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

Abstract

Low‐flammability freeze‐dried cellulose nanofibril (CNF)/sodium montmorillonite (MMT) aerogels with improved mechanical properties were fabricated via a facile cross‐linking of boric acid (BA) and melamine‐formaldehyde (MF) resins. Scanning electron microscopy analysis showed that BA cross‐linking reduced the interspacing of layered CNF/MMT aerogels whereas introduction of MF formed polymeric fibrils that connected the layers. These changes on microstructures resulted in the improvement on compressive mechanical properties of the cross‐linked aerogels. Moreover, the boron (B)/nitrogen (N) containing flame retardant cross‐linkers greatly increased the limiting oxygen index values that could reach 85% and leveled the UL‐94 rating from no rating to V‐0. Cone calorimetric results suggested that BA and MF induced a synergistic effect on the flame retardant properties of the CNF/MMT aerogels. However, the thermal conductivity was little affected because pore structure and size was not substantially modified. This simple approach fabricated highly flame‐resistant and mechanically strong CNF‐based aerogels that could be used in various engineering fields.

Flame‐retardant cellulose nanofiber aerogel modified with graphene oxide and sodium montmorillonite and its fire‐alarm application

“…Table 2 shows a thermal conductivity of 39 mW mK −1 at 25°C for CNF‐MMT‐GO‐30%, indicating similar insulating properties as those of traditional TIMs such as EPS (30‐40 mW mK −1 ) and XPS (25‐35 mW mK −1 ) 45 . This is attributed to the high porosity of aerogels, which exhibit superb thermal insulation 46 . Table 2 shows that the thermal conductivity is insignificantly affected by the increased density of the composite aerogel.…”

Super‐high fraction of organic montmorillonite filled polyamide 6 composite foam: Morphologies, thermal and mechanical properties

“…PA50OMMT50 were pressed using a thick knife under a load of 10 N (Figure S3) and still sustained a crack‐free appearance after the force releasing. Comparing to clay aerogels reinforced by polymers, 39,40 the PA6‐OMMT composite foam showed higher crystalline degree and higher anti‐shearing capacity.…”

Metal Coordination Bonds Crosslinked Polydopamine/Cellulose Nanofibril Composite Aerogels with Significantly Improved Thermal Stability, Flame Resistance, and Thermal Insulation Properties

“…Probably the biggest weakness of CNF aerogels is their poor thermal stability and ammability, which hampers the practical applications of CNF aerogels (Zhao et al 2021). Incorporating inorganic nanomaterials, such as zinc borate (Cheng et al 2020), black phosphorus nanosheets (Du et al 2020), graphene (Guo et al 2019), and montmorillonite (Wang et al 2019), to construct composite aerogels is a common strategy to improve the thermal performance of CNF aerogels. However, the presence of these inorganic materials also gives rise to economic, environment, and even safety concerns as that of inorganic aerogels.…”