Investigation of the heating and curing rate of polymeric materials with thermal energy, continuous and pulsed microwave radiation
The purpose of this work was to study the heating and curing rate of polymers with continuous and pulsed microwave radiation and compare with conventional thermal energy. The heating rate of poly(ethylene glycol) and poly(propylene glycol) has been studied as a function of molecular weight with pulsed as well as continuous microwave radiation, at constant average power. The curing rate of poly(amic acids) have also been studied with thermal energy, continuous and pulsed microwave radiation to better understand the interaction between pulsing the microwave and the polymeric material.
Results from the heating rate studies indicate that the enhancement in heating rate with pulsed microwave radiation depends on the low frequency absorption spectrum (i.e., less than 10,000 Hz) of the polymer. The heating rate of poly(propylene glycol), which has a low frequency absorption, was enhanced by pulsing the microwave energy whereas the heating rate of poly(ethylene glycol), which does not have a low frequency absorption, remained the same when compared to continuous wave. Also results from the curing rate studies with poly(amic acids) indicate that the enhancement in curing rate observed in samples cured by microwave radiation as opposed to those thermally cured may be partially due to microwave power distribution in the cavity. This has been tested by agitating the sample to reduce any temperature gradient arising from the power distribution in the cavity. According to the experimental results, as the agitation rate was increased, the rate of imidization of poly(amic acids) with microwave radiation approached the rate of thermal imidization, at constant temperature. However, more research is required to clarify this complex phenomenon.