Abstract
Cellulose nanofiber (CNF) aerogels offer excellent thermal insulation properties, but high flammability restricts their application. In this study, CNF aerogels were prepared by incorporating sodium bicarbonate (SBC), which effectively improved the fire retardancy without compromising the thermal conductivity of the aerogels, which was only 28 mW m–1 K–1. The minimum burning velocity of flame-retardant aerogels was 0.20 cm s–1 at 40 wt % of SBC, which is significantly lower compared to 5.84 cm s–1 of pure CNF aerogels. At the threshold concentration of 20 wt % SBC, the flame-retardant aerogel demonstrated flameless pyrolysis along with enhanced char formation. SBC additionally provides control over the microporosity and morphology, due to the concentration-dependent formation of lamellar layers during the preparation of aerogels. Overall, this work describes an efficient method for preparing flame-retardant CNF aerogels that could lay the foundation for next-generation bio-based insulation materials.
Highlights
The development of next-generation bio-based insulation materials is driven by the current environmental strive for sustainability, eco-efficiency, and industrial ecology.[1−3] Within this realm, efficient utilization of renewable lignocellulose resources holds potential for the development of green products as alternatives to petroleum and mineral-based materials.[3,4] Cellulose nanofibrils (CNF) have gained renewed interest among the research community in the last two decades.[5]
We present the preparation of flameretardant aerogels by freeze-drying a colloidal suspension of CNF in the presence of sodium bicarbonate (SBC) at different concentrations
The flame-retarding performance of pure and SBC-containing CNF aerogels was determined by a horizontal combustion test (Figure 2b)
Summary
The development of next-generation bio-based insulation materials is driven by the current environmental strive for sustainability, eco-efficiency, and industrial ecology.[1−3] Within this realm, efficient utilization of renewable lignocellulose resources holds potential for the development of green products as alternatives to petroleum and mineral-based materials.[3,4] Cellulose nanofibrils (CNF) have gained renewed interest among the research community in the last two decades.[5]. Han et al.[16] produced flame-retardant aerogels by in situ synthesis of magnesium hydroxide nanoparticles in cellulose gelled in alkaline urea solution. Resulting aerogels exhibited self-extinguishing behavior within 40 s. These composite aerogels exhibited increased thermal conductivity from 56 to 81 mW m−1 K−1 upon higher loading of magnesium hydroxide nanoparticles. A similar approach has recently been adopted by He et al.[17] to prepare cellulose-based composite aerogels with improved flame retardancy by utilizing aluminum hydroxide nanoparticles. Upon freeze-drying, strong anisotropic aerogels were produced, which resisted combustion and exhibited a low thermal conductivity of 15 mW m−1 K−1. We present the preparation of flameretardant aerogels by freeze-drying a colloidal suspension of CNF in the presence of sodium bicarbonate (SBC) at different concentrations. Our results show that thermal decomposition of sodium bicarbonate to nontoxic gases contributes beneficially to the flame-retardant properties, and offers control over the microporosity of the resulting aerogel
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