Faculty of Engineering and Natural Sciences
Molecular Orientation and Crystallization of Various Types of
Polylactide in Fiber Processing
Tokyo Institute of Technology, Department of Organic and Polymeric Materials
High-speed melt spinning (HSS) of various types of polylactides (PLAs) including poly(Llactide) s with various D-lactide contents and racemate polylactide (r-PLA), which is a blend of equal amounts of poly(L-lactide) and poly(D-lactide) molecules, was carried out and the structure and properties of the as-spun fibers were investigated. The highest take-up velocities attained for poly(L-lactide)s with low, middle, and high D-lactide contents (PLA-L, PLA-M, and PLA-H) were 10, 9, and 8 km/min, respectively. Molecular orientation of as-spun fibers increased with an increase in the take-up velocity, whereas the fibers obtained at high take-up velocities showed lower orientation with an increase in the D-lactide content. Distinct crystalline reflections appeared in WAXD patterns of PLA-L and PLA-M fibers spun at 5 and 6 km/min and higher, respectively. On the other hand, PLA-H fibers were found to be amorphous up to the highest take-up velocities attained. HSS of r-PLA could be carried out up to 7.5 km/min. In the fiber structure analysis, particular attention was paid to the formation of stereocomplex (SC) crystals, because this crystal form has a melting temperature about 60 K higher than the homocrystals. Highly oriented and highly crystallized fibers containing the a-form and SC crystals were obtained when the take-up velocity exceeded about 4 km/min. The amount of SC crystal was higher under the spinning conditions where higher tensile stress can be imposed to the spinning line. Annealing of the fibers obtained at high-take-up velocities at a temperature between the melting temperatures of a-form and SC crystals yielded the fiber structure mainly consisting of highly oriented SC crystal. In-situ WAXD measurement of r-PLA fibers during heating process revealed that the formation of SC crystal starts from lower temperatures in the fibers prepared at higher take-up velocities. Drawing and annealing of these fibers under various conditions suggested that the “seeds” for the formation of SC crystals formed during the high-speed spinning process are intact in the drawing process.
Wednesday, 22nd of April, 13:40, FASS 1096