Fiber structure development in high-speed melt spinning of poly (L-lactide)s with various D-lactide contents and racemate polylactide

摘要

High-speed melt spinning of poly(L-lactides) (PLLA) copolymerized with a small amount of D-lactide was carried out. The orientation-induced crystallization of PLLA with the lowest D-lactide content started when the take-up velocity exceeded 4 km/min, and fibers with α -form crystals were formed. The crystallization in the spinning process was suppressed with an increase in the D-lactide content. On the other hand, in the high-speed melt spinning of racemate polylactide (r-PLA), α -form crystals and stereocomplex (SC) crystals were formed, and the relative amount of the SC crystals increased with an increase in the take-up velocity. In the annealing process of the as-spun r-PLA fibers obtained at 6 km/min, reduction of the α -form crystals and steep increase of the SC crystals started at around 110°C, whereas the α -form crystals was found to remain even at around 200°C. As the melting temperature (Tm) of α -form crystals is around 170 °C, it can be said that the α -form crystals started to decrease at a temperature lower than its Tm, however, a certain amount of α -form crystals remained even at a temperature higher than its Tm. Annealing of as-spun and drawn r-PLA fibers was carried out at 190°C, i.e. between the Tm of α—form and SC crystals. Birefringence of the as-spun fibers increased whereas that of the drawn fibers, which showed high birefringence after drawing at 70°C, decreased by the annealing and eventually both fibers showed similar birefringence.