T. Kikutani; "Molecular Orientation&Crystallization...", 22.4, 13:40
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  • T. Kikutani; "Molecular Orientation&Crystallization...", 22.4, 13:40

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 Faculty of Engineering and Natural Sciences

 

SEMINAR ANNOUNCEMENT

 

 

 

 

Molecular Orientation and Crystallization of Various Types of

 

Polylactide in Fiber Processing

 

 

Takeshi Kikutani

 

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