The Effect of Prehistory on Elongational Viscosity and on Crystallization of Running Filament in Melt Spinning

Abstract

ABSTRACT:Three polypropylene samples (sample A, B, and BIO) having different prehistory were prepared: sample A was prepared by quenching the melt screw extrudated, and samples B and B I 0 were prepared by isothermal crystallization from I% solution and from I 0% solution in xylene, respectively. The effects of prehistory on elongational viscosity and on crystallization were studied by a on-line measuring method in isothermal melt spinning and in melt spinning. The elongational viscosities were in the order sample A> sample BIO > sample B. The difference in the results of online measurement between samples A and B is very evident in 'the second region' along the spinning way which is the region from I 0 em to 35 em below the spinneret. In the last half of the second region, the elongational viscosity for sample B takes on a larger value than that of sample A. The crystallization for sample B begins at a point nearer to the spinneret or at higher temperature than that for sample A in this region, but the progress of crystallinity for sample A was more rapid than that for sample B. These results were compared with the data of quiescent crystallization, and are discussed in this paper in terms of the differences in melt structure and in crystal structure of polymers with different prehistories.KEY WORDS Polypropylene I Prehistory I Elongational Viscosity I Crystallization I Isothermal I Melt Spinning I Melt Structure I Entanglement / In a preceding paper/ the effects of prehistory were studied by measuring melt rheological properties and the physical properties of the spun filaments of two polypropylene samples of different prehistory. The first sample (sample A) was prepared by quenching extrudated melt screw. The second sample (sample B) was prepared by solution crystallizing from a 1% xylene solution. The results of shear viscosity, die swell and spinnability of the melts showed differences according to prehistory: the melt properties were affected by the difference in entanglement between sample A and B. The measurements of thermal shrinkage and tensile testing showed that spun filament A had a larger fraction of tie chain and that spun filament B was rich in the fold-type crystal fraction.spinning. Crystallization behavior was studied for both samples A and B. The relationships between crystallization and melt structure or crysral structure is discussed.In this paper, the effect of prehistory is examined by on-line measurements of the running filaments having different prehistory. The elongational viscosity of a melt having a different prehistory was measured by isothermal melt spinning and by melt EXPERIMENTAL MaterialsThe samples investigated in this paper were similar to those prepared in our earlier paper 1 and are summarized in Table I. The prehistory of the shear deformation was applied to each sample by a screw extruder; the extruded melt was then quenched in ice-water at the exit of the extruder (sample A). One half of an extruded sample was freed from the prehistory of shear deformation by dissolving ...

Elongational viscosity for miscible and immiscible polymer blends. II. Blends with a small amount of UHMW polymer

“…To compare the strain-hardening properties among samples, we use the term of strain-hardening viscosity ratio (SH), which is the ratio of the strain-rate-dependent nonlinear elongational viscosity ( nonlinear ) to the strain-rateindependent linear elongational viscosity ( linear ) at the same time. 1,4 We also use the critical strain c , where the strain-hardening property starts to appear. 4 So when SH is greater than 1, it means that the viscosity growth is strain-rate-dependent.…”

“…1,4 We also use the critical strain c , where the strain-hardening property starts to appear. 4 So when SH is greater than 1, it means that the viscosity growth is strain-rate-dependent. Figure 6 represents the strain-hardening viscosity ratio, SH, as a function of Hencky strain for PMMA, AS, homogeneous, miscible, and immiscible blends around the strain rate of 0.1 s Ϫ1 .…”

Constitutive relationships for polymeric materials with power-law distributions of relaxation times

“…Sufficiently small strain rates have reciprocals that are sufficiently large that they correspond to times that lie in the terminal region of the plot of relaxation modulus versus time. The corresponding stresses must approach their linear viscoelastic values; that is 2, (e) approaches unity• Figure 6, a plot by Koyama and Ishizuka of log 2, versus e for the low density polyethylene, Melt I, exem- plifies the conclusions noted above [18]. Figure 7 shows the linear relaxation modulus for this melt [19].…”

“…Koyama and coworkers [15][16][17][18] have defined this normalized stress as the "nonlinearity parameter," 2,, and have noted that for melts of low and high density polyethylene, polypropylene, polystyrene, and polybutene-1, that for each melt, a single relationship, 2, (e), often applies to a range of different strain rates, ~. The single relationship seems to hold even if the slope, "m", of the relaxation modulus, varies somewhat.…”

Flows of constant stretch history for polymeric materials with power-law distributions of relaxation times

“…(2) can account for a number of empirical equations that have been found applicable to polymer melts. These include the Cox-Merz rule [2] that the complex viscosity equals the steady-state viscosity, Bersted's predictions [3] of steady-state shear viscosity and normal stress difference from linear viscoelasticity, as well as Koyama and coworkers' observation [4] that the ratio of the nonlinear to the linear time-dependent elongational viscosity is independent of strain rate.…”