Microwave Dynamic Dielectric Analysis of Curing Neat Resins

Abstract

Microwave reflection resonator sensors have been developed to monitor the complex, dynamic, in situ real and imaginary dielectric permittivity (ε* = ε'_d - jε"_d) of thermoset polymer matrix composites and thermoplastics. These reusable and noninvasive sensors are conformably mounted in the autoclave mold in such a manner that the EM fields are strongly coupled to the resin. Tracking of (ε'_d, ε" _d) during the cure provides in formation about the chemical kinetics, resin viscosity, rigidity, porosity and relative cure index. The sensor is readily adjustable for optimum coupling to the type of material being tested. The existing sensor is rated for temperatures up to 250°C (480°F), but this can be extended to higher temperatures. The technique has been beta-tested in a commercial laboratory over a 9-month period, and is complementary to other analysis techniques such as Differential Scanning Calorimetry (DSC) and Dynamic Mechanical Analysis (DMA). A prototype software and electronics package has been developed to support the sensor. This paper focuses on the testing of neat epoxy resins.