Thermal Treatment and Polymer Matrix Diffusion Effects on Hydroxyapatite Particle Size Evolution

A widely used approach for synthesizing hydroxyapatite (HA) particles is the wet chemical precipitation method, favoured for its cost-effectiveness and straightforward process. Incorporating organic macromolecules with polar functional groups, such as COOH and OH, during synthesis can impact the properties of the resulting HA particles. These functional groups enhance the affinity for positively charged Ca²⁺ ions, promoting HA crystal nucleation in the solution. In this study, solutions at different concentrations of chitosan and sodium alginate are used as nucleation medium for the HA particles in order to decrease their particle size. The calcium and phosphate precursor solutions were adjusted to a pH of 12 and added to the polymer solution with a concentration varying from 5 to 10% w/v, reported to the stoichiometric mass of HA according to the synthesis reaction. After synthesis, the resulting powder was calcinated at 1000 °C. The effects that the polymers have on the properties of HA particles were monitored using SEM, FT-IR, EDAX, DLS, and TGA before and after the thermal treatment to see how the system evolves till crystallization of HA occurs. The largest decrease in average particle diameter-67.7%-was observed in the HA + Alg 10% sample, although a reduction in particle size was evident in all samples.