IN-SITU MONITORING OF POLYMER PROCESSING PROPERTIES

Frequency-dependent dielectric measurements, often called frequency-de pendent electromagnetic sensing (FDEMS), made over many frequency rang es, Hz-MHz, provide a sensitive, convenient automated means for monito ring in situ the processing properties of thermosets and thermoplastic s. Using a planar wafer-thin sensor; measurements can be made in situ in almost any environment. Through the frequency dependence of the imp edance, this sensing technique is able to monitor chemical and physica l changes throughout the entire cure process. In this presentation we discuss how to use the frequency dependence in the Hz-MHz range to sep arate and determine parameters governing ionic and dipolar mobility is discussed. In turn, the relationship between these two molecular prob es, ionic translational mobility and dipolar rotational mobility, and macroscopic processing properties is also discussed. The cure of a hig h-temperature polyimide (PMR-15) and the cure of several epoxy resins were monitored using dielectric sensing. The ionic and dipolar mobilit ies are quantitatively related to the viscosity, degree of cure and th e build up in glass transition temperature. The ability of the change in ionic mobility to detect the gel point through the determination of an inflection point and through the use of a power law (1 - t/t(gel)) (x) is discussed. Finally the application of in situ sensing to monito r processing properties and to control the cure process intelligently in a complex part in an autoclave is described. (C) 1997 by John Wiley & Sons, Ltd.