Super Gas Barrier and Fire Resistance of Nanoplatelet/Nanofibril Multilayer Thin Films

Abstract

of their colloidal stability, mechanical strength, high specific surface area, and thermal stability, [2][3][4][5][6] which have been used to produce transparent paper, biodegradable packaging, complex aerogels, and as the reinforcing phase in composites. [2,4,7,8] Despite all of its beneficial properties, cellulose exhibits poor flame resistance and gas barrier properties. [9,10] Improved barrier, mechanical, and flame resistant properties have been reported when montmorillonite clay (MMT) is used as a reinforcing agent in cellulose-based films. [11][12][13] The performance of polymer-clay barrier films is determined primarily by the clay characteristics (e.g., aspect ratio and density) and dispersion properties (i.e., clay exfoliation and orientation). For cellulose/clay composites, different methods to increase the interaction between clay and cellulose have been reported, including TEMPO-oxidation and by adding poly(vinyl alcohol) or chitosan (CH) as a compatibilizer. [14][15][16] Recently, cationic CNF with a quaternary ammonium functionality has been reported. [17] It was shown that the ionic interaction between the cationic CNF and MMT results in better mechanical properties of the composite, but further improvement is limited due to the formation of nanovoids as well as relatively low clay loading. [12,18] Layer-by-layer (LbL) assembly is a nanocoating technique that has been used to construct functional thin films for gas barrier and gas separation coatings, [19,20] energy storage and conversion, [21,22] drug delivery, [23] and adhesives. [24] By alternately depositing oppositely charged polyelectrolytes and/or clay platelets onto a charged substrate, thin films are assembled with high clay concentration and alignment. [25] In the present study, multilayer films consisting of anionic vermiculite (VMT) clay, with a high aspect ratio (≈2000), and cationic cellulose nanofibrils were investigated. This unique combination of highly aligned VMT platelets and cellulose nanofibrils forms a nanobrick wall structure with high transparency, excellent oxygen barrier, and fire resistance (superior to any other cellulose-based film previously reported). A 20 bilayer (BL) CNF/VMT nanocoating, with a thickness of 136 nm, exhibits a low oxygen transmission rate (OTR) of 0.013 cc (m 2 day atm) -1 . With only 2 BL of CNF/VMT, the melting of flexible polyurethane (PU) foam is prevented when exposed to a butane torch flame. These nanocoatings also exhibit high elastic modulus Cellulose nanofibrils (CNF) are abundant in the fiber cell walls of many plants and are considered a nearly inexhaustible resource. With the goal of improving the flame resistance and gas barrier properties of cellulose-based films, cationic CNF are assembled with anionic vermiculite (VMT) clay using the layer-by-layer deposition process. The highly aligned VMT nanoplatelets, together with cellulose nanofibrils, form a nanobrick wall structure that exhibits high optical transparency, flame resistance, super oxygen barrier, and high modulus. A 20 CNF/VMT...

Fire‐Resistant Structural Material Enabled by an Anisotropic Thermally Conductive Hexagonal Boron Nitride Coating

“…Equation predicts a t ig of 92 s for the BN‐densified wood at an external heat flux of 50 kW m −2 . This is at least 2.3 times as long as most reported fire‐resistant wood samples at that heat flux (Figure c) . Figure d compares the ignition properties of the densified wood and BN‐densified wood.…”

“…This is at least 2.3 times as long as most reported fire-resistant wood samples at that heat flux (Figure 4c). [17][18][19][20][21][22][23][24] Figure 4d compares the ignition properties of the densified wood and BN-densified wood. Ignition temperature (T ig ) is calculated by Equation (3):…”

“…Flame retardants interfere with the combustion process during ignition, pyrolysis, or flame spread either through chemical reactions or by acting as a physical barrier . The addition of flame retardants to wood can improve the material's fire resistance without sacrificing the intrinsic advantages of wood materials .…”

“…In contrast, inorganic flame retardants are greener and more suitable for sustainable applications. Most inorganic flame retardants display outstanding gas barrier functions, including clay, clay nanopaper, silica, titanium dioxide, calcium carbonate, and Mg–Al hydroxide . They reduce the HRR of wood by insulating the surface and delaying the thermal decomposition of the wood material.…”

Hybrid Gibbsite Nanoplatelet/Cellulose Nanocrystal Multilayered Coatings for Oxygen Barrier Improvement

“…To overcome this situation, which causes considerable environmental issues, a world-wide research effort is undertaken to develop eco-friendly packaging materials containing building blocks of renewable origin. In this context, as summarized in numerous recent reviews, nanocelluloses have emerged as a promising class of bio-based colloids, able to fulfill the requirements for the production of thin films and coatings, adapted to packaging applications, in particular exhibiting high oxygen barrier, optical transparency and mechanical resistance (Azeredo et al, 2017; Ferrer et al, 2017; Hubbe et al, 2017; Thomas et al, 2018; Qin et al, 2019). Nanocelluloses comprise both (i) the slender flexible nanofibrils (CNFs) extracted following a mechanical disintegration of cellulose fibers coupled with enzymatic and/or chemical treatments and (ii) the shorter rigid cellulose nanocrystals (CNCs) usually derived from partial sulfuric acid hydrolysis of any cellulose source (Klemm et al, 2011, 2018; Moon et al, 2011).…”