Novel and eco-friendly flame-retardant cotton fabrics with lignosulfonate and chitosan through LbL: Flame retardancy, smoke suppression and flame-retardant mechanism

Bio-based materials have been noticed for the continuous environmental pollution and resource shortage. In this paper, lignosulfonate (LS) and chitosan (CS) were selected to be flame-retardants. In the vertical flame test (VFT), LS/cotton-17.1 wt%, CS/LS/cotton-17.0 wt%, and CS/LS/cotton-25.2 wt% obtained lower afterflame times than that of uncoated cotton fabrics, while LS/cotton-17.1 wt% had serious afterglow time of 70 s. However, the afterglow time of CS/LS/cotton-25.2 wt% was 11 s, which decreased owing to the increased amount of CS. LS/cotton-17.1 wt%, CS/LS/cotton-17.0 wt%, and CS/LS/cotton-25.2 wt% presented limiting oxygen index values of 24.7%, 25.0%, and 26.0%, respectively. The scanning electron microscope images of char residues after the VFT showed that CS and LS formed an intumescent flame-retardant system, and cotton fibers remained intact structure. Meanwhile, the results of thermogravimetric analysis suggested that flame-retardant cotton fabrics can generate stable char residues. In N2 atmosphere, CS/LS/cotton-25.2 wt% generated 27.1% stable char residues. Moreover, the addition of CS/LS decreased the heat release rate and total heat release values and this system performed well in smoke suppression. The flame-retardant mechanism of the system might belong to gas-phased because more non-combustible products were generated in the thermal degradation process. (C) 2020 Elsevier Ltd. All rights reserved.