The properties of PVA-cockle shell derived hydroxyapatite synthesized through wet chemical precipitation method

The increasing demand for biocompatible materials in medical applications has driven the search for sustainable and low-cost sources of hydroxyapatite (HA), a major component of bone and teeth. Conventional HA synthesis relies on expensive or non-renewable calcium sources, which has highlighted the need for alternative, ecofriendly precursors. This study aims to investigate the potential of cockle shells, an abundant biogenic waste material, as a calcium precursor for the synthesis of HA via the wet precipitation method. In addition, incorporating additives such as polyvinyl alcohol (PVA) is proposed to investigate the effects of PVA addition on the chemical and physical properties of synthesized HA, especially in terms of its homogeneity and structural purity. Cockle shells in the form of calcium oxide (CaO) were mixed with diammonium hydrogen phosphate to form HA via the wet precipitation method. Thermogravimetric analysis (TGA) indicated 750 ⁰C as the minimal conversion temperature from CaCO₃ to pure CaO. The obtained CaO was then reacted with diammonium hydrogen phosphate (NH4)2HPO4 to produce HA. Subsequently, PVA was added to synthesized HA with various concentrations (2.5 wt%, 5.0 wt%, and 7.5 wt%) followed by a heat treatment at 1000 ⁰C, which later known as HAP samples. X-ray Diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR) analysis verifies HA formation with a clear peak at 31.8⁰ with the lowest crystallite size of 436.74 nm at HAP 3 (7.5 wt% PVA) and functional groups of phosphate and hydroxyl bands, respectively. Besides that, Scanning Electron Microscopy (SEM) shows that HAP 3 (7.5 wt% PVA) resulted in the spherical morphology with a less agglomerated particle size of 0.172 µm. Overall, calcium source from cockle shells has been successfully employed in producing HA. The addition of 7.5 wt% PVA (HAP 3) successfully enhanced the structural properties of HA as PVA acted as a stabilizing and dispersing agent, improving crystallinity, preserving functional groups, and reducing particle agglomeration.