Synthesis and characterization of eggshellderived hydroxyapatite by microwave-assisted wet chemical precipitation method / Goh Kian Wei

Goh , Kian Wei (2024) Synthesis and characterization of eggshellderived hydroxyapatite by microwave-assisted wet chemical precipitation method / Goh Kian Wei. PhD thesis, Universiti Malaya.

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Abstract

Nowadays, the demand for biomaterials for clinical applications is increasing. Hydroxyapatite (HA) is one of the prevailing biomaterials having a similar chemical composition and crystalline structure for bone regeneration. The high calcium content of biowaste chicken eggshells has been used to synthesize HA with the help of microwave heating. In this research, eggshell-derived HA was successfully synthesized using a simple wet precipitation method assisted by microwave irradiation. Using the microwaveassisted wet precipitation method, HA powders were initially synthesized at various Ph values of 8, 9, 10, 11 and 12 coupled with a lower microwave power (700 W). Optimized HA powders were then determined by calcining at various irradiation times (5, 10, 15, 20, and 30 minutes). Structural characterizations of the derived powders were performed by X-Ray Diffractometer (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Field emission scanning electron microscope (FESEM), and Energy-Dispersive X-Ray Spectroscopy (EDX). The results showed that the pH value and irradiation time were the important parameters in altering the particle size and morphology of HA. The crystallite sizes of eggshell-derived HA powders were calculated using the Scherrer equation and had a similar trend with values obtained from the William-Hall plot. FESEM images showed that a well-formed needle-like HA has an average crystallite size of approximately 10 to 15 nm in width and 60 to 80 nm in length at an optimum pH of 10. In addition, the smallest HA particles of about 22 nm were formed when irradiated for 15 minutes. XRD, FTIR, and EDX analysis revealed that the utilization of biowaste chicken eggshells as a calcium source via microwave-assisted precipitation method was effective in synthesizing stoichiometric HA particles. As compared to the literature, this work clearly confirmed that optimized needle-like HA powder could be obtained at pH 10 with a relatively low microwave power of 700 W for 15 minutes. Furthermore, the dense HA samples were prepared by optimum as-prepared HA powder in a modified domestic microwave oven and were characterized at different sintering temperatures between 900°C and 1200°C. The results revealed that the pure HA phase remains stable up to 1200°C. The sintered HA sample at 1200°C possessed the highest values in bulk and relative density, which were 3.0 g/cm3 and 95.1%, respectively, coupled with the larger grain size of 1.8 μm. Besides, maximum Vickers microhardness and fracture toughness values of 4.1 GPa and 0.90 MPa·m1/2, respectively, were achieved for dense HA samples at 1200°C. These findings demonstrated there is a difference in the sintering behavior of synthetic HA depending on the sintering temperature. Additionally, the modified domestic oven could be successfully used to synthesize HA with excellent mechanical properties.

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