Bacterial cellulose integrated irregularly shaped microcapsules enhance self-healing efficiency and mechanical properties of green soy protein resins

Soy protein isolate (SPI)-based self-healing thermoset resins were prepared using either poly(DL-lactide-co-glycolide) porous microspheres (MSs) and spherical microcapsules (MCs) or elongated MCs containing a combination of ground bacterial cellulose (GBC) and SPI as the healing agent. Spray emulsification, combined with solvent evaporation technique, was used to prepare MCs and MSs. The technique resulted in two MC morphologies: one primarily consisting of a mixture of porous MSs and spherical MCs and the other consisting of elongated MCs with aspect ratios as high as 50, depending on the surfactant and GBC amount used. While porous MSs made the resin stronger, they did not contribute to self-healing since they could not retain the healant. Part of the GBC, added during MC preparation, got successfully encapsulated into MCs to form strong GBC/SPI composite healtant. Most of the remaining GBC stayed on MC surfaces and was seen to enhance the MC/resin interfacial adhesion which, in turn, contributed to increased self-healing efficiency. Overall results indicated that resins with 20 wt% elongated MCs exhibited self-healing efficiencies of about 45% in strength and 59% in toughness. The results suggest that the integration of GBC in the healant could also work in other resin systems to enhance their self-healing efficiencies.