Surface Treatment for Graphite Fiber Composites

High performance graphite/resin composites have not realized their potential because they have poor interface-dependent mechanical properties that degrade by as much as 65% under hot-wet conditions. An RF-plasma/wet-chemistry fiber surface treatment is proposed to establish covalent bonding between the graphite fiber/resin matrix interface. The plasma process will establish reactive moieties on the relatively inert crystallite basal plane of the graphite fiber. The wet-chemical treatment will covalently bond the resin matrix to the reactive plasma-generated moieties thus forming the interfacial covalent bond. The covalently bonded interfaces will improve interface-dependent mechanical properties by at least 50% and prevent degradation of these properties under hot-wet conditions. Prior work that established interfacial covalent bonds in OCF S-2 glass/polysulfone composites demonstrated that interface-dependent mechanical properties degraded by less than 8% during 106 degree C-9 RH aging conditions. Basal plane reactivity treatments will be conducted in a spectrometer-controlled plasma research reactor facility. Titration, IGC, surgace energetics and ESCA techniques will characterize the graphite surface. Processes will be developed for wet-chemical bonding. Peel tests of two-ply laminates subjected to hot-wet aging will provide proof of increased interfacial adhesion.