Epoxy composites based on glass beads. I. Viscoelastic properties

The Effect of Silica Particle Size on the Mechanical Enhancement of Polymer Nanocomposites

In the present work, SiO₂micro/nanocomposites based on poly-lactic acid (PLA) and an epoxy resin were prepared and experimentally studied. The silica particles were of varying sizes from the nano to micro scale at the same loading. The mechanical and thermomechanical performance, in terms of dynamic mechanical analysis, of the composites prepared was studied in combination with scanning electron microscopy (SEM). Finite element analysis (FEA) has been performed to analyze the Young's modulus of the composites. A comparison with the results of a well-known analytical model, taking into account the filler's size and the presence of interphase, was also performed. The general trend is that the reinforcement is higher for the nanosized particles, but it is important to conduct supplementary studies on the combined effect of the matrix type, the size of the nanoparticles, and the dispersion quality. A significant mechanical enhancement was obtained, particularly in the Resin/based nanocomposites.

Viscoelastic behavior and construction of master curve for graphene/polyimide nanocomposites

Dynamic mechanical spectroscopy is used to investigate the variation of the glass rubbery transition temperature ( Tg) of graphene/polyimide nanocomposites. The Tg was obtained as the temperature corresponding to the peak of the tan δ versus temperature curve for the alpha transition. Cole–Cole curve was constructed for the matrix and the composites composite at 1 Hz and a hemispherical curve was obtained suggesting that the constituents have similar relaxation behavior. The time–temperature superposition principle was used to model the behavior of the nanocomposites at lower frequencies and longer times. Frequency sweep was performed in the range of 0.05–100 Hz at different temperatures. The storage modulus curves obtained at different temperatures (isothermal), as a function of frequency, were shifted horizontally to construct a continuous master curve. Both the generalized reduced gradient method and the Williams–Landel–Ferry (WLF) equation were used to calculate the activation energy for glass–rubber transition. The universal constants C1 and C2 were determined using the WLF equation. The dependence of relaxation time on temperature was verified.