Flow-induced crystallization of piezoelectric poly(L-lactide) fibers by a one-step melt-spinning process

Piezoelectric poly(L-lactide) (PLLA) fibers, exhibiting high molecular chain orientation, are promising for biomedical applications. Chain orientation decreases due to fast relaxation during melt–spinning process, which implies that a second process to induce piezoelectric chain morphology is usually necessary. This work introduces a one–step melt–spinning process of piezoelectric PLLA fibers, spun directly from the melt, employing a rheological guidance for the selection of PLLA type and process parameters, based on Rouse's relaxation time. The chain orientation and the relaxation time increased with the optical purity and average molecular weight of PLLA. The reduction of extrusion temperature from 180 °C to 150 °C facilitated in a significant way the preservation of chain orientation, and the impact of the elongation rate was as well intensified. Combining high elongation rates of ≤ 29 s–1 and reduced extrusion temperature of 150 °C led to flow–induced crystallization of oriented crystals directly from melt in a single step. This fiber exhibited piezoelectric properties in form of a deflection of 1.9 ± 0.3 µm when applying an open–circuit voltage of 210 V. The piezoelectric response was similar to that of a fiber, melt–spun at high extrusion temperature of 180 °C, with additional post-annealing in a second step.