Transport and mechanical properties of iPP–sPP fibers

Abstract

The drawing behavior of a blend of syndiotactic and isotactic polypropylene (iPP–sPP 50:50 w/w) was investigated at different temperatures and compared to that of pure polymers. The film of pure sPP showed that the presence of iPP allowed the blend to reach a much higher draw ratio. Fibers were obtained by drawing the blend at 110°C. The axial elastic modulus of the fibers was measured as a function of draw ratio up the highest λ = 10. The sorption and diffusion of dichloromethane vapors in the undrawn and drawn samples were studied in order to provide information about the structural organization of the amorphous phase. The elastic modulus of the fibers displayed a more-than-linear increase with the draw ratio, suggesting a good interconnection of the amorphous phases. The orientation of the chains with increasing λ determined a decrease of entropy and fractional free volume (FFV) and a tighter packing of the chains along the drawing direction, explaining the strong increase of the elastic modulus. The transport properties, which confirmed the mechanical properties, showed a stiffening of the amorphous phase after λ = 6, evidenced by a dual-type sorption isotherm for the fibers and a sharp drop in the zero-concentration diffusion coefficient. As a consequence, the permeability of the fibers was much lower than that of the unoriented sample. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 539–545, 2001