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Commercially available lipase from Pseudomonas stutzeri (Lipase TL) is investigated as biocatalyst for the formation of an acid-epoxy chemical network. Molecular model reactions are performed by reacting 2-phenyl glycidyl ether and hexanoic acid in bulk, varying two parameters: temperature and water content. Characterizations of the formed products by 1 H NMR spectroscopy and GC-MS combined with enzymatic assays confirm that lipase TL is able to simultaneously promote acid-epoxy addition and transesterification reactions below 100°C and solely the acid-epoxy addition after denaturation at T > 100°C. A prototype biobased chemical network with β-hydroxyester links was obtained using resorcinol diglycidyl ether and sebacic acid as monomers and the lipase TL as catalyst. DSC, ATR-IR, and swelling analysis confirm gelation of the network.

The preparation and reprocessing of an epoxy vitrimer material is performed in a fully biocatalyzed process wherein network formation and exchange reactions are promoted by a lipase enzyme. Binary phase diagrams are introduced to select suitable diacid/diepoxide monomer compositions overcoming the limitations (phase separation/sedimentation) imposed by curing temperature inferior than 100 °C, to protect the enzyme. The ability of lipase TL, embedded in the chemical network, to catalyze efficiently exchange reactions (transesterification) is demonstrated by combining multiple stress relaxation experiments at 70−100 °C and complete recovery of mechanical strength after several reprocessing assays (up to 3 times). Complete stress relaxation ability disappears after heating at 150 °C, due to enzyme denaturation. Transesterification vitrimers thus designed are complementary to those involving classical catalysis (e.g., using the organocatalyst triazabicyclodecene) for which complete stress relaxation is possible only at high temperature.

Hybrid networks, including physical and chemical cross-links, were synthesized from biosourced fatty acid fragments, linked to each other by a controlled number of nonexchangeable ether bonds, exchangeable ester bonds, and noncovalent hydrogen bonds. The mechanical properties of these networks are tuned by the ratio of diversus tetraepoxide and the stoichiometry acid/ epoxy. Creep tests and insolubility demonstrated the vitrimer or vitrimer-like nature of the resulting materials. The thermostimulated welding ability of the materials was exploited to incorporate strain sensors by embedding electrically conductive fibers into the rubbery vitrimer matrix. Both the efficiency of the welding procedure at moderate temperatures (80 °C) and the tunability of mechanical properties are attractive assets for the effective incorporation of thermodegradable conductive fibers while preserving their mechanical and electrical integrity. The mechanical and electrical behaviors of the sensor composites were simultaneously tested, either in quasi-static or in cyclic tensile experiments, at room temperature and at a larger distance from T g of the matrices. The study emphasizes the importance of matching Young's moduli of components in composite samples, which is strongly temperature-dependent.

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