Liudmila I. Grishechko

Highly mesoporous organic aerogels derived from soy and tannin

The first organic aerogels natural at the 91% level, based on soy and tannin, are reported. Such materials were prepared from denatured soy protein which was formylated, crosslinked with flavonoid tannin at different pHs, gelled and cured at 85 °C, and finally dried with supercritical CO2. The resultant aerogels presented both low bulk density and high mesopore volumes. Morphology, pore texture, chemical structure and thermal performances have been investigated by SEM, envelope and helium pycnometry, nitrogen adsorption at 77 K, FTIR, elemental analysis, XPS, NMR and hot disk transient plane source methods, respectively. We show that soy–tannin aerogels are among the “greenest” organic aerogels combining low cost, renewable character, highly developed mesopore texture and good thermal performances.

Biosourced, highly porous, carbon xerogel microspheres

The first tannin-based carbon xerogel microspheres were prepared and characterised. The materials were synthesised by inverse emulsion polymerisation in sunflower oil, based on the same formulation but using two main independent variables: stirring speed and surfactant amount. The resultant sol–gel spheres were then washed, dried in air, and pyrolysed. The effect of stirring speed and surfactant amount on carbon microsphere size distribution and porous texture was investigated in detail. Depending on the cases, ultramicroporous carbon microspheres with extremely narrow pore size distributions centred at 0.4–0.5 nm, zero mesoporosity, negligible macroporosity and median diameters close to 40 μm, could be obtained. These characteristics are typical of expensive commercial carbon molecular sieves, whereas the present materials were prepared with cheap and renewable precursors using a very simple method.

Rubber-like materials derived from biosourced phenolic resins

The present work describes new gels derived from cheap, abundant and non-toxic wood bark extracts of phenolic nature, behaving like elastomers. Especially, we show that these materials might be used as rubber springs. Such amazing properties were obtained by a quite simple synthesis based on the autocondensation of flavonoid tannins in water at low pH in the presence of a plasticizer. After gelation and drying, the materials presented elastic properties that could be tuned from hard and brittle to quite soft and deformable, depending on the amount of plasticizer in the starting formulation. Not only the materials containing the relevant amount of plasticizer had stress-strain characteristics in quasi-static and cyclic compression similar to most commercial rubber springs, but they presented outstanding fire retardance, surviving 5 min in a flame at 1000°C in air. Neither flame propagation nor drips were noticed during the fire test, and the materials were auto-extinguishable. These excellent features make these materials potential substitutes to usual organic elastomers.

Optimization of the Process of Synthesis of Lignin–Tannin-Formaldehyde Organic Aerogels

The method of experimental statistical analysis was applied to study the effect of mass ratio of phenol and lignin (factor X1) and the weight ratio of thereof mixture with formaldehyde (factor X2) on the values of specific parameters of the porous structure obtained organic lignin – phenolformaldehyde aerogels. Based on the evaluation of the mathematical model was established that under the observance terms of X1 = 0,65-0,78 and X2 = 1,7 the maximum predicted values of the specific surface area and mesopore volume of obtained organic aerogels are 485 m2 /g and 1,83 cm3/g, accordingly. Under optimal values of X1 = 0.25, and X2 = 1.25 calculated values reach a macropore volume of 4.05 cm3 /g and total pore volume – 4.67 cm 3 /g.