Atmospheric pressure plasma treatment is an alternative surface preparation method for plastics and organic matrix composites prior to structural adhesive bonding. The atmospheric pressure plasmas are a promising technique for replacing traditional methods of surface preparation such as manual sanding, grit blasting, peel ply, or wet chemistry. All surfaces studied were converted from a hydrophobic state into a hydrophilic state with a water contact angle of <40°. Atomic force microscopy confirmed that plasma activation resulted in only minor changes to the composite surface structure. Surface analysis by X-ray photoelectron spectroscopy revealed an increase in oxygen content and showed that carbonaceous contamination was removed by plasma treatment. Helium-oxygen plasma generated specific functional groups on the composite surface, e.g. carboxylic acids. Depending on the material being used, lap shear strength was increased from ~50% up to several-fold. The data to be presented will include detailed bond failure mode evaluations in hot-wet environmental conditions. For example, untreated stainless steel had 30% cohesive failure compared to 97% for steel activated with the plasma.
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