Characterization of hydroxyapatite from recycled fish scale and its application as a filler in a biodegradable food tray

Abstract Fish scale waste can be used as a precursor of hydroxyapatite (HAp). In this work, HAp was extracted from white seabass ( Lates calcarifer ) scale waste by using an alkali heat treatment. The fish scale was pretreated with hydrochloric acid (HCl) concentrations of 0.1, 0.5, and 1 M. The pretreated fish scale was then treated with 2% sodium hydroxide (NaOH) solution at 70°C for 5 h and again (20% NaOH solution) for 1 h to extract HAp. The effects of each pretreatment on the properties of the extracted HAp were investigated. HAp produced after pretreatment with 1 M HCl had the smallest particle size (28.24 ± 5.20 μm), the highest degree of crystallinity (79%), the highest thermal stability, the largest BET surface area (90.80 m ² /g), and the highest whiteness value (97.360 ± 0.01). 1 M HCl could eliminate more protein, collagen, and other organic compounds than lower HCl concentrations without destroying the crystalline domains of the fish scale. Waste L. calcarifer scale is therefore a potential source of HAp. Furthermore, in a preliminary study for further research, HAp extracted in the proposed procedure was used as a filler in a biodegradable starch foam.