1. Introduction

Reactive polymeric systems are widely used in foam blowing or in resin transfer molding (RTM) processes. Numerical modelling of reactive processes is very difficult because the flow kinematics is coupled with the chemical reacting kinetics, which depends mainly on the reaction time (time elapsed since the reactants' mixing). The kinematics - chemical kinetics coupling - is a key point in foam blowing, being less important for example in usual RTM processes, where the chemical formulation can be adjusted in order to finish the mold filling before a significant rise in the resin viscosity.

The polymerization reaction increases the material viscosity and the expansion induces the material growth, generating a porous structure. When the polymerization takes place much faster than the foam expansion, the material becomes too rigid before the conclusion of the expansion. In this case the cellular walls can be broken with direct consequences for the mechanical properties of the conformed pieces. On the other hand, when the expansion finishes before the complete polymerization, the low material consistency is not enough to preserve the final geometry, and the structure collapses when the expansion is finished.

The numerical modelling of forming processes involving the flow of chemically-reacting polymeric foams requires taking into account the different problem scales. Thus, in industrial applications a macroscopic approach is suitable, whereas the macroscopic flow parameters depend on the cellular structure: porosity, size shape and orientation of the...