Conventional lignin functionalization for polyurethane applications and a future vision in the use of enzymes as an alternative method

20/05/2023 20:01

Thayli Ramires Araujo, D. Bresolin, D. de Oliveira, C. Sayer, Pedro Henrique Hermes de Araújo, J. Vladimir de Oliveira

April 2023

The valorization of lignin in polyurethane products allows biorefineries and paper industries to use this biomass with some added value and not waste most of it in combustion to generate energy. Lignin is known as the second most abundant natural polymer in the world. It comprises a complex structure formed by covalent bonds between phenylpropanoid alcohols, making its composition heterogeneous. In recent decades, lignin has been exploited as a raw material in the synthesis of polyurethanes to replace petrochemical derivatives. Despite its promising characteristics in polyurethane products, lignin has limitations in its use due to its highly complex and cross-linked molecular structure. To overcome this challenge, methods have been developed to make lignin more reactive, facilitating its use in various polymeric processes. Among the methods is chemical modification and fragmentation of lignin. Although research has advanced concerning the depolymerization of lignin through chemical catalysis and enzymatic catalysis synthesis, research only focuses on the process of functionalizing lignin for its application in various areas, however, these explored methods are considered as pretreatment of biomass, adding another step in the polyurethane synthesis. Scientific efforts should also be directed to studies on the production of lignopolyols derived from enzymatic catalysis to produce polyurethanes. Thus, this review addresses conventional methods used in the chemical modification of lignin and ways of application, including polyurethane products that can be developed based on lignin, briefly addresses studies related to enzyme vs. lignin, and points out a gap that exists in the literature on enzymatic catalysis in the production of lignopolyols applicable to PUs.