Degradation of Continuous Carbon Fiber Reinforced Polyetherimide Composites During Induction Heating

Abstract

Induction heating of carbon-fiber-reinforced thermoplastic-matrix composites has numerous advantages over conventional methods. Volumetric heating and high heating rates offer a significant reduction in cycle times for processing high-quality thick-section composites. However, the influence of high-frequency electromagnetic fields on the composite is not well understood. Two mechanisms of degradation during electromagnetic induction heating of AS4 carbon-fiber polyetherimide (PEI) were studied—thermal degradation and dielectric breakdown. Crosslinking and chain scission reactions are two major thermal degradation mechanisms that occur during melt processing of PEI. Changes in the molecular weight and glass transition temperature of the polymer were quantified over a wide range of process temperatures and times. The rheological properties of the composite system are also monitored to investigate viscosity changes due to molecular weight changes during the process. Dielectric breakdown during the induction process was also carefully examined. No significant change in polymer properties resulted from exposure to high electromagnetic fields.