Effect of cure cycle on enthalpy relaxation and post shrinkage in neat epoxy and epoxy composites

The effect of cure cycle on enthalpy relaxation and warpage is studied for both neat epoxy and glass/epoxy composites.
An approach for determining the enthalpy relaxation in the matrix of composite materials combining
modulated differential scanning calorimetry and thermogravimetry is presented. The enthalpy relaxation is
coupled to structural dimension changes upon reheating by performing modulated thermo mechanical analysis.
The enthalpy relaxation is affected by the cooling rate and the presence of the fibrous reinforcement, but is unaffected
by variation between a 1-stage and 2-stage cure cycle. Enthalpy recovery is found to exert a minor impact
on the sample dimension during reheating since a non-reversing shrinkage is observed during reheating.
This shrinkage is ascribed to structural changes on molecular level in the specimen and it is inferred that samples
with a high initial disorder only exhibit a small dimensional change during reheating due to structural restrictions
within the amorphous polymer network.