Traditional lignin pyrolysis generates a bio-oil with a complex mixture of alkyl-functionalised guaiacol and syringol monomers that have limited utility to completely replace phenol in resins.
In this work, formate assisted fast pyrolysis (FAsP) of lignin yielded a bio-oil consisting of alkylated phenol compounds, due to deoxyhydrogenation, that was used to synthesise phenol/formaldehyde resins.
Similar thermal and decomposition behaviour
A solvent extraction method was developed to concentrate the phenolics in the extract to yield a phenol rich monomer mixture. Phenolic resins were synthesised using phenol (phenol resin), FAsP bio-oil (oil resin), and an extract mimic (mimic resin) that was prepared to resemble the extract after further purification. All three phenolic sources could synthesise novolac resins with reactive sites remaining for subsequent resin curing. Differential scanning calorimetry and thermogravimetric analysis of the three resins revealed similar thermal and decomposition behaviour of phenol and the mimic resins, while the oil resin was less stable. Resins were cured with hexamethylenetetramine and the mimic resin demonstrated improved curing energies compared to the oil resin. The adhesive strength of the mimic resin was found to be superior to that of the oil resins.
Properties improved over parent bio-oil
These results confirmed that extracting a mixture of substituted aromatics from FAsP bio-oil could synthesise resins with properties similar to those from phenol and improved over the parent bio-oil.
The study is published in: Applied Polymer.