Ultralight, highly thermally insulating and fire resistant aerogel by encapsulating cellulose nanofibers with two-dimensional MoS₂

Abstract

Thermally insulating materials, made from earth-abundant and sustainable resources, are highly desirable in the sustainable construction of energy efficient buildings. Cellulose from wood has long been recognized for these characteristics. However, cellulose can be a flammability hazard, and for construction this has been addressed via chemical treatment such as that with halogen and/or phosphorus, which leads to further environmental concerns. Fortunately, the structure of cellulose lends itself well to chemical modification, giving great potential to explore interaction with other compounds. Thus, in this study, cellulose nanofibers (CNFs) were nano-wrapped with ultrathin 1T phase molybdenum disulfide (MoS) nanosheets via chemical crosslinking, to produce an aerogel. Thermal and combustion characterization revealed highly desirable properties (thermal conductivity k = 28.09 mW m K, insulation R value = 5.2, limit oxygen index (LOI) = 34.7%, total heat release = 0.4 MJ m). Vertical burning tests also demonstrated excellent fire retardant and self-extinguishing capabilities. Raman spectra further revealed that MoS remained unscathed after 30 seconds of burning in a 1300 °C butane flame. Considering the inherently low density of this material, there is significant opportunity for its usage in a number of insulating applications demanding specific fire resistance properties.

Boron/nitrogen flame retardant additives cross‐linked cellulose nanofibril/montmorillonite aerogels toward super‐low flammability and improved mechanical properties

“…This fact suggested a synergistic effect between BA and MF on the flame retardant properties of CNF/MMT aerogels. The LOI value of the B/N FRA modified CNF‐based aerogels was much higher than those reported for flame retardant polymer‐based aerogels or foams, such as CNF/MoS 2 aerogel (LOI = 34.7%), PVA/MF aerogels (LOI = 36.5%), and PVA/MMT/APP (LOI = 42%) …”

“…Flame resistance is another important property expected for porous CNF aerogels that are highly flammable in nature. Inorganic phases have been introduced by in situ formation, physical blending, or layer by layer on the surface to form a char that acted like a barrier preventing burning of the underlying substrate. A synergistic flame retardant effect was achieved via incorporating clay and flame retardant agents (FRAs) or phosphorylation of CNF .…”

Ultralight Industrial Bamboo Residue-Derived Holocellulose Thermal Insulation Aerogels with Hydrophobic and Fire Resistant Properties

“…From a previous report, it is known that the weight loss could eliminate the low-molecular-weight species which adsorbed at the surface of cellulosic substrate if the polysiloxane is not bonded strongly to the CNF substrate [32]. Furthermore, the effective coating of the cellulosic substrate by a modifier can form an excellent physical barrier to prevent CNF from combustion [33]. Thus, the behaviors seen in this study, in which the temperature at 30% weight loss of HCNF/APP/MTMS aerogel was significantly delayed, indicate that the improvement of thermal stability was assigned to the inherent heat resistance of the polysiloxane bonded at the HCNF surface.…”

Nanoreinforcements of Two-Dimensional Nanomaterials for Flame Retardant Polymeric Composites: An Overview

“…On the one hand, MoS 2 has been used for enhancing the thermal, flame-retardant, and mechanical properties of polymer composites [18][19][20][71][72][73][74][75][76][77][78][79][80][81][82][83] due to its small size and high thermal stability. For instance, cellulose nanofibers (CNFs) were nano-wrapped with ultrathin 1T phase MoS 2 nanosheets via chemical crosslinking to produce an aerogel.…”

“…ermal and combustion characterization revealed highly desirable properties (thermal conductivity k = 28.09 mW m −1 K −1 , insulation R value = 5.2, limit oxygen index (LOI) = 34.7%, total heat release = 0.4 MJ m −2 ). Considering the inherently low density of this material, there was significant opportunity for its use in a number of insulating applications [72]. Wang et al reported the synthesis of MoS 2 nanosheets via a "thiol-ene" click reaction between defect-rich MoS 2 nanosheets with sulfydryl groups and ene-terminated hyperbranched polyphosphate acrylate (HPA), and characterized these nanosheets by FTIR and XPS to confirm their covalent functionalization through C-S bonds.…”