An analysis of corrosive species ingress into IM7/PETI-5 Ti honeycomb composites

The ability of the graphite fiber-reinforced thermoplastic polyimide composite IM7/LaRC-PETI-5 to trap species known to cause corrosion was investigated using a solution analysis technique that identifies and quantifies ionic species. The hydrated contents of individual titanium honeycomb cells comprising the core of the structure were accessed through the polymer–matrix composite (PMC) facesheets with syringes. Capillary electrophoresis (CE) was used to identify and quantify inorganic and organic species found trapped inside honeycomb cells. CE analyses demonstrated that the composite structure trapped corrosive species, such as chloride and sulfate, inside the individual honeycomb cells. A likely point of species entry was through the PETI-5 adhesive binding the honeycomb core to the top and bottom PMC facesheets. This entry was facilitated by high temperature exposure. Analyses showed a marked increase in corrosive species concentration after 400 hours of exposure at mildly high temperatures, 250 °C, suggesting that an incubation time may exist for species entry, likely related to degradation of the adhesive.