The chemical and physical properties of lignin bio-oils, facts and needs

Lately, the interest in lignin valorization has notably grown within the scientific community. In the last decade, the number of publications focusing on lignin as an alternative to fossilbased resources has exponentially increased. Different strategies have been employed to valorize lignin as a source of renewable fuel and building blocks for chemicals and materials development. Of these strategies, lignin depolymerization producing lignin oils (bio-oils) has been recently explored on laboratory and pilot scale. The produced bio-oil exhibits unique chemical and physical properties that depend on the type of lignin with regard to the nature of parent biomass and can be further tailored by both the isolation and the depolymerization process conditions. This review aims to group the work done on the production and valorization of bio-oils to provide a common description of the depolymerized lignin oils. This work proposes reporting guidelines of bio-oil properties required to bridge the gap between the depolymerization techniques and chemicals/materials development using the bio-oils properties.