Effect of pressurized CO2 and N2 on the rheology of PLA

Abstract

Melt-polymer processing is conventionally employed for thermoplastic polymeric materials. The rheological behaviour of the polymer is then of critical importance to correctly accomplish the process. The effect of pressurized fluid additives (PFA), such as CO2 and N2, has been investigated in this work to determine the extension of their beneficial plasticization effect on PLA. In-line measurements performed by a custom-designed slit-die rheometer were conducted at different temperatures and PFA concentrations, and the viscosity values of PLA/PFA mixtures were experimentally determined and compared to those obtained when adding a commercial plasticizer, acetyltributylcitrate (ATBC), to PLA. Our results suggested that a twofold reduction of PLA viscosity is achievable using addition of 2.65 wt% pressurized CO2 respect to similar contents of ATBC. Furthermore, a decrease of 10 °C of the processing temperature could be attained when adding 1.70 wt% of CO2. This work aims at shedding light on the rheological behaviour that PLA experiences during assisted-melt extrusion processing, and on how more favourable energetic processing could be achieved by lowering temperature, if the appropriate type and concentration of PFA is employed during processing.