The goal of the SON is to identify efficient and effective chemical strippers for removal of organic coatings and sealants applied to composite substrates to enable development of a specification (e.g., SAE or military specification). Proposals should address various considerations:
- Evaluate alternative chemical strippers, such as peroxide-based strippers for their efficacy in removing coatings at similar strip rates to mechanical methods (e.g., sanding or media blast) without adverse impacts to the composite substrate. Proposals can include evaluation of commercial stripping technologies already used for aerospace stripping operations where data does not exist or development of new or modified existing chemical stripping agents. Candidate strippers should be effective in rapidly removing coatings, such as polyurethanes and epoxies, up to 10 mils (0.01 in) in total thickness in no more than three 8-hour dwell cycles, with no damage to the underlying substrate.
- Provide a hypothesis to justify selection of candidate chemical strippers that addresses thermodynamics and kinetics of stripping and interactions with the composite substrate as well as low flammability considerations, and propose an approach to test that hypothesis.
- Evaluate the candidate strippers on coatings or sealants applied to one or more relevant composite substrates actively being used by the Department of War (DoW).
- Evaluate the effectiveness of removing the coating or sealant under conditions relevant to typical maintenance operations.
- Evaluate the mechanical properties of composite substrates that have been chemically stripped for comparison with mechanical methods (e.g., plastic media blast, sanding).
- Shall not include methylene chloride and should minimize or eliminate the use of Toxic Substances Control Act (TSCA)-restricted chemicals and CERCLA hazardous substances.1
- Reduce or eliminate hazardous air pollutant (HAP) content.
- Reduce or eliminate volatile organic compound (VOC) content.
- The chemical stripper should be safe for use relative to current chemical strippers and safe to use with appropriate personal protective equipment (PPE) and without the use of a respirator. Toxicity evaluations should be cited or performed by an accredited laboratory to justify choice of the chemical stripper.
- The chemical stripper should have the potential to be recycled to reduce chemical consumption and cost.
- Waste streams from the process should be fully considered and efforts should focus on minimization of waste and reduction of its hazard level.
- Provide complete datasets on testing results to SERDP via ASETSDefense2 to aid the establishment of a specification.
All proposals should address how the developed technology will transition towards government or commercial specification development. Teams with expertise in government or commercial specifications and standards could propose using the data gained to draft a specification within the proposed project.
Proposals should include a plan to conduct a preliminary Life Cycle Analysis3 (LCA) to help indicate the life cycle cost benefit associated with the proposed process relative to current processes. Proposals should establish a life cycle framework that can mature as the technology or process advances through the development and acquisition processes. This tiered approach aims to develop and document a minimum data set at each stage of research and development that can be used to make informed decisions and streamline transition to an acquisition program. The LCA may include varying depths of data and information that can inform: the goal and scope of an analysis; the identity and quantity of relevant inputs and outputs to the system; and the estimation of life cycle impacts and costs. A preliminary LCA would help indicate the cost benefit associated with the proposed process relative to current processes. Any proposals that do not include an LCA should provide a reason for exclusion.
The goal of this SON is to identify effective chemical strippers that have reduced hazards versus current chemical strippers and reduce damage relative to the underlying composite substrate relative to current chemical strippers or mechanical coating and sealant removal processes. Projects would generate test data towards development of a composite chemical stripping specification, either in SAE or military specification format, for stripping non-metallic composite substrates used in Defense aircraft manufacture.
Common aerospace coatings that require solvent depainting include polyurethane topcoats, epoxy primers, epoxy topcoats for interior applications, polysiloxane coatings, and polysulfide sealants. The most commonly used composite material in DoW aircraft is epoxy-amine resin with carbon fiber reinforcement. Epoxy-amine with aramid and glass reinforcement is also used in various DoW applications. Higher temperature composites, such as bismaleimide (BMI), PMR, and phenolic resins reinforced with carbon fiber are used in aircraft near engines and other locations requiring high temperature performance. Hybrid composites that combine one or more resins and fiber types are also used.
Solvent depainting can be performed using dip tanks, spray on, and brush on methods. Coating removal on weapons systems includes application to horizontal, vertical, and under wing structures.
Mechanical stripping methods, such as sanding and blasting, atomize coatings and can pose significant hazards to workers, requiring extensive PPE. These methods also produce large amounts of contaminated waste. These methods are also highly subject to operator error which can be damaging to the substrate, resulting in significant downtime of aircraft and large costs.
Examples of regulated chemicals and CERCLA hazardous substances that are used as solvents in relevant industrial operations include methylene chloride, trichloroethene (TCE), perchloroethylene (PCE), dichloroethylene, d-limonene, methyl isobutyl ketone, N-methyl pyrrolidone, benzene, toluene, and xylene among others due to their nature as HAPs or current or potential restrictions on their use. The Environmental Protection Agency (EPA) provides lists of unacceptable, acceptable, and safer chemical alternatives that can be used for these applications.4,5,6 Various alternatives to restricted chemicals as solvents have been developed, but for some processes they have not been adopted due to process issues, such as dwell time, scent, line of sight only applications, lack of corrosion inhibitor, wastewater treatment requirements (e.g., d-limonene issues wastewater treatment plants), inability to meet original specification requirements, unacceptably low flash point temperature, and unacceptable lower explosive limits (LEL).
The cost and time to meet the requirements of this SON are at the discretion of the proposer. Proposers submitting a Standard or Limited Scope Proposal must provide the rationale for the proposed scale. The two options are as follows:
Standard Proposals: These proposals describe a complete research effort. The proposer should incorporate the appropriate time, schedule, and cost requirements to accomplish the scope of work proposed. SERDP projects normally run from two to five years in length and vary considerably in cost consistent with the scope of the effort. It is expected that most proposals will fall into this category.
Limited Scope Proposals: Proposers with innovative approaches to the SON that entail high technical risk or have minimal supporting data may submit a Limited Scope Proposal for funding up to $350,000 and approximately one year in duration. Such proposals may be eligible for follow-on funding if they result in a successful initial project. The objective of these proposals should be to acquire the data necessary to demonstrate proof-of-concept or reduction of risk that will lead to development of a future Standard Proposal. Proposers should submit Limited Scope Proposals in accordance with the SERDP Core Solicitation instructions and deadlines.
John La Scala, Ph.D.
Program Manager for Weapons Systems and Platforms
Strategic Environmental Research and Development Program (SERDP)
