Prediction of cellular structure in polymer foams

Abstract

A theoretical model is presented which predicts the effect of physical properties and operating conditions on the structures formed during the polymer foaming processes. The nucleation rate expression is combined with the bubble growth model which takes into account the transport of momentum and mass in the melt. The initial conditions for bubble growth are determined for low values of the Peclet number by taking into account kinetic and transport effects. The concept of expanding influenced volume is introduced to describe simultaneous nucleation and bubble growth. The results indicate that the surface and viscous forces dominate the bubble growth during the early stages while the mass transfer parameters (Peclet and Solubility numbers, dimensionless ambient pressure) limit the growth during the later stages. The ultimate bubble size distribution is affected by the values of these parameters but is most sensitive to the Gibbs number which appears in the exponential term of the nucleation rate equation.