Hiroshi Yui

Regularly phase-separated structure in an injection-molded blend or isotactic polypropylene and high density polyethylene

Abstract High-density polyethylene (HDPE) is known to be immiscible with isotactic polypropylene (PP) in the quiescent state. In an injection-molded blend of PP HDPE (= 60 40 wt. ratio) , a regularly phase separated structure with periodic distance of about 0.15 μm was found. The regular structure could not be formed by a simple melt mixing of immiscible polymer pair but only by the spinodal decomposition (under zero shear rate in mold) from a single-phase mixture attained (by UCST depression or LCST elevation) in high shear fields in an injection machine. The shear-dependent mixing and demixing mechanism was supported by transmission electron microscopy: the volume ratio of PP-rich region and HDPE-rich region being different from the charge ratio and the HDPE crystal lamellae developed in the PP-rich region. The mechanism was also supported by microscopic observation of the structure development (characteristic to the late stage of spinodal decomposition) during isothermal annealing above the melting point of PP; i.e. bicontinuous structure with nice regularity developed and grew up self-similarly.

Study of factors affecting the formation of a gradient structure in acrylate copolymer/fluoro-copolymer blends

The effects of the solution concentration and the rate of solvent evaporation on the formation of gradient structures were examined for poly(2-ethylhexyl acrylate-co-acrylic acid-co-vinyl acetate) [P(2EHA-AA-VAc)]/poly(vinylidene fluoride-co-hexafluoro-acetone) [P(VDF-HFA)] blends. When the 30/70 P(2EHA-AA-VAc)/P(VDF-HFA) blend was prepared from 10 wt% THF solution, a gradient structure was not formed. When the 70/30, 50/50, and 30/70 P(2EHA-AA-VAc)/P(VDF-HFA) blends were prepared by casting from 5 wt% tetrahydrofuran (THF) solution onto poly(tetrafluoroethylene) (PTFE), the chemical compositions of the surface and bottom sides of the blends were different depending on the blend ratio and rate of solvent evaporation. Therefore, it was concluded that the formation of a gradient structure is strongly influenced by the solution concentration and the rate of solvent evaporation.

ATR-FTIR and SEM Gradient Study of Poly(2-ethylhexyl acrylate)/Poly (vinylidene fluoride-co-hexafluoro acetone) Blends

The segregation structure and the gradient structure of poly(2-ethylhexylacrylate) (P2-EHA)/poly(vinylidene fluoride-co-hexafluoro acetone) [P(VDF-HFA)] blends were confirmed by ATR-FTIR and SEM. For the P2-EHA/P(VDF-HFA) (50/50) blend, the P(VDF-HFA) and P2-EHA layers were observed at the free surface side and bottom side, respectively. The gradient structure was obtained for the P2-EHA/P(VDF-HFA) (30/70) blend. The domain morphology of a cross section of the P2-EHA/P(VDF-HFA) (50/50) blend was dramatically changed by the thickness of the blend film. Finally, we propose that the segregation structure and gradient structure formed in P2-EHA/ P(VDF-HFA) blends were caused by surface tension difference, rate of phase separation, rate of solvent evaporation, and molecular weight difference.