Aromatic building blocks from various lignin types for the production of adhesives, paints, polyurethanes and epoxides
Lignins, with a share of up to 30 percent in woody biomass, are among the most common organic compounds. However, due to the heterogeneity of their aromatic structures, they are difficult to turn into chemical applications.
Within the joint project “Lignoplast”, a consortium – coordinated by Fraunhofer CBP – was working on new methods to be able to use different lignins in polyurethane, adhesive, paint, and epoxy systems. Depending on the pretreatment method, lignins have different properties that significantly influence further processing. It was necessary to process sulfur‑containing lignins from pulp processes as well as sulfur-free lignins from biorefinery processes (e.g. from the Organosolv process, which is also being intensively developed by Fraunhofer CBP [1, 2]).
The base‑catalyzed cleavage proved to be a suitable method to break down all investigated lignin types into smaller phenol derivatives with a simpler structure. Based on preliminary investigations at Fraunhofer ICT, the multi‑stage process consisting the continuous base‑catalyzed cleavage and the subsequent separation and purification of the products, was successfully transferred to the pilot scale at Fraunhofer CBP .
Polyurethanes from lignin
Consortium partners use the resulting lignin fragments for the production of high‑quality polyurethane foams or as polyols for polyurethane coatings of long‑term fertilizers. Application tests revealed positive properties, as well as some additional advantages such as biodegradability. Further work is needed before the products can be placed on the market. Continuous availability of raw materials, improved process stability as well as the economic considerations of the overall process will be aimed at in further activities.