Production of bio-based resols from structure defined lignin oligomers (lignowert)

In the lignowert project, Wood K plus together with the TU Vienna and the industrial partners developed bio-based phenol building blocks from the biorafinery products lignin and lignosulfonates and was successfully producing bio-based binders.

Phenol from petroleum fractionation is a basic chemical for the production of phenolic resins. Phenol is reacted with aldehydes under alkaline or acidic conditions. The three-dimensional network of the cured polymer is responsible for the high chemical and thermal resistance and the good mechanical properties. Phenols are found in abrasives, friction, and other engineering applications such as foaming or high temperature applications, in addition to some wood composites or insulation products. For this reason, thermoset polymers were developed from the bio-based building blocks phenols, lignin and lignosulfonate for use as binders. The thermoset polymers were developed along the value chain from organosolv lignin and kraft lignin as well as lignosulfonate as a side stream of pulp production. The key was the use of radical scavengers for hydrothermal degradation and simultaneous modification of the lignins. The modified lignins were characterised using FT-IR, DSC, 31P-NMR. The lignins obtained were used in resin production both alone and in combination with lignosulfonates. A standard recipe for classic phenolic resin production was tested. In the case of modified lignins, up to 80% petrochemical phenol could be replaced and in the case of lignosulfonate, 100% phenol could be replaced. In the resin production process, the modified lignins show a higher reactivity compared to unmodified lignin. The undesirable effect of very high viscosity and long curing times for lignosulfonate resins, known in resin chemistry, could be overcome by combining them with the new modified lignins and moderate viscosities and curing times could be achieved. The molecular weights, melting behavior and thermogravimetry of the resins were also determined.