Study of Carbon/Epoxy Interface (or Interphase): Effect of Surface Treatment of Carbon Fibers on the Dynamic Mechanical Behavior of Carbon/Epoxy Unidirectional Composites

Abstract

Dynamic mechanical properties of unidirectional carbon fiber / epoxy matrix composites were determined in order to study the influence of the presence of carbon fiber and the effect of surface treatment (untreated, oxidized and sized) on the behavior of epoxy matrix. When carbon fibers are introduced at different volume fractions (from 40 %, to 70 %), the mobility of the macromolecular chains of the epoxy matrix is reduced at the fiber/matrix interface. An oxidization treatment, leading to a larger number of functional groups present at the surface, increases this effect bo creating additional interactions. However, an epoxy sizing induces a higher mobility by creating less crosslinked interphases. By studying the viscoelastic properties in a large range of temperatures and frequencies, the main relaxation of a component of the sizing, displaying a phase separation in the interphase, could be observed as a shoulder of the secondary relaxation peak of the epoxy matrix.