2.1 Polymerisation and phase transformations

Thermosetting resin changes its state from liquid to gel and then solid during the exother- mic cross-linking reactions, which is facilitated by heaters attached to the pultrusion die.2.1 is a schematic diagram showing the cross-linking or polymeri- sation steps of a thermosetting resin.The TTT diagram indicates a well-thought-out framework for key aspects, such as phase separation, gelation, vitrification, full cure, and devitrification, which take place during the isothermal curing of thermosetting resins.During the chemical reactions, the viscosity, density, elastic modulus, and glass transition temperature T, of the thermoset resin change; in addition, the molar mass increases as a result of the cross-linking reactions.Gillham [3] studied the phase transformations for thermosetting resins and proposed a time-temperature-transformation (TTT) diagram depicted in Fig.2.1c), a fully cured state is obtained, in which the resin is solidified into a glassy state.Fig.2.1b.2.2.