Tortuosity Index of Polyimide Foam for Aerospace Application

The PolyMAC™ polyimide foam was characterized in order to produce a methodology for the establishment of a tortuosity index. Tortuosity is an important parameter that represents the absorption capacity of the material related to thermal and acoustical insulation properties. The more complex the path through the interconnected porosity is, the higher the material’s absorption capacity becomes. This investigation seeks to measure the tortuosity of the PolyMAC™ polyimide through different concurrent methods and establish an empirical index of tortuosity. The characterization techniques included were chemical, thermal, mechanical and hydraulic aiming for aerospace applications. Fourier transform infrared spectroscopy and thermo-gravimetric analysis, followed by differential scanning calorimetry were employed for chemical and thermal characterization. Since the main goal was to study the correlation between such tortuosity index with other pertinent mechanical properties, the polyimide foam was subject to dynamic compressions, flow resistivity test and a absorption test. The flow resistivity test was analyzed as a function of the foam mechanical compression at 30%, 60% and 90%. In order to obtain an empirical method, the tortuosity index is being derived by relating all measured properties through Buckingham’s Pi theorem, and generating a dimensionless parameter defined as tortuosity. This work is supported by PR NASA Space Grant IDEAS-ER Program.