Prediction of rheological properties of well‐characterized branched polyethylenes from the distribution of molecular weight and long chain branches

Pedersen, Sven; Ram, A.

doi:10.1002/pen.760181303

Cited by 17 publications

(15 citation statements)

References 19 publications

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“…This model extends a previous approach to predicting the rheological properties of linear [47,50] and branched [31] PEs. Basically, Bersted considered that PEs with very low levels of LCB (less than 0.1 LCB / 10 000 C) behave as blends of linear (HDPE) and branched (LDPE) species.…”

Section: Quantitative Prediction Of Lcb From Rheological Data: Rheolomentioning

confidence: 65%

“…However, despite extensive work on the effects of LCB on the viscoelastic properties of these types of material in the melt in the 1960s, there is no unified picture of their dependence on molecular variables. The following general properties were established for a moderate to high degree of LCB (>> 1 LCB/10 4 carbon atoms): a) lower Newtonian or zero-shear viscosity η o and a higher critical shear rate o γ& for the onset of shear thinning behaviour than linear polymers of the same weightaverage molecular weight, M w [3][4][5][6][7][8][9][10][11][12][13][14]; b) less intense pseudoplastic behaviour [11,[15][16][17]; c) increased activation energy of flow, E a [18][19][20][21][22][23][24][25][26][27][28][29]; and d) enhanced melt elasticity expressed in terms of first normal stress difference N 1 , steady-state compliance J e o and extrudate swell d j /D [4,5,12,13,16,17,[30][31][32].…”

Section: Conventional Polymersmentioning

confidence: 99%

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Effect of long chain branching on linear-viscoelastic melt properties of polyolefins

et al. 2002

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Abstract:The aim of this review is to provide evidence that rheological testing is a potent tool for characterising polymers in the melt. An effort has been made in order to gather results in conventional and model polyolefins, and correlating them with phenomena occurring at the molecular level. We have focused our interest on long chain branching (LCB). In the case of materials containing long side-chain branches, strong effects on viscosity, elastic character and activation energy of flow are general features. Literature results mostly indicate that the effect of polydispersity on these parameters could be very similar to that expected due to the presence of LCB -notwithstanding that the effects of LCB seem to be stronger than those due to polydispersity for a given molecular weight. Different relaxation processes appear as a consequence of the presence of LCB: slower terminal relaxation behaviour than of linear counterparts, and faster additional branch relaxation at higher frequencies, clearly distinguishable from polydispersity effects. To measure the amount of LCB from limited viscoelastic data and molecular properties seems to be a suitable instrument to explain the rheological features of the different polymers, but it fails when the results are compared with measured values of LCB density in model polymers. The actual framework leads us to say that the number of branches is less important than the topology itself. Therefore, the position and architecture of the branches along the polymer main chain are the main factors that control the rheology of the material.

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Section: Quantitative Prediction Of Lcb From Rheological Data: Rheolomentioning

confidence: 65%

Section: Conventional Polymersmentioning

confidence: 99%

Effect of long chain branching on linear-viscoelastic melt properties of polyolefins

et al. 2002

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“…They also probed that this relation is a master curve for linear polybutadienes of different molecular weight, but not for star-branched samples; the values of J , is of the same order of magnitude as conventional LDPEs 52) . It is not possible to extract straight conclusions from these data, however we have to remind that several authors 36,51,[53][54][55][56] …”

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confidence: 97%

Rheological criteria to characterize metallocene catalyzed polyethylenes

Vega

Fernández

Santamarı́a³

et al. 1999

Macromol. Chem. Phys.

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SUMMARY: Dynamic viscoelastic and capillary extrusion rheometry measurements were carried out with a series of 13 metallocene catalyzed polyethylenes and copolymers of ethene and 1-hexene. The structural parameters were analyzed by size exclusion chromatography (SEC) and 13 C NMR, showing that the molecular weights range from M -w = 80 000 to 308 000, the polydispersity index from 2 to 3.5 and the degree of short chain branching (SCB) from 0 to 13.8 SCB/1 000 C. In order to extract the maximum information from the experimental data, the following rheological methods were used: a) Viscosity and relaxation time dependence on molecular weight M ). d) log G 9 versus log G 9 9plots. e) Storage compliance J 9 dependence on storage modulus G 9 . f) Phase angle d dependence on complex modulus G*. g) Relaxation spectra. h) Dependence of the exponent n of the power law model for the viscosity function g (_ c ) on of molecular weight. i) Analysis of the critical rate for sharkskin. These methods, except the last one, allow to separate the samples into three different groups, at least when low frequencies (below 10 -1 Hz) or times higher than 10 s are involved. The definition of these groups cannot be undertaken considering only the molecular parameters obtained by SEC and 13 C NMR. Analyzing our rheological results in comparison with long chain branched polyethylenes (LCB) and looking at the theoretical aspect of the dynamics of long branched chains, we assume that among our samples there are five linear (non-LCB, Group I) polyethylenes and two groups of slightly long chain branched polyethylenes, which differ in the number of branches.

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“…Model 2: The Method of Pedersen and Ram [8] The primary equations in this method use one relating viscosity to a lumped structure parameter (gM) W Ã where A and B are constants:…”

Section: Model 1: Multiple Linear Regressionmentioning

confidence: 99%

Size Exclusion Chromatography of Branched Polyethylenes to Predict Rheological Properties

Balke¹,

Mourey²,

Lusignan³

2006

International Journal of Polymer Analysis and Characterization

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Three methods of predicting dynamic viscosity of branched polyethylenes from size exclusion chromatography (SEC), refractive index=light-scattering detection data were examined: relating parameters in the Cross viscosity equation to molecular weight averages, use of a mixing rule, and a method based on the similarity of the cumulative molecular property distributions to a dimensionless viscosity versus frequency plot. The use of accurate SEC data was emphasized. The third ''curve similarity'' method provided the most promising results. The use of cumulative g 0 (the molecular contraction factor based on intrinsic viscosity) distributions, in addition to cumulative molecular weight distributions, enable very useful sample comparisons.

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Prediction of rheological properties of well‐characterized branched polyethylenes from the distribution of molecular weight and long chain branches

Cited by 17 publications

References 19 publications

Effect of long chain branching on linear-viscoelastic melt properties of polyolefins

Effect of long chain branching on linear-viscoelastic melt properties of polyolefins

Rheological criteria to characterize metallocene catalyzed polyethylenes

Size Exclusion Chromatography of Branched Polyethylenes to Predict Rheological Properties

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