Large-scale, thick, self-assembled, nacre-mimetic brick-walls as fire barrier coatings on textiles

Abstract

Highly loaded polymer/clay nanocomposites with layered structures are emerging as robust fire retardant surface coatings. However, time-intensive sequential deposition processes, e.g. layer-by-layer strategies, hinders obtaining large coating thicknesses and complicates an implementation into existing technologies. Here, we demonstrate a single-step, water-borne approach to prepare thick, self-assembling, hybrid fire barrier coatings of sodium carboxymethyl cellulose (CMC)/montmorillonite (MTM) with well-defined, bioinspired brick-wall nanostructure, and showcase their application on textile. The coating thickness on the textile is tailored using different concentrations of CMC/MTM (1-5 wt%) in the coating bath. While lower concentrations impart conformal coatings of fibers, thicker continuous coatings are obtained on the textile surface from highest concentration. Comprehensive fire barrier and fire retardancy tests elucidate the increasing fire barrier and retardancy properties with increasing coating thickness. The materials are free of halogen and heavy metal atoms, and are sourced from sustainable and partly even renewable building blocks. We further introduce an amphiphobic surface modification on the coating to impart oil and water repellency, as well as self-cleaning features. Hence, our study presents a generic, environmentally friendly, scalable, and one-pot coating approach that can be introduced into existing technologies to prepare bioinspired, thick, fire barrier nanocomposite coatings on diverse surfaces.

Figure 1. Preparation of bioinspired nanocomposite coatings and structural characterization.

(a) Schematic of the self-assembled nanocomposite films based on CMC polymer, (R = H or CH₂-COONa) and montmorillonite (MTM) natural nanoclay via concentration-induced self-assembly of polymer-coated nanoclay platelets with intrinsic hard/soft architecture, and coating of textiles from different concentrations of CMC/MTM = 60/40 w/w dispersions at 10 mm/min. (b) XRD of the pure MTM film, CMC₆₀MTM₄₀ film, and CMC₆₀MTM₄₀-5% coated fabric. The arrow shows the appearance of a diffraction hump for the coated textile. (c–f) SEM images of the cross-sections of (c) CMC₆₀MTM₄₀ film (scale bar 5 μm), (d) CMC₆₀MTM₄₀-1% (scale bar 200 μm, inset: scale bar 10 μm), (e) CMC₆₀MTM₄₀-5% (scale bar 200 μm), and (f) high magnification image of the CMC₆₀MTM₄₀-5% (scale bar 20 μm). CMC₆₀MTM₄₀-1% exhibits only a conformal coating of the fiber (d, inset, and Supplementary Fig. S1), and CMC₆₀MTM₄₀-5% shows the ordered layered structure of the nacre-mimetic coating (f, inset: scale bar 2 μm).

Figure 2. Thermal and thermo-oxidative stability of CMC₆₀MTM₄₀-coated fabrics and the control.

(a) TGA plot of the control and CMC₆₀MTM₄₀-1%, 1.75%, 2.5%, and 5% coated fabrics in N₂. (b) DTGA plots (top) in N₂ and (bottom) in air. (c) The average coating weight added on the textile from different slurry concentrations (calculated gravimetrically), and the residual mass calculated from TGA at 500 and 800 °C in N₂ atmosphere for all samples.

Figure 3. Fire break-through test.

Photographs of (a) the uncoated control, (b) CMC₆₀MTM₄₀-1%, (c) CMC₆₀MTM₄₀-1.75%, (d) CMC₆₀MTM₄₀-2.5% and (e) CMC₆₀MTM₄₀-5% at times indicated during exposure to a high temperature torch flame (ca. 1750 °C) at nearly 90° angle and 130 mm away from the sample. Right column: Shrinkage of the coated fabrics during charring. Sample edges are marked in dotted white line.

Figure 4. Bench-scale vertical flame test (VFT) analysis.

(a) Photographs from VFT of CMC₆₀MTM₄₀-coated fabrics and the control after 5 s of ignition. (b) Corresponding FLIR images after 5 s of ignition with a color scale from 20 to 660 °C. (c) Photographs of VFTs at the end of burning. (d) Maximum burning height and the minimum time needed to reach that height for CMC₆₀MTM₄₀-coated fabrics and the control.

Figure 5. Temperature vs. time plots of the CMC₆₀MTM₄₀-coated fabrics and the control at different sample height during bench-scale VFT.

(a–c) Temperature profiles of the control, CMC₆₀MTM₄₀-1.75%, and CMC₆₀MTM₄₀-2.5% at 10, 50, 100, 120 and 150 mm sample height. (d,f) Comparative study of the temperature profiles of all CMC₆₀MTM₄₀-coated fabrics at (d) 50 and (f) 100 mm. (e) FLIR images of CMC₆₀MTM₄₀-1.75% and CMC₆₀MTM₄₀-2.5% corresponding to the first temperature peak at ca. 5 s (hot gas) and second temperature peak at 50 s and 65 s, respectively, (glowing frontier), (temperature scale bar same as in Fig. 4b).

Figure 6. Cone calorimetry measurements of the CMC₆₀MTM₄₀-coated fabrics and the control.

(a) Heat release rate of the CMC₆₀MTM₄₀-coated fabrics for all slurry concentrations and the control. (b–f) Photos of the residues of the coated fabric and the control after burning in cone calorimetry, (b) control, and (c–f) CMC₆₀MTM₄₀-1%, 1.75%, 2.5% and 5%, respectively.

Figure 7. SEM images of the CMC₆₀MTM₄₀-5% coated fabric and the control.

(a,d,g) Surface and cross-section of the control, and (b,e,h) those of CMC₆₀MTM₄₀-5%, before burning. (c,f,i) CMC₆₀MTM₄₀-5% after burning in VFT showing (c) the surface, and (f,i) the cross-section. (i) Individual hollow fibers are seen after burning of CMC₆₀MTM₄₀-5%, encircled in red. (The control was completely consumed during burning, so no image can be shown after burning) (a,b,c,d, scale bar 1 mm; (e,f) scale bar 300 μm; (g,h) scale bar 100 μm; (i) scale bar 50 μm).

Figure 8. Surface modification and photographs showing amphiphobicity, water roll off and self-cleaning of the coated fabrics.

(a) Schematic representation of surface modification of CMC₆₀MTM₄₀-coated fabrics with trichloro(1H,1H,2H,2H–perfluorooctyl)silane (not in scale). Photographs of (b) water droplets, and (c) salad oil droplets, on both unmodified and modified coated fabrics. (d) Water droplet is soaked on the surface of the unmodified coated fabric, whereas it can easily roll off and bounce off from the modified coated fabric. (e) Self-cleaning behavior of modified coated fabric.