Thermophysical Properties Characterization of Thermoplastic Polyurethane Elastomer Nanocomposites

Abstract

Thermal protection materials are required to protect structural components of space vehicles during the re-entry stage, missile launching systems, and solid rocket motors. Novel materials based on nanotechnology creating nontraditional ablators are rapidly changing the technology base for thermal protection systems. The introduction of inorganic nanomaterials as additives into polymer systems has resulted in polymer nanostructured materials exhibiting multifunctional, high- performance polymer characteristics beyond traditional polymer composites possess. In this study, different polymer nanocomposite compositions were created by melt-compounded montmorillonite nanoclays or carbon nanofibers in a neat thermoplastic polyurethane elastomer (TPU) polymer using twin-screw extrusion. These materials were characterized for their thermal and kinetic properties. Scanning electron microscopy analysis was performed for microstructural studies. Selective results were then compared against the current state-of-the-art insulation material, Kevlar®-filled ethylene-propylene-diene rubber (EPDM) as well as the neat TPU for the investigation of properties enhancement. I. Introduction Thermoplastic polyurethane elastomer nanocomposites (TPUNs) are a novel class of insulation materials developed by Air Force Research Laboratory (AFRL) that are lighter, exhibits better erosion and insulation characteristics, and possesses a more cost-effective manufacturing process than the current baseline material, Kevlar®-filled ethylene-propylene-diene rubber (EPDM). The proposed research combines numerical modeling and experimental characterization of TPUNs for solid rocket motor (SRM) insulation. The TPUN thermophysical properties are characterized using thermogravimetric analysis (TGA) for kinetic parameters, differential scanning calorimetry (DSC) for specific heats, laser flash for thermal diffusivity and thermal conductivity, and dilatometry for coefficient of thermal expansion, as well as other analysis techniques are used in this study. This paper will summarize our research progress on the characterization of thermal behavior and thermophysical properties of these TPUNs, which will later be used in our numerical modeling research. A. Behavior of Thermal Protection Materials Thermal protection materials are required to protect structural components of space vehicles during the re-entry stage, missile launching systems, and solid rocket motors. Polymeric composites have been used as ablative thermal protection systems (TPS) for a variety of military and aerospace applications. Thermal protection materials such as carbon phenolics and carbon-carbon composites are used as spacecraft heat shields, and insulation and nozzle assembly materials for SRMs. These materials are exposed to a thermochemical as well as particle impinging flow and are subjected to high temperatures in excess of