Abstract
To reduce fire hazards and expand high-value applications of lignocellulosic materials, thin films comprising graphene nanoplatelets (GnPs) and multi-wall carbon nanotubes (CNTs) pre-adsorbed with alkali lignin were deposited by a Meyer rod process. Lightweight and highly flexible papers with increased gas impermeability were obtained by coating a protective layer of carbon nanomaterials in a randomly oriented and overlapped network structure. Assessment of the thermal and flammability properties of papers containing as low as 4 wt % carbon nanomaterials exhibited self-extinguishing behavior and yielded up to 83.5% and 87.7% reduction in weight loss and burning area, respectively, compared to the blank papers. The maximum burning temperature as measured by infrared pyrometry also decreased from 834 °C to 705 °C with the presence of flame retardants. Furthermore, papers coated with composites of GnPs and CNTs pre-adsorbed with lignin showed enhanced thermal stability and superior fire resistance than samples treated with either component alone. These outstanding flame-retardant properties can be attributed to the synergistic effects between GnPs, CNTs and lignin, enhancing physical barrier characteristics, formation of char and thermal management of the material. These results provide great opportunities for the development of efficient, cost-effective and environmentally sustainable flame retardants.
Highlights
The use of fire as a source of energy has been critical for the development of human civilization
These results were consistent with IR analysis, where small independent heat spots spread over a large area of the burned paper coated with carbon nanotubes (CNTs), while the heat signature of the burned paper coated with graphene nanoplatelets (GnPs) formed a large and continuous region with temperatures exceeding 450 ◦C, which was higher than the decomposition temperature of cellulose [37]
Cellulosic paper was endowed with extraordinary self-extinguishing properties and flame retardancy by coating its surface with GnPs, CNTs and lignin using a Meyer rod-coating method
Summary
The use of fire as a source of energy has been critical for the development of human civilization. The development of flame retardants with good chemical stability and environmentally sustainable characteristics is critical to improve safety awareness of consumers and meet increasing fire resistance requirements Carbon nanomaterials such as graphene nanoplatelets (GnPs) and carbon nanotubes (CNTs) have drawn tremendous attention due to their superior flame-retarding properties in polymer composites, including polypropylene [13,14], epoxy [15], poly(vinyl alcohol) [16] and poly(methyl methacrylate) [17]. The incorporation of these carbon nanoparticles significantly delayed ignition and reduced the heat-release rate during the combustion of polymer composites. The effects of coating content and formulation—with different ratios of GnPs, CNTs and lignin—on the fire-retardant properties were examined, and the flame-retardant mechanism was discussed
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