The glass transition in novolac phenolic molding compounds and the kinetics of its development during cure and postcure. II

The change in onset temperature of the glass transition in a novolac phenolic molding compound was related to the time and temperature of cure. A mathematical model consisting of a single function of time and temperature fit glass transition onset temperature ranging from 87 to 242°C. These glass transition temperatures had developed during molding at temperatures from 132 to 218°C at times of 10–1800 s. The same model predicted the glass transition and onset temperature of samples postcured to a glass transition temperature of 287°C. The mathematical model resulted from a kinetic rate law treatment. This treatment, however, did not include a secondary reaction which causes a small exotherm above 210°C in DSC testing. The resulting rate law still appears to provide a useful approximation of the development of the Tg and the cure rate in novolac phenolic molding compounds over practical molding and postcure conditions.