Washington, US – A team at Washington State University has developed a mild process for separating high-quality lignin from pine wood. It has the potential for use in the manufacture of polyurethane foam.
The process relies on lactic acid and choline chloride-based deep eutectic solvents (DES), and the extracted lignin is more than 90% pure. It contains about 5mmol/g of hydroxyl groups, with no detectable sulfur, and has good heat stability and a low glass transition temperature.
The lignin was then subjected to an oxypropylation reaction to create lignin-derived polyols. These were used to make flexible PU foam, replacing 20% by weight of the original petroleum-derived polyols. The foam was compared to similar foams made using 20% commercial alkali lignin, and also diluted acid corn stover lignin.
The researchers said that the foam based on the DES-extracted lignin was the only one capable of achieving highly homogeneous morphologies and well-oriented geometry. It also had superior thermal stability, and a comparable compressive stress response to standard industrial foam.
“It’s quite novel in terms of the material we generate and the process we have,” said Xiao Zhang, who led the project. “Our extracted lignin offers a new class of renewable building blocks for the development of bio-based value-added products.”
The work has been published in the journal ACS Sustainable Chemistry and Engineering.