Mechanical properties and toughening mechanism of polyurethane epoxy resin composite materials

Epoxy resin materials have high brittleness and poor toughness, and are prone to aging, cracking, and peeling on the surface, making it difficult to protect concrete from complex working conditions such as marine environments. Polyurethane/Epoxy resin (PU/EP) composite materials with different systems were designed, and orthogonal experiments were conducted using the tensile strength, fracture elongation, and impact toughness of PU/EP composite materials as evaluation indicators. The optimal preparation formula for PU/EP composite materials was determined through response surface analysis method, with an R value of 1, a PU content of 15wt%, and a preparation temperature of 80℃. The results showed that the crosslinking effect of PU and EP was good, and the tensile strength, fracture elongation, and impact toughness of PU/EP composite materials were improved by 37.61%, 52.21%, and 47.07% compared to pure epoxy resin, respectively. With the increase of PU content, the proportion of flexible long chain segments in the material increases, and the area forming the secondary network increases. The coordination effect between molecules and the increase of soft connecting segments greatly improved the mechanical properties of the material, and the hardness and elastic modulus of PU/EP composite materials are reduced to a certain extent.