| During the curing of epoxy resin a large amount of heat is generated: approximately 350 J/g. Under adiabatic conditions and a thermal capacity Cp of 2 J/gK the heat generation results in a temperature jump of 175°C. Because the decomposition of epoxy resins starts at 230°C, the start temperature (for the adiabatic case) must be lower than 55°C. |
| In the following sample, the curing kinetics are determined for a composite containing epoxy resin and a filler. On the basis of kinetics analysis and of caloric data as heat capacity, heat conductivity over the course of temperature is calculated for specific conditions, especially the thermal coupling at ambient temperature.
The goal of this work is the check of maximum temperature which is achieved for the specific conditions. |
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| Conditions of DSC measurements |
| Instrument: |
NETZSCH DSC 204 Phoenix® |
| Heating rates/(K/min): |
1, 2.5, 5, 10 |
| Sample mass/mg: |
4 .. 5 |
| Atmosphere: |
N2 |
| Crucible: |
Aluminum, pierced |
|
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| Kinetic analysis of DSC measurements |
 |
| Using a triple-step model, a useful fit-quality is achieved. |
| |
| Kinetic parameters of the best model: |
| lg A1/s-1: |
10.69 |
| E1/(kJ/mol): |
94.85 |
| React.ord 1: |
1.36 |
| lg A2/(kJ/mol): |
6.04 |
| E2/(kJ/mol): |
72.49 |
| React.ord 2: |
0.91 |
| lg A3/(kJ/mol): |
8.82 |
| E3/(kJ/mol): |
91.62 |
| lg Kcat 3: |
0.70 |
| FollReact. 1: |
4.50E-02 |
| FollReact. 2: |
0.776 |
| Area 1 ..4/(J/g): |
-287.0 |
|
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| Simulation of self-heating |
| On the basis of results of kinetic analysis and conditions of reactor, the simulation is performed. |
| |
| Conditions of simulation |
| Reactor type: |
cylinder |
| Diameter/cm: |
40 |
| Transfer Coeff/(W/cm2K): |
1.36E-3 |
| Start temperature/°C: |
56 |
| Cp/(J/gK): |
1.89 |
| Density/(g/cm3): |
1.28 |
| Heat conductivity/(W/cmK): |
0.0025 |
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 |
| Temperature vs. time at different distances from the center. |
| The self-heating starts very slowly. In the center the curing reaction is finished first. Now the heat is transferred more to the cold border. Because the curing reaction at the border starts from a higher temperature value, here the maximum temperature is located. |
| In order to achieve a full curing after a time of 12 hrs the ambient temperature is increased to 140 °C. |
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 |
| 3D-plot of self-heating |
| In the 3D plot the general behavior is more clearly depicted. The maximum near the border and the general decrease of temperature after full curing is visible. |
| This picture demonstrates the problems which are combined with the curing reaction of a large body: the behavior in the center is very close to the behavior of an adiabatic system. The jump in temperature is approximately Delta T = Heat/Cp. Unexpectedly, the critical position is near the border. |
Thermal Simulations
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