Superstructure and mechanical properties of poly(L-lactic acid) microfibers prepared by CO 2 laser-thinning

Abstract

Poly(L-lactic acid) (PLLA) microfibers were obtained by a carbon dioxide (CO 2) laser-thinning method. A laser-thinning apparatus used to continuously prepare microfibers was developed in our laboratory; it consisted of spools supplying and winding the fibers, a continuous-wave CO 2-laser emitter, a system supplying the fibers, and a traverse. The laser-thinning apparatus produced PLLA microfibers in the range of 100–800 m min −1. The diameter of the microfibers decreased as the winding speed increased, and the birefringence increased as the winding speed increased. When microfibers, obtained through the laser irradiation (at a laser power of 8.0 W cm −2) of the original fiber supplied at 0.4 m min −1, were wound at 800 m min −1, they had a diameter of 1.37 μm and a birefringence of 24.1×10 −3. The draw ratio calculated from the supplying and winding speeds was 2000×. The degree of crystal orientation increased with increasing the winding speed. Scanning electron microscopy showed that the microfibers obtained with the laser-thinning apparatus had smooth surfaces not roughened by laser ablation that were uniform in diameter. The PLLA microfiber, which was obtained under an optimum condition, had a Young's modulus of 5.8 GPa and tensile strength of 0.75 GPa.