| Nitric acid oxidation (60 min., 115{dollar}spcirc{dollar}C) of PAN-based carbon fibers increased the surface concentration of hydroxyl and carboxyl groups ten fold with a -COOH/-OH ratio of 3.25:1. Subsequent treatment with thionyl chloride and tetraethylenepentamine (TEPA) gave surfaces with up to 41 {dollar}mu{dollar}eq/g of amino groups. Isocyanate-terminated prepolymers with molecular weights of 920 and 9000 were grafted onto TEPA-functionalized fibers with grafting efficiencies of 8.6% and 1.4%, respectively. Grafting efficiencies decreased with diisocyanate molecular size whereas the weight gains increased. Cured polyurethanes, {dollar}sim{dollar}1000 and {dollar}sim{dollar}6000 A thick were bonded to carbon fibers which had already undergone different pretreatments. Fiber/epoxy matrix composites were prepared from these systems and examined using DMTA, single-filament fragmentation tests, three-point bending tests, Izod impact tests and SEM. The ILSS increased 10% while the impact strength decreased 50% after HNO{dollar}sb3{dollar}/SOCl{dollar}sb2{dollar}/TEPA-treatment. With a 1000 A thick cured polyurethane interphase (T{dollar}sb{lcub}rm g{rcub}{dollar} = 50{dollar}spcirc{dollar}C, shear storage modulus G{dollar}spprime{dollar} = 49 MPa), the impact strength increased 30% whereas the ILSS decreased 2% for the HNO{dollar}sb3{dollar}/SOCl{dollar}sb2{dollar}/TEPA-treated carbon fiber/epoxy matrix composites. |
