More than ever before, the automotive industry is using thermoplastic polyolefin (TPO) blends to manufacture exterior plastic applications such as bumper fascias and cladding. Recent efforts to improve TPO foaming technologies have been motivated, in part, by the need to lower production costs, develop lighter-weight materials, and promote better fuel economy. The goal of this research is to improve on the fundamental understanding of the cell nucleation and growth patterns that characterize TPO blend systems.

In order to gain a better understanding of the foaming behavior of TPO, I first employ various physical blowing agents such as nitrogen (N₂), carbon dioxide (CO₂), nbutane, and water to manufacture TPO foams. Furthermore, water foaming technology that uses hydrophilic silica particles is introduced to produce a fine-celled TPO foam that is both larger and more expanded.

There is, however, little research on the use of nitrogen N₂ as a blowing agent, despite its numerous advantages. In this work, the effect of talc on TPO foams with N₂ is studied. The simulated foaming results are compared to the actual foam extrusion results. The influence of N₂ content and operating conditions on cell nucleation behavior is discussed.

This thesis also presents fundamental studies on the effect of TPO blend morphology on cell nucleation. For immiscible polymer blends such as TPO, it has been often noted that the dispersed particles can act as foam nucleating agents;​ they are, therefore, typically expected to enhance the heterogeneous nucleation. Little work has been done so far, however, to assess the impact of blend morphology on nucleation behavior. TPO blends with different blend morphologies are prepared by controlling the viscosity ratio between the blending components. Theoretical work and experimental results indicate that the foam structure is influenced by the size and the total surface area of the dispersed particles. By considering both the thermodynamic and kinetic aspects of the cell nucleation phenomena, I determine that there is an optimal particle size in the dispersed phase for a given TPO composition in order to achieve a maximal cell density of the resulting foam