Polymer Blends. Volume 1

Three generations of PBI and polyamide blends have been evaluated for use as high temperature matrix resins for carbon fiber composites in aerospace applications. To enable property testing, a neat resin molding cycle was developed to produce plagues with less than 2 void volume. Phthalic anhydride end-capping of the PBI was shown to significantly reduce crosslinking as measured by the change in Tg after high temperature exposure. This reduction in end-group chemistry provided for maximum thermoplasticity of the blend during molding. Thermo-oxidative stability studies indicated that at 60 deg F and above, the weight loss of the blend was approximately proportional to its PBI content. Attempts to mitigate this effect by incorporating 6F moiety into the PBI backbone were unsuccessful. Phosphoric acid treatment of 8515 molded blend samples was shown to provide a four-fold increase in weight retention. However this effect was due to surface oxidation barrier effect. A series of nine copolymer polyimides were synthesized and evaluated. The blend of 1090 ecPBI6FcoPI-2 was chosen to be moved forward for aerospace evaluations. The blend with end capped chemistry was scaled up in steps from gram quantities to 50 kilograms. Prepregging of the neat resin onto plain weave AS-4 carbon fabric and onto AS-4 unidirectional tape was successfully demonstrated by YLA Incorporated. Three prepregging trials produced a total of 1450 linear feet of fabric and over 450 feet of unidirectional prepregs. Composite laminate fabrication was demonstrated by both Lockheed and Hoechst Celanese. Composite properties were demonstrated which either approached or exceeded GE Aircraft Engines specifications for PMR-15 composites.