Nonflammable materials based on renewable ammonium alginate and nano fillers (nanoscale magnesium hydroxide, nanoscale aluminum hydroxide, layered double hydroxide, sodium montmorillonite, and Kaolin) were fabricated through a simple, environmentally friendly freeze-drying process, in which water was used as a solvent. A simple and economic post-cross-linking method was used to obtain homogeneous samples. The microstructure of the cross-linked alginate aerogels show three-dimensional networks. These materials exhibit low densities (0.064-0.116 g cm(-3)), low thermal conductivities (0.024-0.046 W/m K), and useful mechanical strengths (0.7-3.5 MPa). The aerogels also exhibit high thermal stabilities and achieve inherent nonflammability with limiting oxygen indexes (LOI) higher than 60. Related properties were conducted and analyzed by cone calorimeter (CC), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). These results combine to suggest promising prospects for use of these aerogel nanocomposites in a range of applications.

Recent research of hydrogel actuators is still not sophisticated enough to meet the requirement of fast, reversible, complex, and robust reconfiguration. Here, we present a new kind of poly( N-isopropylacrylamide)/graphene oxide gradient hydrogel by utilizing direct current electric field to induce gradient and oriented distribution of graphene oxide into poly( N-isopropylacrylamide) hydrogel. Upon near-infrared light irradiation, the hydrogel exhibited excellent comprehensive actuation performance as a result of directional bending deformation, promising great potential in the application of soft actuators and optomechanical system.

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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.

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Three novel, environmentally friendly, flame-retardant adhesives (FRAs), i.e., (1) poly-N-β-(aminoethyl)-γaminopropyltrimethoxysilane [P(NTMS)], (2) P(NTMS-phosphoric acid) [P(NTMS-PA)], and (3) P(NTMS-phosphorous acid) [P(NTMS-POA)], are synthesized via a versatile sol−gel method. The chemical structures are characterized by FTIR and 1 H NMR. The thermal stabilities of the FRAs are revealed by thermogravimetric analysis (TGA) and they exhibit single, double, and triple degradation processes, respectively. Flame-retardant expanded polystyrene foams (EPSFs) are prepared with these novel environmentally friendly FRAs by a simple coating method, and their flammability is investigated by limiting oxygen index (LOI), UL-94 vertical burning test, and cone calorimeter (CC). With as high as 57 wt % of P(NTMS) coating, the foam gains no rating in the UL-94 test. In contrast, EPSF with 57 wt % of P(NTMS-PA) coating passes the UL-94 V-0 grade with a LOI of 31%, and the foam with only 40 wt % of P(NTMS-POA) also passes the UL-94 V-0 grade with a LOI of 26.5%. CC results demonstrate that 40 wt % of P(NTMS-PA) coating reduced the peak heat release rate (PHRR) of EPSF by 62.1% and increased the residue from 0 to 36.2%. For P(NTMS-POA), the corresponding values are 68.8% and 34.0%, respectively. The morphology of the residues was revealed by SEM, and the corresponding chemical compositions and carbonaceous structure were studied by FTIR, EDX, and Raman spectra. These results indicated a synergy in charring among phosphorus, nitrogen, and silicon, and the resulting protective layers were responsible for the higher fire safety.