Anomalous rheological behavior of polyethylene melts in the gross melt fracture regime in the capillary extrusion

Lee, Hwi-yong; Kim, Dong Hak; Son, Younggon

doi:10.1016/j.polymer.2006.03.084

Cited by 21 publications

(14 citation statements)

References 18 publications

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“…Details of experiment and apparatus are described elsewhere. 6 To assess the effect of long-chain branching (LCB) on the abnormal rheological behavior, degree of LCB was estimated by the rheological method. 8 Dynamic storage and loss moduli, G 0 (w) and G 00 (w) are determined with a strain-controlled rheometer (ARES from TA Instruments) in dynamic mode with a parallel-plate configuration of 25-mm diameter at temperatures ranging from 140 to 2008C.…”

Section: Apparatus and Methodsmentioning

confidence: 99%

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Anomalous rheological behavior of polyethylene melts in the gross melt fracture regime in the capillary extrusion: Effect of long‐chain branching

Lee

Kim

Son

2007

J of Applied Polymer Sci

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During a capillary extrusion with several different polyethylenes, we observe an abnormal rheological behavior. The nominal viscosity of some polyethylene melt in the gross melt fracture regime does not change with the temperature. Several metallocene-catalyzed linear low density polyethylene are investigated. Among them, polyethylenes, which have long-chain branches in their main chain, show this abnormal rheological behavior. By capillary extrusion experiments with various dies of different L/D ratios, it is inferred that the abnormal rheological behavior is originated in the die land, not die entrance nor die exit. From various experiments, we notice that this abnormal phenomenon may be used to detect long-chain branch of PE.

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Section: Apparatus and Methodsmentioning

confidence: 99%

“…In our previous study, 6 in which we explored the nature of GMF during a capillary extrusion, we observed an abnormal rheological behavior of metallocene-catalyzed linear low density polyethylenes (mLLDPE). The flow curves of the mLLDPEs in the GMF regime show no-temperature and even no-molecular weight dependency.…”

Section: Introductionmentioning

confidence: 99%

Anomalous rheological behavior of polyethylene melts in the gross melt fracture regime in the capillary extrusion: Effect of long‐chain branching

Lee

Kim

Son

2007

J of Applied Polymer Sci

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“…However, this is limited by the occurrence of flow instabilities at flow rates greater than a critical value. These instabilities manifest themselves as surface defects on the surface of extrudates and are collectively known as melt fracture phenomena [1–4]. These include sharkskin (small amplitude periodic distortions) or surface melt fracture, slip‐stick or oscillating melt fracture (alternating relatively smooth and distorted portion on the surface), and gross melt fracture (large amplitude periodic and/or nonperiodic, chaotic distortions).…”

Section: Introductionmentioning

confidence: 99%

Melt fracture of two broad molecular weight distribution high‐density polyethylenes

Ansari¹,

Hatzikiriakos²,

Sukhadia³

et al. 2011

Polymer Engineering & Sci

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The melt fracture instabilities of two broad molecular weight distribution (MWD) high‐density polyethylenes (one Ziegler–Natta and one metallocene HDPEs) are studied as functions of the temperature and geometrical details and type of die (cylindrical, slit, and annular). It is found that sharkskin and other melt fracture phenomena are distinctly different for these resins, despite their almost identical rheology. It is also found that the critical conditions for the onset of various melt fracture phenomena depend significantly on the type of die used for their study. For example, sharkskin melt fracture in slit and capillary extrusion was obtained at much small critical shear stress values compared with those found in annular extrusion. Moreover, the metallocene HDPE shows significant slip at the die wall in the sharkskin flow regime. On the other hand, the Ziegler–Natta HDPE has shown no sign of slip. These differences are discussed on the basis of differences in their MWDs that influence their melt elasticity. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers

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“…On the basis of these findings, there have been numerous trials to eliminate or delay melt fractures in efforts to realize higher production rates. These include modifications of the die5, 6 and materials by incorporation of processing aids, such as boron nitride,7 hyperbranched polymers,8 and fluoropolymers,9–11 into the base polymer. The use of a slipping agent (fluoropolymer) has thus far yielded the most successful results, and numerous studies have used fluoropolymers 9–11.…”

Section: Introductionmentioning

confidence: 99%

“…These include modifications of the die5, 6 and materials by incorporation of processing aids, such as boron nitride,7 hyperbranched polymers,8 and fluoropolymers,9–11 into the base polymer. The use of a slipping agent (fluoropolymer) has thus far yielded the most successful results, and numerous studies have used fluoropolymers 9–11. Fluoropolymers are known to reduce the extensional force of polymer melts flowing from the die land to the free surface of extrudates near the die exit; they enhance the slippage between the die land and polymer melts.…”

Section: Introductionmentioning

confidence: 99%

Influence of the die configuration on the gross melt fracture of linear polyethylene

Son

2011

J of Applied Polymer Sci

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In this study, capillary extrusion experiments and rupture visualization experiments were carried out with a combined die configuration where two different dies were attached in a capillary rheometer. We observed that the gross melt fracture (GMF) and rupture of the melt occurred simultaneously when the diameter of the die located at the upstream position was larger than that of the die located downstream. However, when the location of the dies were interchanged, that is, the diameter of the upstream die was smaller than that of the downstream die, the upstream rupture did not accompany GMF up to a certain extent of shear rate. From these observations, we present a new theory on the origin of GMF.

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Anomalous rheological behavior of polyethylene melts in the gross melt fracture regime in the capillary extrusion

Cited by 21 publications

References 18 publications

Anomalous rheological behavior of polyethylene melts in the gross melt fracture regime in the capillary extrusion: Effect of long‐chain branching

Anomalous rheological behavior of polyethylene melts in the gross melt fracture regime in the capillary extrusion: Effect of long‐chain branching

Melt fracture of two broad molecular weight distribution high‐density polyethylenes

Influence of the die configuration on the gross melt fracture of linear polyethylene

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