Fused Filament Fabrication of Poly(l-Lactic Acid): A Thermal Analysis Approach to Optimize Processing Conditions

Fused filament fabrication (FFF) is an inexpensive and flexible additive manufacturing technology, widely used for thermoplastic polymers to produce parts with complex geometry. However, some thermoplastics may undergo thermal degradation upon FFF, with loss of material properties. This is the case of poly(L-lactic acid) (PLLA), a biodegradable and bio-based semicrystalline polyester, largely used in FFF. For the temperature-sensitive polymers, FFF processing should be optimized, to limit as much as possible thermal degradation. In this work, the minimum temperature and time needed to melt PLLA, thus the best conditions to limit thermal degradation, have been determined by calorimetry. The attained results were used to produce 3D printed parts using a PLLA filament: the analysis of the effect of nozzle temperature and extrusion rate (the main processing parameters linked to polymer melting kinetics) on the thermal properties of the printed parts confirmed the need of proper setting of the melting conditions to optimize properties of FFF 3D printed products. Modeling and simulation of flow and temperature fields inside the liquefier, accounting for the filament melting, are also proposed and used to evaluate the molten fraction in several printing conditions.