Separation of the Glass Transition and Postcuring (TOPEM)

Purpose

To demonstrate how TOPEM^® (a temperature-modulated DSC method) can separate different effects and so allow the determination of the glass transition temperature, T_g and the post-curing enthalpy Δh_post-
A postcuring reaction usually begins just above the glass transition. In conventional DSC measurements, this often makes it difficult or even impossible to determine the glass transition temperature and the postcuring enthalpy. 

Sample

Laminated composite material made of carbon fibers and epoxy resins with a very high glass transition temperature. 

Conditions

Measuring cell: DSC

Pan: Aluminum 40 μL

Sample preparation: Pieces weighing 19.326 mg (conventional DSC) and 24.188 TOPEM^®  were sawn out of a sheet of the composite.

DSC measurement: Heating from 50 to 280°C at 2 K/min. TOPEM^®: Pulse heigh 0.5 K, pulse width 15 to 30s.

Atmosphere: Nitrogen

Interpretation

The conventional DSC measurement (upper curve) shows the postcuring reaction as an exothermic peak which is overlapped by the beginning of the exothermic decomposition process. A step in the curve that could be used to determine the T_g is not apparent. 

Conclusions

The postcuring enthalpy can be determined by conventional DSC, but the accompanying glass transition can often only be observed using a TMDSC method (e.g. TOPEM^®)

_{Separation of the Glass Transition and Postcuring | Thermal Analysis Handbook No.HB13 | Application published in METTLER TOLEDO TA Application Handbook Thermosets, Volume 1}