An Environmentally Friendly Phosphorus-Modified Cellulose/Silica Hybrid 1 Hydrogel for Fire Prevention and Firefighting

11 Wildfires have been recognized as a natural incident in some forests, however, fire 12 season is now more severe and extensive, even in tropical rainforests in which fire could 13 have damaging impacts. A hydrogel is a 3-D polymeric structure encompassing cross- 14 linked and hydrophilic macromolecules. In comparison with water, hydrogels have 15 shown some superiorities in terms of water-binding, cooling, and sealing, which make 16 them be applied in forest fire prevention programs for improving fire-extinguishing performance. In this study, an environmentally friendly phosphorus-modified 18 cellulose/silica hybrid hydrogel was prepared based on the modified methylcellulose 19 by 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide–itaconic acid (DOPO-ITA) 20 and silica nanoparticles. The storage (G') and loss (G") moduli increased with the 21 increment of silica nanoparticles content, owing to the role of silica nanoparticles as crosslinking agent. In the fire prevention experiments, the grass treated with the 23 methylcellulose@DOPO-ITA@silica hybrid hydrogel shows self-extinguishing 24 behavior, whereas those treated with ordinary water or methylcellulose hydrogel can 25 be easily ignited after one week. In the firefighting experiments, the 26 methylcellulose@DOPO-ITA@silica hybrid hydrogel displays much shorter 27 extinguishing time and lower consumption volume than ordinary water and the 28 methylcellulose@DOPO-ITA hydrogel. This work presents an environmentally- 29 friendly, non-toxic, and biodegradable cellulose-based hybrid for 30 prevention and firefighting of wildfires. 31 This study reported a bio-based organic-inorganic hybrid hydrogel by MC structurally modified with DOPO–ITA and silica nanoparticles were added as a linking agent for promoting the thermal stability of MC. Morphology, thermal stability, gelation time, water retention, swelling, rheological parameters of the hydrogels were studied, and fire prevention and extinguishing effects of the hydrogels on grass and wooden pallet were examined. The fire prevention and extinguishing mechanisms of the hydrogels were further explored.

Over the past few decades, rescue worker and scientific expertise get together in a 61 team effort to develop efficient technologies for bringing forest fires under control 62 (Korobeinichev et al., 2012). Water has the potential for absorbing a large quantity of 63 heat produced from thermal evaporation process, due to its large specific heat capacity 64 (Vega et al., 2010) and high latent heat of evaporation (Torquato & Stell, 1981). Water 65 is mostly used as a fire extinguisher from antiquity to the present day. On contact with 66 4 flammable materials, water naturally produces an oxygen barrier performance to 67 prevent fires and explosions. Given the changing shape of water at room temperature, 68 its direct exploitation as a material completely resistant to fire is a difficult work.

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Besides using water directly, the intensity and spread rate of wildland fires can be 70 reduced by fire retardants so that on-ground firefighters can enter to the area creating 71 safer containment lines close the fire (Agueda, Pastor, & Planas, 2008). North America,

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Australia and the Mediterranean basin countries have extensively utilized fire retardants 73 to battle forest fires. The fire retardants fall into two categories of short-and long-term.

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Foam is an example of short-term retardants. It is a cheap alternative that enables 75 water to douse the flames with an increased efficiency. The effectiveness of foam is of 76 shorter duration than long-term retardants (Liodakis, Tsapara, Agiovlasitis, & Vorisis, 77 2013). For long-term retardants, the solving water plays a secondary role as a carrier 78 medium enabling the retardant product to get access to the fuel. These chemicals can 79 hinder the flame modifying the combustion processes; they can remain active even after 80 the evaporation of all the water. The key active components in the long-term retardants 81 include inorganic salts (ammonium phosphates and ammonium sulfates), while the 82 thickening and coloring agents as well as corrosion inhibitors are also contained in the 83 formulations (Kalabokidis, 2000). Among long-standing retardants which inhibit forest 84 fires, diammonium phosphates, monoammonium phosphates as well as ammonium 85 sulphates have been widely utilized across the world. However, the fire prevention and      Table 1.

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The preparation of MC@DOPO-ITA@silica hybrid hydrogel involves two steps.

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The hydrophilic silica is firstly hydrolyzed in the water so silanol groups are formed, 239 which then condensed giving rise to a silica hybrid network. Then, the hydroxyl group 240 of methylcellulose interacts with silica through hydrogen bonding (Fig. 1).   The study of the flow profile can help better understanding the role of shear rate 306 in power law parameters such as consistency coefficient (k) and flow behavior index 307 (n). The rheological findings suggest a decline in the hydrogel viscosity upon raising 308 the shear rate (Fig. 5a). Two mathematical models (e.g., power law and Herschel-  Table S1. Based on the previous reports, 'k' can be applied to determine the  subjecting to various conditions. The dependence of G' and G" on angular frequency 332 (ω) was evaluated to examine the viscoelastic nature of synthesized hydrogels (Fig. 5b).  were also measured, as depicted in Fig. 7 and To further examine the impact of water and hydrogels spraying on the wood, the

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In conclusion, we have prepared an environmentally friendly bio-based organic-