STEREOCOMPLEX FORMATION BETWEEN ENANTIOMERIC POLY(LACTIC ACID) .8. COMPLEX FIBERS SPUN FROM MIXED-SOLUTION OF POLY(D-LACTIC ACID) AND POLY(L-LACTIC ACID)

To obtain poly (lactic acid) (PLA) complex fibers, spinning was performed by wet and dry methods from 5-10 g/dL chloroform solutions of poly(D-lactic acid) (PDLA) and poly(L-lactic), both with a viscosity-average molecular weight of 3 x 10(5). The dope was extruded from a mono-hole nozzle into coagulation baths from ethanol and chloroform for wet spinning and into a drying column kept at 60-degrees-C for dry spinning. Scanning electron microscopic observation of the as-spun fibers showed that the surface of the wet-spun fiber had large basins with diameters of 50-100 mum and many pores with diameters from sub mum to 10 mum, whereas the surface of dry-spun fiber had a microporous structure with the pore diameter of 1-3 mum. The tensile strength of the wet-spun complex fiber was very low and could not be drawn at high temperatures, in contrast to the dry-spun fiber. The tensile strength of dry-spun complex fiber increased upon hot drawing and showed the tensile strength of 94 kg/mm2 by drawing at 160-degrees-C to the draw ratio of 13. Differential scanning calorimetry revealed that the complex fibers contained both the stereocomplex crystallites (racemic crystallites) and the crystallites of the single polymers, PDLA and PLLA, regardless of the spinning methods. The ratio of the racemic crystallites to the single-polymer crystallites increased with the draw ratio of the com lex fiber. (C) 1994 John Wiley & Sons, Inc.