Influence of Functionalized Titanium Dioxide on Composite Mechanical Properties

Metal oxide particles are incorporated in the formulation of solid rocket fuels to offer increased burning rate and improved mechanical properties of the polymeric binder (e.g., hydroxyl-terminated polybutadiene or HTPB). Altering the surface chemistry of these particles affects the dispersion and interaction between the HTPB matrix and the particles. This study investigated the effects functionalizing titanium dioxide (TiO2) using phosphonoundecanoic acid to modify the particle surfaces by adding terminal COOH groups with different ligand lengths (2,6, 11, and 16) and at concentrations of 2mM and 5mM. The COOH ligands cross-link with the HTPB polymer and isophorone diisocyanate (IPDI) curative. Tensile tests were performed to investigate the affect different ligand lengths and concentrations of the functionalization on the mechanical properties of TiO2 HTPB composite samples. For the 2mM and 5mM concentrations, increasing ligand lengths corresponded to increases in ultimate strength of 60% and 105%, respectively. Increasing ligand length and concentration also resulted in improved material toughness and ductility of the HTPB composites, demonstrating desirable improvements to material properties through modifying the surface chemistry of titania nanoparticles.