Preparation and mechanical properties of poly(γ-benzyl l-glutamate) modified nano-silica reinforced polyurea composites

To improve the mechanical properties of polyaspartate polyurea (PAEP), functionalized nano-silica reinforced polyurea composites were prepared. The original nano-silica (O-SiO₂) was treated with 3-aminopropyltriethoxysilane (APTES), and the amino group at the end of APTES was used as the initiation site to realize the coating modification of poly(γ-benzyl l -glutamate) (PBLG) onto O-SiO₂. The dispersion, wettability, and interfacial properties of functionalized nano-silica (PBLG-SiO₂) in PAEP were analyzed. The tensile and tear properties of PBLG-SiO₂/PAEP composites were tested, and the reinforcement mechanism was revealed. The results showed the dispersibility of PBLG-SiO₂ in PAEP had been improved markedly. The contact angle of PBLG-SiO₂ with PAEP was 29.31°, which was significantly lower than that of O-SiO₂ (76.48°). The adhesion work between PBLG-SiO₂ and PAEP was 97.16 mJ/m², an increase of 51.7% compared with O-SiO₂. When the content of PBLG-SiO₂ was 2 phr, the tensile strength, Young's modulus, and tear strength of PAEP composites reached the maximum of 17.43 MPa, 157.12 MPa, and 127.38 N/mm, an increase of 33.6%, 77.9%, and 71.3%, respectively, compared with pure PAEP. The analysis of cross-section showed that the strengthening mechanism of PBLG-SiO₂ on PAEP was mainly manifested by non-planar cracks, deflection and bifurcation of cracks, and plastic deformation of PAEP matrix caused by peeling of PBLG-SiO₂ from matrix.