Preparation of a novel bio-flame-retardant liquid for flame retardancy of natural fibers and their composites

The resistance of natural fibers toward flames is essential for their use in engineering applications. Hence, the present research focused on the preparation of a bio-flame-retardant liquid (BFL) to enrich the sustainability of natural fibers (kenaf fibers (KF), animal (WF), and cocoon (SF)) towards flame by employing a low cost, bio-waste chitosan and phosphoric acid (PA) through a chemical approach. Scanning electron microscopy, Fourier-transform infrared spectroscopy, thermogravimetric analysis, UL-94 testing, and microcalorimetry were conducted to evaluate the essential characteristics of the treated BFL on various natural fibers. The BFL altered the surface chemistry and exhibited remarkable fire-extinguishing properties (V-0 flammability rating in the UL-94 test and suppression of peak heat release rate of approximately 78%), as well as enhanced thermal stability (49 wt.% residue at 700°C) for the natural fibers without significant differences among them. Furthermore, the treated fibers were reinforced individually into vinyl ester (VE) matrix and manufactured respective composites, namely, VE_TKF, VE_TWF, and VE_TSF. The experimental results concluded that the BFL-treated fiber effectively improved the flame resistance (30% reduction in peak heat release rate) of VE composites. The findings of this study can be used to introduce flame retardancy in natural fibers to enable their use in the present and next-generation engineering applications.