Designing polymer coatings for aerospace industry

Protective wood coatings for aircraft interiors are essential to serve specific functions such as protecting the wood surface and providing high-gloss aesthetically appealing surfaces. Such coatings must also withstand cracking, provide sufficient hardness, adhesion to the wood, and fire-retardant properties. Additionally, the application of bio-sourced feedstock and the reduction of volatile organic compounds are important factors in the interior coatings. Recent advances in radical polymerization techniques allow the synthesis of such polymers with multiple functions, desirable macromolecular structures, and low dispersities, the last of which leads to low solution viscosities and easier coating application. We used nitroxide mediated polymerization (NMP) as it only requires heat and alkoxyamine to initiate and control the polymerization. It does not require extensive post-polymerization treatments, making it a facile approach for many industrial applications. In this thesis, we focused on methacrylic monomers with suitable functional groups for the development of coating formulations. We used commercially bio-based feedstock in the coating, as much as possible. To develop the coating formulation, we used isobornyl methacrylate (IBOMA, from pine sap) and C13 methacrylate (C13MA, from vegetable oils) along with other functional monomers. We started with the copolymerization of IBOMA and C13MA and achieved polymers with relatively low dispersities. We also used hydroxyethyl methacrylate (HEMA) to improve the adhesion to the wood substrates.Other components of developing the new coating were the incorporation of fire-resistant additives and cross-linkable monomers. We first used methacrylate-functionalized polyhedral oligomeric silsesquioxane (POSSMA) to copolymerize with C13MA to improve the thermal stability of the coatings. Interestingly, POSSMA-rich copolymers revealed improved thermal stabilities. However, the low ceiling temperature of POSSMA prevented achieving high molecular weight polymers. Thus, we sought an alternative technique, using POSS nanoparticles and used IBOMA and (2-acetoacetoxy) ethyl methacrylate (AAEMA). AAEMA was utilized to react with a bio-based diamine for subsequent cross-linking based on dynamic transamination network. Such cross-linked networks, called vitrimers, impart recyclability features to thermosetting polymers. We added amine-functionalized POSS at different loadings to achieve recyclable nanocomposite thermosets with enhanced thermal and mechanical properties. The vitrimers and nanocomposites showed reprocessability up to 3 cycles without substantial decrease in the mechanical properties. Additionally, the cross-linked coating revealed improved impact resistance and adhesion to the wood compared to the uncross-linked coating. Moreover, high POSS loadings up to 20 wt% could enhance the flame retardancy behavior of the coatings. We explored two other approaches to impart flame retardancy to the polymers based on using phosphorus compounds. The first method involved the incorporation of strongly acidic and cross-linkable HEMAP monomer (comprising 70% ethylene glycol methacrylate phosphate (EGMP) and 30% methyl methacrylate (MMA)). We demonstrated that NMP fails in the polymerization of HEMAP but reversible addition fragmentation transfer polymerization of HEMAP was achievable. Copolymerization of HEMAP with IBOMA and MMA notably improved the char residue and decomposition behavior. Later, we synthesized hybrid nanoparticles of organophosphorus-titanium-silicon (PTS) to serve as additives to simultaneously enhance thermal and mechanical properties. We developed copolymers of glycidyl methacrylate and C13MA cross-linked by a bio-based diamine and reinforced by PTS. Incorporation of PTS not only improved the decomposition behavior but also increased the mechanical properties, indicating a promising flame-retardant additive in coating resins

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