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Modulated DSC experiments for chemorheology

The above example of the determination of the change in Cp as the epoxy resin underwent crosslinking is an example of a reversible thermal event Cp decreases on vitrification) convoluted by a non-reversible chemical change due to the formation of the network by the ring-opening reaction of the epoxy resin (which produced a large exotherm). Experimentally this separation of the events is achieved by applying a small temperature oscillation on top of the isothermal temperature. The conditions are thus quasi-isothermal. The condition may be described (Jones et al, 1997) by [Pg.202]

The frequency of modulation is adjusted so that there are many cycles over the duration of the transition, which in this case is the glass transition and is therefore broad. A typical modulation condition is 0.5 C in a 60-s period for studying cure of an epoxy resin (Van Assche et al, 1997). The MDSC instrument provides a modulated heating programme of [Pg.202]

The combination of Equations (3.5) and (3.6) enables the DSC signal to be separated into an underlying component (the first two terms) and a cyclic component (the second two terms)  [Pg.202]

The first two terms are the equivalent of what is measured in a conventional DSC during the cure of an epoxy resin. The software of the instrument enables the non-reversing [Pg.202]

The three curves correspond to cure below, near and above Tg o, and it may be seen that only in the first case is there a clear step-change in heat capacity. The processing of the resin above Tgco (150°C) results in complete chemical reaction since there is no vitrification during cure. [Pg.203]


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