ELASTIC EFFECTS IN THE FOAMING OF THERMOPLASTICS

We have investigated shear and bulk elastic stresses in non-Newtonian fluids in which bubble formation due to a blowing agent is taking plac e. In the absence of shear, these elastic fields manifest themselves s trongly during the formation of bubbles, and during coalescence events . At later times, their activity is confined to the surface of the bub bles. These effects cause a significant slow-down in radial growth. In the presence of steady shear, elasticity tends to stabilize bubble sh apes, as the maximum number of droplets decreases with sheer rate, whi le their growth rate increases. [S1063-651X(98)16109-3].