Si-Polyols as flame retardants for polyurethane clear coatings

 
In a research project of the Institute for Wood Technology Dresden, flame retardants were to be developed which are suitable for the use in clear coat applications. For this purpose, hydrolysis-stable silicon polyols of the general structure OH-"C"-Si-R-Si-"C"-OH were synthesized and characterized in high purity, which could be covalently introduced in consistently transparent and well-cured polyurethan coatings with a Si-solids content of up to 15 %. Even with an Si-solids content of 7.5 %, these flame retardants showed significantly improved thermal degradation in thermogravimetric investigations in reference to the unmodified clear coat; residue after thermal degradation: 9.0 %/Si-modified vs 2.5 %/untreated. In fire tests according to ISO 5660-1, significantly better properties could also be demonstrated for several of these Si-Polyols. Even with Si-solid contents of 2.5 %, a heat release rate of 281.1 kW/(g*m²) and a total heat release of 61.5 MJ/(g*m²) could be achieved, which corresponds to an improvement of 82 % (heat release rate) and 70 % (total heat release) compared to the untreated reference.