High Strength and High Thermal Stability of Polylactide Fibers with Stereocomplex Crystal Obtained by High-Speed Melt Spinning and Subsequent Drawing and Annealing Processes

为了阐明分子取向对消旋体聚乳酸晶体结构变化的影响，研究了高速熔融纺丝纤维在加热和冷却过程中的结构形成。通过原位WAXD、DSC和双折射测量分析了外消旋体聚乳酸纤维和膜在加热和冷却过程中晶体结构的变化。在4 km/m in的卷取速度以上，观察到α晶型和立体络合物晶体共存，且立体络合物晶体的反射强度随卷取速度的增加而增加。在加热过程中，初生纤维的α晶型在80℃左右开始增加，这与初生纤维的分子取向无关。当α晶型开始减弱时，初生纤维的立体络合物晶体出现反射强度。即使在170kJ的α晶相熔融温度下，也证实了α晶相的存在。在70℃拉伸条件下，纤维中也观察到了PZT晶型的生长。拉伸纤维的双折射在2 km/min时达到最大值，并随卷绕速度的增加而减小。而高速纺丝纤维经190℃退火热处理后，双折射降低，接近于高速纺丝纤维在相同温度下直接退火得到的双折射。

To clarify the effect of molecular orientation on crystal structure change of racemate polylactide, structure formation of fibers obtained by high-speed melt spinning was investigated during heating and cooling processes. Changes in crystal structure of racemate polylactide fibers and films were analyzed by in-situ WAXD, DSC, and birefringence measurements during heating and cooling processes. The co-existence of α-form and stereocomplex crystals was observed above the take-up velocity of 4 km/min, and reflection intensity of stereocomplex crystal increased with an increase in the take-up velocity. During heating process, α-form crystals of as-spun fibers started to increase at around 80℃ which was independent of molecular orientation of as-spun fibers. The reflection intensity of stereocomplex crystal of as-spun fibers appeared when α-form crystal started to decrease. Existence of the α-form crystals in these fibers was confirmed even at melting temperature of α-form crystal of 170℃. The development of α-form crystal was also observed in the fibers drawn at 70℃. Birefringence of drawn fibers showed the highest value at 2 km/min, and decreased with increasing take-up velocity. On the other hand, birefringence of drawn decreased by annealing at 190℃ and became close to the birefringence of fibers obtained by directly annealing the high-speed spun fibers at the same temperature.