Influence of unwoven roving and woven fabric carbon fiber reinforcements on reaction‐to‐fire properties of polymer matrix composites

Summary The influence of carbon fiber orientation on reaction‐to‐fire characteristics of layered polymer matrix composites is investigated in detail. M18‐1/G939 as woven fabric and M18‐1/G947 as unwoven roving prepregs with identical, epoxy based matrix composition were laid‐up to give 1 to 8 mm thick unidirectional and quasi‐isotropic laminates. Fundamental reaction‐to‐fire properties of these composites are interpreted on basis of the matrix components: epoxy resin and polyetherimide, as well as contained flame retardants magnesium hydroxide and zinc borate. Cone calorimetry and temperature distributions through the laminate show, that the velocity of combustion is influenced by fiber orientation for a given resin. For an unwoven roving it is confirmed that a quasi‐isotropic fiber orientation leads to faster ignition, due to preferred delaminations, but retards burning processes more effectively than a unidirectional lay‐up. This fundamental principle is extended to woven fabric reinforcements, however with less pronounced effects. Migration velocities of the pyrolysis zone are measured and additionally, decomposition of carbon fibers is considered. A comparison with a similar epoxy based matrix system without toughener and flame retardants: RTM6/G939 is carried out, in order to assess the effects by fiber orientation.