The understanding of lignin thermoplasticity is important both for the processing of lignocellulosic raw materials and for developing new lignin-containing materials. However, there are some obstacles to studying the calorimetric and viscoelastic properties of lignin. One illustration of this is that there are few examples of glass transition determinations of high molecular weight lignins in the literature. These lignins exhibit broad glass transitions with a small change in heat capacity, which makes the determination of the T<sub>g</sub> difficult with DSC. Lignins also typically exhibit exothermic behavior around the T<sub>g</sub>, likely due to the reactions of mobilized radicals, which further obstruct the transition. DMA, which records the mechanical response during heating, is more sensitive to the glass transition than DSC and is often used to determine the softening temperature of lignin composites: wood, paper, and blends with synthetic polymers. However, as most isolated lignins are not free-standing, films or blocks cannot be made for DMA analysis. In this study, a powder pocket for DMA has been used to analyze lignins isolated from different sources: Norway spruce, wheat straw, and softwood kraft pulp. Solvent fractionated softwood kraft lignin has also been studied with DMA and DSC. Correlations are made between the lignin chemical structure and thermoplastic properties based on the viscoelastic and calorimetric measurements.

Thermal transitions of several lignins studied with powder sample holder for DMA

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