Polypropylene/nylon 6 blends: Phase distribution morphology, rheological measurements, and structure development in melt spinning

Abstract

SynopsisA series of polypropylene (PP)/nylon 6 (N6) blends of composition 75/25,50/50, and 25/75 have been prepared in a screw extruder combined with a Koch static mixer. The phase morphology was observed with a scanning electron microscope. The influence of heating in the reservoir of a rheometer followed by subsequent extrusion through a capillary on the phase morphology was investigated. Phase size growth as a function of time was observed under quiescent and mild deformation rate conditions. The discrete phase size was observed to decrease with increasing extrusion rate through dies. The shear viscosity and principal normal stress difference of the blends were measured as a function of composition. The crystalline orientation of both polypropylene and nylon 6 in blend melt spun fibers was characterized by wide angle X-ray diffraction and interpreted in terms of Hermans-Stein orientation factors. The orientation increases with drawdown ratio. The orientation factors for the polypropylene phase vary with spinline stress in a manner independent of composition and identical to that for pure polypropylene. Extracting melt spun blend fibers with formic acid has produced small-diameter polypropylene minifilaments with diameters of the order of microns.

Interfacial tension of immiscible polymer blends: temperature and molecular weight dependence

“…dispersed particle size) in incompatible polymer blends is directly proportional to the interfacial tension. [2][3][4] Fundamentally, interfacial tension is a thermodynamic property of the system which may be calculated directly from statistical thermodynamic theories. Experimental measurement of interfacial tensions is therefore a straightforward means for evaluating the validity of these theories.…”

On modeling the composition dependence of the bulk viscosity of immiscible polymer blends

“…Thus, I conclude that the viscosity data of immiscible polymer blends reported in the literature [2][3][4][5][6][7][8], which were determined from the use of a plunger-type capillary viscometer with the aid of Eq. 4 with or without the Bagley end-correction n B , are subject to serious criticism.…”

“…11 with or without the Bagley end-correction does not make sense for dispersed immiscible polymer blends. Nevertheless, some investigators [2][3][4][5][6][7][8] did just that without realizing the fact that Eq. 4 is only valid for homogeneous fluids and that the morphology (the state of dispersion) of an immiscible polymer blend keeps changing, undergoing very large drop deformations and possibly drop breakup (see Figs.…”

“…6). In the past, several research groups [2][3][4][5][6][7][8] mistakenly used a plunger-type viscometer (e.g., Instron viscometer) to erroneously calculate the shear viscosities of immiscible polymer melts using Eq. 4, with or without n B .…”

“…The purpose of this review article is to clear the confusion in the literature on the following two issues. First, I will point out that measurement of the total pressure drop across the entire length of a capillary die, while using a plunger-type viscometer, to determine the bulk viscosity of immiscible polymer blends forming two phases, which was reported by some research groups [2][3][4][5][6][7][8], is not justified. Second, I will point out that it is of no rheological significance to determine the composition dependence of the bulk viscosity of immiscible polymer blends using such empirical expressions as inverse additivity or logarithmic additivity relationships, which were used by some investigators [5,6,[9][10][11][12][13].…”