Processing and characterization of carbon-carbon nanofiber composites
Carbon-carbon composites (CCCs) have extremely high thermal stability and shock resistance and find use in aerospace applications and aircraft disk brakes. The processing of CCCs can be divided into three stages: curing of precursor resin/fiber-reinforced-laminate; carbonization; and
densification. During carbonization, the precursor resin (such as phenolic and furfuryl alcohol) develops microcracks and oftentimes delaminations, which reduce the mechanical properties of the material. In this study, we investigated the influence of carbon nanofibers (CNFs) when mixed with
phenolic matrix precursor on the microstructure and interlaminar shear strength (ILSS) of the ascured and carbonized composite specimens. CNFs offer low cost benefits, unlike traditional carbon nanotubes (CNTs) that tend to be expensive. Different loadings (0%, 2%, and 5% weight/weight of
resin) of CNFs, in conjunction with various percentages of surfactant (0%, 12.5%, and 50% by weight of acetone) treated carbon fabric reinforcement were used for the study. The rationale for treating the fabric with surfactant was to vary interfacial conditions of reinforcing fiber-CNF-matrix.
This paper outlines the work done in the processing of CCC-CNF composites, and the influence of surfactant and various percentages of CNFs on the resulting microstructure and ILSS properties. The use of CNFs provided a bridging mechanism for matrix microcracking and reducing matrix shrinkage
that occurs during first carbonization. Porosity and delaminations were found to increase with increase in surfactant treatment. An inverse relationship was observed between ILSS and porosity. At the as-cured and carbonized stages, an optimal value of 2% CNFs yielded the highest ILSS values
of ∼40 MPa and 6 MPa respectively.