Inorganc silica-based aerogels, the earliest and widely used aerogels, have poorer mechanical properties than their organic substitutes, which are flammable. In this study, a novel polymeric aerogel with high strength, inherent flame retardancy, and cost-effectiveness, which is based on poly(vinyl alcohol) (PVA) cross-linked with melamine-formaldehyde (MF), was prepared under aqueous condition with an ecofriendly freeze-drying and postcuring process. Combined with the additional rigid MF network and benifited from the resulting unique infrastructure of inter-cross-linked flexible PVA segments and rigid MF segments, PVA-based aerogels exibited a significantly decreased degradation rate and sharply decreased peak heat release rate (PHRR) in cone calorimeter tests (by as much as 83%) compared with neat PVA. The polymer aerogels have a limiting oxygen index (LOI) as high as 36.5% and V-0 rating in UL-94 test. Furthermore, the aerogel samples exposured to harsh temperatures maintain their dimensions (<10% change), original mechanical strength and fire safety. Therefore, this work provides a novel stragegy for preparing pure organic polymeric aerogel materials with high mechanical strength, dimensional stability, and fire safety.

In this manuscript, contradiction between the non-flammability and non-dripping of polyesters could be solved by copolymerizing terephthalic acid and ethylene glycol together with a pendent phenylethynyl-based monomer named 4-(phenylethynyl) di(ethylene glycol) phthalate (PEPE), which exhibited a cross-linkable nature at a proper temperature. TG-DSC simultaneous thermal analysis, FTIR, dissolution tests and rheological investigations proved the thermal cross-linking behavior of the copolyester, which was not active at the temperature of polymerization and processing but could crosslink rapidly at higher temperature before burning. LOI tests, cone calorimetry and small-scale flame tests further confirmed the self-extinguishment and inhibition for melt-dripping could be achieved through the cross-linking during burning, despite the absence of any flame-retardant element (say, bromine, chlorine, phosphorus, or nitrogen, etc.). Rheological analyses and the SEM microphotographs of the char showed P(ET-co-P)s exhibited a greater complex viscosity through the cross-linking at high temperature, leading to compact char residue, flame-retardant and anti-dripping effects.

Biocomposite of wood flour (WF)/polypropylene (PP) composite (WPC) is not easily flame-retarded because of the different flame retardant mechanisms of PP and WF. In order to improve the flame retardancy of WPC, a single flame retardant of ammonium polyphosphate (APP) modified via ion exchange reaction with ethanolamine, which is named as ETA-APP, was used to prepare flame-retardant WPC. The flammability was investigated by limiting oxygen index (LOI), UL-94 vertical burning test, and cone calorimeter. The results show the flame retardant properties of the flame-retardant WPC are improved greatly. The limiting oxygen index is 43.0%, which is increased by 71.6% compared with that of WPC with the same content of APP. And the vertical burning test can pass UL-94 V-0 rating. The results of cone calorimeter test show that the heat release rate (HRR) and total heat release (THR) of the WPC with ETA-APP are decreased in comparison with WPC/APP. The flame-retardant mechanism of WPC/ETA-APP system was investigated by thermogravimetric analysis (TGA), Fourier transform infrared (FTIR), and X-ray photoelectron spectroscopy (XPS). It is found that the hydroamine groups and phosphate acid in ETA-APP might promote the etherification and dehydration reactions in WPC/ETA-APP, which facilitated the formation of stabile char residue of WPC. Consequently, the flame-retardant efficiency is improved greatly. The flexural properties of WPC/30 wt % ETA-APP increase a lot in comparison with WPC/30 wt % APP, which is because of the better compatibility of ETA-APP with WF.

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Flexible silicone foams (SiFs) are high-performance but flammable materials that emit dense smoke in a fire. Two type of low-cost, eco-friendly nanocoatings, i.e., chitosan (CH)/ammonium polyphosphate (APP) and CH/montmorillonite (MMT), were fabricated on SiFs through a layer-by-layer (LbL) assembly. With seven bilayers (BL) of CH/APP coatings, the limiting oxygen index (LOI) increases from 20.2% to 23.8%, the peak heat release rate (pHRR) decreases by 27.6%, and the total smoke production (TSP) decreases 42%. Further deposition of CH/APP, however, partly damaged the fire resistance. In contrast, fire hazard and smoke release of CH/MMT coated SiFs were monotonously reduced. Every 7 BL of coating leads to ca. 12% reduction of TSP. Moreover, thermogravimetric analysis (TGA) was used to follow the pyrolysis of the coated foams, and scanning electron microscopy (SEM) and energy-dispersive X-ray spectrometry (EDX) were applied to analyze the char residues systematically.