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Thermosetting polyurethane foams by physical blowing agents: chasing the synthesis reaction with the pressure

Di Caprio Maria Rosaria ⁽¹⁾, Brondi Cosimo ⁽¹⁾, Di Maio Ernesto ^(1)*, Mosciatti Thomas ⁽²⁾, Cavalca Sara ⁽²⁾, Parenti Vanni ⁽²⁾, Corti Maurizio ⁽³⁾, Iannace Salvatore ⁽⁴⁾

⁽¹⁾ University of Naples Federico II - NA - Italy, ⁽²⁾ Dow Italia - RE - Italy, ⁽³⁾ Cannon Afros S.p.A. - VA - Italy, ⁽⁴⁾ National Research Council - MI - Italy

The aim of the present study was the introduction of a novel method to produce microcellular thermosetting polyurethane foaming by the gas-foaming technique, using high-pressure physical blowing agents. In particular, to tackle the inherent difficulties of imposing a rapid pressure quench O(10-2 s) to a material whose synthesis timing is much larger O(102 s), we utilized a two-stage foaming. In a first stage, a rapid pressure quench O(10-2 s) was imposed to nucleate a large amount of bubbles, from the saturation pressure to a low, non-zero pressure; in the second stage, the growth of the nucleated bubble is then controlled by slowly O(102 s) decreasing the pressure to ambient (zero) pressure. In this way, by separating the nucleation from the growth rate and by chasing the synthesis reaction with the pressure to avoid excessive stresses to the curing polymer, we achieved microcellular (size diameter below 10 um), medium-to-low density (below 200 g/L) thermosetting polyurethane foams.