Effect of Post-Drawing Thermal Treatment on the Mechanical Behavior of Solid-State Drawn Poly(lactic acid) (PLA) Filaments

In this work, two commercial extruded filaments for 3D printing obtained from different NatureWorks PLA resins (Ingeo™ Biopolymer 3D850 and Ingeo™ Biopolymer 4043D) were solid-state drawn at varying temperatures and subsequently heat treated by annealing. The aim was to analyze the effect of post-processing of industrial fibers (solid-state drawing and annealing treatment) with varied composition (PLA grades with different contents of D-isomer) on the mechanical performance and thermal stability of the obtained PLA fibers. Morphological, thermal, and mechanical characterizations were performed for the undrawn filaments and drawn fibers, both before and after heat treatment. Drawn fibers presented a fibrillar core–shell structure, and their mechanical properties were greatly improved with respect to undrawn filaments in accordance with their higher crystallinity. The resin with the higher content of D-isomer (4043D) resulted in lower crystallinities with a subsequent decrease in mechanical properties. After heat treatment, drawn fibers exhibited completely different behaviors depending on the PLA resin, with 3D850 fibers being much more stable than 4043D fibers, which underwent molecular orientation upon drawing rather than crystallization. The solid-state drawn fibers obtained herein are comparable to commercial fibers in terms of mechanical properties.