Masahiro Naiki

The effect of talc on the crystallization of isotactic polypropylene

Isotactic polypropylene (iPP) has been crystallized in the presence of talc under the quiescent state and shear flow of injection molding. The resulting morphology has been investigated by means of polarizing microscopy, transmission electron microscopy, and wide angle X-ray diffraction. In the quiescent state, the iPP lamellae grew from the surface of talc and the transcrystalline region was formed at the interface between iPP melt and the talc. The nucleation of iPP was very frequent on the cleavage plane of talc. The X-ray diffraction pattern of the transcrystal showed a*-axis orientation to the crystal growing direction. In injection-molded samples of the talc-filled iPP, the morphology of lamella growing from talc appeared as same as that of the transcrystal. However, the crystalline orientation of injection-molded talc-filled iPP, in which the b axis was oriented to the thickness direction and the a* and the c axis was oriented to the flow direction, was quite different from that of the transcrystal. This b-axis orientation results from the orientation of the plate plane of talc, which induces the nucleation and the crystallization under shear flow.

Crystal ordering of α phase isotactic polypropylene

Abstract Structural ordering from the α1 to the α2 phase of isotactic polypropylene has been investigated. The DSC studies showed that reorganization or recrystallization occurred in the wide endothermic region. In the high-temperature X-ray experiment of the sample annealed at 135°C, the 231 and 161 reflections ascribed to the α2 phase began to increase from 160°C and to decrease above 172°C. The b-axis length and the angle β of the unit cell increased up to 155°C and decreased afterward. The latter decrease was well correlated with an increase in the α2 phase. The α2 fraction increased in the temperature region where the degree of overall crystallinity decreased. Reorganization or recrystallization into the α2 phase is thus considered to occur with the fusion of the α1 phase, and the growth of the α2 phase in the solid state seems to be difficult.

Crystallization of α and γ phases in isotactic polypropylene with low ethylene content: Isothermal crystallization and secondary crystallization

Crystallization and melting behaviors of isotactic polypropylene (iPP) with low ethylene content during an isothermal process and on heating just after it are investigated by means of in situ x-ray diffraction. At every isothermal temperature investigated here, the formations of α and γ phases are confirmed. The ratio of γ to α increases with an increase in isothermal temperature. On heating just after the isothermal process, the γ starts melting at a lower temperature than the α. This may be due to the small crystallite size of the γ crystallization during the isothermal process. On cooling after the completion of the isothermal crystallization, the secondary crystallization accelerates, and the γ phase crystallizes predominantly. The fractionation is considered to occur in the primary crystallization during the isothermal process. The low-molecular-weight portion of the materials, which remained in amorphous regions of the spherulite during the isothermal process, crystallizes into the γ phase in the secondary crystallization. Furthermore, the fractionation behavior seems to be enhanced at higher temperatures.

Chain-Folding Conformations in Isotactic Polypropylene.

α型イソタクチックポリプロピレンのchain-foldingの構造について考察した. 結晶の (100) 面および (140) 面における分子鎖のfold部分のコンホメーションを, 分子動力学および分子力学計算によって求めた. fold部分のエネルギーはfold部分のプロピレン連鎖数が3個ごとに極小値をとる周期性を示した. fold部分でらせんの巻き方向が反転する様子を主鎖炭素原子の二面角の変化として表した. この結果, 結晶格子中のらせんの巻き方向とメチル基の上下の向きの規則性を満足しながら, コンホメーションの変化のみで分子鎖が折りたたまれている様子を明示できた.