Historical aircraft paints: Analytical pyrolysis for the identification of paint binders used on two Messerschmitt Bf 109 planes

Historical airplanes have entered museum collections to show the development of aviation and are part of our technical heritage. The period between the 1920′s and 1945 is characterized by giant progressions in the chemical industry. During these years a wide increase in the production of new materials and solvents was observed, that replaced the natural materials used in the aircraft industries due to their improved properties. In Germany this industrial development was counteracted by preparations for the war that aimed at a self-sufficiency based on German products and thus an independency of the international market. This work presents the analyses of the organic binders of painted layers of a Messerschmitt Bf 109 model E-3 used until the 1955 and repainted several times until the 1974 and a cabin roof from a Bf 109 model B built in the 1937–1938 lost during the flight and never repainted. The microscopic analyses performed on the samples from the two planes allowed us to characterize the presence of a high and variable number of paint layers. These layers adhere extremely well on each other and are very brittle. For this reason, it was almost impossible to separate them for analytical purposes by mechanical means. In this study we applied for the first time analytical pyrolysis coupled with gas chromatography and mass spectrometry for the characterization of the painted layers from the two planes. The combination of the versatility of analytical pyrolysis together with the high selectivity of gas chromatography and mass spectrometry allowed us to fully characterize and discriminate the synthetic and natural materials used in both airplanes, and to characterize the original paint binders as being composed of alkyd resin, phenol formaldehyde resin and nitrocellulose.