Gelation, Vitrification and Shrinkage of Thermoset Polymers - Methods for Investigation and Modelling

Thermosets play an important role in composite processing, adhesive bonding and coating. In all these applications, shrinkage my cause a significant amount of residual stress, leading to distortion, reduced load carrying capacity and cracking. The chemical curing reaction is accompanied by a reduction in volume called “chemical shrinkage”. If curing is performed at elevated temperature, cooling to ambient conditions afterwards is accompanied by “thermal shrinkage” and further shrinkage due to so-called “physical ageing”. A skillful combination of available methods makes it possible to separate chemical shrinkage in the viscous state from shrinkage in the gelled and vitrified state. Modeling of the time-and temperature-dependent properties is the prerequisite for the prediction and control of residual stresses caused by shrinkage in thermoset polymers.