Hiroaki Miyagawa

The effect of chemical modification on the fracture toughness of montmorillonite clay/epoxy nanocomposites

The change in fracture toughness and its dependence on the content of clay nanoplatelets and adhesion at the interface between clay nanoplatelets and anhydride-cured epoxy matrix are discussed. Three clay nanoplatelets with different chemical modifications were used in this investigation. To fabricate nanocomposites, the clay nanoplatelets were sonicated in acetone for 2 h. The role of the clay nanoplatelets in the mechanical/fracture properties was investigated by transmission electron microscopy (TEM). Bright-field TEM micrographs showed excellent dispersion of clay nanoplatelets in epoxy matrix. Both intercalation and exfoliation of clay nanoplatelets were observed depending on clay modification. Compact tension specimens were used for fracture testing. The fracture toughness increased with increasing clay content. The fracture toughness of clay/epoxy nanocomposites varied with the clay morphology in the epoxy matrix. Different morphologies of the fracture surfaces, highly dependent on the morphology of dispersed clay nanoplatelets, were observed using environmental scanning electron microscopy (ESEM). The fracture toughness was found to be correlated with the fracture surface roughness measured by confocal laser scanning microscopy (CLSM).

Nanocomposites from biobased epoxy and single-wall carbon nanotubes: synthesis, and mechanical and thermophysical properties evaluation

The synthesis, and thermophysical and mechanical properties of anhydride-cured biobased epoxy containing diglycidyl ether of bisphenol F (DGEBF) epoxy and epoxidized linseed oil (ELO) reinforced with fluorinated single-wall carbon nanotubes (FSWCNT) are reported. Sonication was used to disperse FSWCNT in the biobased glassy epoxy network, resulting in great improvement of the modulus of nanocomposites containing extremely small amounts of FSWCNT. The glass transition temperature of the obtained nanocomposites decreased by approximately 30 °C after the addition of 0.20 wt% (0.16 vol%) FSWCNT, without adjusting the amount of the anhydride curing agent. This was because of the non-stoichiometry of the epoxy matrix, caused by the fluorine on the single wall carbon nanotubes. The adequate amount of the anhydride curing agent needed to achieve stoichiometry was experimentally determined by dynamic mechanical analysis (DMA). The storage modulus of the epoxy at room temperature, which is below the glass transition temperature of the nanocomposites, increased up to 0.44 GPa with the addition of only 0.24 wt% (0.20 vol%) of FSWCNT, representing an up to 14% improvement from the modulus of the biobased ELO neat epoxies. The fracture toughness of the neat biobased ELO epoxies was also improved by approximately 43% upon addition of FSWCNT. The excellent improvement of the modulus was achieved without sacrificing the fracture toughness.