Abstract
A framework for describing growth of the deformed bubbles and thinning of the interstitial films during the late stages of the foaming process of a viscoelastic foam cell is established. A two-dimensional cell model is proposed to depict the geometrical constraints imposed by the existence of neighboring growing bubbles. The viscoelastic behavior of the polymer melt as well as the effect of the intermolecular forces on foam stability are investigated. An analysis of the results indicates the competing effects of polymer elasticity and the long range intermolecular forces on the thin film hydrodynamic stability. Van der Waals intermolecular forces act to destabilize the thin film between bubbles and cause coalescence, whereas elasticity combats this instability and increases film rupture time. Compared to Newtonian foams, viscoelastic systems have more resistance to deformation and higher stability for disturbances. The developed computer simulation can be used to study the effects of the process operating conditions and base material properties on the dynamics of the foaming process and the characteristics of the final product. It provides a basis for predicting the lower limits of foam density possible with given polymer systems.
Allaboun, Hussein Raji (1996). Deformed bubble growth and coalescence in polymer foam processing. Master's thesis, Texas A&M University. Available electronically from
https : / /hdl .handle .net /1969 .1 /ETD -TAMU -1996 -THESIS -A454.