Molecular Dynamics Study of Polyurethane and KH550/SiO₂ in Enhancing Epoxy Resin (EP) Mechanical Properties

To enhance the mechanical properties of epoxy resin (EP), this study utilizes polyurethane (PU) and KH550/SiO₂ nanoparticles as synergistic modifiers to develop an epoxy resin composite model. In this paper, five models are established, namely: EP, PU-EP, SiO₂-SR, KH550/SiO₂-EP, and KH550/SiO₂-PU-EP model. The mechanism of PU and KH550/SiO₂ synergistic modification of EP mechanical properties is systematically studied through analyses of the cohesive energy density, free fraction volume, radius of gyration, radial distribution function, hydrogen bonding, and pull-out simulations. The results show that SiO₂ nanoparticles modified with the KH550 coupling agent enhance the interaction energy between SiO₂ and the EP matrix in the composite. At different temperatures (300-450 K), both fillers demonstrated the ability to lower the free fractional volume within EP composites. Additionally, they enhanced the quantity of hydrogen bonds, shortened the hydrogen bond distances within the system, and increased the proportion of hydrogen bonds exhibiting higher angles. Among them, KH550-SiO₂/UP/EP has the most obvious improvement effect on the system, indicating that KH550/SiO₂ and PU synergistically modified epoxy resin can improve the mechanical properties of the composites. At 300 K, the Young's modulus, shear modulus, bulk modulus, and bulk modulus/shear modulus of KH550-SiO₂/UP/EP system are 8.12%, 7.03%, 16.05%, and 8.43% higher than those of EP system, respectively. At 450 K, it increased by 18.26%, 17.30%, 23.87%, and 27.57%, respectively. The findings of this study are anticipated to offer valuable insights for the design and performance enhancement of epoxy resin composites.