Enthalpy relaxation and post shrinkage of sub and sup-Tg cured epoxy

The effect of sub and sup Tg cure and the cooling rate from the cure temperature on the enthalpy recovery of epoxy is explored. Further, it is investigated whether the enthalpy state is linked to shrinkage of the epoxy upon reheating. From modulated DSC measurements it is found that enthalpy relaxation is greater for slower cooling at sup Tg cure, whereas at sub Tg cure, the enthalpy relaxation appears independent of the cooling rate. From modulated TMA measurements it is found that all samples exhibit a linear shrinkage around 0.3% upon reheating irrespective of the cure schedule. The molecular phenomena that could explain this shrinkage are discussed.