Can the melt flow index be used to predict the success of fused deposition modelling of commercial poly(lactic acid) filaments into 3D printed materials?

The melt flow index (MFI) of seven commercial poly(lactic acid) (PLA) grades is investigated in view of 3D printing quality. A threshold value of 10 g (10 min)(-1) (2.16 kg; ISO 1133) is put forward for a successful printing (190-220 degrees C), enabling a fast and practical screening of PLA materials. It is however shown that a sole focus on MFI is insufficient, as the plasticiser type and crystallinity also play a role after the polymer melt deposition. The latter is supported by scanning electron micromorphology and differential scanning calorimetry measurements. In particular, blending with poly(hydroxyl butyrate) (PHB; 20 m%) allows to control both MFI and crystallinity without the need for annealing.