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see also:
Algorithm of Analysis using
ChemRheo,
Applications,
The program ChemRheo is
used to analyze the influence of temperature and time on the
viscosity of both reactive and non-reactive materials.
In the case of reactive systems, two effects are superposed
in rheometric measurements: namely the temperature
dependence of viscosity and its increase with increasing
reaction degree. The separation of these two effects can be
managed by investigating the curing/cross linking kinetics
by means of Differential Scanning Calorimetry (DSC) and
based on this, describing the increase of viscosity during
curing/cross linking.
The program offers 6
different models in order to fit the relation between the
degree of conversion and viscosity:
Pahl-Hesekamp (epoxy resin)
Extended Pahl-Hesekamp (epoxy resin)
Macosko (epoxy resin)
Gel-switch
Exponential gain
Exponential gain with energy change (powder
paints)
The Pahl-Hesekamp models are preferred for curing reaction
of reactive systems as epoxy resins. In these models the
glass transition temperature in dependence on the reaction
degree plays a central role (fig. 1). This dependence is
approximated for the further analysis by equation (1)
[J.P. Pascault, R.J. Williams: J. Polym. Sci. Part B
28(1990) 85].
Dependence of glass
transition temperature on the reaction degree for the system
DGEBA and aniline.
Based on the results from the kinetic analysis of DSC
measurements, the degree of reaction x is calculated for a
preset temperature regime and the respective glass
transition temperature Tg(x) using equation 1. Now it is
possible to determine the yet unknown parameters C1, C2 as
well as B1 and B2 with dynamic and/or isothermal
measurements of viscosity via equation 2.
Kinetic analysis of
DSC measurements
Thus all parameters are available to carry out simulations
of time and temperature dependence of viscosity. In similar
way the parameters are estimated also for another fitting
model of viscosity, using multivariate non-linear regression
.
Analysis of dynamic
rheometer measurements.
The DSC data supply the kinetic parameters.
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