Biobased gelatins were used to improve the compressive properties and flammability of poly(vinyl alcohol)/montmorillonite (PVA/MMT) aerogels, fabricated using a simple and environmentally friendly freeze-drying method. Because of the excellent compatibility and strong interfacial adhesion between PVA and gelatin, the compressive moduli of aerogels were enhanced dramatically with the incorporation of gelatin. PVA/MMT/porcine-gelatin aerogels exhibit compressive modulus values as much as 12.4 MPa, nearly 300% that of the control PVA/MMT aerogel. The microstructure of the PVA/MMT/gelatin aerogels shows a three-dimensional co-continuous network. Combustion testing demonstrated that with the addition of gelatin, the self-extinguishing time of the aerogel was cut by half and the limiting-oxygen-index values increased to 28.5%. The peak heat-release rate, obtained from cone calorimetry, also decreased with the incorporation of gelatin. Thermogravimetric analysis demonstrated that the gelatins slowed the sharp decomposition of the PVA matrix polymer and increased the thermal stability of the aerogels at the major decomposition stage of the composite aerogels. These results indicate that as a green, biobased material, gelatin could simultaneously improve the mechanical properties and the properties of flame retardancy.

Poly(vinyl alcohol) (PVA), tannic acid (TA) and sodium hydroxide (NaOH) were used to prepare low-flammability, mechanically-strong aerogels via an environmentally-friendly freeze-drying method. Because of the strong interaction between TA and PVA through hydrogen bonds, PVA/TA/NaOH aerogels exhibited compressive moduli as high as 12.7 MPa, 20 times that of the control PVA aerogel. The microstructure of the aerogels in this study showed that the addition of NaOH disrupted the typical “card of house” aerogel structure, while the samples with TA showed a stereoscopic uniform structure. The thermal stabilities of aerogels were tested by thermogravimetric analysis, showing both a decrease on the onset of decomposition temperature, and a reduction in decomposition rate after initial char formation. The peak heat release rate and total heat release, as measured by cone calorimetry, dropped by 69% and 54%, respectively, after adding TA and NaOH.

Improving the mechanical properties and fire resistance at the same time has become a tough challenge in the study of high-performance biomass foamlike materials. To tackle this dilemma, fully biomass-based aerogels based on renewable porcine gelatin (PG) and phytic acid sodium salt (PA) were designed through a green freeze-drying method. Owing to the low flammability and the strong interaction of these two compounds, the resulting aerogels exhibited both high fire resistance and extra-strong strength, offering a novel solution to the aforementioned difficulty. Benefitting from the design of the strong physical cross-linking structure of PG, PA, and clay, the compressive modulus value of the aerogel was as high as 25.1 MPa, nearly 180 times that of the poly­(vinyl alcohol) control. These biobased aerogels exhibited extremely low flammability and superior smoke suppression, that is, the limiting oxygen index values of the aerogel were as high as 50.1%, and the total smoke release decreased from 213 to 13.5 m2 in comparison with those of commercial PU foam. All the results indicated that green aerogels with excellent combination properties will be promising in the future.