Preparation of lignin-based imine vitrimers and their potential application as repairable, self-cleaning, removable and degradable coatings

Biobased materials are developed and utilized to reduce dependence on petroleum-based resources, protect the environment and reduce carbon emissions. Meanwhile, chemical recycling of thermosetting materials is an emerging strategy to increase the added value of post-consumer waste. Nevertheless, most thermosets have proved difficult to recycle due to the high stability of their crosslinked structure. Vitrimers, crosslinked by dynamic chemical bonds, are the perfect solution to recycling problems. Here, we report lignin-based vitrimers prepared by imine chemistry. First, aldehyde-modified lignin was successfully prepared by treating OH functionalized lignin with a dialdehyde via an acetalization reaction. The modified lignin acts as both a hard segment and crosslinker and the soft segment is a fatty acid diamine (Priamine™ 1075), which is chemically crosslinked via imine chemistry. The mechanical properties of lignin-based vitrimers (LPs) with more than 81.4% biobased content can be adjusted by blending the ratio of hard to soft segments. The resulting imine bond in LPs is highly dynamic at elevated temperatures (LP-40%, Ea = 49.6 kJ mol−1) allowing the material to be thermally recycled three cycles via imine metathesis and transimination without any catalyst. Unique hydrolytic properties of the imine bond endow the material with chemical recycling properties under acidic conditions (LP-40%, 62.0% tensile stress recovered). A potential application for this work is a coating, which can be prepared by hot pressing. In addition to the excellent coating properties, the LP coatings also possess thermal repairable, self-cleaning, removable, and degradable properties, which are not available with conventional coatings.