PMI foam is produced by heating methacrylic acid/methacrylonitrile copolymer sheet and foaming. During the process of foaming the copolymerized sheet, the copolymer is converted into polymethacrylimide. The foaming temperature is above 170℃, which varies according to the density and model. In the linear elastic state, when the foam is made from a liquid member, there are many such foams, such as polyurethane foam, the surface tension can pull the material towards the edge, leaving only a film across the cell face, it is easy to rupture.

Thus, although the foam has initially closed cells, its stiffness is entirely derived from the cells and edges, and its modulus is equivalent to that of an open-cell foam. But PMI foam pore surfaces are made up of real solid parts, and these pore surfaces add to the stiffness of the porous body. The compression deformation mechanism of closed-cell foams consists of three parts: cell wall bending, edge shrinkage and membrane extension, and the pressure of the enclosed gas.

It can be seen that the strength of the PMI structural foam is related to the relative density, and more importantly, it is related to the volume fraction of the solids contained in the edge of the cell, which is the ratio of the cell edge material to the foam material in the foam structure. The poorer form of foam material is a fully open-celled foam material, all materials are rod-like distributed at the edges of the pores, and the volume fraction of solids contained in the edges of the pores is equal to 1.

A good distribution form of PMI foam material is that all the foam material is located at the position of the cell wall of the pores. At this time, the volume fraction of the solid contained in the edge of the cell is equal to 0, and the relative yield strength is proportional to the relative density. So expect relatively low values. The cell edges of ROHACELL (RC) contain a lower volume fraction of solids than other structural foams. The range of this ratio is to 0.80.

It can be seen from this that the foam with higher specific shear strength can be obtained by: developing a new manufacturing process to reduce the volume fraction of solids contained in the edge of the cell. Improves shear strength for producing foamed resins. The size of the pores is smaller than the critical diameter for crack propagation or instability. The foam is reinforced with rod-shaped reinforcements.