How To: Create Kinetic Model with Diffusion Control

Curing of Epoxy Resin with Diffusion Control

Introduction

If the glass-transition appears during the cross-linkage of a thermoset, then the reaction is separated into two domains that are dominated by different mechanisms: The part taking place far above glass-transition depends on the chemical reaction and can be described by the Arrhenius relation. In the part below glass-transition diffusion controlled mechanisms dominate the reaction behavior. Therefore, the reaction rate around the glass-transition is influenced by both processes.

That's why the kinetic model has to be expanded by the special diffusion control algorithms in order to take into account the change of the material behavior.

In this "How To:", two single-step kinetic models for DSC data will be created:

  • preliminary kinetic model without diffusion control,
  • final kinetic model with partial diffusion control.

In this system kinetic mechanism changes when sample temperature crosses glass transition temperature.

We will start by loading a sample data project included in Kinetics Neo, will then create a preliminary kinetics model, will then add the diffusion control mechamism in order to have the final model.

Sample data:

  • Data type: DSC Curing (Differential Scanning Calorimetry with Diffusion Control)
  • Project file: DSC_Diff_Control_Epoxy_Data.kinx

Load the Sample Data Project

1. Start the Kinetics Neo software.

Click on the blue "File" tab to open the application menu.

2. Open Sample Data DSC Curing project.

Click on "Open" in the menu on the left side, then select "Samples". The Kinetics Neo samples directory will be opened in Windows Explorer.

Select directory "DSC_Diff_Control_Epoxy".

3. Open the Kinetics Neo project file "DSC_Diff_Control_Epoxy_Data.kinx" .

4. In the tree panel select Glass transition Data and check if the glass transition data are present and fit is created.

Create Preliminary Model of Cn Type without Diffusion Control

5. In the left tree panel select Model based-Add new and select reaction type Cn.

6. Write Cn in Description and Select Optimize in Step box

7. Switch to Conversion in order to see, where this model is still not OK

8. Switch to Signal-Relative in order to see, where this model is still not OK

Create Final Model of Cn Type with Diffusion Control

9. Create the copy of the previous model: Select the model in tree panel and click on Plus symbol +

10. For the second model change the Description to Cn diff same as above

11. Switch to Conversion and check the checkbox Diffusion control. Three additional parameters appear in the parameter list for this reaction step. The default values for these additional parameters are usually not too far away from the optimum parameters.

These Parameters K, C1 and C2 are the parameters from WLF (Williams-Landel-Ferry) equations, which is used for the calculation of diffusion coefficient near glass transition temperature.

12. Switch to Signal and select Optimize in Step box

13. Switch to Conversion in order to see, how good is the fit

14. Switch to Signal-Relative in order to see how good is the fit

Conclusion

The curing of epoxy resin containing the crossing of glass temperature and sample temperature, can be described by the kinetic model with diffusion control. Diffusion near glass transition temperature is described by WLF (Williams-Landel-Ferry) equation.