Dynamic mechanical properties of hydroxyapatite-ethylene vinyl acetate copolymer composites

Dynamic mechanical thermal analysis (DMTA) was carried out to explore the dependence of temperature on the viscoelasticity of composites consisting of synthetic hydroxyapatite (HAP) particulate filled ethylene vinyl acetate copolymer (EVA). Two forms of HAP, differing in their surface characteristics and particle size, were used for the study. The freeze-dried HAP (FDHAP) had a mean particle size of 49.18 μm and an irregular surface morphology. In the contrary the spray dried form of HAP (SDHAP) had a mean particle size of 5.84 (m and a spherical morphology. The dynamic mechanical analysis of the composites showed that both, particle size and morphology, had a significant effect on viscoelastic properties. A tremendous increase of the storage modulus was noted with the addition of HAP. Above the Tg of the polymer matrix, the values were marginally higher for the composites containing FDHAP than for those with SDHAP. The damping (tan δ) was found to decrease with the inclusion of HAP. A marginal upper shift in the value of the glass transition temperature (Tg) was observed for the composites fabricated from SDHAP indicating a slightly strong interaction between this HAP and the EVA matrix.