ-quinacridone (LTQ), a commercial nucleator
NJ Star (NJS) and an experimental product (CGX-220). The efficiency and the
selectivity of Ca-sub and Ca-pim are extremely high. NJS is efficient above
a critical concentration, which is connected with its partial dissolution
in polypropylene melt. LTQ and CGX-220 possess strong overall nucleating ability
and moderate selectivity. Using TMDSC, we found that three consecutive processes
take place during the heating of β-nucleated samples cooled down to room
temperature: reversible partial melting of the β-form, irreversible βα-recrystallisation,
and the melting of the α-modification formed during βα-recrystallisation
or being present in samples prepared with non-selective β-nucleators.
Melting of the α-phase contains both reversible and irreversible components.
TOPEM is a new temperature modulated DSC technique, introduced by Mettler-Toledo
in late 2005, in which stochastic temperature modulations are superimposed
on the underlying rate of a conventional DSC scan. These modulations consist
of temperature pulses, of fixed magnitude and alternating sign, with random
durations within limits specified by the user. The resulting heat flow signal
is analysed by a parameter estimation method which yields a so-called ‘quasi-static’
specific heat capacity and a ‘dynamic’ specific heat capacity
over a range of frequencies. In a single scan it is thus possible to distinguish
frequency-dependent phenomena from frequency-independent phenomena. Its application
to the glass transition is examined here.
A new method is presented to analyze the irreversible melting kinetics of polymer crystals with a temperature modulated differential
scanning calorimetry (TMDSC). The method is based on an expression of the apparent heat capacity,
. The present paper experimentally examines the irreversible melting of nylon 6 crystals on heating. The real and imaginary
parts of the apparent heat capacity showed a strong dependence on frequency and heating rate during the melting process. The
dependence and the Cole-Cole plot could be fitted by the frequency response function of Debye's type with a characteristic
time depending on heating rate. The characteristic time represents the time required for the melting of small crystallites
which form the aggregates of polymer crystals. The heating rate dependence of the characteristic time differentiates the superheating
dependence of the melting rate. Taking account of the relatively insensitive nature of crystallization to temperature modulation,
it is argued that the ‘reversing’ heat flow extrapolated to ω → 0 is related to the endothermic heat flow of melting and the
corresponding ‘non-reversing’ heat flow represents the exothermic heat flow of re-crystallization and re-organization. The
extrapolated ‘reversing’ and ‘non-reversing’ heat flow indicates the melting and re-crystallization and/or re-organization
of nylon 6 crystals at much lower temperature than the melting peak seen in the total heat flow.
One of the benefits of temperature-modulated DSC (TMDSC) is its ability to measure thermal conductivity and thermal diffusivity
without DSC cell modifications or additional accessories. Thermal conductivity of solid materials from 0.1 to about 1 W m-1 K-1 measured. Applications of this approach have been discussed in the literature but no description is yet available concerning
the derivation of the working equations. This presentation provides a detailed derivation of the working equations used to
obtain thermal conductivity and thermal diffusivity from TMDSC data.
The quality of measurement of heat capacity by differential scanning calorimetry (DSC) is based on the symmetry of the twin
calorimeters. This symmetry is of particular importance for the temperature-modulated DSC (TMDSC) since positive and negative
deviations from symmetry cannot be distinguished in the most popular analysis methods. Three different DSC instruments capable
of modulation have been calibrated for asymmetry using standard non-modulated measurements and a simple method is described
that avoids potentially large errors when using the reversing heat capacity as the measured quantity. It consists of overcompensating
the temperature-dependent asymmetry by increasing the mass of the sample pan.
Temperature modulated DSC (TMDSC) at low temperatures requires attention to the selection of experimental parameters that
are within the capability of the instrumentation as well as special care in calibration of heat capacity measurement when
high precision is required. Data are presented to facilitate selection of appropriate modulation periods and amplitudes at
low temperature when using a mechanical cooling accessory. The standard error of the mean heat capacity measurement for a
sapphire standard increased with decreasing temperature, decreasing period, and increasing pan mass. For ice in hermetically
sealed pans, the standard error of the mean heat capacity measurement was larger than for sapphire and did not follow a predictable
trend with changes in temperature and period of modulation. This was attributed to changes in sample geometry between successive
measurements due to melting and resolidification. A simple one-point temperature calibration by TMDSC may be unsuitable for
precise measurement of heat capacity because of the random error caused by sample placement and the systematic error caused
by cell asymmetry, temperature dependence of the calibration constant, and different sample thermal conductivities. An alternative
calibration procedure using standard DSC and either a linear or second order fit of the calibration constant over the temperature
range of interest is proposed.
Temperature-modulated DSC (TMDSC) was used to enhance the perfection of crystals of different poly(p-phenylene sulfide) samples formed during slow cooling from the melt. The sample preparation was made with modulated cooling using a cool-heat mode. Re-heating the samples prepared by slow conventional and modulated coolings indicated that the melting point of the samples prepared by modulated cooling is considerably higher than the melting point of the samples crystallized with conventional cooling. Thus, the perfection of crystallites can be improved if the outer layers just deposited on their surface are re-melted and re-crystallized immediately.
The frequency dependences of the complex-specific heat of the sodium borate glasses, xNa2O·(100 − x)B2O3, where x denotes molar concentration of Na2O, have been investigated by temperature-modulated DSC. The temperature dependences of α-relaxation time have been analyzed
in Angell plot, and the fragility index has been determined. The composition dependence of the fragility index has been discussed
on the basis of the variations of the structural units of the borate network. The origin of the fragility of the borate system
relates to the distribution of the coordination number of boron atom.
The curing reaction of a thermosetting system is investigated by DSC and temperature modulated DSC (TMDSC). When the material
vitrifies during curing, the reaction becomes diffusion controlled. The phase shift signal measured by TMDSC includes direct
information on the reaction kinetics. For long periods the phase shift is approximately proportional to the partial temperature
derivative of the reaction rate. This signal is very sensitive for changes in the reaction kinetics. In the present paper
an approach to determine the diffusion control influence on the reaction kinetics from the measured phase shift is developed.
The results are compared with experimental data. Further applications of this method for other reactions are proposed.
The application of non-linear heating program to a heat-flux DSC apparatus has attracted much attention. From thermodynamics
viewpoint, it is shown that the variation of enthalpy of a sample changing with temperature change is due, to both the true
heat capacity of the sample and the enthalpy of some transformations occurring in the sample, characterized by its degree
of advance. Using the simple assumption that the rate of the transformation is proportional to the distance from the thermodynamic
equilibrium, an electrical model of the thermal event is given. Using the coupled cell model of the DSC apparatus, we show
how to obtain the rate of transformation of the sample and heat capacity, which is directly related to the base line of the