Facile construction of flame‐retardant, heat‐insulating agar/polyvinyl alcohol composite aerogels via in situ formation of magnesium hydroxide and palygorskite‐assisted strategy

Abstract

Natural polymer aerogel is a candidate material with broad application prospects in the field of building insulation because of its lightweight, low thermal conductivity, and biodegradability. However, poor mechanical properties and easy combustion greatly limit its development. In this work, magnesium hydroxide (MH) was synthesized in situ in the agar (AG)/polyvinyl alcohol (PVA) composites using magnesium oxide as raw material. Furthermore, the one-dimensional rod-like nanoclay palygorskite (Pal) was introduced into the composites. A series of composite aerogels with different ratios of MH and Pal were prepared by a simple freeze-drying process, and their microstructure, mechanical properties, water resistance, thermal stability, thermal insulation, and flame-retardant properties were investigated. Cone calorimeter tests showed that MH/Pal synergistic flame retardant had excellent performance in reducing heat release rate and suppressing smoke. The AG/PVA/MH/Pal composite samples had a limiting oxygen index of 37.5% and achieved V-0 rating in the UL-94 test. In addition, the introduction of MH and Pal has enabled the AG/PVA composite aerogels to exhibit superior mechanical, thermal insulation, and water stability properties. K E Y W O R D Sflame-retardant polymer, in situ generation, magnesium hydroxide, palygorskite | INTRODUCTIONAerogels, a type of material with porous structure, are made from SiO 2 or polymers. [1][2][3] The ultra-low density and ultra-high porosity considerably reduce the quality and thermal conductivity of aerogels. [4,5] Polymer-based aerogels have shown excellent effects in the field of heat insulation compared to traditional insulation materials such as rock wool board, glass wool, and polystyrene foam. [6,7] They have broad application prospects in the fields of building energy-saving insulation and thermal pipeline. [8,9] Among polymer-based aerogels, biodegradable matrix materials such as polyvinyl alcohol (PVA), [9,10] cellulose, [11] and starch [12] have attracted wide attention due to friendly environment. [13] Agar (AG), a natural polymer, is soluble in hot water and can form hydrogel after cooling, [14,15] and after freeze-drying, AG-based aerogels can be formed. [16] However, pure AG

Remarkable tailoring of thermal and dielectric properties of poly(vinyl alcohol) nanocomposite via hydrothermal grown ZnAl layer di hydroxide nanostructures and graphene fillers

“…11,12 From the last decade, numerous nanofillers such as halloysite nanotubes (HNT), montmorillonite clay (MMT), nanocarbon based graphene, carbon nanotubes (CNT), aluminum trihydrate (ATH), Ti 3 C 2 T x (MXenes) and 2D materials have been used to improve the thermal stability of polymers. [13][14][15][16] However, improving the thermal and dielectric properties is still very challenging due to weak interfacial strength, delamination, poor dispersion, polarity, and nature of fillers and their percolation limit. [17][18][19] Among various nanostructures, LDH (double layered hydroxides) has received wide popularity as ecofriendly and biocompatible inorganic filler due to their unique properties such as high thermal stability ($500 C), high dielectric constant, ion-exchange property, high absorption, high aspect ratio and fireretardant behavior.…”

“…It was also reported that the size, shape, dispersion and the chemistry of the nanofiller strongly influence the thermal stability and dielectric properties of polymers 11,12 . From the last decade, numerous nanofillers such as halloysite nanotubes (HNT), montmorillonite clay (MMT), nanocarbon based graphene, carbon nanotubes (CNT), aluminum trihydrate (ATH), Ti 3 C 2 T x (MXenes) and 2D materials have been used to improve the thermal stability of polymers 13–16 . However, improving the thermal and dielectric properties is still very challenging due to weak interfacial strength, delamination, poor dispersion, polarity, and nature of fillers and their percolation limit 17–19 .…”

Flame retardancy and smoke suppression effect of an organic–inorganic hybrid containing phosphaphenanthrene‐modified magnesium hydroxide/zinc borate on epoxy resin

“…The low flame‐retardant efficiency of MH, which has become a pressing issue that needs to be addressed 19–21 . Additionally, because of the high interfacial energy and strong hydrophilicity of MH, it exhibits poor compatibility with the polymer matrix, which greatly destroys the mechanical properties and machinability of matrix material 22–24 …”

“…[19][20][21] Additionally, because of the high interfacial energy and strong hydrophilicity of MH, it exhibits poor compatibility with the polymer matrix, which greatly destroys the mechanical properties and machinability of matrix material. [22][23][24] Synergistic flame retardants can be used to simultaneously reduce the amount of MH added to the polymer material and improve the low flame retardancy efficiency of MH. Synergistic flame retardants include zinc borate (ZB), black phosphorus, graphene, carbon nanotubes (CNTs), and so forth.…”