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<p>Sustainable chemistry is driving attention to the use of lignocellulosic materials. Among those, lignin stands out as an alternative for phenolic compounds. Lignin is a powdered amorphous biopolymer, which glass transition temperature (T<sub>g</sub>) is commonly assessed by differential scanning calorimetry (DSC). As T<sub>g</sub> is related to molecular relaxation of the polymer structure, it varies according to the plant species, isolation method, etc., and many authors report the difficulty in clearly assessing lignin’s T<sub>g</sub> by DSC. Another technique which is sensitive and precise in determining relaxation processes is Dynamic Mechanical Analysis (DMA) but is usually employed to self-supporting samples. Here, we assessed the T<sub>g</sub> of different powdered samples of technical <i>Eucalyptus</i> lignins by DMA and compared it with DSC and chromatographic analysis. The nature of <i>Eucalyptus</i> lignins (MWL, Kraft, Pyrolytic, and Organosolv lignins), heating rate (3, 5, and 10&#xa0;K min<sup>-1</sup>), and humidity were evaluated. The results revealed well-defined relaxation processes occurring at temperatures similar to the baseline shift observed in the DSC thermogram, which is typically considered as the T<sub>g</sub>. Furthermore, it was found that some factors such as heating rate and humidity did not significantly affect the T<sub>g</sub> values obtained by DMA, but it exerts a considerable influence on those obtained by DSC. The main conclusion is that DMA is a precise tool for assessing the T<sub>g</sub> of lignin and therefore should be considered by researchers as a new instrument for lignin characterization.</p>

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Innovative application of dynamic mechanical analysis for accurate glass transition determination in technical lignins

  • 期刊论文

  • 发表日期：

    2025年7月29日

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  • Diego Lomonaco,
  • Francisco Avelino,
  • Maurício Matos,
  • Tainise Lourencon,
  • Washington L. E. Magalhães

摘要

Sustainable chemistry is driving attention to the use of lignocellulosic materials. Among those, lignin stands out as an alternative for phenolic compounds. Lignin is a powdered amorphous biopolymer, which glass transition temperature (Tg) is commonly assessed by differential scanning calorimetry (DSC). As Tg is related to molecular relaxation of the polymer structure, it varies according to the plant species, isolation method, etc., and many authors report the difficulty in clearly assessing lignin’s Tg by DSC. Another technique which is sensitive and precise in determining relaxation processes is Dynamic Mechanical Analysis (DMA) but is usually employed to self-supporting samples. Here, we assessed the Tg of different powdered samples of technical Eucalyptus lignins by DMA and compared it with DSC and chromatographic analysis. The nature of Eucalyptus lignins (MWL, Kraft, Pyrolytic, and Organosolv lignins), heating rate (3, 5, and 10 K min-1), and humidity were evaluated. The results revealed well-defined relaxation processes occurring at temperatures similar to the baseline shift observed in the DSC thermogram, which is typically considered as the Tg. Furthermore, it was found that some factors such as heating rate and humidity did not significantly affect the Tg values obtained by DMA, but it exerts a considerable influence on those obtained by DSC. The main conclusion is that DMA is a precise tool for assessing the Tg of lignin and therefore should be considered by researchers as a new instrument for lignin characterization.