Blistering in carbon fiber-filled fluorinated polyimide

A blistering study was performed on a fluorinated polyimide resin and its carbon-fiber composite in an effort to determine the blister-formation temperature and the influence of blisters on composite performance. The fluorinated resin and carbon-fiber composite exhibit higher glass-transition (435–455°C) and decomposition temperatures (above 520°C) than similar polyimide resins and their carbon-fiber composites currently used. Two techniques were used to determine moisture-induced blister formation. A transverse extensometer with quartz lamps as a heating source measured thickness expansion, as did a thermomechanical analyzer as a function of temperature. Both methods successfully measured the onset of blister formation with varying amounts of absorbed moisture (up to 3 wt%) in the samples. The polyimide resin exhibited blister temperatures ranging from 225 to 362°C, with 1.7–3.0 wt% absorbed moisture, and the polyimide composite had blister temperatures from 246 to 294°C with 0.5–1.5 wt% moisture. The blistering effects of the polyimide composites were found to have little correlation with modulus.