Effects of a rotary shear field on the interlayer bond and mechanical properties of polylactide fabricated using fused filament fabrication

Polylactide (PLA) is a kind of distinct semicrystalline polymer and widely applied for fused filament fabrication (FFF), because of its low price and high mechanical properties. But the bad interface of FFF printed PLA parts and their high mechanical anisotropy limit their industrial application deeply. In this work, an innovative FFF 3D printer with a rotary shear head was developed to control the interface and crystallization of FFF printed PLA parts. Compared with traditional FFF, the tensile strength of specimen fabricated via the rotary shear field increases from 21.1 MPa to 59.3 MPa, and the degree of mechanical anisotropy decreases from 0.41 to 0.09. As indicated by the meso-structure morphologies, not only the triangular voids between adjacent strands were disappeared, but also the randomly-distributed shish-kebab structure crystals and fibrils were obtained by the rotary shear field treatment. And the DSC results showed a high crystallinity value of 26.1% of specimen with the rotary shear field treatment. Therefore, the good interface, randomly-distributed crystals and high crystallinity contribute the effort to increase the tensile strength and decrease the degree of mechanical anisotropy of FFF printed PLA parts.