Espumas fenólicas à base de taninos de Stryphnodendron adstringens (Mart.) Coville E Acacia mearnsii DE Willd. reforçadas com pó de cortiça de Quercus suber L.

Abstract

Among the various possible uses of tree bark, the exploitation of its chemical compounds stands out for its high commercialization potential. In this context, tannins surpass other compounds due to their greater presence and numerous technological applications, ranging from pharmaceuticals and leather tanning to the production of adhesives for wood panels. Tannin-based phenolic foams are among these applications and have been studied since the 1990s, presenting advantageous characteristics over conventional synthetic foams, especially regarding fire resistance and the absence of toxic smoke emission during combustion. The main challenge in developing these materials lies in obtaining structures with satisfactory mechanical properties, since tannin-based foams generally exhibit brittle behavior and high friability. Therefore, this research aimed to produce tannin-based phenolic foams from Stryphnodendron adstringens (Mart.) Coville (Barbatimão, Fabaceae), evaluating the influence of incorporating cork powder from Quercus suber L. (Cork oak) as a reinforcing filler and polysorbate 80 (Tween 80) as a surfactant additive on their properties. For comparison purposes, all formulations were reproduced under the same conditions using tannins from Acacia mearnsii De Willd. (Black wattle). Eight foam formulations were defined, four based on Barbatimão tannins (BA1, BA2, BA3 and BA4) and four based on Black wattle tannins (AN1, AN2, AN3 and AN4), varying the presence and combination of reinforcing filler and surfactant additive. The produced foams were characterized regarding apparent density, true density and porosity, compressive mechanical strength, mechanical durability through the friability test, water absorption, contact angle, cellular morphology, and scanning electron microscopy analysis. The results demonstrated that S. adstringens produces tannins with suitable characteristics for the production of rigid phenolic foams, with mechanical performance superior to that of foams produced with Black wattle tannins under the same conditions. The incorporation of cork powder and polysorbate 80 contributed positively to the mechanical and morphological properties of the foams, resulting in more homogeneous structures with lower friability and greater mechanical durability.