Tannin-based phenolic foams of Anadenanthera peregrina: synthesis and characterization

Abstract

Tannin-based foams are lightweight porous materials of natural origin, obtained by polycondensation of tannins and furfuryl alcohol. They have excellent fire-resistant and thermal insulation properties comparable with phenol-formaldehyde flammable non-environmental friendly foams; however, their brittleness and relatively low mechanical resistance challenge further improve these characteristics. In this study, four types of tannin-based foams (ST, TT, TB, and TTB) were prepared without formaldehyde, by using Anadenanthera peregrina tannins (ST) and the incorporation of polysorbate 80 as a surfactant (TT), bamboo fibers as filler reinforcement (TB), and the combination of both (TTB). The extracted tannins’ average values of Stiasny’s index and condensed tannin content were 72,41 %, and 12,81 % respectively. Besides, the resulting foams’ morphology and physical-mechanical properties were evaluated by density, porosity, mechanical compression, water absorption, fire resistance, scanning electron microscopy (SEM), Infrared Spectroscopy (FTIR) and Thermogravimetry (TGA). Thus, the addition of bamboo fibers and polysorbate 80 to the formulations had a minimal impact on the foam density around 1,383 ± 0,05 g·cm−3

, and an average porosity of 87 %; meanwhile, their compressive strength slightly improved (0,12 - 0,19 MPa). Finally, the foams produced showed self-extinguishing behavior, and TGA results showed similar thermal stability of the foams, increasing the degradation onset temperature and still presenting residual matter around 800 °C.