2, ATSP Innovations, Champaign, Illinois, United States
3, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States
Polymer nanocomposite foams bear a technological potential by exclusively embodying multifunctional material properties within low-density structures. Yet, contemporary configurations could only attain limited performance caused either by modest properties of host polymers or nanofiller-averse processing techniques. Delibrately controlled interfacial interactions between nanoparticles and backbone chains constitute another critical element for the nanocomposites to optimize physical properties beyond the state-of-the-art. Aromatic thermosetting copolyester (ATSP), introduced in the late 1990s, utilizes low cost, easily processable and highly crosslinkable oligomers to develop a high-performance polymer system. Here, we present carbon nanoparticle incorporated high-performance ATSP nanocomposite foams. These foams are fabricated through a facile solid-state mixing method wherein carboxylic acid and acetoxy-functional group oligomers are initially combined with chemically pristine carbon nanofillers, all in powder form. The mixtures are then subjected to a thermal condensation polymerization reaction in which the constituent oligomers form the ester backbone of the ATSP matrix and advanced the molecular weight while acetic acid is emitted as the by-product, and generates a porous nanocomposite morphology. In situ hydrodynamic forces induced during the polycondensation reaction enables homogeneous and intact dispersion of the nanoparticles in molten oligomer domain, and correspondingly yields significant improvements in the thermophysical properties. As compared to a neat ATSP foam, the nanocomposite foams exhibit a reduced coefficient of thermal expansion by 25% to 75 x 10-6 °C-1. Thermal stability temperature at 5% mass loss is increased by 30 °C exceeding 500 °C. Compressive mechanical strength is enhanced two-fold, reaching 16 MPa along with a nearly doubled fracture strain, which ultimately produces improved material toughness. In addition, the controlled nanoparticle size promotes different electrical percolation thresholds and ultimate electrical conductivities in the nanocomposite foam structures. Microstructural analysis further illustrates nanoparticle distributions in the matrix as well as morphological modifications induced by the conductive percolating networks of the nanofiller particles. Cure characteristics reveal the thermochemical changes formed in the polymerization processes for the GNP content. Besides, chemical spectroscopy of the ATSP nanocomposite morphology exhibits the formation of a robust interfacial coupling mechanism between the carbon nanofillers and ATSP backbone. The aromatic thermosetting copolyester nanocomposite foams are lightweight, mechanically strong, electrically conductive and thermally durable multifunctional structures utilizing strong interactions with the carbon nanofillers which can potentially be used for variety of technological applications.