Investigation on mechanical properties and reinforced mechanisms of hyperbranched polyesters functionalized nano-silica modified epoxy composites

The grafting and coating of hyperbranched polyesters (HBP) was successfully achieved by treating the nano-silica with 3-aminopropyltriethoxysilane (APTES) to introduce amino reactive groups as the growth points. Hyperbranched polyesters functionalized nano-silica reinforced epoxy composites (HBP-APTES-SiO2/EP) was prepared by solution casting. The variation of surface functional groups and chemical elements of HBP-APTES-SiO2 were analyzed, and the mechanical properties of HBP-APTES-SiO2/EP were investigated. The results show that 2 phr HBP-APTES-SiO2/EP composites exhibits the best mechanical properties and the microhardness, fracture toughness, tensile strength and Young's modulus can reach 70.2 HD, 1.02 MPa × m1/2, 64.6 MPa and 3353.34 MPa, respectively. The cross-sectional analysis shows that for HBP-APTES-SiO2/EP composites, the nano-silica in the crack initiation zone may contribute to a high level of plastic deformation around the crack tip to produce the significant stick-slip behavior and effectively slow down the crack propagation rate. The nano-silica in the crack propagation zone may change the stress state near the crack tips, resulting in some plastic deformation and crack deflection and bifurcation of the EP matrix as well as a few of HBP-APTES-SiO2 particle debonding to consume much more fracture energy.