Isothermal curing of an epoxy resin by alternating differential scanning calorimetry

The quasi-isothermal curing of a diepoxide resin with a triamine of polyoxy propylene was studied by alternating differential scanning calorimetry (ADS C), which is a temperature modulated DSC technique. The complex heat capaci ty measurements allows to analyse the vitrification process at curing tempe ratures (T-c) below the maximum glass transition of the fully cured epoxy ( T-g infinity = 85.8 degrees C). Initially, the modulus of the complex heat capacity \C-p*\, increases until a maximum (conversion between 0.42 and 0.5 6) and then decreases. This step is followed by an abrupt decay of \C-p*\ d ue to the vitrification of the system, which allows the determination of th e vitrification time. This value agrees well with that determined by the pa rtial curing method. The phase angle and out-of-phase heat capacity show an asymmetric wide peak during the vitrification process. The change in \C-p* \ at vitrification decreases with the increase of T-c becoming zero at temp erature T-g infinity This epoxytriamine system shows a delay of the vitrifi cation process respect to other model epoxy systems probably due to the pre sence of polyoxypropylene chains in the network. The decay of \C-p*\ during vitrification may be normalised between unity an d zero by defining a mobility factor. This mobility factor has been used to simulate the reaction rate during the stage where the reaction is controll ed by diffusion. The observed reaction rate is simulated by the product of the kinetic reaction rate, determined by the autocatalytic model, and the m obility factor. (C) 1999 Elsevier Science B.V. All rights reserved.