| The effect of surface pretreatment on the adhesive bonding and bond durability of carbon fiber/epoxy and carbon fiber/bismaleimide matrix composites was studied. Methyl ethyl ketone (MEK) wipe, peel ply, grit blast and gas plasma treatments were the pretreatments of interest. Chemical and physical changes which occurred in the cured composite surfaces following pretreatment were characterized with x-ray photoelectron spectroscopy (XPS), ion scattering spectroscopy (ISS), contact angle analysis, diffuse reflection infrared spectroscopy (DRIFT), profilometry and scanning electron microscopy (SEM).; Fluoropolymer residues which were found on the composite surfaces were fully removed by grit blasting and oxygen plasma treatments, but not by an MEK wipe. The use of a peel ply prevented fabrication contamination from depositing on the bonding surfaces. In addition to its cleaning effect, oxygen plasma was also capable of incorporating additional polar functionality into the composite surface. The presence of the fluoropolymer contamination on the MEK-wiped surface resulted in low surface energy and wettability, whereas peel ply, grit blast and oxygen plasma improved both the surface energy and the wettability of the composite surfaces. The grit blasted and peel ply surfaces were observed to have a significant degree of roughness, as measured by profilometry and seen by SEM.; A rubber-toughened epoxy film adhesive was used for the bonding studies. Lap shear strengths were evaluated under ambient conditions as well as at 82{dollar}spcirc{dollar}C, both dry and following a 30 day/71{dollar}spcirc{dollar}C water exposure. Wedge durability testing was carried out in a dry 75{dollar}spcirc{dollar}C oven, 75{dollar}spcirc{dollar}C water, 100{dollar}spcirc{dollar}C water and aircraft de-icing fluid. Relative to the MEK-wiped controls, lap shear strength as well as hot/wet durability was improved by the peel ply and oxygen plasma treatments for both epoxy and bismaleimide composites. Grit blasting was seen to have some utility for the epoxy composites at room temperature, but was generally observed to be detrimental to strength and durability, particularly in the case of the bismaleimide composites.; In order to separate the effect of surface chemistry from the effect of surface roughness on composite bond strength, a study was carried out in which surface functionality was varied while the topography remained constant. For this purpose, peel ply surfaces, which have a consistent and reproducible degree of roughness, were treated with fluoropolymer compounds and gas plasmas, as well as left untreated.; The effect of elapsed time following oxygen plasma treatment of epoxy composites was also studied. XPS atomic concentration, wettability by water and a liquid epoxy resin, and lap shear strengths were plotted as a function of time following removal from the plasma reactor.; A study was carried out using model epoxy and bismaleimide compounds in thin film form, for the purpose of studying surface chemistry and interfacial reactions following an oxygen plasma treatment. XPS and infrared reflection-absorption spectroscopy (IR-RAS) were used to probe the reactions which occurred. Close correspondence was found between the XPS and IR-RAS analysis of functional groups incorporated into the surface of the films by the plasma treatment. IR-RAS analysis of the model surfaces following exposure to a neat, liquid epoxy resin revealed that, while adsorption of the liquid epoxy occurred on both plasma-treated and nonplasma-treated surfaces, the oxygen plasma treated surface alone was capable of initiating ring-opening reactions in the epoxy. (Abstract shortened by UMI.)... |
