Shear stress nucleation in microcellular foaming process

Abstract

The effect of shear stress on the foaming process has been studied using the Foaming Process Simulator developed previously. The polymer samples were saturated with gas in the test chamber. A rotor was used to apply shear stress to the polymer samples. Foams were obtained by releasing the pressure quickly. Polystyrene. Hled and unfilled, was used as the material. The cell density was analyzed with a scanning electron microscope. It was found that the cell density was s - -cantly increased by introducing shear stress. The higher the shear stress, the more significant the effect. A cell stretch model has been developed to explain the cell nucleation enhancement with shear stress. The nucleation sites are stretched under the shear stress. The stretched nuclei are much easier to expand for cell formation owing to their larger surface areas and non-spherical shapes. The model prediction shows the same tendency of the effect of shear stress observed in the experiment. The key issue with shear stress nucleation is the transformation of mechanical shear energy into surface energy.

Assisted heterogeneous multinucleation and bubble growth in semicrystalline ethylene-vinyl acetate copolymer/expanded graphite nanocomposite foams: Control of morphology and viscoelastic properties

“…Among the polymer foaming community, the discrepancy between the classical theory and experimental results is sometimes attributed to the intervening heterogeneous nucleation provided by filler solid surface and has led to the classical theory modifications by incorporating certain aspects specific to the polymer foaming process [9,[32][33][34]. Nanoparticles have been validated that undoubtedly serve with heterogeneous nucleation sites and their influence on the cell density has been qualitatively represented by the classical nucleation theory [32,34].…”

Tunable Microcellular Morphologies from Poly(ferrocenylsilane) Ceramic Precursors Foamed in Supercritical CO2

“…Chen et al [51] have introduced shear in their study of bulk polymer foaming by constructing a chamber wherein a polymer/CO 2 solution is sheared for a specified duration and then foamed without shear. If the sheared material is confined, the oriented nucleation sites produce cells that are elongated along the direction of shear.…”

Effects of Mechanical Vibration on Cell Density and Cell Morphology in the Dynamic Microcellular Foaming Process

“…Recently, a cell stretch model has been developed by Chen et al [3] to explain the shear stress nucleation. They concluded that the key issue with shear stress nucleation was the transformation of mechanical shear energy into surface energy.…”