PMI foam is made by heating methacrylic acid and methacrylonitrile copolymer board and foaming. In the process of foaming the copolymer board, the copolymer is transformed into polymethacrylimide. The foaming temperature is above 170oC, depending on the density and model. Although the foam has initially closed pores, its stiffness comes entirely from the pore edges, and its modulus is equivalent to that of an open-cell foam. However, the pore surface of the PMI foam material is composed of real solid parts, and these pore surfaces increase the rigidity of the porous body.

The compression deformation mechanism of closed-cell foam consists of three parts: cell wall bending, edge contraction and film extension, and the pressure of the enclosed gas. The structural advantages of PMI foam sandwich structure In the sandwich structure, PMI foam material can be used as a structural unit. In the past, foam was only used as a filling material, and the contribution of its strength and rigidity to the structure was not considered. 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 the quality, uniformity and mechanical properties of the foam are difficult to guarantee.

PMI foam adopts unique solid foaming technology, and the quality, uniformity and mechanical properties of the foam can be guaranteed. PMI foam is currently the polymer rigid foam material with the highest specific strength and specific stiffness. Through calculation, if the PMI foam is used as the structural unit of the sandwich structure, the panel can reduce 1-2 layers of carbon fiber layup. The PMI foam sandwich structure can be used as a structural sandwich structure, and the application field breaks through the traditional view of non-structural sandwich structures such as honeycombs in the past.