Fused filament fabrication of copolyesters by understanding the balance of inter- and intra-layer welding

Abstract

To extend the diversity of commercial materials relevant for fused filament fabrication (FFF), the relation of nozzle temperature and layer thickness with respect to final product mechanical performance is examined for the less studied group of (co)polyesters, considering tensile and impact strength and microscopic imaging. It is demonstrated that with limited polymer degradation, one can focus on increasing the layer height (from 0.1 to 0.3 mm) by tuning of the contribution of inter-layer welding, whereas with significant degradation, a lower layer height (0.1 mm) is needed to exploit the contribution of intra-layer welding for which a higher nozzle temperature (e.g. 260°C) is beneficial. The relevance of degradation is studied by both melt flow index and rheological analysis. The study ultimately provides the best FFF parameters for three commercial copolyesters and highlights the competition of inter- and intra-welding as a key microscopic material design strategy.