Influence of long‐chain branching on the viscoelastic properties of low‐density polyethylenes

Wild, L.; Ranganath, R. V.; Knobeloch, D. C.

doi:10.1002/pen.760161206

Cited by 55 publications

(25 citation statements)

References 8 publications

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“…The molecular weights of the polymers were estimated following the standard calibration procedure using monodisperse polystyrene samples and the corresponding Mark-Houwink coefficients for polystyrene and linear polyethylene in TCB. [12,13] The corresponding coefficients for EPDM in TCB were not found in the bibliography, so the molecular weights must be only considered qualitatively.…”

Section: Experimental Partmentioning

confidence: 99%

Characterization of Metallocene Epdm Terpolymers with High Diene and Propylene Content Crosslinked by Dicumyl Peroxide and β‐Radiation

Nicolás

Ressia

Vallés

et al. 2004

Macro Chemistry & Physics

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Summary: Two metallocene EPDMs with the same weight fraction of ethylene but differing in diene content were crosslinked, either by dicumyl peroxide (DCP) or β‐radiation. The effect of different diene and propylene content on the molecular structure and the mechanical properties once the materials were crosslinked was studied. The final gel content was very high due to the large level of unsaturations. The crosslinking process was monitored by FTIR spectroscopy by following the decay of unsaturations and the variation of the carbonyl groups that are related to the oxidation grade. It was found that β‐radiation crosslinked samples exhibited a lower oxidation grade than those crosslinked by DCP. An oscillant disc rheometer was employed to follow the evolution of the rheological properties, the scorch time, and the time corresponding to full cure during the crosslinking reaction with DCP. In addition, in order to characterize the state of cure we have studied the rheological properties in shear employing a dynamic parallel plate geometry. These results were correlated with those obtained from the molecular characterization of the soluble fraction by size exclusion chromatography. The experiments indicate that, at low irradiation doses, there is a high rate of chain scission reactions that cause an important decrease in storage modulus. Whereas, at high irradiation doses the rate of chain scission reactions diminishes, thus the storage modulus increases but it still remains at lower levels than those corresponding to the original terpolymers. The tensile properties, hardness (Shore A) and compression set tests also suggest the presence of chain scission reactions.Storage modulus (G′) versus frequency for a β‐irradiated sample.magnified imageStorage modulus (G′) versus frequency for a β‐irradiated sample.

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Section: Experimental Partmentioning

confidence: 99%

Characterization of Metallocene Epdm Terpolymers with High Diene and Propylene Content Crosslinked by Dicumyl Peroxide and β‐Radiation

Nicolás

Ressia

Vallés

et al. 2004

Macro Chemistry & Physics

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“…Wild et al [46] explained these features by pointing out the predominant effect of entanglements at low degrees of LCB (differences in g are not noticeable and the polymers are 'essentially linear') and the molecular size reduction effect at medium and high degrees of LCB (values of g < 1). Using this approach, Bersted [47,50] developed a model that predicts a Newtonian viscosity peak at a branching level of approximately 2.5 LCB/10 4 C and a subsequent decrease at higher LCB density, as a consequence of the decrease in molecular size (see Fig.…”

Section: Conventional Polymersmentioning

confidence: 99%

“…[7] When the LCB content is very low (less than 1 LCB /10 4 C), its effect on the radius of gyration goes unnoticed and values of g ≈ 1 are obtained [42]. The effect of such a low amount of LCB has been explored in LDPE and in modified linear polymers of ethylene/α-olefins and propylene (PP) by irradiation, electron-beam treatment, peroxide reaction, and thermal/mechanical degradation [7,10,17,[44][45][46][47][48][49][50][51][52][53][54][55][56][57][58][59]. In principle, lowpressure processes (chromium-based and Ziegler-Natta type catalysts, developed in the 1950s and 1970s, respectively) yield linear species.…”

Section: Conventional Polymersmentioning

confidence: 99%

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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“…This object is readily achieved by comparing the swell ratio of sample A-0 with that of In conclusion, we can say that the swell ratios of the solvent-treated materials increase with increase in M , and MWD but decrease with increase in A. By the way, classifying the swell ratios on the basis of the MI range, i.e., [3][4][5][7][8]22-24, the swell ratios increase with increase in A as shown by the solid lines in Figure 1. This finding seems to be in conflict with the conclusion already mentioned.…”

Section: Resultsmentioning

confidence: 99%

Influence of shearing history on the rheological properties and processability of branched polymers. V. Effect of molecular structural parameters on die swell of low‐density polyethylenes

Rokudai

1981

J of Applied Polymer Sci

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Influence of long‐chain branching on the viscoelastic properties of low‐density polyethylenes

Cited by 55 publications

References 8 publications

Characterization of Metallocene Epdm Terpolymers with High Diene and Propylene Content Crosslinked by Dicumyl Peroxide and β‐Radiation

Characterization of Metallocene Epdm Terpolymers with High Diene and Propylene Content Crosslinked by Dicumyl Peroxide and β‐Radiation

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

Influence of shearing history on the rheological properties and processability of branched polymers. V. Effect of molecular structural parameters on die swell of low‐density polyethylenes

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