Piezoelectric sensors for cure monitoring of thermosets

The results of the experiments directed to further development of the method to monitor the state of small samples of resin and polymers during curing are given. The method is based on the change of structure of oscillating transducers leading to the change of oscillation form and/or mode. The thin layer of epoxy resin was placed between two piezoelectric transducers in a form of piezoceramic plates. Curing epoxy resin forms the bimorph and its characteristics change with the changes of resin viscosity or, after gel point, stiffness. It is possible to establish epoxy resin curing level by monitoring changes in resonance parameters of bimorph elements. The main purpose of cure monitoring of small samples is to develop new method to evaluate the parameters of resin both before and after gel point, taking into consideration that the use of rheological data measured on small samples will be applied for designing or interpreting bulk-flow processes where epoxy may be considered a continuum. A small sample here is considered to have a volume in the range I - 20 mu l, since sample loading becomes difficult for volumes below this range.