Renewable micro hydroxyapatite (mHA) extracted from animal bones, and fabricated mHA-Jute-vinyl ester bio-composite as an intumescent green flame retardant material

Abstract

In this paper, we synthesized highly functionalized micro hydroxy apatite (mHA) from animal bones by a decomposition method using extended base treatment, and applied it as a flame-retardant material (FRM) through a dip-coating method as a heat-shielding layer on pure jute (PJ). Wet depositions of charged anionic and cationic polyelectrolytes create a few to several coating layers by the L-B-L method on the surface of PJ through strong electrostatic interactions, generating mHA-Jute. In addition, a strong cementing action materializes through inter-ionic interactions between the PJ surface and mHA, and is compared in flame-retardancy tests through cone calorimetry analysis. The heat release rates (HRRs) of PJ and mHA-Jutes (0.5 wt%, 1.0 wt%, 2.0 wt%, and 3.0 wt%) are displayed in the primary and secondary stages. The HRRs gradually decreased from PJ (177) to 3.0 wt% mHA-Jute 36 (388%), owing to the strong thermal shielding effect of the mHA deposited on the PJ core due to lignocellulose fiber linked with mHA. Next, we fabricated mHA-Jute with vinyl ester resin (VER) bio-composites and calculated the HRRs. The HRRs of mHA-Jute-VER bio-composites showed superior thermal shielding action over the blank PJ-VER bio-composite and superior HRRs of 291 s, 131 s, and 41 s were observed from PJ-VER to 1.0 wt%, 2.0 wt%, and 3.0 wt% mHA-Jute-VERs, respectively, due to the formation of thermal shielding layers. Higher burning times and burning rates were reported for mHA-Jute-VERs compared to PJ-VER bio-composites. The impact energies of mHA-Jute-VER increased up to 47% from 0.5 wt% to 3.0 wt% mHA deposition. In addition, the limiting oxygen index (LOI) of 3.0 wt% mHA-Jute-VER showed a superior value (27%) compared to the PJ-VER bio-composite. Moreover, ignition resistance and self-extinguishing competencies were observed on coated fabrics with 3.0 wt% mHA-Jute-VER, which could be a great advantage for indoor fire-quenching applications. We have also explained the FR mechanism of the proposed mHA-Jute-VER bio-composite by comparing the elimination of various combusted gases of CO₂, CO, CH₄, and O₂.