Freeze-drying preserves sulfonated lignin’s functional integrity, new study finds

Lignin, the world’s second most abundant biopolymer, has long been recognized for its potential as a sustainable raw material in industries ranging from textiles to construction. However, one critical challenge in scaling up its use lies in processing and stabilization. A recent study in the Journal of Bioresources and Bioproducts provides unprecedented insights into how drying temperatures affect sulfoethylated kraft lignin (SEKL), a water-soluble derivative designed to expand lignin’s industrial applications.

Researchers synthesized SEKL under alkaline conditions and subjected it to different drying treatments: freeze-drying at –55 ℃ and oven drying at 55, 80, 105, and 130 ℃. They then analyzed the chemical and physical properties using a suite of advanced techniques, including nuclear magnetic resonance (NMR), X-ray photoelectron spectroscopy (XPS), gel permeation chromatography (GPC), and differential scanning calorimetry (DSC).

The results were clear. Freeze-drying preserved SEKL’s functional integrity, producing samples with the highest charge density (–1.95 meq/g), complete solubility in water, and well-maintained sulfonic acid groups. By contrast, oven drying triggered chemical changes that compromised performance. At 55 and 80 ℃, sulfonic acid groups underwent alkylation, reducing solubility and charge density while increasing glass transition temperature. At higher drying temperatures of 105 and 130 ℃, hydrolysis of sulfonic acid groups at phenolic positions occurred, further lowering molecular weight, charge density, and solubility.

These findings underscore the dual role of drying: while necessary for product preparation, it can dramatically alter lignin’s structure and properties. For instance, industries requiring high solubility and electrostatic charge for dispersants would benefit from freeze-dried SEKL, whereas applications such as adhesives might favor thermally dried forms with higher glass transition temperatures.

The study also highlights practical implications for large-scale production. Industrial lignin is often dried at 105 ℃ to remove moisture, but the research suggests this could degrade desirable functionalities. By fine-tuning drying temperatures, manufacturers could balance cost efficiency with targeted material performance.

Ultimately, this research demonstrates that drying is not a neutral step in lignin processing but a transformative stage that dictates downstream usability. The authors recommend carefully optimizing drying protocols to tailor SEKL for specific applications, paving the way for more sustainable and versatile lignin-based products.

See the article:

DOI

https://doi.org/10.1016/j.jobab.2025.09.001

Original Source URL

https://www.sciencedirect.com/science/article/pii/S2369969825000611

Journal

Journal of Bioresources and Bioproducts