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

Biodegradable poly(L-lactic acid) (PLLA) fibers were processed by a two-ste p melt-spinning method (melt extrusion and hot draw) from PLLA with three d ifferent viscosity-average molecular weights (494,600, 304,700. and 262,800 ). Before spinning, the polymer flakes were first milled into powders and d ried under vacuum. Viscosity-average molecular weight of PLLA following the fabrication process was monitored. Tensile properties of as-spun and hot-d rawn fibers were investigated. Morphology of the PLLA fibers was viewed und er a scanning electron microscope. Crystallinity of these fibers was assess ed by thermogram analysis of differential scanning calorimetry. Results sho wed that the extent of decrease in the viscosity-average molecular weight o f 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 eff ect on the viscosity-average molecular weight of PLLA. Smoother fibers coul d be obtained for the die temperature at least 230 degreesC for raw materia ls with higher crystallinity (more than 75%) and at least 220 degreesC for raw materials with lower crystallinity (about 60%). The as-spun fibers show ed 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 fiber s with 110-160 mum diameters showed tensile strengths of 300-600 MPa. (C) 2 001 John T;Wiley & Sons, Inc.