Hybrid Network Structure and Mechanical Properties of Rodlike Silicate/Cyanate Ester Nanocomposites

Silicate nanorods (attapulgite, ATT) were organically modified and homogeneously dispersed in a cyanate ester (CE) resin. ATT dispersions and networks were characterized by rheological and microscopic measurements. Amine groups grafted onto the particle surface catalyzed the cyclotrimerization of the CE monomers and enabled the CE monomers to enter the inter-rod spacing of loose aggregates easily, resulting in homogenization of the particle size distribution in the nanocomposites. The addition of nanorods decreased the density of organic networks and increased intracyclizations. Covalent bonding at the inter-face was confirmed by Fourier transform infrared (FTIR) spectroscopy and dynamic mechanical analysis (DMA), which establishes a basis for enhancing/optimizing mechanical properties of CE resins. Nanocomposite modulus, strength, and toughness increased 40, 42, and 55%, respectively, relative to the neat resin, although high nanorod loadings (e.g., 8 wt %) showed negligible benefit. The interplay between nanorod and resin networks governed the mechanical properties of the nanocomposites. The curing reaction decreased the size of particle aggregates and thus reduced the percolation threshold of particle networks. Particle networks induced the formation of more linear or branching polymer molecular structures, resulting in weaker particle-matrix interactions. These factors reduced the stress transfer efficiency and crack propagation resistance, impairing the extent of reinforcing at high particle loadings.