Characterization of atmospheric plasma as a surface preparation process for the bonding of space composite materials

Abstract

There is a growing interest in the use of atmospheric plasma treatment techniques for the surface preparation of fiber-reinforced composite hardware before bonding. In this article, we will discuss the effects of atmospheric plasma treatment on the chemical and physical properties of two types of composites (cyanate ester and epoxy) and the resultant mechanical properties. Atomic force microscopy and X-ray photoelectron spectroscopy were used to investigate the surface morphology and chemistry of the treated composites and were correlated to lap shear bond strengths. We observed a strong correlation between the increases in lap shear strength with the surface carboxyl concentration of the composite after treatment as verified by X-ray photoelectron spectroscopy. Changes in surface roughness appeared to be secondary in nature. As a result, we have separated the mechanical contributions caused by etching-induced surface roughness from chemical contributions due to formation of specific reactive surface functional groups. The mechanical and chemical mechanisms that govern surface properties and contribute to the observed enhanced bonding will be discussed.