If low-density closed-cell foams are used deep in the sea, the high hydrostatic pressures either compress the foam, or fracture the cell faces, so the foam loses its buoyancy. Consequently syntactic foams are used for buoyancy at depth. These contain hollow glass microspheres in a polymer matrix, and have a density less than that of water.
When closed-cell rigid PU foams are subjected to high water pressures, the cell faces fail and the water enters the structure. Mondal and Khakhar showed the pressure vs. loss of buoyancy graph for a foam of density circa 150 kgm−3 was a function of the surfactant used in the foaming process, hence of the thickness (strength) of the cell faces. In a subsequent article they modelled the breakdown process and showed that the threshold pressure for hydraulic collapse occurred when 9% of the cell faces had fractured.
This article comes from sciencedirect edit released
