Thermal stability and flame retardancy of cotton fabric coated with PVA-boric acid-cellulose nanofiber hybrid: Role of chemical interactions

An ecofriendly, polymer coating to impart fire retardancy to cotton fabric is introduced in the current study. Polyvinyl alcohol-boric acid-cellulose nanofiber (PVA-BA-CNF) hybrid coating with different compositions of boric acid and 2.5 wt% cellulose nanofiber (CNF) were coated over cotton fabric. The CNF used in the study was extracted from onion skin, an agricultural waste. The nanofibrous morphology of extracted CNF was confirmed from Transmission Electron Microscopic (TEM) images. The surface morphology of treated cotton was compared with that of bare cotton using scanning electron microscope (SEM) and optical microscope (OM). The dispersion of the coating formulation over the cotton fabric and the porosity after coating were confirmed. Chemical interactions developed in the coating formulations were characterized by Fourier transform infrared spectroscopy (FTIR). In addition to hydrogen bonding established between the coating formulation and cotton fabric, the existence of chemical bonding (B-O-C) between the components of the coating formulation and between the crosslinked coating and cotton fabric has been evident. The thermal stability of the coated cotton fabrics was evaluated using thermogravimetric analysis (TGA). The high char residue recorded for PVA-BA-CNF coated fabric, especially with 17phr BA content indicated the efficiency of crosslinked coating matrix in enhancing the thermal stability of the cotton fabric. The coated cotton degraded in two stages and with a different degradation kinetics than that of uncoated cotton fabric. Flame retardant performance of the coated fabric has been evaluated by vertical flammability tests and pyrolysis combustion flow calorimetry (PCFC). The peak temperature of heat release rate (pHRR) showed 32% reduction for PVA-BA-CNF coating with 17phr BA content compared with pure cotton indicating a decreasing flame spreading rate due to the inhibition of oxygen diffusion by chemically crosslinked PVA-BA-CNF coating.