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Study on the Structure of Lignin Isolated from Wood Under Acidic Conditions
Andrzej Antczak1, Aneta Skręta1, Anna Kamińska-Dwórznicka2
1Institute of Wood Sciences and Furniture, Warsaw University of Life Sciences-SGGW, 159 Nowoursynowska St., 02-776 Warsaw, Poland.
Molecules (Basel, Switzerland)
|December 31, 2025
Summary
Investigating lignin from pine and poplar wood revealed a highly condensed structure, suitable for high-value applications like carbon fibers despite solubility challenges. Acetylation improved analysis of this valuable biomass waste.
Area of Science:
- Biomass valorization and polymer science.
- Characterization of natural polymers and waste streams.
Background:
- Lignin, a byproduct of pulping and bioethanol production, is often a waste material.
- Understanding lignin structure is key to unlocking its potential for high-value applications.
- Acidic conditions during isolation can significantly impact lignin's structural properties.
Purpose of the Study:
- To investigate and compare the structure of lignin isolated from *Pinus sylvestris* L. and *Populus deltoides* × *maximowiczii* wood under acidic conditions.
- To evaluate the effectiveness of different isolation methods (Klason vs. sulfuric/phosphoric acid) and lignin acetylation.
- To assess the potential of condensed lignin for advanced material applications.
Main Methods:
- Lignin isolation using the Klason method and a sulfuric/phosphoric acid mixture.
- Lignin acetylation followed by analysis in a 0.5% LiCl/DMAc system.
- Instrumental analysis including Size Exclusion Chromatography (SEC), Attenuated Total Reflection-Fourier Transform Infrared Spectroscopy (ATR-FTIR), and Scanning Electron Microscopy (SEM).
Main Results:
- Lignin isolated from both pine and poplar wood under acidic conditions exhibited a highly condensed structure, confirmed by high weight-average molar mass (up to 118,700 g/mol) and surface morphology (precipitates, aggregates).
- ATR-FTIR analysis showed characteristic signals of condensed lignin (767 cm-1 band) and a decrease in the 814 cm-1 band.
- Lignin acetylation proved effective, particularly for condensed poplar lignin, enhancing its analysis and confirming structural modifications via SEM.
Conclusions:
- Acidic isolation conditions yield highly condensed lignin from both softwood and hardwood species.
- Despite solubility issues, this high-molecular-weight condensed lignin is a valuable precursor for materials like carbon fibers and thermoplastic blend additives.
- Lignin acetylation is a beneficial pretreatment for characterizing and potentially utilizing condensed lignin structures.
