High-Strength, Flexible, Hydrophobic, Sound-Absorbing, and Flame-Retardant Poly(vinyl alcohol)/Polyelectrolyte Complex Aerogels

Abstract

Biodegradable aerogels with flexibility and high strength are attractive for construction, and acoustic and thermal insulation but are seriously plagued by their flammability. Improving the flame retardancy of these aerogels has been a hot topic of research and inorganic fillers, and layered materials have been widely used for this purpose. However, the poor interfacial compatibility of these fillers has affected the processability and mechanical properties of the aerogels and reduced their overall performance. In this study, we have used a completely organic and sustainable polyelectrolyte complex (PEC) as a filler for fabricating mechanically strong, sound-absorbing, and flame-retardant poly­(vinyl alcohol) (PVA) aerogels with the aid of an environmentally friendly freeze-drying method. The noncovalent interactions between the polymer and filler ensured excellent compatibility as well as interfacial adhesion of the filler, and we could achieve a perfect balance between the density and mechanical properties of the aerogels. The prepared aerogels exhibited flexibility, good sound absorption ability in the mid-frequency range, and excellent flame retardancy (LOI ∼28%) with self-extinguishing behavior. A simple silane modification endowed sticky hydrophobicity to the aerogels and further enhanced their antifire properties. These sustainable multifunctional aerogels could find a plethora of applications in real life, particularly in buildings and structures as fire safety materials and sound insulators.

Layer-over-Layer Electrostatic Self-Assembly of Bioresourced Compounds in Thermoreversible Polylactide Gels as an Effective Approach to Enhance the Flame Retardancy of Aerogels

“…Therefore, the weakened interactions between the SA and CS due to the interlayer diffusion of small PA molecules might be the reason for the low modulus of PLLA@SA@CS@PA aerogel. Yet, this aerogel is stronger than the neat PLLA aerogel and also the other reported semicrystalline polymer-based aerogels. ,,,,, …”

“…The schematic in Figure c illustrates the possible flame retardant mechanism of the PLLA@SA@CS@PA aerogel. When exposed to fire, PA in the outer layer of the aerogel can decompose to produce phosphoric or polyphosphoric acid, which can promote the dehydration of CS and the formation of the carbonized layer. , Similar to CS, SA also acts as a charring agent with its polysaccharide rings and enormous hydroxyl groups and can further enhance the intensity of the carbonized layer Figure S2 shows the Raman spectrum of the char residue obtained after the burning of PLLA@SA@CS@PA aerogel.…”

“…In recent times, intumescent flame retardants based on biomass-derived molecules such as chitosan (CS), phytic acid (PA), alginate, etc. have become popular for enhancing the flame retardancy of bulk PLA. ,, CS is an environment-friendly biodegradable cationic polysaccharide with multiple hydroxyl groups, PA is a biosourced phosphorus-rich anionic molecule, and alginate is an inherently flame retardant natural anionic polysaccharide (linear copolymer), all of which are readily water-soluble. − Therefore, electrostatic interactions between these differently charged molecules can be exploited for the flame retardant modification of polymer surfaces by assembling them layer-over-layer (LoL) in an organic solvent-free environment. − Such LoL assemblies have also been successfully employed for the generation of core–shell structured flame retardant particles for PLA. For example, Xiong et al fabricated core–shell flame retardants using ammonium polyphosphate as the core and CS and PA as the shell molecules .…”

Directional-Freezing-Enabled MXene Orientation toward Anisotropic PVDF/MXene Aerogels: Orientation-Dependent Properties of Hybrid Aerogels

“…This char formation helps to protect the underlying polymer matrix and prevents the pyrolysis products from spreading into the flammable gases. 59,60 To further demonstrate the flameretardant behavior of pristine PVDF and PMX-30 aerogels, horizontal burning tests were carried out by placing the Similar burning behavior was noticed in other PMX aerogels (Figure S12). As seen in TGA thermograms, the char residue formed during the initial burning of the hybrid aerogel acts as a barrier to protect the underlying polymer.…”

“…The char residue of PMX aerogels at 800 °C increased significantly with the MXene loadings. This char formation helps to protect the underlying polymer matrix and prevents the pyrolysis products from spreading into the flammable gases. , To further demonstrate the flame-retardant behavior of pristine PVDF and PMX-30 aerogels, horizontal burning tests were carried out by placing the aerogels in a Bunsen flame for 10 s. The images and video of the burning tests of PVDF and PMX-30 aerogels are shown in Figures a,b and Movie S1. The PVDF aerogel shows volume shrinkage readily after 4 s and complete collapse after 10 s due to its flammability, as seen in Figure a.…”