2. Reactive foaming stages

Whether for flexible casting or injection molding, the reagents are mixed in the injection head and then injected. Reactions start immediately – or with a delay (induction) – and the mixture deposited by the head begins to expand and polymerize from a macroscopic point of view.

From a physical point of view, a number of concomitant phenomena, whose kinetics are associated with those of chemical reactions, oppose or combine to create foam:

• nucleation of thermodynamically stable gas pockets;

• the growth of these gas pockets, linked to their internal pressure (a function of temperature and the outgassing reaction, and therefore a function of the diffusion mechanisms of gases dissolved in the mixture and the permeability of the polymer/CO ₂ ...