Processing of polyamide 11 with supercritical carbon dioxide

The supercritical carbon dioxide induced swelling and plasticization of pol yamide 11 were investigated. The swelling kinetics exhibit an initial regio n of large swelling, in which the diffusion of CO2 into the polymer follows Fickian behavior, and a subsequent region of small volume increase that as ymptotically approaches an equilibrium swelling value. The diffusion coeffi cient of CO2 in polyamide 11 was calculated from the initial slope of the s welling kinetics data. CO2, injected up to 3 wt % using an extrusion rheome ter, is shown to be an effective plasticizer for polyamide 11, lowering the viscosity of the polymer melt by as much as 50%. The use of CO2 as a blowi ng agent was also investigated, and we report preliminary foaming attempts using a batch process. We obtained homogeneously distributed foams, featuri ng well-defined closed cells with an average diameter of 30 mum that had an unfoamed skin layer.