Lignin could replace phenol in wood glue

A MODIFIED form of lignin could be used to replace toxic phenol compounds in wood adhesive for plywood and laminates, according to researchers at VTT Technical Research Centre of Finland.

Consumers and wood product manufacturers alike are increasingly calling for bio-based, more sustainable adhesives and resins for wood products, while new laws in Finland have given impetus to the research. Lignin has a carbon footprint around 20% of the size of phenol. In plywood, for example, which relies on phenol formaldehyde resin, around half of its carbon footprint comes from the resin, so replacing the phenol would have a significant impact. Around 6m t of phenol formaldehyde resins are produced annually. Senior scientists Hanne Wikberg and Juha Leppävuori led the research to develop the so-called CatLignin technology.

The researchers say that the reactivity of CatLignin makes it ideal for the purpose. CatLignin is derived from kraft black liquor, a byproduct of paper and pulp production that is often used for energy production onsite. Leppävuori explained to The Chemical Engineer that the researchers subject the liquor to a thermal treatment which leads to the demethylation and demethoxylation of the lignin. This treatment increases the number of reactive sites on the lignin, which makes it suitable for resin production. The lignin structure can be tailored by controlling the thermal treatment.

“High reactivity has been proven both by direct analysis of the chemical structure and by fast curing of the resins in resin synthesis, where a fraction of phenol is substituted with lignin. Lignin activation has been demonstrated for both softwood and hardwood black liquors,” Leppävuori said.

Wikberg said that it is the first time researchers have been able to use lignin as a phenol substitute in significant quantities in resins, and that CatLignin is a “technological leap”.

CatLignin technology could be integrated into existing pulp mills. The researchers believe that CatLignin material has the potential to be used in a much broader range of petroleum-based products, including rubbers and plastics. They are now seeking partners to scale up the process.

The research will be presented at the 7th Nordic Wood Biorefinery Conference 2017 (NWBC 2017), in Stockholm, Sweden from 28–30 March.