Polyurethane foam core material for high-strength low-cost composite material as well as preparation method and application of polyurethane foam core material

The invention provides a polyurethane foam core material, and the polyurethane foam core material comprises a polyurethane cross-linked network structure and a second polymer network structure chemically cross-linked on the polyurethane cross-linked network structure, the second polymer is prepared from one or more of urea formaldehyde resin, melamine formaldehyde resin and benzene-substituted melamine resin. According to the invention, a specific polymer is adopted to carry out chemical cross-linking modification on polyurethane, so that the high-strength low-cost polyurethane foam core material with a specific structure is obtained. A specific type of thermosetting amino resin is introduced to a main chain of polyurethane resin, and the amino resin is cured to form a high-crosslinking network system, so that the temperature resistance and the strength of the modified polyurethane foam core material are improved by a step and a new height, and the use requirements of a composite material bearing structural c