Laccase-mediated polymerization of tannins from a pine bark extract: Toward an eco-friendly valorization of forest wastes

The valorization of tannins from forest by-products is a major opportunity for the sustainable development of the forestry industry. Herein we report the laccase-mediated polymerization of tannins obtained from an aqueous pine bark extract. The reaction was conducted under an oxygen atmosphere at 50°C for 60 min and followed by UV–Vis, fluorescence intensity, phenol content, and viscosity measurements. An insoluble polymer was obtained after 45 min, which was attributed to coupling reactions triggered by phenoxyl radicals within the tannins mixture. The polymer showed a marked increase in thermal stability compared with the precursor pine bark extract, with a total mass loss of less than 12% at temperatures up to 500°C, suggesting potential practical applications in flame retardant materials. Additionally, the polymer showed an 85% DPPH activity and a 60% attenuation of singlet oxygen release upon light irradiation, which supports antioxidant and photoprotective properties for the prepared material. To the best of our knowledge, this is the first report to describe the formation of an insoluble polymer by direct enzymatic reaction of an aqueous tannin extract. In this case, soluble tannins are the sole reactants used to produce a promising versatile material for forest waste valorization.