Processing and Properties of IM7/LARCTM-SCI Composite

Abstract

LARC^TM-SCI (Langley Research Center - Semi-Crystaline polyImide) is an aromatic polyimide based on 3,4′-oxydianiline and 3,3′,4,4′-biphenyl tetracarboxylic dianhydride. This polyimide was synthesized and evaluated for use as a neat resin and a matrix resin for advanced composites. Three 30% w/w solids polyamic acid/N-methypyrrolidone solutions were prepared using 2, 3 and 4% stoichiometric imbalances end-capped with phthalic anhydride to provide polyimides with theoretical number average molecular weights of approximately 22 800, 15 100 and 11 400 g mol⁻¹ respectively. Unidirectional IM7 carbon fibre prepreg was prepared from these three resins using the Langley multipurpose tape machine. Thermal and rheological properties and the solvent/volatile depletion rates along with crystallization kinetics were characterized for the resin scraps taken from the prepreg tapes. Processing characteristics of the LARC^TM-SCI resin were thoroughly understood from these results, and a workable moulding cycle was designed for this composite. Composite laminates were moulded at 410 °C at either 200 or 300 psi, which consistently yielded good consolidation and high-quality panels as measured by C-scan, acid digestion and optical photomicrography. The composite mechanical properties were also obtained. Short beam shear strength was 15 ksi at RT. Longitudinal flexural strength was 295 ksi at RT and 200 ksi at 177 °C. Excellent fracture toughness of 6.9 in-lb/in² was obtained. Excellent values of transverse flexural strength and longitudinal tensile strength indicated a good translation of fibre properties into the composite. Un-notched longitudinal compression strength of 163 ksi was comparable to typical thermoplastic composites. An open hole compression strength of 55 ksi suggested good damage tolerance for this composite.

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