Relationship between Apparent Density and Mechanical Properties of Microcellular Thermoplastic Polyurethane Foam

A series of microcellular thermoplastic polyurethane foams with different apparent densities were prepared by temperature-increasing foaming method with high-pressure CO2 as blowing agent, and the relationship between the apparent density and mechanical properties was investigated. The structure of microcellular thermoplastic foam was characterized by scanning electron microscopy. The mechanical properties of the materials with different apparent densities were characterized by universal material testing machine and rotational rheometer. The results show that the apparent density of the microcellular thermoplastic polyurethane foam is mainly determined by the thickness ratio of the skin layer and the area occupation of cell. The smaller the ratio of the thickness of the skin layer and the higher the area occupation of cell, the smaller the foam density; the relationship between compression modulus E and apparent density rho of the samples in the linear strain region is as follows: E proportional to rho(1.7), which is consistent with the basic conclusion that the relationship between modulus and density of foam materials is exponential; in the cyclic compression experiment, as the density of the foam material decreases, the residual strain decreases, and the hysteresis increase; in the rheological experiment, the modulus of the foamed material does not change significantly with the density, and the damping factor tan delta does not vary monotonically with the foam density. At the same time, the dependence of compression modulus E and hysteresis with foam density was also explained.