Degradation of continuous carbon fiber reinforced polyetherimide composites during induction heating

Induction heating of carbon-fiber-reinforced thermoplastic-matrix composite s has numerous advantages over conventional methods. Volumetric heating and high heating rates offer a significant reduction in cycle times for proces sing high-quality thick-section composites. However, the influence of high- frequency electromagnetic fields on the composite is not well understood. T wo mechanisms of degradation during electromagnetic induction heating of AS 4 carbon-fiber polyetherimide (PEI) were studied-thermal degradation and di electric breakdown. Crosslinking and chain scission reactions are two major thermal degradation mechanisms that occur during melt processing of PEI. C hanges in the molecular weight and glass transition temperature of the poly mer were quantified over a wide range of process temperatures and times. Th e rheological properties of the composite system are also monitored to inve stigate viscosity changes due to molecular weight changes during the proces s. Dielectric breakdown during the induction process was also carefully exa mined. No significant change in polymer properties resulted from exposure t o high electromagnetic fields.