Foaming of thermoplastic polyurethane using supercritical CO2 AND N2: Antishrinking strategy

Abstract

The transformation of thermoplastic polyurethanes into polymeric foams is attracting great interest nowadays. However, this technology has some challenges that it is necessary to resolve, being one of the most important the shrinkage suffered by the polymeric foams over time. For that reason, this work explores several alternatives to mitigate this phenomenon. These alternatives are divided into two groups: on the one hand, the refoaming of the shrunken foams using supercritical CO₂ and N₂ was explored; on the other hand, the foaming using mixtures of supercritical CO₂ and N₂ as foaming agents was carried out. After experiments, it was seen that, the refoaming with N₂ of shrunken foams obtained by supercritical CO₂ technology can increase and keep constant the initial expansion ratio of the shrunken foams. Moreover, it was also observed that ratios of CO₂/N₂ between 80/20 and 60/40 can avoid the shrinking issues suffered by the polymeric foams after foaming using supercritical technology.