Interpenetrating Network Strategy for Highly Effective Toughening of Epoxy Resin Using Cellulose Microgels

Epoxy resin (EP) is widely used in coatings, adhesives, and molding materials. EP's high crosslinking density provides a strong modulus but also leads to reduced elongation at break and lower toughness. In this study, bacterial cellulose microgel (BC-M) is employed to toughen EP through in situ polymerization, to form an interpenetrating network with EP. Bacterial cellulose nanofibers (BC-CNF) and ethylated bacterial cellulose microgels (EM) are used as controls to highlight the advantages of the 3D network in enhancing polymer toughness. BC-M demonstrates the most effective toughening performance for EP. At a filler content of 0.3 wt.%, BC-M/EP nanocomposites exhibite significant improvements in mechanical properties, including a fracture strength of 107.8 MPa, strain of 3.53%, Young's modulus of 3.09 GPa, and toughness of 1.98 kJ m⁻³. Compared to EP, these values represent enhancements of 40%, 9.5%, 27.3%, and 58.4%, respectively. Comparisons with BC-CNF/EP and EM/EP nanocomposites clearly demonstrate that BC-M provided superior toughening effects. The exceptional toughening capability of BC-M is attributed to its 3D network structure, which effectively dissipates applied energy, and its strong interfacial interaction with the epoxy matrix through covalent bonding.