Browsing by Author "Yamamoto, Masaki"

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Effect of the melt-mixing condition on the physical property of poly(L-lactic acid)/poly(D-lactic acid) blends
(Journal of Applied Polymer Science, 2017) El-Khodary, Esraa; Fuku, Yoko; Yamamoto, Masaki; Yamane, Hideki
The effect of the mixing condition in a mill-type mixer on the thermal property and the crystal formation of the poly(L-lactide)/poly(D-lactide) blends is investigated. The blends melt-mixed at 200 and 210 8C under application of a high shear flow tend to show a single melting peak of the stereocomplex crystal (SC) in the differential scanning calorimetry first and second heating processes without indicating the trace of the melting of homo-chiral crystal. The mixing at an elevated temperature causes a serious thermal degradation. Further kneading of the blends at an elevated temperature higher than Tm of SC causes the transesterification between the same enatiomeric chains forming block copolymers of L- and D-chains. This block copolymer acts as a nucleating agent of SC and the compatibilizing agent between poly(L-lactide) and poly(D-lactide) and promotes the formation of SC. VC 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45489.
Electrospinning and Characterization of Aligned Nanofibers from Chitosan/Polyvinyl Alcohol Mixtures: Comparison of Several Target Devices Newly Designed
(SOC FIBER SCIENCE TECHNOLOGY, 2011) Afifi, Amalina M.; Yamamoto, Masaki; Yamane, Hideki; Kimura, Yoshiharu; El Salmawy, Ahmed; Nakano, Shigeyuki
Electrospinning of pure chitosan or chitosan/poly(vinyl alcohol) (PVA) (blend) was carried out with an optimization of the electrospinning conditions. The electrospinning of the pure chitosan was only possible at a relatively high electric field of 5 kV/cm into fibers with a diameter as thick as 30 gm, and its reproducibility was very poor. Blending of PVA into chitosan significantly improved the spinnability and the chitosan/PVA blend fiber was electrospun for further characterization. Several target devices were designed and examined to collect aligned nanofibers of chitosan/PVA. The most efficient was a rotating collector having grounded short wire bars arranged on a drum. Over 90 % of electrospun fibers were collected in parallel to the take-up direction with this collector. The fiber alignment was further improved with increasing the collector rotation speed up to a maximum speed of 4.7 m/s. The aligned chitosan/PVA fibers were subjected to drawing to 1.5 times and the crystallization of chitosan fractions was induced without indicating the clear crystal orientation.
Physical Properties of Stereocomplex Type Poly (lactic acid) Biaxially Drawn Films
(The Society of Fiber Science and Technology, Japan, 2017) El-Khodary, Esraa; Fukui, Yoko; Yamamoto, Masaki; Yamane, Hideki
Equal amounts of PLLA and PDLA were melt-mixed in a mill type mixer at 190 ̊C and further extruded at 250 ̊C. The blend obtained was compression molded into films and biaxially drawn and annealed. The changes in various physical properties such as mechanical and thermal properties and the higher-order structure of the films in the biaxial drawing and annealing processes were investigated. The biaxially drawn films showed a broad crystalline WAXD reflection similarly to the uniaxially drawn PLLA/PDLA blend fibers and the application of annealing at 190 ̊C completely changed the reflections into those of SC. The higherorder structure was completely transferred into SC after annealing at an elevated temperature. The mechanical property was improved by the biaxial drawing and the annealing for short period of time, and the films showed an excellent thermal resistance. However the annealing for a long period deteriorated the mechanical property.