Linear viscoelastic behavior of bimodal polyethylene

Kwakye-Nimo, Shadrach; Inn, Yongwoo; Yu, Youlu; Wood‐Adams, Paula M.

doi:10.1007/s00397-022-01340-5

Cited by 11 publications

(43 citation statements)

References 55 publications

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“…The linear viscoelastic studies of these materials have been previously published . Examples of the output of an SPR test is a shear stress transient curve, as shown in Figure .…”

Section: Resultsmentioning

confidence: 99%

“…A set of four bimodal linear polyethylenes provided by Chevron Phillips Chemical are studied in this work. The absolute molecular weight distributions were obtained by gel permeation chromatography, as explained previously . The MWD curves of the four materials are shown in Figure .…”

Section: Methodsmentioning

confidence: 99%

“…The weight and number-averaged molecular weights, the polydispersity indices M w / M n and M z / M w , the bimodal separation ( S B ), and the bimodal ratio ( R B ) for the four materials of this study are summarized in Table . The two populations in the MWD have been resolved using the approach described previously . The weight, number and Z -averaged MW, and weight fraction of each population are presented in Table .…”

Section: Methodsmentioning

confidence: 99%

“…We use the bimodal separation ( S B ) and the bimodal ratio ( R B ) to describe the bimodality characteristics of our samples, as described previously . The variable S B is defined as the distance between the means of the two distributions, and R B is the ratio of the amplitude of the peak of the HMW population to that of the LMW: where M̅ p,H and M̅ p,L are the MW peak values, σ p,H and σ p,L are the standard deviation from the average, and A p,H and A p,L are the amplitudes for the high and low molecular populations, respectively.…”

Section: Methodsmentioning

confidence: 99%

“…The SAOS tests were conducted using Anton-Paar’s MC502 rheometer with a plate–plate geometry of 25 mm diameter at a 1 mm gap. The small-amplitude oscillatory shear (SAOS) tests at 190 °C over the frequency range of 0.01–500 rad/s are described previously . The cubic spline method is applied to interpolate between the SAOS data points.…”

Section: Methodsmentioning

confidence: 99%

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Wall Slip of Bimodal Polyethylene

2022

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Cohesive slip occurs in the flow of linear polyethylene melts over high-surface-energy walls, changing both the velocity profile and the stress. The slip behavior of bimodal molecular weight distribution (MWD) polymers is different from that of unimodal MWD polymers and is not yet fully understood. Here, we study a set of four polyethylenes with a systematic change in MWD, making it possible to examine the effect of bimodal molecular weight distribution on the slip behavior. The results show that slip in simple shear occurs over a broad range of stress. Higher short-chain content increases slip velocity at all stresses within the transition region before strong slip is fully engaged. At stresses where strong slip is fully engaged, the slip behavior is independent of molecular weight distribution. The stress at which the slip velocity is independent of MWD lowers as the short-chain content increases. Disentanglement between the adsorbed and mobile chains is evaluated via the change in friction coefficient with stress. This analysis reveals that the degree of entanglement at the cohesive failure interface drops sharply in the transition region. This region is only accessible in simple shear and not in capillary flows. Finally, melt rupture was observed to occur after the onset of slip for certain conditions.

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“…The linear viscoelastic studies of these materials have been previously published . Examples of the output of an SPR test is a shear stress transient curve, as shown in Figure .…”

Section: Resultsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

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Wall Slip of Bimodal Polyethylene

2022

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Splitting for strength: Manipulating polymerization reactor split ratios to control mechanical and rheological properties in bimodal polyethylene resins

Jandaghian,

Sepahi,

Hosseini

et al. 2023

J of Applied Polymer Sci

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This study integrates advanced mathematical modeling and experimental methodologies to investigate the simultaneous impact of modifications in the split ratio and molecular weight (MW) of chains on the rheological and mechanical properties of bimodal polyethylene (BiPE) resins. The outcomes underscored the viability of fine‐tuning the molecular weight distribution (MWD) of a BiPE resin by augmenting the MW of high molecular weight (HMW) chains while simultaneously diminishing their proportion in the final alloy formulation. In addition, the experimental results illuminated the prospect of attaining a targeted melt flow index for the final polymers by elevating the MW of HMW chains alongside an increase in the proportion of low molecular weight chains. Significantly, these adjustments resulted in remarkable enhancements in the shear thinning index and strain hardening modulus of the fabricated resins.

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Influence of trimodal polymerization on melt rheology, thermal, and mechanical properties of HDPE resin

Bazgir,

Hosseini,

Sepahi

et al. 2024

Polymer Engineering & Sci

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Trimodal polymerization of polyethylene has become a research interest in recent years due to its excellent potential for altering material properties and overcoming the limitations of the bimodal process. Here, we have comprehensively investigated the effects of manipulating polymerization parameters, such as split value (SV), hydrogen‐to‐ethylene ratio (H2/C2), and stage switching, on the rheological, thermal, and mechanical properties of synthesized trimodal high‐density polyethylene (HDPE). The synthesized samples were obtained through three consecutive stages in a slurry lab‐scale reactor. The results of molten state analysis demonstrate that recipe modification, particularly SV and H2/C2 balancing in the second and third stages, had a dramatic effect on the rheological properties including dynamic moduli, G′‐G″ crossover, and the shear‐thinning behavior. Concurrently, improvements in physio‐mechanical properties, such as sagging behavior and slow crack growth resistance (SCG), were observed compared to the bimodal resin. The thermal characterization indicates that the polymerization adjustments made did not notably impact the thermal properties of HDPE samples (e.g., Tm), throughout the all‐recipe manipulation. However, minor fluctuations in crystallinity and crystallization kinetics were observed which was presumably attributed to the molecular weight of the final resin. Overall, in our trimodal polymerization recipe, the HDPE powder is within the specified range of particle size distribution, which ensures excellent bulk density and flowability.Highlights Influence of polymerization parameters such as split value, H2/C2, and stage switching in properties of trimodal HDPE. HDPE resin received from split value and H2/C2 balancing have superior SCG and sagging resistance. All HDPE samples synthesized by different recipes have similar thermal properties.

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Linear viscoelastic behavior of bimodal polyethylene

Cited by 11 publications

References 55 publications

Wall Slip of Bimodal Polyethylene

Wall Slip of Bimodal Polyethylene

Splitting for strength: Manipulating polymerization reactor split ratios to control mechanical and rheological properties in bimodal polyethylene resins

Influence of trimodal polymerization on melt rheology, thermal, and mechanical properties of HDPE resin

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