Validated modeling of bubble growth, impingement and retraction to predict cell-opening in thermoplastic foaming

•The sequence of operations involved in gas foaming process is modeled.•The dynamics of bubble growth and impingement is used to predict rupture and retraction.•A new retraction criterion is proposed for bubble wall opening.•The model is validated with poly(ε-caprolactone) foamed with CO2.

In this work a design tool to control cell-opening in gas foaming of thermoplastic polymers is developed. The sequence of events following bubble nucleation, namely, bubble growth and impingement, is modeled to gain a comprehensive, perspective view on the mechanisms of bubble wall rupture and on the conditions for achieving a fully open-cell morphology. In particular, unlike the previously published literature, the polymer elastic recovery is recognized as an important factor for wall retraction, which is typically considered as solely driven by surface tension. The new approach is experimentally validated on poly(ε-caprolactone) (PCL), foamed with CO2, as a model polymer/gas system.

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