Microstructural and thermal investigation of the bioinspired and synthetic fire-retardant materials deposited on cotton using LBL process

A detailed comparison of the bio- and synthetic polymers based layer by layer (LBL) coatings on a singular cotton fabric substrate was carried out. The growth of the deposited layers and subsequent properties, that could govern the fire protection of the substrate, were studied using low voltage-scanning electron microscope (LV-SEM) and thermal analysis techniques. From the 2D and 3D microstructural evaluation, uniform layered structure, agglomerated/precipitated structures and inter-fibers connecting layered-structure were explored, more thoroughly for chitosan and alginate based (CHI-2, ALG-2) biopolymer coatings, whereas the microstructure of synthetic polymers-based coatings ammonium polyphosphate and Polyvinyl Alcohol (APP-2 and PVA-2) showed only uniform layers. From the microthermal evaluation (TGA and MCC), a two-step degradation was recorded for all samples with a higher char residue recorded for APP-2 (TGA, ∼39.2%, at 600 °C, MCC ∼33.0% at 800 °C) followed by CHI-2 (TGA, ∼12.5% at 600 °C, MCC, ∼8.92% at 800 °C) suggesting superiority of the APP-2 based deposition over that of CHI-2. In addition, the same pattern of dominance was found consistent with the peak heat release rate (PHRR) values and total heat release (THR) values for APP∼ (85.1 W/g, 6.53 KJ/g), and CHI-2∼ (227.74 W/g, 17.17 KJ/g), respectively. However, from the VFT analysis, both samples were found to have comparable properties, in terms of structural integrations, char residue, and flame resistance.