Surface modification of natural and synthetic hydroxyapatites powders by grafting polypyrrole

The modification of hydroxyapatite surface by grafting polypyrrole has been investigated with two hydroxyapatites (HA) powders. One is natural derived from bovine bone, it was prepared by calcination at 750 °C. The other is synthetic synthesized by the sol–gel method using Ca(NO₃)₂·4H₂O and P₂O₅. The presence of (C₄H₃N) _n polymeric fragment bound to HA surface was evidenced by infrared analysis. X-ray powder analysis has shown that the apatite structure remains unchanged during the surface modification. The thermogravimetric analysis has shown that the weight loss exhibited by HA increased from 8.7 to 47.8 and from 18.3 to 42.8 wt% for natural hydroxyapatite (NHA)/polypyrrole and synthetic hydroxyapatite (SHA)/polypyrrole, respectively, as the pyrrole solution concentration increased from 5 to 15 wt%. Grafting of polypyrrole on HA surface caused an increase in specific surface area up to 113 m²/g for SHA and up to 107 m²/g for NHA aged in 15 wt% pyrrole solution (HA/15Pyrrole). According to the results found for these two apatites, a mechanism of surface modification was proposed for the formation of N–H hydrogen bonds as the result of a reaction between the C₄H₅N organic reagent and OH⁻ ions of the HA.