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<p>Forestry by-products, particularly bark, offer opportunities to add value to the forest production chain. Tannins are renewable, less toxic alternatives to formaldehyde-based adhesives, supporting sustainable, and circular bioeconomy strategies. This study valorizes <i>Pinus taeda</i> bark by developing and assessing an optimized extraction process for condensed tannins under conditions compatible with industrial implementation. Firstly, the magnitude of the solvent effect (hot water and ethanol/water mixture) was evaluated using a screening factorial design. When comparing bark extraction with both solvents, ethanolic extracts presented lower extraction yields but higher total polyphenol content (TPC), condensed tannin content (CT), and Stiasny number (SN) than aqueous extracts. Then, the optimization involved the ethanol/water mixture. Response surface methodology, utilizing a three-factor (ethanol concentration, temperature, liquid/solid ratio) central composite design, was employed to maximize CT and SN. The optimized extract was characterized by total carbohydrate content, TGA, and gel time. The optimal extraction condition was 65% (v/v) ethanol, 90&#xa0;°C, and an 8:1 liquid/solid ratio (L/S). The obtained extract presented 215.6 ± 0.2&#xa0;mg catechin equivalents per gram of extract of CT on a dry basis&#xa0;(d. b.), and the SN was 81.9 ± 5.9%. The extract also contained 13.41% d.b. carbohydrates, which affects final resin properties. The degradation temperature was 263 ± 5&#xa0;°C, and the gel time was 100.5 ± 6.3&#xa0;s using paraformaldehyde as a hardener. Partial substitution of phenol in phenol-formaldehyde resin was achieved. Results confirm that tannin-rich bark extract obtained from <i>Pinus taeda</i> can be incorporated into adhesive formulations, offering a potential method for valorizing bark before its final disposal. These results demonstrate the potential of <i>P. taeda</i> bark as a renewable source of tannins for partially substituting phenol in adhesive formulations. The originality of this work lies in employing conditions closer to industrial practice, including bench-scale extraction and the use of larger bark particles instead of finely ground powders in laboratory-scale. By analyzing the relationship between extraction parameters, particle size, and the functional properties of the resulting extracts, the work evaluates the potential of <i>P. taeda</i> bark as a source of bio-based adhesive components. This approach advances the transition from laboratory research to scalable industrial application.</p>

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Optimization of condensed tannin extraction from Pinus taeda bark for sustainable wood adhesives

  • 期刊论文

  • 发表日期：

    2026年5月9日

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  • Eliana Isabel Fernández Sosa,
  • Fernando Esteban Felissia,
  • María Guadalupe Chaves,
  • María Cristina Area

摘要

Forestry by-products, particularly bark, offer opportunities to add value to the forest production chain. Tannins are renewable, less toxic alternatives to formaldehyde-based adhesives, supporting sustainable, and circular bioeconomy strategies. This study valorizes Pinus taeda bark by developing and assessing an optimized extraction process for condensed tannins under conditions compatible with industrial implementation. Firstly, the magnitude of the solvent effect (hot water and ethanol/water mixture) was evaluated using a screening factorial design. When comparing bark extraction with both solvents, ethanolic extracts presented lower extraction yields but higher total polyphenol content (TPC), condensed tannin content (CT), and Stiasny number (SN) than aqueous extracts. Then, the optimization involved the ethanol/water mixture. Response surface methodology, utilizing a three-factor (ethanol concentration, temperature, liquid/solid ratio) central composite design, was employed to maximize CT and SN. The optimized extract was characterized by total carbohydrate content, TGA, and gel time. The optimal extraction condition was 65% (v/v) ethanol, 90 °C, and an 8:1 liquid/solid ratio (L/S). The obtained extract presented 215.6 ± 0.2 mg catechin equivalents per gram of extract of CT on a dry basis (d. b.), and the SN was 81.9 ± 5.9%. The extract also contained 13.41% d.b. carbohydrates, which affects final resin properties. The degradation temperature was 263 ± 5 °C, and the gel time was 100.5 ± 6.3 s using paraformaldehyde as a hardener. Partial substitution of phenol in phenol-formaldehyde resin was achieved. Results confirm that tannin-rich bark extract obtained from Pinus taeda can be incorporated into adhesive formulations, offering a potential method for valorizing bark before its final disposal. These results demonstrate the potential of P. taeda bark as a renewable source of tannins for partially substituting phenol in adhesive formulations. The originality of this work lies in employing conditions closer to industrial practice, including bench-scale extraction and the use of larger bark particles instead of finely ground powders in laboratory-scale. By analyzing the relationship between extraction parameters, particle size, and the functional properties of the resulting extracts, the work evaluates the potential of P. taeda bark as a source of bio-based adhesive components. This approach advances the transition from laboratory research to scalable industrial application.