Search

As additive manufacturing (AM) increasingly gains commercial and academic interest, government agencies, such as NASA Johnson Space Center, seek to produce thermal protection systems using AM methods, such as fused filament fabrication (FFF). The purpose of this study is to develop a suitable polyetherimide (ULTEM™ 1010) nanocomposite with enhanced ablation and thermal properties while maintaining compatibility with commercially available FFF machines. Eleven formulations were compounded using the twin-screw extruder with varying amounts of nanoclay, glass bubbles, and flame-retardant additives. All formulations were characterized via multiple instruments to be down-selected to four candidates for aerothermal testing. After discovering specific characteristics of some formulations, aerothermal test models were 3D printed for four formulations. Enhanced thermal properties among the composite formulations were demonstrated. Aerothermal testing also displayed promising results. In addition to experimental data, microstructural analyses were performed.

Tremendous effort is focused on improving epoxy toughness, but common approaches diminish processability and mechanical properties. This work presents hybrid additives which simultaneously enhance toughness, modulus, and other mechanical properties without reducing the network's processability. The hybrid herein was molecularly designed to contain “hard” nanoparticles and “soft” organic segments which both covalently bond and interact to form strong interfaces with epoxy networks. It is shown that a hyperbranched epoxy (HBE) reacted with a molecular silica, polyhedral oligomeric silsesquioxane (POSS), can provide the desired simultaneous reinforcement and toughness enhancements while maintaining processability. Epoxy network incorporation of the hybrid toughener led to a 220% increase in fracture toughness while also bringing about an increase in Young's modulus of over 20%. These significant improvements are described by the cured network's multi-scale morphologies and toughener dispersion states, and are related to strong interactions which occur between POSS's pendants and the HBE.

Hyperbranched polymers have been shown to improve epoxy fracture toughness at the cost of other mechanical properties. In this study an aliphatic, epoxide-functional hyperbranched polymer was synthesized and incorporated at different concentrations into an aromatic epoxy-amine network without cure-induced phase separation. The resulting homogeneous network architecture and thermomechanical properties were studied using DSC, DMA and FTIR, while the mechanical properties were investigated using uniaxial compression and single edge notch beam 3-point bending. It was found that although the flexible hyperbranched structure decreased the glass transition temperature of the network, it also allowed for simultaneous enhancement in both fracture toughness and Young's modulus. These findings were attributed to relationships between chemical structure, crosslink density and non-bond interactions, and indicate the potential for further glassy network fracture toughness improvement without loss of critical mechanical properties by tailoring of the hyperbranched structure.