The objective is to investigate the use of an Atmospheric Plasma Coating Removal (APCR) process to selectively strip organic coatings from various composite substrates. The project will determine if the APCR process causes any changes to the chemical and mechanical properties of the underlying composite substrates with an emphasis on detecting any potential damage mechanisms. Assuming successful implementation, this technology has the potential to selectively remove coatings from composites with a one-step process that eliminates the need for hand sanding, traditional blast media or toxic chemicals while reducing processing times. Testing on plasma etched substrates will be used to develop a preliminary set of “safe” APCR plasma processing parameters on the different composites of interest. The surface and mechanical properties of each sample will be analyzed before and after APCR, using various analytical tools, to develop a quantitative understanding of the mechanisms involved in the removal process. The proposed work will be conducted on carbon fiber/ epoxy composites that are of particular interest for Air Force, Navy and Army applications.

Under the proposed APCR approach, only the organic topcoats on the composite will be modified; the matrix material will remain effectively the same, conforming to original specifications. The primer and topcoat compositions and application procedures will not be changed, and the methods for testing strength, durability, and impact resistance will all be performed according to the original requirements.

The AFRL Materials and Manufacturing Directorate, Materials Durability and Sustainment Branch and Materials Integrity Branch will generate coated composite coupons for atmospheric plasma coating removal testing. The composite samples will be graphite/epoxy material similar to those found on the outer mold line (OML) of many DoD aircraft. Some of the samples will be simple plaques for coating removal and, if time and budget allow, samples with a honeycomb core to enable mechanical testing to assess any surface changes to the resin cap during the coating removal process will be produced. Because the atmospheric plasma process generates monatomic oxygen to chemically etch rather than ablate the surface, testing will focus on determining if the plasma causes structural changes to the face sheet. Coating systems will include the typical system for the OML of aircraft (MIL-PRF-23377 and/or MIL-PRF-85582 primer, and MIL-PRF-85285 Type IV topcoat). Coatings will be applied using standard practices from Technical Order 1-1-690 (General Advanced Composite Repair Process) and Technical Order 1-1-8 (Application and Removal of Organic coatings, Aerospace, and Non-Aerospace Equipment).

Plasma coating removal will be performed using existing Atmospheric Plasma Solutions’ commercial APCR product, PB-7000 APCR system. Results will demonstrate the reduction in hazardous waste, processing times, energy consumption and adhesion properties.