Effect of Cell Morphology on Energy Absorption of Nitrile Rubber Foam

High energy absorption capacity of rubber foam, during the large compression deformations of cell structure, is an important variable that is considered by engineers as a design criterion. In this respect, the energy absorption behavior of acrylonitrile butadiene rubber (NBR) foam with different densities was studied by efficiency and acutest parameters.

The closed cell NBR foams with densities of 0.51, 0.63, 0.72 and 0.79 g/cm3 were prepared by changing the amount of compound in the equal volume of the mold. The cell morphology and compressive properties of the foams were analyzed by scanning electron microscopy (SEM) and compression tests, respectively.

The cell morphology analysis has indicated that by decreasing the foam density, the average cell diameter becomes larger, the number of cells per unit volume decreases and the cell size distribution becomes heterogeneous. In the compression test, by decreasing density from 0.79 to 0.51 g/cm3, the plateau stress decreases from 750 to 246 kPa and the corresponding stress with the maximum efficiency decreases from 1.13 to 0.27 MPa. In the low stress range, 0.3 MPa, by decreasing density from 0.79 to 0.51 g/cm3, the energy absorption of foam changes from 0.39 to 0.009 MJ/m3. As a result, in the low stress range, lower density foams show more energy absorption. While in the high stress range, higher density foams absorb more energy. For example, in the 1.3 MPa stress, the energy absorption of foams with the density 0.51 g/cm3 and 0.79 g/cm3 is about 0.88 MJ/m3 and 0.1 MJ/m3, respectively. Therefore, the energy absorption capacity of the foam depends on the density and stress range, which determines the maximum allowable stress of the foam based on its density.