The effects of thermal annealing on the performance of material extrusion 3D printed polymer parts

This article presents the effects of thermal annealing at elevated temperatures (> glass transition temperature Tg) on the performance of polymer parts via material extrusion 3D printing. Both semi-crystalline and amorphous filaments were used. As-printed parts were designed to be amorphous and then annealed at 60, 110 and 150 °C for different durations ranging from 50 to 6400 s. The flexural strength and Young’s modulus increased by a maximum of approximately 10%. The increase was ascribed to crystallisation development during annealing, as confirmed by thermal and morphology characterisations. Hence, this effect was only observed with semi-crystalline materials. On the other hand, all the annealed parts expanded in the thickness direction and shrank in the perpendicular plane. The maximum linear strain reached 20%, while the volume strain was negligible. These morphology changes after annealing reversed the strain-hardening of the strand and led to inferior strand performance against local tensile deformation. The degradation can outweigh the benefits of crystallinity development. For amorphous parts, the degradation reached approximately 25% in both the flexural strength and the modulus.