Thermoplastic polymers are quite often sensitive to thermal degradation. As a result of conventional melt polymer processing technologies, molecular weight is considerably reduced with respect to the neat polymer, and the mechanical properties of the final material suffer from this reduction in molecular weight. This, however, is the best case scenario allowed for certain polymers, such as PET, P3HB[1], while others are not even able to be processed due to their higher melting point in comparison to the degradation temperature. In recent years, several publications were focused on the use of CO2 as an assisted fluid to carry out polymer melt extrusion[2]. CO2 can be dissolved into the polymer, promoting higher mobility of polymer segments and therefore acting as a plasticizer. The extent of the plasticizing effect will then depend on the amount of CO2 introduced to the system, which should be finely selected according to the thermodynamics of the polymer-CO2 system. In this work, we extend the applicability of assisted melt extrusion processing to melt spinning of polylactic acid (PLA). A new design of a conventional melt spinning plant to allow a continuous assisted CO2 processing has been evaluated, and different CO2 concentrations have been tested regarding morphological properties of the final fibers. Increasing amounts of CO2 lead to the production of porous fibers with pore sizes in the range of few micrometers, contrary to what has been observed at low CO2 concentrations, where the obtained pores are bigger. However, even these low amounts of CO2 are able to reduce the processing temperature, enabling in that way to preserve PLA from further degradation. References: [1] R. Hufenus, F. Reifler, M.P. Fernández-Ronco, M. Heuberger. Eur. Poly. J. 71 (2015) 12-26. [2] M. Sauceau, J. Fages, A. Common, C. Nikitine, E. Rodier. Prog. Polym. Sci. 36 (2011) 749-766.