Rheological properties of long chain branched polyethylene melts at high shear rate

Kim, Jaewhan; Kim, Dong Hak; Son, Younggon

doi:10.1016/j.polymer.2009.08.013

Cited by 12 publications

(11 citation statements)

References 22 publications

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“…However, the onset of sharkskin and GMF was not much affected by the addition of LDPE into LLDPE. Kim et al13 investigated the melt fracture behavior of mLLDPE/LDPE blends and obtained similar results on the spurt flow, i.e., small amount of LCB from LDPE influences significantly the amplitude of pressure oscillations.…”

Section: Introductionmentioning

confidence: 79%

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Effects of long chain branching on melt fractures in capillary extrusion of metallocene‐catalyzed linear low‐density polyethylene melts

yoo

Kim

Son

2012

J of Applied Polymer Sci

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To investigate the effect of long chain branching (LCB) on melt fractures of metallocene-catalyzed linear low-density polyethylene (mLLDPE), we prepared a series of sparsely long-chain-branched mLLDPEs with well-defined degrees of LCB. Gross melt fractures were observed to decrease as the degree of LCB increases. This is in accordance with a prediction based on the observation that LCB enhances chain entanglement and consequently increases the melt strength of a polymer. However, sharkskin melt fracture (SMF) was observed to be more severe with the degree of LCB. There have been debates over the effect of LCB on SMF. According to a well-known mechanism of SMF, SMF is expected to decrease with the degree of LCB. Therefore, the majority of research groups believe that SMF decreases with the degree of LCB. This study clearly shows that the SMF becomes more severe with an increase of the degree of LCB and suggests another possible mechanism for the SMF. V C 2012 Wiley Periodicals, Inc. J Appl Polym Sci 126: E322-E329, 2012

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Section: Introductionmentioning

confidence: 79%

“…There have been a few studies on the melt fracture behavior of sparsely long‐chain‐branched LLDPE 11–20. Doerpinghaus and Baird investigated the melt fracture behavior of polyethylenes having various molecular characteristics 11.…”

Section: Introductionmentioning

confidence: 99%

Effects of long chain branching on melt fractures in capillary extrusion of metallocene‐catalyzed linear low‐density polyethylene melts

yoo

Kim

Son

2012

J of Applied Polymer Sci

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“…Improved melt processability can be achieved through use of linear polymers in combination with branched polymers to enhance melt strength and stabilization . Branching and modification for enhanced melt flow properties of polyethylene, polypropylene, polycaprolactone, as well as polylactide have been studied extensively. PLLA has also been modified by blending with a second polymer, in order to improve processability or with a polymeric plasticizer such as polyethylene glycol (PEG).…”

Section: Introductionmentioning

confidence: 99%

Preparation and characterization of linear and star‐shaped poly L‐lactide blends

Khajeheian

Rosling

2015

J of Applied Polymer Sci

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A series of star-shaped poly(L-lactide) (sPLLA) with different branch length was synthesized by ring-opening polymerization of L-lactide using pentaerythritol as initiator and stannous-octoate as catalyst. The structures and properties of the sPLLAs were characterized by 1 H-NMR, rheology, differential scanning calorimetry, and size-exclusion chromatography. The star-shaped polymers were blended with a linear PLLA resin (3051D; NatureWorks) and studied for their melt flow and thermal properties. Blends containing 10 wt % of sPLLA displayed equivalent zero shear viscosities to PLLA 3051D, however displaying stronger shear thinning and increased melt elasticity. The blends exhibited also similar thermal and crystallization properties as the PLLA 3051D. A higher ratio of low molecular weight sPLLA (30 wt %; Mw total : 2500 and 15,000 g mol 21 ) lowered the zero viscosity and increased shear thinning of PLLA 3051D. Crystallization of PLLA 3051D appears to increase at 30 wt % blends with the higher molecular weight sPLLA, while the star-shaped structure acts as a nucleating agent.

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“…Considering their simplicity and reliability, capillary viscometers have been used extensively to measure the viscosities of polymer melts at the shear rates covering the low range in the micro-injection molding [13,14]. The online capillary rheometers have been developed based on the injection-molding machine to further extend the measuring range to much higher shear rate levels [7][8][9][10][11][12].…”

Section: Introductionmentioning

confidence: 99%

Comparison of superimposed effects in high-shear-rate capillary rheology of polystyrene, polypropylene, and linear low-density polyethylene melts

2014

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Polymer melts exhibit unique rheological behaviors at high shear rate up to 106 s−1, which is a common phenomenon in micro‐injection molding. Both online and commercial capillary rheometers, which were modified to allow regulation of back pressure, were used for measuring the melt shear viscosities of polystyrene (PS), polypropylene (PP), and linear low‐density polyethylene (LLDPE) under high shear rates. The rheological characteristics of the three melts were compared through the systematical analyses for three significant effects, namely the end pressure loss, pressure dependence, and dissipative heating in capillary flow. Pronounced end effect begins to appear at the shear rates of 1.6 × 105, 8.0 × 105, and 2.8 × 106 s−1 for the PS, PP, and LLDPE melts, respectively. The significance of the end effect can be ordered as PS > PP > LLDPE. It seems that the polymers with more complex molecular structures exhibit a higher degree of divergence between the comprehensively corrected and uncorrected melt viscosity curves. Moreover, the dissipation effect begins to predominate over the pressure effect under the lowest shear rate of 105 s−1 for the PS melt among the three melts. POLYM. ENG. SCI., 55:506–512, 2015. © 2014 Society of Plastics Engineers

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Rheological properties of long chain branched polyethylene melts at high shear rate

Cited by 12 publications

References 22 publications

Effects of long chain branching on melt fractures in capillary extrusion of metallocene‐catalyzed linear low‐density polyethylene melts

Effects of long chain branching on melt fractures in capillary extrusion of metallocene‐catalyzed linear low‐density polyethylene melts

Preparation and characterization of linear and star‐shaped poly L‐lactide blends

Comparison of superimposed effects in high-shear-rate capillary rheology of polystyrene, polypropylene, and linear low-density polyethylene melts

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