Comparative swelling behavior of various thermoplastic polymers

Metzger, A. P.; Matlack, J. D.

doi:10.1002/pen.760080206

Cited by 20 publications

(12 citation statements)

References 3 publications

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“…Theoretical prediction of melt elasticity dependence upon molecular structure for broad (and continuous, e.g., monomodal) MWD polymers in the shear rate range of commercial interest (and of die swell measurement capability) appears to be lacking, and published experimental data are far from consistent. [15][16][17][18][19][20][21][22][23] Moreover, serious difficulties are encountered in measuring the higher moments of MWD in these polymers. The larger part of the data which are available tends to indicate, though ambiguously, that die swell in this shear rate range increases with increasing RIW and with broadening MWD.…”

Section: Introductionmentioning

confidence: 99%

High‐density polyethylene melt elasticity—some anomalous observations on the effects of molecular structure

Mendelson

Finger

1975

J of Applied Polymer Sci

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synopsisThe die swell behavior of polymeric melts is a manifestation of melt elasticity of these materials and is of considerable commercial as well as fundamental importance. Hence, knowledge of the effect of such molecular variables as molecular weight (MW) and molecular weight distribution (MWD) on melt elasticity is important from both commercial and basic rheological points of view. The effect of these variables on melt elasticity of broad-distribution polymers in the shear rate region of commercial interest is not unambiguously known, with most published theory and experiment being applicable to the low-shear behavior of narrow-distribution polymers and blends thereof. There is indication that die swell increases with increasing MW and broadening MWD. However, the current investigation of carefully characterized broad-distribution HDPE materials prepared specifically to examine the effects of various molecular variables on melt elasticity does not support this contention and, in fact, provides consistent evidence for the opposite result, i.e., decreasing die swell with increasing MW or broadening distribution. The various samples studied were prepared by fractionation removal or addition of component molecular species or by polymerization designed to provide systematic variation of molecular parameters. Overall MWD's of the samples were characterized, and die swell behavior was determined at 2OOOC over a wide shear rate region in a high L/D capillary both with and without annealing of extrudates. The results are presented showing effects of specific moIecular variables.

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Section: Introductionmentioning

confidence: 99%

High‐density polyethylene melt elasticity—some anomalous observations on the effects of molecular structure

Mendelson

Finger

1975

J of Applied Polymer Sci

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“…Both parameters are normally measured with the aid of cone and plate or parallel plate rheometers. Extrudate swell has also been long used to measure melt elasticity: however, collection of true extmdate swell data may be tedious and time consuming: steady isothermal flow, abscence of gravitational sagging and swelling, and extrudate in a state of complete elastic recovery are conditions to produce reliable data as suggested first by Metzger and Matlack (7), Mendelson et al (81, and later by Utracki et al (9).…”

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confidence: 99%

Measurement of melt viscoelastic properties of polyethylenes and their blends—a comparison of experimental techniques

Xanthos

Tan²,

Ponnusamy³

1997

Polymer Engineering & Sci

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Two polyethylene resins (LDPE and HDPE) and their blends were characterized for dynamic shear rheology, extrudate swell in a capillary rheometer, and recoverable strain as measured by the Melt Elasticity Indexer in attempts to compare parameters related to the so‐called “melt elasticity” as obtained by different experimental techniques. Such parameters may be useful in screening materials for their melt processability. Data were obtained at equivalent shear rates/frequencies and different temperatures. With respect to the individual blend components, the LDPE resin with the lower Melt Index (MI) had higher storage modulus and Weissenberg number than the HDPE resin. However, by using criteria based on “recoil” and strain recovery, ranking was different with the LDPE resin shown to exhibit lower “melt elasticity.” In this case, extrudate swell data were found to correlate reasonably well with equilibrium recoverable strain data. With respect to blends, complex viscosity and storage modulus versus composition curves showed positive deviations from linearity, similar to those observed in melt heterogeneous blends. Similarities between the short time recoverable strain vs. composition and the storage modulus vs. composition curves suggest that similar morphological states may exist in the melt over the experimental times and conditions applicable to these different experimental techniques.

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“…Moreover, in comparing WRG and die swell data, we implicitly equate the average first normal stress difference in the capillary to the essentially unique value in the cone-and-plate instrument at a fixed calculated shear rate, and in calculating S , in the WRG measurement we ignore the current controversy over the "factor of two" [211 in eq. (7).…”

Section: Resultsmentioning

confidence: 99%

“…from the leading end of this strand and to report this as the extrudate diameter. However, it has previously been demonstrated in the case of polyethylene [7,11,191 that, if t h s extrudate is allowed to anneal at temperatures above its melting point, a further significant (up to as much as 100%) increase in the swelling iatio occurs due to the recovery of frozen-in strain. Therefore, in the work reported here, 1/2 to 3/4 in.…”

Section: Methodsmentioning

confidence: 99%

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Die swell and recoverable shear strain in polyethylene extrusion

Mendelson

Finger

Bagley

1971

J. polym. sci., C Polym. symp.

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The present paper treats die swell as unretarded recovery of elastic strain imparted during flow into and through the die. Three mechanistic models are developed. All three models treat the material as an elastic solid for the purpose of elucidating die swell, and two models utilize rubber‐like elasticity theory. Equations relating swelling ratio, recoverable shear strain (SR), axial normal stress, shear stress, and shear modulus are derived for the three models. While the forms of the results differ somewhat from model to model, the numerical results are quite similar. Experimental die swell data were obtained for four high density polyethylene resins in several large L/D capillaries using an Instron Capillary Rheometer. A procedure for obtaining equilibrium, or strain‐free, values of the swelling ratio by annealing the extrudates above the melting point is discussed. Values of SR and normal stress were calculated and compared to corresponding quantities obtained directly from measurements using a cone‐and‐plate Weissenberg Rheogoniometer. Excellent agreement between results from the widely divergent methods of measurement was obtained.

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Comparative swelling behavior of various thermoplastic polymers

Cited by 20 publications

References 3 publications

High‐density polyethylene melt elasticity—some anomalous observations on the effects of molecular structure

High‐density polyethylene melt elasticity—some anomalous observations on the effects of molecular structure

Measurement of melt viscoelastic properties of polyethylenes and their blends—a comparison of experimental techniques

Die swell and recoverable shear strain in polyethylene extrusion

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