Immobilization of polyvinylacetate macromolecules on hydroxyapatite nanoparticles

Concentration dependence of the storage modulus, E′, was investigated for polyvinylacetate (PVAc) filled with hydroxyapatite (HAP) nanoparticles. The filler volume fraction, vf, varied from 0 to 0.05 and the E′ and loss tangent, tan δ, were measured below neat matrix Tg at −40 °C and above neat matrix Tg at +50 °C at 1 Hz. The Tg determined as the position of the maximum on the temperature dependence of tan δ increased by 14 °C compared to the neat PVAc (39 °C) by adding 5 vol.% of HAP. At −40 °C, the observed small increase of E′ with vf was in agreement with the prediction based on the simple Kerner equation. At +50 °C, the increase of E′ with vf observed was an order of magnitude greater than that predicted using the simple continuum mechanics model. An attempt was made to explain the observed deviation employing the hypothesis of immobilized entanglements.