Valorizing depolymerized lignin oil through the green synthesis of a thermoplastic non-isocyanate polyurethane

Abstract

Polyurethanes are the sixth most-produced plastic worldwide and rely heavily upon petroleum resources for their production. The goal of reaching carbon-neutral plastic production depends on finding renewable resources as feedstocks for polymer synthesis. The biorefinery concept of the future relies upon valorizing each biomass component to create cost-competitive materials for commercial applications. One promising technique for valorizing biomass is the process of reductive catalytic fractionation (RCF), where whole biomass is separated into a processable carbohydrate pulp and a stable depolymerized lignin oil composed of phenyl propyl monomers, dimers, and oligomers. In this study, lignin oil from the RCF process is subjected to a green functionalization scheme using organic carbonates and polymerized with a biobased diamine to create a non-isocyanate thermoplastic polyurethane. The reaction progress associated with carbonate functionalization is detailed to reveal a high reactivity with lignin oil precursors. The thermoplastic nature of the resulting polymers is explored through rheological experiments, and the synthetic protocol is tuned to increase the glass transition temperature. The results demonstrate the ability to employ depolymerized lignin oil in a green synthetic sequence toward a high-use thermoplastic polymer class. Such polymers are profoundly useful in creating advanced fiber-reinforced composites for various applications.