Renewable Thiol-yne Click Networks Based on Propargylated Lignin for Adhesive Resin Applications

In this study, the development of lignin-based resins for wood adhesion applications was demonstrated. We investigated two lignin fractions: commercial Protobind 1000 lignin and methanol-soluble Protobind 1000 lignin fraction after mild solvolysis. Although lignin has previously been incorporated into various cross-linked systems, this is the first report on lignin-based thermosets obtained via thiol-yne click chemistry. In this approach, lignin was functionalized with terminal alkyne groups followed by cross-linking with a multifunctional thiol, resulting in polymeric network formation. The influence of the curing conditions on the resin characteristics and performance was studied, by varying the amount of reactive monomeric diluents. Additionally, a post-curing strategy utilizing the Claisen rearrangement was investigated. These resins were tested as a wood adhesive and were proven to possess a desirable performance, comparable to the state-of-art phenol-formaldehyde resins. Lignin-based thiol-yne resins turn out to be an alternative to phenol-formaldehyde resins, currently used as adhesives and coatings. Although it is possible to use lignin in phenol-formaldehyde resins, lignin addition is compromising the resin's performance. The main benefits over the phenol-formaldehyde approach are that higher lignin loadings are possible to achieve, and no volatiles are emitted during the resin processing and use.

Automated summary

This study demonstrates the development of lignin-based resins for wood adhesion applications. Lignin was functionalized with terminal alkyne groups and cross-linked with a multifunctional thiol to form polymeric networks. The curing conditions and reactive monomeric diluents were varied to study their influence on resin characteristics and performance. The lignin-based resins showed comparable performance to phenol-formaldehyde resins and have the advantages of higher lignin loadings and no volatile emissions.