A low-moisture polyetherimide (PEI) foam for composite aircraft structures not only reduces weight, aiding fuel conservation and emissions reduction, but it also reportedly lowers systems costs while delivering equal or better performance than traditional materials.
SABIC Innovative Plastics Ultem PEI foam, which would replace a material like polymethacrylimide (PMI), has proven flame-smoke-toxicity (FST), dielectric, acoustic and thermal performance.
Ultem foam products are available in three densities and manufactured as boards for use in skin-core-skin composite structures. Applications include luggage bins, galleys and lower wall panels. They were displayed at Seattle's Aircraft Interiors Expo as side wall panels.
Ultem and PMI foam boards were exposed to elevated heat 70°C (158°F) and humidity (85% relative humidity) in an environmental chamber. Those tests demonstrated that the Ultem foam absorbed less than 0.5% moisture by weight at 1000 hours. In contrast, PMI absorbed 5-6% moisture by weight at just 150 hours and maintained those results through 1000 hours.
Weight gain from moisture absorption adds to the aircraft's weight and impacts fuel consumption and emissions. On average, an aircraft will burn about 0.03 kg (0.06 lb) of fuel per hour for each kilogram (2.2 lb) carried on board. Moisture absorption can disrupt electronics or cause condensation on sensitive areas of the interior. The cycle of absorption and drying that occurs as the aircraft travels through different environmental conditions also has the potential to cause delamination of a composite structure and can distort the dimensions of a part.
The product line is produced in three densities:
- Ultem foam XP060 is 60 kg/m3 (3.8 lb/cu ft)
- Ultem foam XP080 is 80 kg/m3 (5 lb/cu ft)
- Ultem foam XP110 is 110 kg/m3 (6.9 lb/cu ft)