Air based atmospheric pressure plasma jet removal of FreKote 710-NC prior to composite-to-composite adhesive bonding

This paper evaluates the use of an air based atmospheric pressure plasma jet for the activation of carbon fibre epoxy composites. In addition the performance of the jet in the removal of a 5-8 nm thick layer of FreKote 710-NC from the composite surface prior to heat-cured epoxy adhesive bonding was also investigated. The plasma treated composites were examined using thermal infra-red imaging, WCA, profilometry and SEM. A reflectance-IR technique was used to monitor the removal of FreKote as well as changes in the functional chemistry of the plasma treated composite surface. The optimised plasma pretreatment conditions were identified which help to maximise composite-to-composite adhesive bond strength based on LST. This involved a treatment at a 14 mm nozzle to composite distance and scan rate of 30 mm/s. The air plasma process was bench marked against a manual methanol solvent wipe process, for the removal of FreKote. Both the plasma and the solvent wipe treatments yielded similar composite to composite bond strengths, demonstrating that both were successful in the removal of the FreKote. A comparison was also made between the plasma treated composite and a composite which had been grit blasted using 50 pm aluminium oxide grit. A 7% enhancement in lap-shear strength was achieved with the plasma treatment compared to grit blasting. (C) 2014 Elsevier Ltd. All rights reserved.