THE MICROWAVE PROCESSABILITY OF SEMICRYSTALLINE POLYMERS

The overall objective of these studies was to investigate the relation ship between polymer structure and microwave absorptivity. In this pap er, the microwave processing of semicrystalline polymers such as poly( ether ether ketone) (PEEK), nylons, and poly(ethylene terephthalate) ( PET), via a cylindrical resonance wave cavity and a rectangular standi ng wave applicator is described. These polymeric materials were irradi ated in low power (< 50W) electric fields at 2.45 GHz. Silicone flexib le molds were necessary for improved processing of nylons and PEEK at temperatures below their T(c). Rapid heating rates were observed betwe en the glass transition temperature, T(g), and the melting temperature , T(m), for all these polymers provided that T(c) was exceeded. Both d ynamic mechanical thermal analysis (DMTA) and dielectric thermal analy sis (DETA) spectra were utilized to predict the heating phenomena betw een amorphous and semicrystalline materials and to explain the rapid c rystallizing rate of PEEK above its glass transition temperature. Corr elations were drawn between a) the apparent activation energy and the critical temperature (T(c)) and b) the shape of the dielectric spectra at 2.45 GHz and its shape in kHz region.