Process dynamics of starch-based microcellular foams produced by supercritical fluid extrusion. II: Numerical simulation and experimental evaluation

This paper presents the numerical simulation results for the process dynamics model for SCFX processing and post-extrusion drying developed in Part I. The SCFX model was written in Visual Basic, and experimental data for pregelatinized. corn and potato starch based SCFX extrudates with 4-7% whey protein concentrate were used for validation. Predicted bubble radius (R) was 50-220 mum, expansion ratio (ER) 4-11 and open cell fraction (f(o)) 0.05-0.27, as the drying temperature varied from 70 to 95 degreesC. Moreover, the model predicted decrease in extrudate collapse and open cell fraction with increase in yield and failure stresses of the melt, respectively. Simulation results compared well with experimental R and f(o). The model provided a good understanding of the mechanisms of bubble growth and collapse, post extrusion drying and open cell formation during SCFX processing. The model was also used to estimate the effect of various processing and material parameters on extrudate structural characteristics, and can be a useful tool in a priori design of extrudates of specific characteristics. (C) 2003 Elsevier Science Ltd. All rights reserved.