The MI foam is foamed by heating a methacrylic/methacrylonitrile copolymer plate. During the foaming of the copolymerized sheet, the copolymer is converted into polymethacrylimide. The foaming temperature is above 170oC, depending on the density and model.
At present, the world's main PMI foam product is the ROHACELL series of products produced by Degussa, Germany. In the elastic state, when the foam is made by a liquid crew (there are many such foams, such as polyurethane foam), the surface Tension pulls the material toward the edge, leaving only a thin film across the hole surface, which breaks easily. Thus, although the foam has an initially closed cavity, its stiffness is entirely derived from the hole edge and its modulus is equivalent to the open cell foam. However, the PMI foam hole faces are made up of real solid parts that increase the stiffness of the porous body. The compression-deformation mechanism of closed-cell foam consists of three parts: wall bending, rib shrinkage and film extension, and pressure of the enclosed gas, structural advantages of the PMI foam sandwich structure. In the sandwich structure, the PMI foam can be used as a structural unit. In the past, foam was generally only used as a filler material, regardless of its contribution to the structure of strength and stiffness. The main reason is that the foam materials used in the past, such as PUR foam, are generally foamed in the cavity after the structure is completed, so that the quality, uniformity and mechanical properties of the foam are difficult to ensure. PMI foam uses a unique solid foaming technology that guarantees the quality, uniformity and mechanical properties of the foam. PMI foam is currently the polymer rigid foam with the highest specific strength and specific stiffness. By calculation, if PMI foam is used as a structural unit of the sandwich structure, the panel can reduce 1- to 2-layer carbon fiber layup. The PMI foam sandwich structure can be used as a structural sandwich structure, and the application field has broken through the traditional view of non-structural sandwich structures such as honeycombs.