Characterization of poly(L‐lactic acid) fibers produced by melt spinning

Abstract

AbstractBiodegradable poly(L‐lactic acid) (PLLA) fibers were processed by a two‐step melt‐spinning method (melt extrusion and hot draw) from PLLA with three different viscosity‐average molecular weights (494,600, 304,700, and 262,800). Before spinning, the polymer flakes were first milled into powders and dried under vacuum. Viscosity‐average molecular weight of PLLA following the fabrication process was monitored. Tensile properties of as‐spun and hot‐drawn fibers were investigated. Morphology of the PLLA fibers was viewed under a scanning electron microscope. Crystallinity of these fibers was assessed by thermogram analysis of differential scanning calorimetry. Results showed that the extent of decrease in the viscosity‐average molecular weight of PLLA dropped sharply by 13.1–19.5% during pulverization and by 39.0–69.0% during melt‐extrusion. The hot‐draw process in this study had a little effect on the viscosity‐average molecular weight of PLLA. Smoother fibers could be obtained for the die temperature at least 230°C for raw materials with higher crystallinity (more than 75%) and at least 220°C for raw materials with lower crystallinity (about 60%). The as‐spun fibers showed crystallinity of 16.5–22.8% and the value increased to 50.3–63.7% after hot draw. Tensile moduli of the as‐spun fibers were in the range of 1.2–2.4 GPa, which were raised to 3.6–5.4 GPa after hot draw. The final PLLA fibers with 110–160 μm diameters showed tensile strengths of 300–600 MPa. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 251–260, 2001