PROCESSING AND PROPERTIES OF IM7 LARC((TM))-SI POLYIMIDE COMPOSITES/

LARC(TM)-SI (NASA Langley Research Center-Soluble Imide) is an aromati c thermoplastic polyimide. LARC(TM)-SI is synthesized from equimolar a mounts of oxydiphthalic anhydride (ODPA), 3,3',4,4'-biphenyltetracarbo xylic dianhydride (BPDA) and the equivalent amount of 3,4'-oxydianilin e (3,4'-ODA). Phthalic anhydride (PA) was used as an endcapper to cont rol molecular weight. A 30% solid LARC(TM)-SI solution (in NMP/Xylene: 9/1 v/v) with 3% stoichiometric imbalance was made into unidirectiona l long-fibre-reinforced prepregs. Thermal properties, volatile depleti on behaviour and resin rheology were thoroughly characterized. Using t his information, two composite moulding cycles were developed that con sistently yielded well consolidated, void-free laminates. Composite me chanical properties such as short-beam shear strength, longitudinal an d transverse flexural strength and flexural modulus, longitudinal tens ile strength and notched and un-notched compression strengths, fractur e toughness, open-hole compression strength and compression after impa ct (CAI) strength were measured at room temperature (RT) and elevated temperatures. LARC(TM)-SI composite exhibited very good toughness and damage tolerance. The interlaminar fracture toughness and the CAI stre ngth were measured at 1.72 kJ m(-2) at 35.2 GPa respectively.