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varnish and sol-gel multifunctional ProtectIve cLear cOat for aeronauTics

Periodic Reporting for period 2 - PILOT (varnish and sol-gel multifunctional ProtectIve cLear cOat for aeronauTics)

Reporting period: 2018-02-01 to 2019-05-31

PILOT, acronyms of varnish and sol-gel multifunctional Protective cLear cOat for aeronauTics, aims to develop two types of coating, a UV hybrid silicone varnish and a hybrid sol-gel coating, that are resistant enough to protect wings from environmental damaging. The main goal will be to develop an optically transparent functional clear coat applied over a final paint scheme to protect plane surfaces. This clear-coat shall be resistant enough to keep the laminar properties of the wings of plane including leading edge as well as fairings at their optimum and prevent any increase of drag during service life. The main performance of this topcoat will be:Anti-erosion properties (rain and sand), Anti-icing performance, Anticontamination performance and Anti-static properties.

This means that the developped materials should satisfy the following technical challenges :
- adhesion to polyurethant top-coat.
- chemical resistance.
- ageing resistance to UV and temperature.
- mechanical resistance to scratch, abrasion.
- reistance to liquid erosion.
- being anti-ice and anti-contamination (limit their adhesion).
- being processable by psray.
- being cured at low temperature.

and for the overall cleansky objectives :
- design eco-friendly material and concept.
- reduce process duration and process.
- improve innovation and integration of new knowledge.
"The aim of WP1 is to manage the project in terms of communication, IP, data management and administrative management. During the 2 first period, main work was focused on the edition of the the 2 project amendment (AMD-738123-2 et 6). It was also edited during this period the implementation and consortium agreement (D1.2). A dissemination and exploitation plan was summed up in the D1.3. According to this deliverable, it was hightlight the different conference and topics to introduce with the PILOT technical subject.

The aim of Work package 2 was to perform a literature review and edited in the deliverable D2.1 ""literature review report"". it carried out a state of the art of the formulations, technologies, coatings and process, which could be used to develop the coating to achieve the technical requirements. The state of the art focused on the following properties: Erosion phenomena, Anti-ice effect, Electrical conductivity and highlighted for each property: its principle, how to prevent it and how to characterize it. The second part of the WP dedicated to the identification of critical property that must satisfy the coating and the definition of a road map that will ensure the coating characterization, its implementation and validation. This road map will be used for coating development (WP3) and was presented in the deliverable D2.2 ""development work report"".

The aim of Work package 3 , which is the most important of the project, is to:
- Develop the two coating solutions (hybrid silicone technology and sol-gel technoloogy) by both partners based on WP2 road map.
- Implement their process.
- Validate that their properties fit the specification.

The work carried out during the first period consisted in evaluating ""on the shelf"" coating in order to identify how to improve their performances :
Concerning the UV hybrid silicone, critical thickness was identified at 25 µm. Characterization tests have shown the main strength of the silicone hybrid coating as water repellence, flexibility, hardness and optical clarity. It has also showed its inertia against water immersion. The major drawback is adhesion. This drawback had been studied during the second period of the project.
Concerning sol-gel solution, the coating presents relevant properties in terms of whydrophobicity and brightness but their properties need to be improved in order to present enhanced adhesion and mechanical performance (resistance to scratch and abrasion, erosion resistance). Consequently, these first tests highlighted that:
- poor wettability and adhesion on the polyurethane basecoat.
- sol-gel solutions are brittle and rigid. These phenomenon are mainly due to the coating thickness, curing and mechanical properties. After curing stress relaxation forces appear through the coating, which lead to the apparition of cracks.
- Optical properties satisfy specification.
There is a need to improve hydrophobic properties by adding specific agent in the varnish formulation. These improvement had been studied during the second period.

During the second period, both ELKEM and RESCOLL investigate how to improve their coating.
one of the major drawback of ELKEM coating is the lack of adhesion onto the polyurethane top-coat (PU). As a consequence, Elkem investigates the best strategy to enhance adhesion during all the second period of the project. The strategies were focus in finding an anchorage technique that will solve adhesion issues :
- Using a transparent primer => no solution were carried out.
- Mechanical abrasion of the PU => improvement of the adhesion but loss of aesthetic properties.
- Chemical attack of the PU => no gain in adhesion.
- Processing an ionic treatment as plasma => no gain in adhesion.
- Modification of the formulation (precursors) => gain in adhesion but loss of aesthetic aspect or in coating stability.
- use of adhesion promoters, a wide range of promoters were tested based on various chemistry. a solution had been identified at the end o"
"At this stage of the project (may 2019) the PILOT consortium confirms that the information of how our project will contribute to the expected impacts is still relevant. At the end of second period, both coatings satisfy technical objectives and overall cleansky objectives. The remaining technical objectives will be validated during the third period.

According to the obtained results, both partners start introducing the ""as developped"" technology to other customer. Discussion are in progress with an aeronautical end-user that is not in scope of topic manager application.

In the end, please note that the impact section will be implemented once relevant results will be obtained on the coatings. This means that, once coating first results will integer coating processing and performance (end of the project).

Coating technology will be introduced through the launching of a website on the PILOT project within few weeks.
Trials for Curing optmization of clear-coat