A A C C   2 0 0 0   A n n u a l   M e e t i n g

This presentation will focus on nucleation and expansion in extruded and microwaved products. The factors which affect the air nucleation during extrusion, the effect of the processing conditions on air nucleation and the effect of the biopolymeric system will be discussed. Expansion in polymeric glasses during microwave expansion and the similarities and differences with extruded expansion will be elucidated. The presentation will demonstrate how expansion is governed by the biaxial extension of individual bubbles and the role that moisture plays. The biaxial extensional viscosity and also integrity of cells are affected by the initial moisture content. It is moisture content which enables the polymeric matrix to exist in the rubbery state where integral bubbles are formed and extrudates expansion and microwave expansion is maximized. The rubbery state is preceded by the free flowing state where the resistance to deformation is minimized and moisture loss during the expansion and heating process results in a shift in the state diagram from the free flowing state to the rubbery state allowing expansion be maximal. These ideas will be quantitatively presented with data that supports the conclusions will be presented.