Numerical simulation of polymeric foaming processes using modified nucleation theory

摘要

This paper develops a modified nucleation theory and examines its application to simulate the bubble nucleating phenomena in polymeric foaming processes.Bubbles typically nucleate homogeneously in the bulk phase of the polymer/gas solution and heterogeneously at the boundaries between the bulk phase and the nucleating agents.Although past research had attempted to consider the heterogeneous nucleation to simulate the plastic foaming process,the assumption of a flat nucleating surface might not be realistic.In this context,the authors have modified the heterogeneous nucleation theory by considering random surface geometries,and have developed a computer simulation program to predict the cell nuclei density based on this heterogeneous nucleation scheme with random surface geometries.Homogeneous cell nucleation was also included in the simulation.The simulation results obtained in this study are compared with the experimentally observed data from a batch foaming process to evaluate the validity of the theory proposed herein.It is found that the modified theory does in fact account for the quantitative aspects of the experimental observations when an iterative approach is used to determine the contact angle theta_c.Although the appropriateness of the values selected for theta_c requires further investigation from both experimental and theoretical points of view,this study illustrated that the modified nucleation theory can represent a new access point for exploring the cell nucleating phenomena in plastic foaming processes.