Neutron scattering, electron microscopy and dynamic mechanical studies of carbon nanofiber/phenolic resin composites

Carbon nanofiber (CNF)/resole phenolic resin (Hitco 134A) composites exhibited very large increases of bending storage modulus above the glass transition temperature and had higher glass transition temperatures with increasing CNF weight percentage. Small angle neutron scattering (SANS) from dilute suspensions of surface-oxidized CNF in D2O exhibited a Guinier plateau in the q range examined, indicating that isolated scatterers exist. The CNF dispersion, average fiber diameter, average core diameter and polydispersity within the composites and in D2O were quantified by approximating the small angle neutron scattering data with a hollow tube model. The scattering from CNF/phenolic resin composites exhibited a q−4 power law behavior, indicating the presence of sharp interfaces between fibers and phenolic resin. Surface-oxidized (PR-19-PS) CNF nanocomposites exhibited lower surface to volume ratio values and larger shell thickness compared with heat-treated (PR-19-HT) CNF composites. However, carbon nanofibers, with and without oxygenated surface groups, exhibited some agglomerates with fractal dimensions within the phenolic resin composites. Fiber surface treatment with nitric acid appears to promote dispersion and results in looser bundles of nested fiber networks.