| Existing models for microcellular foam nucleation fail to predict observed experimental results. Experimental results were compared to classical nucleation models and revealed irreconcilable differences. Based on the knowledge that microscopic defects exist in polymer systems, a new physical mechanism for foam cell formation is proposed which is consistent with experimental results. Rather than nucleating a new gas phase during foaming, one is instead trying to grow microscopic voids and cracks into the bubbles. From this concept, a thermodynamic model has been proposed for the activation of microvoids into viable foam cells. Study of the resulting model reaffirms the validity of the microvoid mechanism; but, it also demonstrates that foam cell nucleation can no longer be treated separately from the bubble growth phenomena. |
