| 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. |
ChemRheo®
back