Quality Assurance of Graphite/Epoxy by High-Performance Liquid Chromatography

Factors contributing to the reliability and reproducibility of high-performance composites include advanced resin matrixes with consistent purity and concentration of chemical constituents, as well as mix homogeneity and processing uniformity. Variation of these matrix parameters can affect manufacturing processibility and finished laminate quality. For these reasons, a wide variety of analytical tools have been evaluated for their capability of ensuring matrix reproducibility. In most cases, test development has been required to optimize and tailor the methodology for each new matrix system. In this way analytical information more precisely characterizes the matrix and monitors batch-to-batch consistency.

This paper covers work under U.S. Air Force Contract F33615-78-C-5177, “Chemical Composition and Processing Specifications for Air Force/Navy Advanced Composite Matrix Material.” It discusses the development of high-performance liquid chromatography (HPLC) as a quality-assurance method of certifying resin matrix composition of Air Force/Navy graphite/epoxy AS/3501-6 advanced composite matrix material. A gradient-elution/binary-solvent separation technique was developed by using a Spectra Physics 8000 liquid chromatograph in reverse-phase mode.

Resin and derived prepreg from full-scale production lots having predefined concentration variations were investigated. Lot variations were verified quantitatively by using a standard production batch for baseline comparisons. Resin matrix ingredients were used as concentration standards for test calibrations. Test data are reported in weight percent for two types of epoxies and one curing agent (diaminodiphenyl sulfone).

Details concerning the evolution of method development are discussed. Data are included to demonstrate test capabilities for quantitative measurements of unreacted epoxies and diaminodiphenyl sulfone. Data are presented for test verification of intentional ingredient alterations and tracking capability for compositional changes due to ambient aging and short thermal advancements due to hot-melt fiber impregnation.