(77f) Nanocomposites of Polyurea and Aminopropyl Isobutyl POSS Functionalized Graphene Nanoplatelets: Chemistry and Applications to Force Protection

In this study, we report on the design, chemical synthesis, characterization, and fabrication of novel nanocomposite systems comprising one-part polyurea (PU) and aminopropyl isobutyl polyhedral oligomeric silsesquioxane (POSS) functionalized graphene nanoplatelets (GNP-POSS), tailored as a coating for force protection applications. We efficiently synthesized GNP-POSS through a two-step protocol, including ultrasonication-assisted reaction and precipitation, and carefully characterized the reaction products with respect to their chemical and crystalline structure, morphology, and thermal stability. Spectroscopic analyses, including FTIR and XPS, highlighted the interactions between POSS and residual oxygen moieties of GNPs, confirming both covalent and noncovalent bonding. The X-ray diffraction patterns of GNP-POSS further revealed that the GNP crystallinity was not altered after functionalization with POSS. We successfully incorporated GNP-POSS in the PU resin at contents of 1, 3, 5, and 10 wt.% to yield PU/GNP-POSS nanocomposite films. ATR-FTIR analysis confirmed strong interfacial interactions between the urea groups of PU and GNP-POSS functionalities in these films. Notably, PU/GNP-POSS nanocomposites exhibited superior thermal stability and mechanical properties compared to neat PU films. Quasi-static tensile testing revealed substantial enhancements in the tensile strength of the PU film (an increase from 7.9 to 25.1 MPa) and Young’s modulus (an increase from 238 to 617 MPa), with notable improvements in elongation-at-break and toughness by 14% and 125%, respectively, when around 1 wt.% GNP-POSS was added to the matrix. We further investigated the impact of GNP-POSS content on the morphological and dynamic behavior of the PU/GNP-POSS nanocomposite films under high-strain-rate conditions . Utilizing a split-Hopkinson pressure bar setup, we observed significant increases in film strength (from 147.6 to 199 MPa) and marginal enhancement in energy density (from 38.1 to 40.8 kJ/m³) at a low GNP-POSS content. These results confirm the suitability of PU/GNP-POSS nanocomposite films for force protection applications.