Sorption of Fuels in Additively Manufactured Thermoplastic Polyurethanes

This study investigates the swelling and diffusion behavior of additively manufactured thermoplastic polyurethane elastomers with aviation fuels. It aims to demonstrate that replacement parts can be additively manufactured and can be used in contact with fuels in the near future. Thermoplastic polyurethane is studied as a function of the printing parameter “form factor” (FF), which defines the distance between individual polymer droplets used in the Arburg Plastic Freeforming (APF) process. The samples were chemically characterized and mechanically tested before and after immersion in jet fuel. Sorption experiments show that the chemical composition of the polymer is primarily responsible for compatibility with the fuel and, thus, mainly for equilibrium absorption. Samples with a higher FF exhibit higher diffusion rates due to a larger free volume than the ones with a lower FF. As swelling progressed, an increase in mass and volume was accompanied by a decrease in residual stress at break. In addition to the chemical composition, the “form factor” offers a variety of possibilities to influence not only the mechanical material properties but also the swelling behavior.